Origin of the hominidae: The record of african large hominoid evolution between 14 my and 4 my

YEARBOOK OF PHYSICAL ANTHROPOLOGY 31~49-83 (1988)

Origin of the Hominidae: The Record of African Large Hominoid Evolution Between 14 My and 4 My

ANDREW HILL A N D STEVEN WARD Department ofAnthropology, Yale University, New Haven, Connecticut 06520 (A. H.); Department of Sociology and Anthropology, Kent State University, Kent, Ohio 44242 (S. W); Human Anatomy Program, Northeastern Ohio Universities College of Medicine, Rootstown, Ohio 44272 (S. W)

KEY WORDS Hominoid Hominid, Africa, Miocene, Pliocene

ABSTRACT The Hominidae probably originated in Africa sometime between 14 my and 4 my ago. Unfortunately the fossil evidence from this time period and region is relatively poor. We regard only 11 specimens as unambig- uous hominoids, and none preserves a great amount of anatomy. They come from a very restricted geographical region. Two are from Ethiopia and the rest from Kenya, where most have been found in the Tugen Hills succession west of Lake Baringo. No unequivocal fossil evidence of ancestral Gorilla or Pan has yet been recognised. The oldest hominid yet known-in the sense used here-probably dates to greater than 5.6 my. One especially interesting question in the paleobiology of the hominoidea, as in other taxa, is the relation of extrinsic factors to speciation. To resolve this issue, diagnostic and well-dated specimens are necessary. However, they need not be anatomically spectacular. Fragmentary specimens, although imperfect anatomically, can be just as effective as more complete material in defining taxonomic branching points. The origin of Hominidae, or a t least bipedalism, has been conjec- turally associated with a regional environmental change from tropical forest to widespread grassland. Evidence accumulating from various parts of Africa, particularly the Tugen Hills, suggests this was not an abrupt transition. The pattern of habitats was probably patchy in space and time. This may have been a factor in the origin and development of the hominid clade. Much progress has recently been made, but further hominoid specimens, coupled with environmental information from well-calibrated sequences, is necessary to elucidate the nature and causes of cladistic branching within the superfamily .

Some perennial problems in human evolution are the basic ones. Where did the first hominid species diverge from other hominoids? When did this event take place? What did the first hominid look like? And what were the proximate causes of the divergence and subsequent radiation of the Hominidae?

It is easier to answer some of these questions than others, a t least in a general way. With regard to the location of human evolution, selective quotation often attributes to Darwin the perception, now believed to be correct, that hominids evolved in Africa. In The Descent of Man (1871), having pointed out the general relation between extinct and extant species in each great region of the world, Darwin writes with typical caution:

“It is therefore probable that Africa was formerly inhabited by extinct apes closely allied to the gorilla and chimpanzee; and as these two species

0 1988 Alan R. Liss, Inc.

50 YEARBOOK OF PHYSICAL ANTHROPOLOGY [Vol. 31, 1988

are now man’s nearest allies, it is somewhat more probable that our early progenitors lived on the African continent than elsewhere.”

Of course, at that time the fossil record of our early progenitors was somewhat sparse, but not nonexistent, and Darwin was even more circumspect and astute than this isolated reference implies. In the less-cited following passage he continues:

“But it is useless to speculate on this subject; for two or three anthropomorphous apes, one the Dryopithecus of Lartet, nearly as large as a man, and closely allied to Hylobates, existed in Europe during the Miocene age; and since so remote a period the earth has certainly undergone many great revolutions, and there has been ample time for migration on the largest scale.”

Since 1871 more than two or three fossil “anthropomorphous apes” have been found, and the number of specimens of fossil hominids has increased from the one or two that Darwin knew to many hundreds. The presence of australopithecines in Africa, with only inconclusive and relatively unconvincing evidence of their existence on other continents (Franzen, 1985; Zhang, 1984, 1983, is consistent with the idea that the evolution of the Hominidae should be considered in relation to the radiation of the Ethiopian fauna. However, it is only recently that an African origin for the family has become more certain.

In answering some of the questions with which we began our paper both paleontological evidence and evidence from comparative molecular studies of living primates are both relevant. Once in conflict, they are now seen to be complementary.

There have been numerous definitions of Hominidae, but classically and conven- tionally hominids are considered members of the hominoid lineage postdating the ancestor common to them and African great apes. In this scheme Pongidae do not constitute a monophyletic lineage, and hence the family is invalid in a strictly cladistic sense. Therefore, some cladistic systems also include in Hominidae the African great apes (e.g., Andrews and Cronin, 1982). Other workers, wishing to emphasize grade distinctions, prefer to perpetuate the more traditional terminology. The information presented in this paper is valid regardless of these taxonomic preferences. However, without wishing to adjudicate on either opinion, we use the word hominid here in the conventional sense.

Anatomical information appears to remove Asian “Ramapithecus” (Sivapithecus) and other asiatic hominoids from consideration as hominids (Andrews, 1985; An- drews and Cronin, 1982; Ward and Kimbel, 1983; Ward and Pilbeam, 1983). And despite recent reports (Leakey and Walker, 1985), there is no evidence that Siuapi- thecus is present in Africa (Leakey and Leakey, 1986). In Europe and the Near East hominoids probably more closely related to African forms are known from various sites. However, they extend only up to about 8 my, despite decent paleontological samples after that time, which suggests that hominids did not evolve in those areas. Accumulating molecular evidence from work on modern hominoids indicates a very strong relationship between the African apes and humans and so also points to an African origin for the family (Andrews, 1986; Andrews and Cronin, 1982; Sibley and Ahlquist, 1984).

What about the time of the divergence? Good and varied samples of large hominoid taxa are found in Africa at a variety of localities, dating from about 22.5 my at Meswa Bridge (Andrews et al., 1981; Bishop et al., 1969) up to Fort Ternan (Andrews and Walker, 1976), usually thought of as about 14 my (Bishop et al., 1969), although there is ambiguity in the dates and the Fort Ternan sample may be slightly younger. Most of these hominoids come from sites in western Kenya and eastern Uganda (Kelley and Pilbeam, 1986). Of these, only one genus, Kenyapithecus, has been seriously considered as a possible hominid (Leakey, 1967; Simons and Pilbeam, 1978). From about 3.6 my onward, beginning with Australopithecus afarensis at Laetoli, Tanzania (Leakey et al., 1976; White, 1977, 1980) and later in the Hadar

Hill and Ward] ORIGIN OF THE HOMINIDAE 51

Formation in Ethiopia (Johanson et al., 1978,1982; Johanson and White, 1980) there are good samples of undoubted hominids.

Some of the anatomical reasons for Kenyapithecus being a hominid were those that prompted the belief that Sivapithecus was a hominid, too. With the removal of Sivapithecus from consideration as a member of the hominid lineage less weight can be placed on these criteria in the case of Kenyapithecus, and new material, as yet not described in detail, is reported to show “none of the apomorphic characters that define the Hominidae” (Pickford, 1985, 1986a; Ishida, pers. commun.). However, possibly the main reason for the exemption of Kenyapithecus from the family comes from molecular studies. When molecular data derived from a variety of methods are suitably calibrated by using paleontological information they suggest a divergence time much more recent than was formerly entertained by most paleoanthropologists (Pilbeam, 1985, 1986). By this criterion, specimens belonging to Kenyapithecus are too early to be considered members of the Hominidae.

The implication of the paleontological evidence and the strong suggestion of the molecular data are that the Hominidae originated in Africa some time between 14 my and 4 my, probably within 8 my to 6 my. However, very little is known about the Hominidae or the rest of the fauna and their habitat during this 10 million years of time. Comparative molecular work bearing upon the origin of the Hominidae is frequently discussed, but the limited paleontological information has received less attention.

One of the very interesting subjects that arise from considerations of time and place is possible environmental correlates of speciation. A number of recent contributions have focussed on this issue (Kappleman, 1985a,b, 1986; Vrba, 1985a,b; Hill, 1987). To correlate speciation with various extrinsic environmental factors it is necessary to establish the origin of clades to a high degree of accuracy. For this purpose fragmentary materials can be just as important for diagnosing taxa as is more anatomically complete material. Also, data regarding the exact age of specimens take on added importance.

This review summarizes paleontological evidence concerning African large hominoids from this time period, between Fort Ternan and Laetoli, 14 my and 3.6 my, when hominids presumably evolved. We describe the relevant hominid material and comment on its significance by treating the separate specimens and sites systemati- cally. As it is increasingly realized that the dynamics of human origins and evolution cannot be properly understood other than in an environmental context, we supply contextual data relating to the geology and dating of appropriate successions and sites, as well as providing anatomical descriptions of specimens. Where necessary, WAr dates have been revised according the formula provided by Ness et al. (1980) to take into account new decay and abundance constants. We discuss associated fauna at each site or formation in terms of its biostratigraphic significance and summarise overall paleontology, faunal change, and paleoenvironments in East Africa over this time in separate sections. Such data are essential for appreciating the pressures leading to evolutionary change and to the origin of the distinctive human adaptations.

PALEONTOLOGICAL EVIDENCE

Over this crucial time period hominoids are poorly sampled. From the earliest horizon that possibly might be included, a t Nachola, Kenya, there are a relatively large number of specimens that have been placed in a taxon known from earlier periods, Kenyapithecus. However, recent estimates (Pickford, 1985; 1986a,b; Ishida, pers. commun.) suggest that these are as old as 15 or 16 my. But after this, for the whole 10-million-year period there are fossil remains of only 11 undoubted large hominoid individuals (Table 1). None of the specimens preserves comprehensive anatomical information about the taxa within the superfamily that they represent. Indeed, in a number of cases they preserve insufficient information to determine definitively what their taxonomic position exactly is.


TABLE 1. African large hominoids and localities between 4 and 14 my’

Locality Specimen Age Middle Awash: Maka Proximal femur < 4.0 Middle Awash: Belohdelie Frontal >4.0 Kanapoi Distal humerus ca. 4.0 Chemeron: KO37 Chemeron: KO77

Proximal humerus Partial mandible

> 4.2 ca. 4.9

Lothagam Partial mandible >5.6 Lukeino: KO29 Sahabi: P21A Sahabi: P33A Sahabi: P4A Namurungule: SH-22 Ngorora: KO60 Ngorora: KO65 Muruvur

Mandibular molar crown Parietal Distal fibula Partial ?clavicle Hemi-maxilla Maxillary molar crown Mandibular P4 crown Partial talus

ca. 6.0 ca. 5.0 ca. 5.0 ca. 5.0 ca. 8.0 ca. 11.0 ca. 11.0 ca. 14.0

‘Although three Sahabi specimens are listed here, they are likely not hominoids

In addition to this poor sampling of individuals and poor sampling in time, there is poor sampling in space as well. All of the sites in Kenya, from which the majority of the specimens come, can be enclosed by a rectangle of about 300 km by 100 km- a mere 30,000 km2 of eastern Africa which serves to represent the whole 30,335,000 km2 of the continent (Fig. 1). The two Ethiopian sites fall in a very small area. This has implications for our ability to work out the causes of hominid speciation (Hill, 1987).

Six of the 11 relevant hominids come from the Tugen Hills, west of Lake Baringo in northern Kenya, which sample this time period better than anywhere else yet known. Another potentially good succession is that of the Middle Awash in Ethiopia, but so far hominoids have only been found at the top of this time span and are only slightly older than the collection from Laetoli (Clark et al., 1984). The other definite hominoids come from isolated sites in the Kenya Rift Valley. They are the Samburu Hills on the eastern side of the Rift, and Lothagam and Kanapoi on the western side of Lake Turkana. Also, the Sahabi area of Libya has produced three specimens claimed to be hominoid. As the Tugen Hills sequence covers most of the whole time span, and as most of the specimens have come from there, we describe it first. Then follow descriptions of the other sites and specimens in order of their estimated age. All the Kenyan specimens, accessioned under the prefix KNM, are housed in the National Museums of Kenya, Nairobi. The specimens from Ethiopia are in the care of the National Museum of Ethiopia in Addis Ababa.

THE TUGEN HILLS SEQUENCE

The Tugen Hills is a complicated faulted block west of Lake Baringo extending about 60 km north-south along the northern Kenya Rift Valley, and a thickness of over 3,000 m of rocks is exposed in its fault scarps and eastern foothills. Fossiliferous sediments range in age from earlier than 14 my to the Pleistocene. The area has been known to geologists for over 100 years, being first visited by Thomson (1884), with subsequent work carried out by Gregory (1896, 19211, Willis (19361, Fuchs (1934, 1950), and Shackleton (1951). Gregory, in establishing a basic geological framework for the region, was hampered a little by the lack of fossils in the sediments he had discovered. He decided they were Miocene in age and attributed them to the Kamasian deposits of his Nyasan Series. Fuchs (1950) reported vertebrate fossils from some of these sediments which he was able to show were middle Pleistocene.

Later investigations, from the mid-1960s to the mid-l970s, were carried out by the East African Geological Research Unit (EAGRU), directed by King, and an associated group working with Bishop (Bishop et al., 1971; King and Chapman, 1972;


J1 S A H A B l

-. '. \

N

N A I R O B I

0 ~

50 100 150 200 K h

Fig. 1. Regions from which African large hominoids and specimens claimed to be hominoids have been collected in the time interval between 14 and 4 million years. Locality designations appearing in the North Kenya Rift Valley insert on the right are Kenya National Museum (KNM) accession numbers for individual hominoid and hominid specimens as follows: LT 329: Lothagam mandible; KP 271: Kanapoi humerus; SH 8531: Samburu Hills maxilla; BN 1378: Ngorora molar; BN 10489: Ngorora premolar; BC 1745: Chemeron humerus; LU 335: Lukeino molar; TH 13510: Tabarin mandible, MY 24: Muruyur talus.


Chapman and Brook, 1978; Chapman et al., 1978; Williams and Chapman, 1986). A major achievement of this work was the clarification of the stratigraphy and dating. It was clear that a number of sedimentary units existed ranging in age from the Miocene to the Holocene, some spanning the period of time from 14 my to 4 my, that were otherwise missing in sub-Saharan Africa. A number of these formations were defined. The Tugen Hills were paleontologically important as well. Many fossil sites were discovered with diverse vertebrate faunas, one or two of them including hominoids.

Over the last few years work in the region has been resumed by the Baringo Paleontological Research Project (BPRP). This has resulted in a more refined stratigraphy and calibration, along with further fossil material, again including hominoids. A recent review which discusses paleontological information is provided by Hill et al. (1985). Tame et al. (1985) deal with the paleomagnetic stratigraphy and its relation to the geomagnetic reversal timescale (GRTS), and Hill et al. (1986) focus on stratigraphy, dating, and faunas.

A number of bodies of sediments exist at the base of the succession but appear to be more or less unfossiliferous. The earliest with any substantial fossil content is the Muruyur beds, which are older than 13 my. The overlying fossiliferous units, in order of age, are the Ngorora Formation, Mpesida beds, Lukeino Formation, and Chemeron Formation. Many Chemeron sites are between 5 my and 4.5 my in age and mark the end in the Tugen Hills of the period under present consideration. However, some sites in the Chemeron Formation are much younger than this, ranging to 1.6 my, and there are younger formations in the Tugen Hills succession, such as the Kapthurin Formation. Hominoids have been discovered in the Muruyur beds and Ngorora, Lukeino, and Chemeron Formations. In the following account, site numbers with a K prefix are those of the BPRP. Others, such as those prefixed 21 or JM, were provided by members of the EAGRU and its associates.

MURUYUR BEDS Geology

The Muruyur beds were originally described by Chapman (1971), and Pickford (1975a) carried out additional work, considerably supplementing the faunal list. However, they remain little known. On geological grounds it is fairly certain that they are older than 13 my, and Jacobs (pers. commun.) suggests at least some sites may be as old as 16 my, based on the presence at one site of the rodent Diamantomys. Consequently they may be outside the time period to be discussed here, being contemporary with or even older than Fort Ternan. One hominoid has been reported from the unit (KNM-MY 24).

The Muruyur talos KNM-MY 24) The Muruyur hominoid has so far been recorded only in tables in Pickford (1983)

and Pickford et al. (1983), and it is alluded to mistakenly as a calcaneum in Hill et al. (1985). The specimen is a partial talus (Fig. 2). While badly damaged, the preserved parts of the specimen, particularly the trochlea and the lateral malleolar surface, bear strong morphological and metrical resemblances to, and are almost indistinguishable from, Proconsul major (Rose, pers. commun.)

NGORORA FORMATION Geology

Remains of two definite large-bodied hominoids come from sites in the Ngorora Formation, and there are other less certain specimens. One of the former is a molar tooth (KNM-BN 1378) found at site KO60 (219) in 1968 (Bishop and Chapman, 1970); the other is a lower fourth premolar (KNM-BN 10489) from site K065, which so far has been mentioned only briefly (Hill et al., 1985) in the literature. From this same site is a canine tooth which might conceivably be hominoid. The Ngorora Formation is a large body of sediment, both in thickness and areal extent. Bishop and Chapman (1970) defined the Formation and described the type section in the north of its

Hill and Ward]

A

ORIGIN OF THE HOMINIDAE

B

55

' 1 C M ' Fig. 2. The Muruyur talus. A Superior view, showing the damaged trochlear surface, and plane of fracture separating the talar head and neck. The damaged area extends onto the lateral malleolar surface of the trochlea. B: Inferior view. The small anterior and large posterior calcaneal articular surfaces are clearly evident, as is a wide talar groove (sulcus tali). In both views, anterior is toward the top of the page.

outcrop, a t Kabarsero. They also subsumed under the unit the Poi Tuffaceous Sandstones and Kapkiamu Shales previously described by Martyn (1969). Chapman (1971) provided further details, and more information on the fauna was given by Bishop et al. (1971). New taxa were reported by Aguirre and Leakey (1974). Subse- quently Pickford performed more detailed work on the Formation, treating stratigraphic correlation between disjunct outcrops, environments, and fauna (Bishop and Pickford, 1975; Pickford, 1978a). The most recent work of BPRP is reported in Hill et al. (1985, 19861, and Tame et al. (1985).

The Formation is defined as bounded by the Tiim Phonolite Formation beneath and the Ewalel Phonolites above, and in the Kabarsero type section there are about 370-400 m of sediments. Radiometric dates on the Tiim Phonolites have been various, ranging from 15.3 my to 13.3 my on lower units, and from 13.5 my to 11.7 my for upper flows. There are two dates from the south of its outcrop of 10.2 my and 11.7 my, which have been regarded as aberrant (Chapman and Brook, 1978). A published BPRP date on the top of the Phonolite in the Kabarsero type section of 12.3 & 0.50 my has recently been revised to 13.5 my (Deino, Curtis and Drake, pers. commun.) and is no longer in conflict with a sanidine date of 12.71 f 0.09 my from Ngorora sediments just above it. This latter determination fits better with paleomagnetic stratigraphy, as the best correlation with GRTS suggests the base of Chron 13, dated a t 12.74 my (Mankinen and Dalrymple, 1979 [GRTS: MD 79b]), is near the base of the sedimentary section (Tame et al., 1985). Sanidine WAr dates through the type succession are reasonably concordant and fit very well with paleomagnetic determinations. The youngest WAr date in the succession is 10.16 my, and we believe that paleomagnetic samples extend into Chron 9, and are therefore younger than 10 my. Consequently the type section spans over 3 my fairly continuously, an unusually long time period for African continental sediments. Fauna suggests that


other outcrops may be even younger than rocks in the type section-at Ngeringerowa in the south, for example. The earliest African colobines come from there (Benefit and Pickford, 1986>, and there are equids, reduncine bovids, and other advanced elements. Pickford has implied such sites may not be part of the Ngorora Formation (e.g., Pickford, 1986131, and this may in fact be so, but his criteria are paleontological rather than lithostratigraphic. Also, at present we have very little fossil material from the top parts of the Formation in the type area with which to compare Ngeringerowa and other Ngorora sites that include equids in their fauna.

The fauna from the Ngorora Formation is very rich and comes from a large number of sites (see Hill et al., 1986). In addition, at one level, dated at 12.2 my, there are abundant plant remains (Jacobs and Kabuye, 1987).

The Ngorora molar (KNM-BN 1378) Background

This isolated maxillary molar tooth was found on a track about 0.5 km south of Bartabwa by Kiptalam Cheboi in 1968 while working with Chapman (Bishop and Chapman, 1970). Adhering matrix indicates that it came from a black manganese layer about 4 cm in thickness which crops out a few centimeters away. A small excavation conducted by Hill in 1968 at the site (K060, 2/9) revealed no further material of any kind, and there is no associated fauna except for some fish fragments from neighboring horizons. There are traces of plant roots in the 15-cm overlying stratum of green fine sand and silt.

Leakey (in Bishop and Chapman, 1970) provisionally referred the specimen to the Hominidae, indicating affinities with Kenyapithecus (which he believed to be a hominid) and with both Homo and Australopithecus. The specimen has received mention in many publications since. Corrucini (1975) attempted a crown component analysis on the occlusal features of the specimen, but the results failed to offer any taxonomically useful information.

Preservation and morphology The specimen is a left maxillary molar crown, incompletely preserved to the cervix

(Fig. 3A). The crown is only lightly worn, with some faceting present on the buccal slope of the hypocone and on the mesial marginal ridge. A weakly developed interproximal (IP) wear facet is present mesially, but a distal IP facet is not visible, perhaps due to damage on the distal crown margin. The crown is quadritubercular, with each cusp separated by developmental grooves. The cusps appear to be relatively low, and there is a moderate amount of crenulation in the mesial and distal foveae. The protocone is the largest cusp, the metacone the smallest. The paracone and hypocone appear to be roughly equal in size. The large size of the hypocone and its separation from the trigone indicate that the specimen is either a first or a second molar. All the cusps are blunt a t their apices, and the two lingual cusps are inflated basally, resulting in a moderate amount of lingual flare.

We have compared the Ngorora molar with all major Miocene large hominoid collections and cannot assign the specimen to any currently accepted taxon. Corruc- cini and McHenry (1980) noted some similarities to Siuupithecus without documenting what they are. Our examination of the Siwalik hominoid maxillary molar sample fails to reveal any consistent similarities, except for the possibility that the Ngorora molar may have a relatively thick molar cap. But since this condition could well be primitive for large hominoids, it is not helpful in higher taxonomic rank assignments. It is clear that the tooth is not attributable to the taxon represented by the large hominoid maxilla from Samburu Hills, which may be about 1 miIlion years younger. Nor can we find any consistent similarities with the Hadar maxillary molar sample. The best phenetic comparison is with modern chimpanzee second molars, although they are consistently smaller than KNM-BN 1378. For these reasons we must follow earlier authors and assign the specimen to Hominoidea, gen. et sp. indet.


C D E

I 1 C M I Fig. 3. A Ngorora molar (KNM-BN 1378). B: Ngorora lower P4 (KNM-BN 10489) occlusal view. C: Ngorora lower P4 buccal view. D: Ngorora lower P4, distal view, showing inflated buccal cervix, tips of the protoconid and metaconid, and talonid fovea. E: Lukeino molar (KNM-LU 335). In each of the occlusal views (A, B, and E) mesial is toward the top of the page.

The Ngorora premolar RNM-BN 10489) Background

A premolar of a large hominoid was found by Cheboi in 1983 near Bartabwa at what became site K065, and it is referred to in Hill et al. (1985). Among specimens found when clearing and sieving the surface was a canine (KNM-BN 10556) which might ossibly be hominoid, but its poor condition precludes exact determination. If it is a Eorninoid it is unlikely to belong to the same species as the premolar. Other associated fauna includes fragments of rhinoceros and artiodactyl. Preservation and morphology

KNM-BN 10489 is an isolated left mandibular fourth premolar from a large hominoid (Fig. 3B,C). It consists of a complete crown and the proximal part of the

58 YEARBOOK OF PHYSICAL ANTHROPOLOGY [Val. 31, 1988

root system. The tooth had two complete roots, although they appear to have been fused just beneath the cervix. The crown is compressed mesiodistally, and both the protoconid and metaconid are of approximately equal height. These cusps are connected by a short but distinct crest that is dissected by a mesiodistally trending groove. The mesial fovea is small, being only approximately half the size of the distal fovea. The crown is characterized by pronounced buccal flare, and the mesiobuccal corner of the crown is slightly distended. A pair of pits flank the buccal face of the protoconid; otherwise there is no other evidence of cingulum formation. When viewed lingually, the talonid appears elevated, and it approximates the level of the trigonid portion of the crown.

A comparative survey of all large-bodied Miocene hominoid dental samples indicates that the Bartabwa premolar bears closest anatomical similarity to Proconsul. The features shared with Proconsul include the contours of the buccal surface of the crown, buccal pitting, and proportions of the mesial and distal foveae. Difference9 when compared to Proconsul primarily involve the shape of the crown, which is trapezoidal in the Bartabwa specimen and rectangular in Proconsul, and the differential levels of the trigonid and talonid. In Proconsul the talonid forms a distinct heel when viewed lingually, while the Bartabwa premolar has a high talonid. We can find no other later Miocene hominoid fourth premolars with this pattern, although the large Kenyupithecus dental series from Nachola, when made available, may help resolve this issue. However, it should be noted that the Kenyupithecus wickeri P4 from Fort Ternan shows the same rectangularAow talon pattern seen in almost all other large Miocene hominoids. Based on the preserved morphology, we tentatively proposed to assign KNM-BN 10449 to Proconsul sp. indet. This then would represent the last known occurrence of Proconsul in the Miocene fossil record.

LUKEINO FORMATION Geology

The sedimentary unit succeeding the Ngorora Formation in the Tugen Hills sequence is the Mpesida beds dated at around 6.5 my (Hill et al., 1985). Unfortu- nately no hominoids, or primates of any kind, are yet known from these strata.

Above the Mpesida beds is the Lukeino Formation, a large unit which crops out much more extensively. It was originally described as a member of the Kaparaina Basalts Formation by Chapman (19711, and additional work was done by Martyn (1969) and McClenaghan (1971). Pickford (1975a) carried out more extensive map- ping and collecting of the unit, elevated it to formational status, and published a type section. In the course of these investigations the hominoid was discovered. More detailed information appears in Pickford (1975b, 1978b). Further collecting, stratigraphy, and dating has since been undertaken by BPRP (Hill et al., 1985,1986).

The Lukeino Formation lies on top of the Kabarnet Trachytes, and for most of its outcrop it is overlain by the Kaparaina Basalts. These two volcanic units provide bracketing ages. BPRP dates on upper flows of the Kabarnet Trachytes range from 6.36 my to 6.20 my. Dates on the Kaparaina Basalts cover a wide range, from 5.5 my to 4.0 my with three dates that are regarded as anomalous, of 6.9 my, 7.1 my, and 8.4 my. Recent BPRP dates are more consistent, possibly because of more restricted geographical sampling, and they cluster around 5.6 my. From an analysis of the paleomagnetic results of Dagley et al. (1978), Johnson and McGee (1983) suggest that the episode represented by the Kaparaina volcanic flows was short- lived. Two determinations on materials within the Formation are consistent with these bracketing dates; they are 6.06 my on sanidines from the basal part and 5.62 my on a basaltic unit. More details on dates, including error estimates, are given in Hill et al. (1985, 1986).

The most recent faunal list appears in Hill et al. (1986). Among first appearances in taxa at Lukeino are a porcupine, Hystrix, an elephantid Primelephas gomphoth- eroides, the oldest representative of the Chalicothere genus Ancylotherium, and the suid Sivuchoerus tulotus.

ORIGIN OF THE HOMINIDAE 59

The Lukeino molar (KNM-LU 335) Background

The Lukeino specimen (KNM-LU 335) comes from the site of Cheboit, KO29 (2/ 219), about 5.5 km west of Yatya. It was a surface find, discovered by Cheboi in 1973, while working with Pickford. Andrews (in Pickford, 1978b) originally described this specimen as Hominidae but has since suggested that a more judicious identification would be Hominoidea indet. (Andrews, pers. commun.). This specimen has been the subject of considerable comment, and a crown component analysis by Corruccini and McHenry (1980)) and McHenry and Corruccini (19801, suggested phenetic similarities with modern chimpanzees. Their analysis also showed that this tooth has an expanded talonid and very low cusp height. Preservation and morphology

KNM-LU 335 is evidently the unerupted crown of a first, or possibly second, left mandibular molar (Fig. 3D). The roots are not present. Pickford (1975b) suggests they had been dissolved away and uses this assumption to support statements concerning provenience. Andrews, in the same publication, remarks that there is no sign of root development, and we agree with him in supposing the roots had probably not formed. There are no wear facets occlusally, nor interproximal facets. Five cusps are present, and accessory cusps are absent. As noted by Corruccini and McHenry (1980), the cusps are low and obtuse. The fissure pattern is of the basic hominoid “Y” type, resulting in a bilobate appearance when the tooth is viewed from its buccal surface. Both the mesial and distal marginal ridges are compressed, and the hypoconulid is strongly appressed to the distal-buccal surface of the crown,

Little else can be added to the current state of knowledge concerning the Lukeino molar. Its small size and distinctively chimpanzee-like anatomy certainly render KNM-LU 335 a possible ancestral morphotype for lower first and second molars in the last common ancestor of chimpanzees and humans.

CHEMERON FORMATION Geology

Three hominoid fossils have been described from sites in rocks referred to the Chemeron Formation. Two of these derive from the time period in question. They are a fragment of proximal humerus from site KO37 (2/211) (KNM-BC 1745) and a fragment of mandible with M1 and M2 from KO77 (KNM-TH 13150). The third specimen, a temporal bone (KNM-BC 1: Martyn, 1967; Tobias, 1967), is younger in age and will not be discussed here (see Ward and Hill in MS).

The rocks that now constitute the Chemeron Formation are part of the Kamasian sediments first described by Gregory (1896, 1921) and later investigated by Fuchs (1934, 1950). McCall et al. (1967) showed that there were two distinct sedimentary units involved, separated by an angular unconformity, and they thought also separated by lavas. They named the younger unit the Kapthurin beds and the older one the Chemeron beds. These were informal terms. Martyn (1967, 1969) conducted much more detailed investigations and formalized the nomenclature, providing type sections. For the Chemeron Formation he recognised two separate areas of outcrop, the Chemeron basin and the Kipcherere basin, equated lithologically. It is also possible to trace the Formation northward. Chapman (1971) had already described sediments from there which lay on Kaparaina Basalts, and Pickford, working sub- sequently in that area, allocated these and new exposures to the Chemeron Forma- tion along with other sediments that had previously been attributed to another separate formation. The equivalence of many of these outcrops with Chemeron sediments in the south is fairly certain. Others present a more complex situation, and Pickford’s suggestions as applied to these cases are still disputed by some (Chapman and Brook, 1978; Williams and Chapman, 1986).

Over most of its outcrops the Chemeron Formation is separated from the underlying Lukeino Formation by the Kaparaina Basalts, which therefore provide a lower boundary to the age of the sediments. The age of the Kaparaina Basalts, for which

YEARBOOK OF PHYSICAL ANTHROPOLOGY [Vol. 31, 1988 60

we favor a date of 5.6 my, has been discussed in connection with the Lukeino Formation. Most Chemeron fossil sites appear to be only slightly younger than this in age. This is supported by additional radiometric dates from tuff horizons within the sediments. McCall et al. (1967) and Martyn (1967, 1969) believed the top of the unit to be delimited by lavas which occur in the type section. In fact these occur within the formation, but very near the top. Dates on them are 1.57 my and 2.13 my.

These dates highlight a problem with the formation. Many of the rocks and fossil sites are around 5 my; some others are around 2 my. Yet there is no evidence of complete stratigraphic continuity between these dates. We hope that future stratigraphic work will resolve this issue. We see no reason to agree with the suggestion of Pickford et al. (1983) that the Chemeron Formation is represented as part of the Pleistocene sedimentary sequence at Chesowanja to the east of Lake Baringo, from which has come specimens of Australopithecus boisei (Carney et al., 1971; Bishop et al., 1975, 1978).

At most Chemeron sites the fossil fauna is rather similar to that of the underlying Lukeino Formation. The suid Sivachoerus tulotus has disappeared and been replaced by Nyanzachoerus jaegeri and Nyanzachoerus kanamensis, which probably evolved from it (Harris and White, 1979). The elephantid Stegotetrabelodon orbus is no longer present and is replaced by L,i)xodonta adaurora.

The Tabarin mandible (KNM-TH 13150) Background

In 1984 Cheboi found a fragmentary mandible of a hominid at a new site, Tabarin (K077), when working with BPRP, and the specimen has been attributed to Austra- lopithecus afarensis (Hill, 1985b; Ward and Hill, 1987; Hill and Ward, in MS). Tabarin is a site in the northern extension of the Chemeron Formation, 2 km north of Rondonin, and there is little doubt of its equivalence to Chemeron strata in the Kipcherere basin further south. The sediments lie on Kaparaina basalts. About 20 m from the base is an ignimbritic tuffaceous unit about 10 m thick, and then about 17 m of silts and sands followed by a dark ferruginous horizon. Judging by their situation and matrix, the hominid and some of the other fauna undoubtedly come from this horizon. There are other fossiliferous horizons higher in the sequence.

Dates on the tuff units within the sedimentary sequence at the site, just below the horizon of the hominid, are 4.96 my and 5.25 my. These dates conform to others that come from tuffs at outcrops further along strike. Faunal evidence agrees with these dates and also puts an upper limit on the whole unit of about 4.15 my. This is based primarily upon the presence of the suid Nyanzachoerus jaegeri, which is not known elsewhere younger than this date. The gomphothere proboscidean Anancus is also present at Tabarin, and is not known in sub-Saharan Africa later than 4 my. This makes the specimen second only in antiquity to the Lothagam mandible among Pliocene hominids.

Preservation and morphology The specimen consists of a fragmentary right mandibular corpus, with the first

and second molars present and in undistorted anatomical position (Fig. 4 A-C). The corpus is transversely broad, but it is shallow, measuring 26.9 mm at the second molar. This dimension falls within the low end of the range reported for Austral@ pithecus afarensis (White and Johanson, 1982). On the lateral surface contours are quite pronounced. The lateral prominence is strongly developed and attains its maximum lateral projection opposite the M2-M3 contact. From the broken surfaces it seems probable that the entire third molar and perhaps a small part of the second molar were positioned medial to the ascending ramus. The extramolar sulcus appears to be large for so small a mandible but is in keeping with the massively constructed lateral eminence.

Anterior to the lateral prominence, the lateral surface of the corpus becomes markedly concave. The cortical bone at the alveolar crest adjacent to P4 as well as


A

B

C

Fig. 4. Tabarin mandible (KNM-TH 13150) A Lateral. B: Occlusal. C: MediaUoblique. In C, note the serrate root arrangement present in the first molar. See text for discussion.


at the inferior broken edge of the specimen is deflected outward in the same fashion as the Lothagam mandible, lending credence to the notion that anterior corpus hollowing is characteristic of early hominids.

The lingual surface of the Tabarin mandible is extensively damaged. It can be determined that there is moderate relief under the second molar, with a discernible submandibular fossa, thickened alveolar margin, and only minimal basal swelling. Apart from the degree of relief present, these contours are concordant with those present in A ustralopithecus afarensis and the Lothagam mandible.

Occlusal anatomy of both molars preserved in the specimen is obscured by wear and weathering, but a number of details are nonetheless discernible. Due to moderate buccal swelling of the protoconids, the trigonids are slightly broader than the talonids in both teeth. The hypoconulids are mesiodistally compressed, and the metaconids and protoconids are similar in size; the metaconids are slightly larger. The buccal developmental grooves are well expressed, giving the molars a bilobate appearance in lateral view. The buccal cusps of both teeth are expanded, producing a moderate amount of buccal flare.

The state of occlusal wear on M1 is quite similar to that present on the Lothagam first molar with two deeply excavated basins bounded by outwardly convex enamel rims defining the buccal surfaces of the protoconid and hypoconid. Small point exposures are present on the metaconid and hypoconulid. The metaconid shows evidence of being flattened apically, which is typical of early as well as later hominids, rather than forming an elevated and sharp rim, which frequently occurs in pongids.

The state of wear on the second molar is obscured by weathering, but it appears that there was a small dentin exposure on the protoconid. It is quite unlikely that the remaining cusps were heavily worn, if they were in fact worn at all, suggesting that there was a delay in M2 eruption of perhaps several years following the appearance of the first molar. This of course would be expected in a hominid dentition and further supports assignment of the Tabarin mandible to the Homini- dae (see Ward and Hill, 1987). Finally, examination of the two molars present in KNM-TH 13150 indicates that a sinusoidal or helicoidal occlusal plane is present, with pitch reversal occurring on the talonid of M2.

The subocclusal anatomy of the Tabarin mandible is in all respects the same pattern present in the Pliocene mandibles from Hadar, Laetoli, and Lothagam. Lateral radiographs show that the pulp chambers in both molars are low and cynomorph, with blunt pulp horns that do not project up into the dentinal mass of the cusps. The root furcations are arch-shaped and fairly low, rather than cleftlike and high as in modern pongids. As is the case in the Lothagam and Australopithecus afarensis mandibles, the roots of all molars are of equivalent length. From the broken sockets of P4 and M3, it is apparent that the former tooth had a pair of mesiodistally arranged roots while M3 had a mesial root with a well-expressed bifid apex. Both of these characters are also consistently present in other Pliocene hominid mandibles. Finally, both the Tabarin molars have mesial roots that are transversely broader than their distal counterparts, and the mesial roots are more vertically implanted than the distal, which produces the serrate implantation pattern that is characteristic of Australopithecus afarensis.

The Chemeron proximal humerus KNM-BC 1745) Background

In 1973 Cheboi discovered a proximal humerus when working with Pickford. It was initially thought to be hominid, but closer examination made this identification seem unlikely. In 1980, having by then seen A ustralopithecus afarensis postcranials, Pickford rediscovered the specimen in the Kenya National Museum collections and recognized its hominoid affinities.

The specimen was recorded in Pickford et al. (1983) as coming from site 2/210, but Pickford informs us that this is an error and that the site concerned is site 2/211. In fact it is referred to as coming from 21211 once in that paper. However, the locality


is in the position of 21210 on the map in Pickford et al. (1983), and it is BPRP site K037. The fossil comes from sediments that Pickford (1975a) referred to the northern extension of the Chemeron Formation.

The local succession consists of about 150 m of volcanic and other sediments, including a massive development of a unit known as the Cheseton t&. The hominid is found in sediments about 50 m above this tuff. Three dates from a “volcanic bomb” in the tuff give an average of 5.07 0.4 my. Associated fauna is similar to that found at Chemeron sites further south, such as Tabarin. In particular the presence of Nyanzuchoerus jaegeri is useful in establishing an age of greater than 4.15 my.

Preservation and morphology KNM-BC 1745 is a fragmentary left proximal humerus. It was from a subadult

individual, as is attested by the presence of a clearly discernible epiphyseal line between the head and anatomical neck. Parts of the specimen are missing-specifi- cally, portions of the greater and lesser tubercles and the lateral one-third of the head (Fig. 5A-D). The excellent primary description of the specimen by Lovejoy in Pickford et al. (1983) obviates the need for additional comments other than to note what we believe to be its hominid synapomorphies.

From what is preserved, it appears that the head of the Chemeron humerus was elliptical in its circumference rather than spherical as in living pongids. An examination of other hominid proximal humeri, including Sts 7, ER 1473, ER 739, ER 1531, AL 288-1m, and AL 333-107 also shows an elliptical vs. spherical pattern in these later hominids.

Enough of the intertubercular groove is preserved to determine that it was probably relatively shallow, rather than forming an osseous-fascia1 tunnel as in living pongids. There is some variation in this feature among fossil hominids, but in general the groove is shallow in hominids and deep and excavated in living apes. The reason for this difference involves the morphology of the lesser tubercle rather than the size or implied strength of the long head tendon of the biceps brachii. In living pongids the lesser tubercle projects inferiorly and posteriorly as an undercut flange, which augments the concavity forming the intertubercular groove. Attach- ment on the posterior lip of the intertubercular groove (crest of the lesser tubercle) also augments its depth in pongids, in which this surface is characteristically elevated and roughened by the insertion of the pectoralis major. This surface in KNM-BC 1745 is not strikingly developed and does not contribute significantly to the depth or radius of curvature of the groove.

According to Pickford et al. (19831, additional topographic relationships of the Chemeron humerus can be deduced from examination of the position of the preserved part of the lesser tubercle relative to the floor of the intertubercular groove. Such an examination indicates that the head was anteromedially oriented, as in hominids. In general, the contours preserved in KNM-BC 1745 appear most similar to the Hadar hominid humerus AL 288-1r (Lucy), and attribution to Australopithecus cf ufurensis would seem warranted. However, we shall follow Pickford et al. (1983) in refraining from formal taxonomic assignment of the specimen, although we believe, despite Senut (1983), that it is clearly hominid in its affinities.

SAMBURU HILLS Geology

Hominoid specimens within the time period 14 my-4 my that come from areas outside the Tugen Hills will be discussed in order of age. The oldest is on the eastern side of the Rift Valley in Kenya, a little further north than the Tugen Hills. This region has been investigated by a Japanese team led by Ishida in association with the National Museums of Kenya. Work began in 1980, and in the 1982, 1984, and 1986 field seasons important hominoid specimens were discovered from two areas (Ishida et al., 1982, 1984; Ishida, pers. commun.). Until the visit of the Japanese expedition the region had been little studied, other than by Baker, leading to a

64

A

B

YEARBOOK OF PHYSICAL ANTHROPOLOGY [Vol. 31, 1988

C

D

Fig. 5. Chemeron humerus (KNM-BC 1745) A Medial. R: Anterior. C: Posterior. D: Superior. In the superior view (D), the position of the intertubercular groove is indicated by an arrow.


regional geological report, which also recorded the existence of fossil sites containing wood (Baker, 1963). Baker’s main interest was the Precambrian basement rocks, and his suggestions regarding later strata have been revised by the subsequent investigations (Ishida, 1984).

One occurrence, Samburu Hills, definitely falls within the relevant time period. The other, Nachola, provides a very important assemblage of hominoids apparently attributable to Kenyapithecus and now thought to be 15 or 16 my in age. However, if the Nachola specimens are as young as first suggested, then they would be particularly important here. Consequently we provide a few notes concerning the issue of their dating.

Nachola is one of four adjoining physiographic areas on the eastern side of the northern Rift studied by Ishida’s team (Ishida, 1984); from several localities a total of around 150 hominoid specimens have been recovered (Ishida et al., 1984). Al- though Pickford (1985,1986a-c) provides valuable information relevant to taxonomy and phylogeny, the specimens have not yet been described in any detail-some not at all; and there is contextual information reported for only one of the localities, site BG-X. All the hominoids come from the Nachola Formation. The fossil occurrences are dated radiometrically by two determinations on underlying and overlying basalts. The lower gave a date of 10.1 f 1.4 my; the upper, 11.8 f 1.4 my. This led to a suggestion that the hominoids are about 11 my old (Matsuda et al., 1984, 1986). The faunal evidence is compatible with this interpretation. However, as Pickford et al. (1984b) concede, the published fauna is compatible with any of a relatively wide range of ages, and it is of limited use biostratigraphically. The absence of elements from the fauna may be of more significance than those that are present. No equids are known from the unit, which suggests an age in excess of the date of arrival of equids in sub-Saharan Africa, estimated at about 10.5 my-9 my.

Ishida et al. (1984) allocate most of the 18 large hominoid specimens in their preliminary description to Kenyapithecus africanus (KNM-BG 9145, 9146, 9148-53, 9155[A+B]-58,9161,9162). Two are referred to as Kenyapithecus sp. (KNM-BG 9154, 91601, and one is a deciduous tooth “compatible in size with Kenyapithecus africanus” (KNM-BG 9159). While they allude to Leakey’s belief (in Bishop and Chap- man, 1970) that the Ngorora molar shows strong similarities with Kenyapithecus, they also note that this genus is otherwise only known from sites older than these estimates for Nachola, such as Maboko in western Kenya. Pickford (1985, 1986a-c), discussing these and additional undescribed material, goes further than this, assert- ing that the Nachola hominoids are 15 my-16 my in age. This was apparently based on a rethinking of the character of the limited fauna rather than on unpublished data on radiometric calibration, because Matsuda et al. (1986) reaffirm the earlier radiometric results. However, Ishida has since informed us that new unpublished radiometric dates give results more in accord with the older estimates.

It is quite possible, in fact probable, that Kenyapithecus or taxa very similar to it do in fact extend into our time period. But we are treating these specimens as outside our time constraints. However, Pickford (1985, 1986a,c) has published cur- sory descriptions of the Nachola hominoid sample, and from these comments, it appears that Kenyapithecus, at least as it is represented in the Samburu Hills, had molar cingulae, thick molar enamel, a well-developed and posteriorly projecting inferior mandibular torus, a Dryopithecus-like subnasal pattern rather than the configuration present in Siuapithecus, and possibly external rotation of the canines. In addition, a well-developed canine fossa is reported to be present. Some of these features might be regarded as uniquely shared with Siuapithecus from Turkey and Indo-Pakistan, but from what has been reported to date, we are inclined toward the view that Kenyapithecus represents a large hominoid radiation from which modern large hominoids could well be derived. Questions concerning Kenyapithecus that await resolution include the number of species present in East Africa, whether or not the Nachola sample is related to the Fort Ternan specimens (Kenyapithecus wickeri) and western Kenya specimens, and the extent of sex dimorphism within the two species of Kenyapithecus that are currently recognized.


The Samburu Hills is the other of the two areas designated and investigated by the Japanese expedition (Ishida, 1984). It is about 30 km west of Baragoi and presents a more extensive geological succession than Nachola, but fewer hominoids, there being but one specimen, a very interesting left maxilla with P3-M3 (KNM-SH 8531).

The hominoid comes from the Namurungule Formation, from site SH-22. The whole sequence of strata in the Samburu Hills area begins with the Aka Aiteputh Formation, an estimated 370 m of basalts, trachytes, and welded tuff. It is overlain unconformably by the Namurungule Formation, which consists of about 200 m of clastic sediments in three main regions of outcrop. It corresponds to Baker’s “lake beds and interbedded volcanics” (Baker, 1963). The type section is in the middle portion of the Namurungule River. The Kongia Formation is unconformably above the Namurungule Formation and is composed of about 120 m of clastics, lavas, and volcanic weathering products. A fourth unit, the Nagubarat Formation, formed of black basaltic lavas, lies on the Aka Aiteputh and Namurungule Formations with a n angular unconformity. More geological information, including sections, regional maps, and maps of the hominoid site, is provided by Makinouchi et al. (1984).

The Samburu Hills Maxilla (KNM-SH 8531) Background

The hominoid maxilla (KNM-SH 8531) was found by Cheboi, working with Ishida in 1982, on the surface of a conglomeratic lens in the Namurungule Formation. This site, SH-22, is about 1.5 km upstream from the confluence of the Asanyanait and Nakaporatelado rivers, where the thickness of the Namurungule Formation sediments is about 30 m. The hominoid comes from a 20-cm-thick horizon of angular mud clasts cemented by a calcareous matrix (Makinouchi et al., 1984). Further work at the site in 1984 produced no additional hominoid material (Ishida, pers. commun.).

Dating has been carried out by using WAr, fission-track and paleomagnetic methods (Matsuda et al., 1984, 1986). WAr provides the broad framework. Two samples were taken from two superimposed basalt flows in the upper part of the Aka Aiteputh Formation. Basalts do not form the top unit of this Formation; there are up to 40 m of weathered basaltic sediments above this before the base of the Namurungule Formation is reached. The two samples gave dates of 14.6 k 1.2 my for the lower flow and 12.0 k 1.0 my for the upper. Samples were also taken from flows in the base of the Kongia Formation, which overlies the Namurungule unit. One was from a lava flow lying directly on Namurungule sediments and the other from the second-lowest Kongia lava. They produced dates of 6.3 & 1.0 my and 6.4 f 0.5 my, respectively. Fission-track samples came from 4 m above the hominoid horizon at the same site, and one from another site (SH-20) is stratigraphically 1 m above the hominoid horizon. The former gives a date of 6.7 my f 1.8 my and the latter a date of 16 my k 4 my. (We presume 15 my k 4 my in the text of Matsuda et al., 1984, is a misprint.) Both determinations were carried out on apatite. A low- density collection of 29 samples was taken through the succession for paleomagnetic determinations. Basaltic samples from the top flows of the Aka Aiteputh Formation are reversed. In six samples from the two sites SH-22 and SH-21, which span a section of about 18-m thickness, the lowermost three samples are also reversed; the topmost three are normal. As defined by these determinations the hominoid horizon lies in a reversed zone. If correct the WAr determinations restrict the age of the hominoid to between about 13 my and 6.4 my. One fission-track determination clearly does not accurately date the hominoid horizon, and it has been suggested that the relevant apatite crystals are derived. Even the sample which produces concordant results suffers from having a small number of spontaneous tracks and only eight grains measured. Consequently it has a large error. The low density of the paleomagnetic determinations precludes accurate correlation with GRTS. Based on the results of all of these methods Matsuda et al. (1984, 1986) suggest a date for the hominoid of around 7 my.

Hill and Wardl ORIGIN OF THE HOMINIDAE 67

Paleontological information very loosely agrees with this. SH-22 is just one of a number of sites in the Formation, and a reasonably diverse fauna has been recovered from them (Nakaya et al., 1984; Pickford et al., 1984a,b). Two species of equid have been identified, Hipparion primigenium and Hipparion sitifense, which imply an age younger than about 10 my. On the basis of the existence of primitive giraffids, Palaeotragus and ?Samotherium, and the gomphothere Tetralophodon it is reasonably suggested that the Namurungule sites are appreciably older than those of Lothagam and Lukeino. Among suids there is a primitive-looking Nyanzachoerus, and the hippopotamid is the early Kenyapotamus. These and other considerations lead Pickford et al. (1984a) to suggest an age of about 9 my. They believe it falls into Pickford’s “Faunal Set IV” (Pickford, 1981) and is most similar to faunas from the top of the Ngorora Formation at Ngeringerowa and from Nakali (Aguirre and Leakey, 1974). We agree with this, but it has to be pointed out that the ages of these two sites are not known very precisely either. In summary, the age of the Samburu Hills hominoid is not very tightly constrained by the published results of either paleontological or physical methods, and a date of about 8 my with an error of up to nearly 2 my either way seems to be the best that can be achieved at present.

Preservation and morphology The specimen is a left partial maxilla, with the crowns of P3-M3 in undistorted

position, the canine socket, and a small part of the lateral incisor socket also preserved. The premaxilla is largely missing, precluding an assessment of subnasal morphology.

From the position and size of the canine alveolus, it can be determined that the canine was relatively small, that its root was an elongate ellipse in section, and that it was anteroposteriorly aligned rather than externally rotated as in Sivapithecus and all hominids. The dentition is reminiscent in some ways of Proconsul major, with certain significant differences. The premolar crowns are large, with P3 possess- ing a mesial notch for apposition to the distal edge of the missing canine crown. The mesiobuccal ridge of the anterior premolar is long and angled. The paracone is considerably taller than the protocone, to which it is connected by a robust crest. As is generally the case in hominoids, the P4 paracone and protocone show less height differential. As in Proconsul major, molar lingual cingulae are pronounced. The cingulae begin mesially under the protocones and flex sharply around the bases of the protocones to terminate on the lingual surfaces of the hypocones. From what can be determined from point exposures on the cusp apices of the second and third molars, the enamel is thick, although this perception may be due to the massiveness of the teeth. It is apparent however, that for teeth equivalent in size to large male gorillas, the enamel is clearly thicker in the Samburu Hills maxilla than is the case in gorillas. Unlike Proconsul major, the three molars occur in an ascending size series (M1< M2 < M3), and as a result, the third molar is considerably larger than the first.

Little else can be said at the moment about the specimen, except to note that the morphology of the mesial surface of the third premolar strongly indicates the presence of a large, anteroposteriorly aligned canine. The P3 is very similar in its overall anatomy to that of a female gorilla, and given the estimated size of the canine in this specimen, it is a reasonable guess that the maxilla represents a female of a highly canine dimorphic species. Ishida et al. (1984), Pilbeam (1986), and Andrews and Martin (1987) have noted what appear to be similarities between the Baragoi maxilla and modern gorillas, especially the anatomy of the premolars and mesiodistal expansion of all the postcanine teeth. One approach to resolving the taxonomic relationships of this specimen would be to determine if remnants of an inflated nasolachrymal bulla are present in the floor of the maxillary sinus. Among contemporary hominoids, only the modern gorilla has a nasolachrymal bulla. Its presence in the Samburu Hills specimen would suggest cladistic affbities with Gorilla


LOT HAG AM Geology

Lothagam is a fault-block hill with a set of fossiliferous sites west of Lake Turkana, Turkana District, northern Kenya, between the Kerio and Lomunyenkupurat rivers, at approximately 2'53' N, 36'04' E. Fossils were found in the area in 1965 by Lawrence Robbins. The Harvard University expedition, led by Patterson, and which had been working in Turkana since 1963, made more detailed investigations in 1967 and 1968. In the course of this a hominoid mandible with a single molar tooth was found (KNM-LT 329) (Patterson et al., 1970). Behrensmeyer (1976) provides additional geological information, and Smart (1976) provides an overview of the fauna. Some additional comments on biostratigraphy appear in Hill et al. (in manuscript).

The succession at Lothagam is over 950 m in thickness, beginning with two series of volcanics separated by a major disconformity. There is another disconformity at the top of the highest basalt flow, followed by three sedimentary units totalling 750 m and referred to as Lothagam 1, Lothagam 2, and Lothagam 3. Lothagam 2 and 3 are separated by a basalt sill. The sedimentary units and the sill constitute the Lothagam Group.

Few vertebrates have been collected from the Lothagam 2 sediments, which are predominantly lacustrine silts, clays, and water-laid tuffs, 75-90 m thick. There is a slightly better fauna from Lothagam 3, more than 100 m of coarse sandstones, silts, and clays. A more diverse fauna, of generally high quality, comes from the relatively extensive Lothagam 1 sediments. They range from about 480 m in thickness in the north to about 350 m in the south and are divided into three members, labelled from bottom to top A, B, C.

0.5 my and the upper at 8.53 my + 0.25 my. A radiometric determination on the sill, which is said to postdate Lothagam 3, gives a result of 3.81 my -t 0.23 my. It also shows reversed polarity, and Patterson et al. (1970) suggested a correlation with the terminal third of the Gilbert Reversed Epoch of GRTS. Given these constraints, the fauna was compared to data from other sites for which age estimates were then available, such as Kaperyon in the Tugen Hills sequence and Sahabi in Libya. On the basis of this a plausible estimate for the date of Lothagam 1 was given as 5.0 my to 5.5 my. A tuff at the base of Lothagam 1C gave a wide range of dates from 12 my to 24 my (Behrensmeyer, 1976). Clearly none of these accurately dates the fauna. Given the date on the sill and the character of the fauna a correlation of Lothagam 3 with Kanapoi was suggested, somewhere between 4.0 my and 4.5 my. These suggestions on the whole have been reinforced by more detailed taxonomic work (Cooke and Ewer, 1972; Harris and White, 1979; Maglio, 1970, 1973) coupled with improved radiometric and faunal data from other sites, such as the Tugen Hills sequence (Hill et al., in manuscript).

The Lothagam mandible (KNM-LT 329) Background

The Lothagam mandible (KNM-LT 329) was found by Lewis in 1967 when working with Patterson as part of the Harvard expedition. It was a surface find in the upper half of Member C of Lothagam 1. The mandible is the earliest-recognized occurrence of Hominidae. The most plausible estimate of its age is now in excess of 5.5 my (Hill et al., in manuscript). As far as the allocation to the Hominidae is concerned, it has been suggested that this specimen may in fact not be a hominid but rather another large-bodied hominoid, perhaps similar to Proconsul major (Ekhardt, 1977). There is a consensus, however, that KNM-LT 329 is in fact a hominid mandible, although the specimen has been historically viewed as too fragmentary to permit more than an indeterminate assignment to both genus and species (Howell, 1978). Patterson et al. (1970) attributed the specimen to Australopithecus cf africanus on the basis of its relatively gracile corpus contours and the small size of the first molar crown. There the matter has rested, while in the intervening decade the Hadar and Laetoli

The lowest set of lava flows is dated at 17.2 my


Formations yielded a large sample of Pliocene hominid mandibles (Johanson and White, 1980; White, 1977, 1980; White et al., 1981; White and Johanson, 1982), and the new fragmentary hominid mandible was recovered from Tabarin (Hill, 1985b; Ward and Hill, 1987). These many new Pliocene hominid mandibles obviously place the Lothagam specimen in a completely new comparative context, making a more definitive taxonomic assignment possible.

Preservation and morphology The Lothagam mandible consists of a right corpus broken anteriorly through the

distal root socket of P4 and posteriorly through the distal portion of the third molar socket with a portion of the lower region of the ramus also preserved inferiorly (Fig. 6A-C). The first molar is the only complete tooth, but the roots of the second molar and the mesial root of the third molar are also preserved. Other discrete anatomical elements present are the mental foramen, buccinator groove, oblique line and lateral prominence, most of the mylohyoid line, the submandibular fossa, and the intertoral sulcus. The mandibular base is complete from the level of the M1-M2 interdental septum anteriorly to a point just posterior to the anteromost attachment of the medial pterygoid muscle. The crown of the first molar is moderately worn, with large dentin exposures on the protoconid and hypoconid. These exposures were in the process of coalescing at the time of death. The metaconid shows a small point exposure and the entoconid, while slightly damaged, shows no evidence of dentin exposure. There are no indications of dental or periodontal pathology.

Surface contours on the lateral corpus of KNM-LT 329 are muted, and changes in relief are ill defined. As a consequence, the oblique line and the lateral prominence, both features comprising the union of the ramus and corpus, are modestly expressed. The extramolar sulcus is narrow, and from the broken surfaces preserved on the specimen, it would appear that the anterior edge of the ramus extended to the level of the distal root of the second molar. Depending on the obliquity of the ramus with respect to the corpus, all of the third molar crown was medial to the ramus. This general pattern of surface contours is concordant with that in the Tabarin mandible (see above), the Hadar mandible collection, and the adult mandible (LH-4) from Laetoli. In terms of individual specimens, the Lothagam mandible is most similar to AL 198-1, a left corpus broken through the symphysis anteriorly, and through the corpus just behind M3 posteriorly, and to AL 188-1, a right corpus fragment, lacking the symphyseal region. The latter specimen shows evidence of alveolar pathology and damage to the buccal cortex, but its surface contours are preserved intact. Both Hadar mandibles have modestly expressed lateral prominences, narrow extramolar sulci, and oblique lines that terminate in the vicinity of the M2-M3 contact.

Two other features considered by White (1977, 1986) and White et al. (1981) as diagnostic of A ustralopithecus afarensis anterior mandibular corpora are the vertical position of the mental foramen and the presence of pronounced hollowing of the corpus under the premolars.

In the Lothagam mandible the position of the mental foramen is difficult to assess given the absence of the mandibular base in the premolar region, but it appears that this opening is placed at either midcorpus level or slightly higher. This is also the usual condition in other Pliocene hominid mandibles and may reflect changes in the relative contribution of the alveolar process to the total vertical dimension of the corpus following shortening of the canine and premolar roots, which appears to have occurred in early hominids. Finally, despite the absence of the symphyseal region and canine tooth, there is some evidence that the lateral surface of the Lothagam mandible was distinctly hollowed below the premolars. The alveolar crest adjacent to what is preserved of the P4 socket is deflected laterally in a manner similar to that seen in other Pliocene hominid mandibles with pronounced anterior corpus hollowing. In addition, if the contours preserved in this region are not the result of postmortem deformation, and they appear not to be, then it is quite possible that the Lothagam mandible had a fairly large canine tooth, with associated canine eminence.

YEARBOOK OF PHYSICAL ANTHROPOLOGY [Vol. 31, 1988

A

B

C

M Fig. 6 . Lothagam mandible (KNM-LT 329). A: Lateral. B: Medial. C: Occlusal. See text for discussion.


The medial surface of the corpus is relatively unusual for all early hominids, as it is characterized by considerable relief. There is marked hollowing between the slightly thickened base and the alveolar process above. The mylohyoid line is well expressed, and a submandibular fossa is well developed. A long crack present along the entire length of the medial surface of the corpus may be in part responsible for inwardly flexing the corpus along its anteroposterior axis, thereby accentuating the appearance of relief. However, there is no obvious evidence of mechanical damage, and the pronounced contours in this region are best regarded as representative of the antemortem pattern. Of all the mandibles assigned to A ustralopithecus afarensis, the only specimens that approach KNM-LT 329 in terms of medial corpus relief are AL 198-1 and AL 333-w60. The most common Pliocene hominid pattern involves minimal sculpting of the medial corpus, with poorly defined submandibular fossae and intertoral sulci.

Although the first molar crown offers the only occlusal anatomical and metric information available for the Lothagam jaw, these data are of some use in identify- ing the affinities of the specimen. Corrucini and McHenry (1980) noted that the metaconid is large and that the remaining cusps are arranged in the following order according to diminishing size: hypoconid, protoconid, hypoconulid, and entoconid. These proportions are considered by Corrucini and McHenry (1980) to be most similar to A ustralopithecus afarensis among fossil hominids and that they also reflect an early hominid trend toward enlargement of the talonid cusps. The crown itself is small, especially when compared to the estimated size of the missing second molar crown, and Corrucini and McHenry construe this arrangement as symple- siomorphic for hominids.

Although the occlusal anatomy of the Lothagam M1 is to some extent obscured by wear, it is clear that this tooth is similar in most respects to the first molars of A ustralopithecus afarensis. In occlusal view, the crown is roughly square, with obvious inflation of the hypoconid. Buccal flare is clearly evident, while the lingual side of the crown is almost vertical. Owing to occlusal wear, it is difficult to determine if a true hypoconulid was present, but if it was, it must have been strongly appressed to the distal rim of the crown. In lateral view the crown is clearly bilobate, with pronounced development of the buccal developmental groove. All of these features are also diagnostic of Australopithecus afarensis (White et al., 1981).

The subocclusal anatomy of the Lothagam mandible is revealed both by periapical radiographs and by direct observation of fractured surfaces. The radiographs show the arrangement of the first and second molar roots and provide some information concerning the position of the M3 roots. The root system of M1 appears t o be slightly extruded from the socket with the result that its roots appear to be shorter than those of the second molar. They are in fact similar in length in both teeth. This is a point of some significance, since later Pliocene hominid mandibular molars have roots of essentially equal length. In the later Miocene hominoid genus Siuapithecus, the first molar roots are short while the second and third molar roots are considerably longer. Early and middle Miocene hominoids share with hominids molar root systems of equal length.

The root system of the Lothagam third molar is sufficiently preserved to show that the mesial root had a distinctive bifid apex, as occurs in both Australopithecus afarensis and the South African australopithecines. The distal root of this tooth is missing, but parts of its alveolus are preserved, which indicates that the root was single, strongly constructed, and deflected distally as well as buccally. This third molar root arrangement only occurs in Australopithecus afarensis (Ward et al., 1982).

Finally, it can be determined both from radiographs and the specimen itself that a “serrate” root arrangement is present. This pattern, which only appears in Austra- lopithecus afarensis, is manifested as an axial arrangement of molar roots that results in progressive buccal inclination of distal molar roots, with a concomitant lingual tilting of the crowns. The distal roots are always more angled in frontal projection than are their mesial counterparts, which produces a serrate appearance when the teeth are viewed distally. It has been suggested that this root arrangement


is at least partly responsible for the development of a helicoidal occlusal pattern in the molars, as well as dictating the accumulation of helicoidal wear on the crowns of these teeth. As we have previously noted, this arrangement of molar roots only appears in Pliocene hominid mandibles and should be considered diagnostic of A ustralopithecus afarensis.

There is now a reasonably large sample of Pliocene hominid mandibles on hand, which was not the case in 1966, when the Lothagam mandible was recovered. Mandibles have been traditionally regarded as rather poor sources of taxonomically useful features, but within the appropriate comparative context phylogenetically useful information can be identified. If, as we currently believe, the taxon Australo- pithecus afarensis is valid, then there is no reason not to assign the Lothagam mandible to that taxon, a position we share with Kramer (1986). As we have noted elsewhere (Ward and Hill, 1987) the describers of A ustralopithecus afarensis developed a hypodigm of mandibular size and shape that quite satisfactorily accommo- dates the Tabarin mandible, and the same is true for the Lothagam specimen. Since the diagnosis of A ustralopitheous afarensis is concordant with the preserved morphology of KNM-LT 329, we propose that it be assigned to that taxon.

SAHABI

Geology Three specimens from the later Mio-Pliocene sequence in the Sahabi area of Libya

have been described as fragments of hominoid clavicle (26P4A), hominoid fibula (114P33A), and hominoid parietal (21P21A) (Boaz et al., 1979; Boaz, 1980,1987; Boaz and Meikle, 1982). Doubts have been expressed regarding their hominoid status (White et al., 1983; White, 19871, and Boaz himself acknowledges that “the taxonomic affinities, and thus the overall significance for hominoid evolution, of the Sahabi remains are difficult to assess” (Boaz, 1987).

Paleontological work in the Sahabi region was first carried out by Italian expedi- tions in the 1930s (e.g., Desio, 1931; Petrocchi, 1934) and was resumed in the late 1970s through the early 1980s by the International Sahabi Research Project, directed by Boaz and Gaziry. De Heinzelin and El-Arnauti (1982, 1987) divide the geological succession into three formations, of which the Sahabi Formation is upper- most, lying on the others with an erosional unconformity. They subdivide it into a number of members. The lower parts of the unit represent a marine transgression, but higher members reflect littoral, estuarine, and lagoonal conditions.

No suitable materials for radiometric or paleomagnetic determinations have been found but large-scale lateral correlation suggests a Pliocene age. This estimate is substantiated by the fauna. Cooke (1987) infers from the suids, particularly Nyan- zachoerus kanamensis, an age near the Mio-Pliocene boundary, and the proboscidea also imply a Pliocene attribution (Gaziry, 1982,1987). In reviewing the whole fauna Bernor (1982) and Bernor and Pavlakis (1987) favor a date of about 5.0 my. The Sahabi units were probably deposited after the refilling of the Mediterranean Basin around 5.3 my.

Sahabi clavicle (26P4A) This specimen, from a site in Member U-2, has been identified by Boaz (1980,1987;

Boaz et al., 1979) as a partial left hominoid clavicle. White et al. (1983; see also White, 1987) have criticized this attribution, stating instead that the specimen is actually a posterior rib of a dolphin belonging to a genus known from other skeletal remains in the Sahabi fauna. At present we believe that the specimen, which lacks the lateral one-third of its shaft (and therefore its acromial articulating surface), cannot be attributed to Hominoidea with any degree of confidence.

The Sahabi distal fibula (114P33A) Boaz (1987) describes a distal left fibula with features that prompt him to assign

the specimen to Hominoidea gen. et sp. indet. It derives from a lower member, U-1, than the clavicle. The specimen preserves approximately 5 cm of the terminal part


of the shaft, and the entire malleolar component. The shaft is clearly robust and is unlikely on this basis alone to be that of a large cercopithecoid. However, the malleolus itself is small and does not project laterally in the manner of extant pongids. A deep fossa for the peroneus brevis muscle excavates the posterior surface of the shaft, and Boaz (1987) notes that the specimen shows evidence of hypertrophy of the peroneal muscle complex. He further notes that the specimen presents a general pattern that is more reminiscent of Homo than of other living or more “arboreally adapted” hominoids. This very interesting specimen awaits further comparative and functional assessment.

The Sahabi parietal (21 €21 A) A fragmentary right parietal bone, from a site probably in Member U-1, has also

been described by Boaz (1987) as that of a hominoid of unknown genus and species. Hominoid features are cited as general flatness of the specimen, large middle meningeal vascular channel on the endocranial surface, lack of a sagittal crest a t a state of development where one would be expected in a cercopithecoid, and thickness of the specimen.

We are not certain that these elements in themselves can be used to attribute this specimen to Hominoidea. Lack of a sagittal crest is to be expected in a subadult, as Boaz points out, but does this exclude the specimen from Cercopithecoidea? In addition, the size of endocranial vascular channels has not been sufficiently studied in Miocene monkeys and hominoids to be used as an undoubted hominoid synapo- morphy. While it is quite possible that the Sahabi parietal is in fact that of a hominoid primate, more complete anatomical studies will be required to determine its precise affinities, if in fact they can be determined at all.

KANAPOI Geology

Kanapoi is another site discovered and worked by Patterson’s Harvard University MCZ expedition. It is south of Lothagam, and about 51 km west and 14 km south of Teleki’s Volcano, a t the south end of Lake Turkana (approximately 2’19’ N, 36’04’ E). Sediments were discovered in the area in 1965, and a rich fauna was recovered, which included a hominoid (KNM-KP 271) (Patterson, 1966). The Kanapoi Forma- tion (Patterson et al., 1970) consists of some 70 m of sediments of lacustrine and fluvial facies, overlain by a basalt. Three whole-rock WAr determinations on the basalt, which is of reversed polarity, gave dates of 2.6 my k 0.2 my, 2.78 my k 0.26 my, and 3.0 my -t 0.3 my. As there seemed to be little time elapsed between the top of the sediments and the basalt flow, these dates were thought to be too young given faunal considerations. A subsequent date produced by FM Consultants is cited by Behrensmeyer (1976) as “about 4.0 my”. This appears to be more in accord with the paleontology but in fact is a step-heating date with an error of & 1.0 my (Fitch and Miller, 1976).

The Kanapoi humerus KNM-KP 271) Background

The humeral fragment (KNM-KP 271) was discovered by Patterson in 1965 and has been the subject of intense interest since then (Patterson and Howells, 1967). As is the case for other early hominid specimens, the Kanapoi humeral fragment now exists in a fundamentally new comparative setting following the discoveries at Hadar and in the East Turkana Basin. Currently there are 15 published Plio- Pleistocene distal humeral specimens from eastern and southern Africa available for comparison. (For a comprehensive list see Senut, 1981b.) As is always the case with such specimens, there is at present fundamental disagreement concerning both the taxonomic placement and basic functional characteristics of the Kanapoi distal humerus. Preservation and morphology

KNM-KP 271 is a complete left distal humerus with all epiphyseal elements intact and well preserved (Fig. 7A-C). The specimen is cleanly fractured along an oblique

74 YEARBOOK OF PHYSICAL ANTHROPOLOGY

A

B

C

w Fig. 7. Kanapoi humerus (KNM-KP 271). A Anterior. B: Posterior. C: Distal

[Vol. 31, 1988


plane that begins proximally about 5 cm above the medial epicondyle and termi- nates about 3 cm above the same point. The fracture continues distally to terminate on the lateral epicondyle, but only the actual spine of the supracondylar crest is missing. There is no other damage.

The specimen is large, as reported by Patterson and Howells (1967). However, despite its size, it is considered by most who have examined it to be anatomically quite similar to the distal humerus of Homo. This is somewhat disconcerting given the age of the specimen, but both metric analyses (McHenry and Corruccini, 1975; McHenry, 1976, 1984) and morphological ones (Senut, 1980, 1981a,b, 1982, 1983; Senut and Tardieu, 1985) have been reported to support this contention.

Our examination of KNM-KP 271 leads us to conclude that the specimen is not so distinct from the general pattern present in known A ustralopithecus distal humeri to exclude it automatically from the genus. First, it must be recognized that despite the comments of Senut (1981a,b) and Senut and Tardieu (19851, there is considerable intraspecies variation in hominoid distal humeral anatomy, especially in the degree of expression of the lateral trochlear crest as well as in the size of the capitulum. The lateral trochlear crest is supposedly poorly expressed in Homo according to Senut and Tardieu, which suggests to them (among other things) that there are two functionally distinct distal humeral patterns at Hadar. Senut and Tardieu (1985) also aver that the Kanapoi humerus has a poorly developed lateral trochlear crest and that this feature is “neither long nor strongly angulated.” We find the opposite to be true, and an examination of 100 distal humeri from the late Woodland Libben Collection at Kent State University shows that in this genetically homogeneous population of Homo sapiens, the degree of expression, angulation, and length of the lateral trochlear crest of the humerus covers the gamut of pongid and hominid patterns, at least as defined by Senut and Tardieu.

According to Lovejoy (pers. commun.) part of the problem here stems from the fact that the lateral trochlear crest is strongly expressed when the radius of curvature of the capitulum is small but is reduced when a large capitulum encroaches on the trochlea medially. In humans, the capitulum ranges in size from small to quite expansive, and the lateral trochlear crest varies accordingly in its degree of expression. There are no implied functional differences in the Homo sapiens sample, despite a pattern of lateral trochlear crest variation that encompasses the informal taxonomic categories proposed by Senut and Tardieu. In their scheme, KNM-KP 271 and AL 333-29 fall into one set of distal humeral patterns while a mixed collection of East Turkana and Hadar specimens fall into another. Within this second group Senut and Tardieu recognize two subgroups based largely on lateral trochlear crest expression and vertical position of the lateral epicondyle. It is uncertain what functional conclusions can be drawn from these observations, and as noted previously, we believe that when typical intraspecies ranges of variation are taken into account, the sorting criteria proposed by Senut and Tardieu become superfluous.

There is a legitimate question to be asked concerning the taxonomic status of early hominid distal humeri. Simply stated, can the distal humeri of Australopithe- cus and Homo be accurately identified? The answer to this question is equivocal, but in general, it is, “No, they cannot.” We agree with McHenry that the “human” arrangement of distal humeral features appeared early in hominid evolution and is a poor indicator of affinity below family rank. The Kanapoi humerus does strongly resemble a typical Homo sapiens specimen, and if it in fact is 4 million years old, then either the genus Homo is twice as old as is currently believed or the hominid distal humeral pattern is rather generalized. Based on currently available evidence, it appears that the latter is more likely. Since the morphological pattern of the Kanapoi distal humerus is completely concordant with that described for Austral@ pithecus afarerzsis (Lovejoy et al., 19821, and given the stratigraphic placement of the specimen between the older Tabarin mandible locality and the somewhat younger Laetoli unit, it is quite probable that KNM-KP 271 belongs to Australopithecus afarensis.


MIDDLE AWASH Geology

The Middle Awash is an area of the Awash Valley in Ethiopia presenting a succession of late Neogene and Pleistocene sedimentary deposits. It is about 75 km south of the Hadar region noted for the discovery of specimens of Australopithecus afarensis (Johanson et al., 1982). As at Hadar, the paleontological potential was revealed by Taieb in the course of geological work in the 1960s. Kalb and his Rift Valley Research Mission in Ethiopia made the first paleontological investigations and set up a stratigraphic framework (Kalb et al., 1982a-d,1984). During this time the Pleistocene Bod0 hominid was discovered (Conroy et al., 1978; Kalb et al., 1980). Subsequent work by a group led by Clark found even older hominids that border on the time boundary set for this paper. Two occurrences date most probably to a little older and a little younger than 4 my in age (Clark et al., 1984; White, 1984). Additional geological and paleoenvironmental details are provided by Williams et al. (1986).

Like the younger Hadar Formation, the Middle Awash sediments form part of the Awash Group. They have been placed in two formations-the lower Adu-Asa For- mation and the upper Sagantole Formation. The Sagantole Formation is divided into four members, named from bottom to top, Haradaso Member, Aramis Member, Beearyada beds, and Kalaloo beds. At the base of the Kalaloo beds is a prominent lapilli tuff‘, referred to as the Cindery Tuff (CT), which crops out over a distance of a t least 30 km. The sediments immediately below it, forming the Beearyada beds, are also very consistent laterally and appear to have been deposited in a shallow freshwater lake. Those above it reflect a change, documenting more varied sedimentary conditions.

WAr determinations on the Cindery Tuff have given concordant dates on glass and feldspar of 3.9 my-4.0 my, which agree with fission-track estimates of 4.0 my f 0.2 my (Hall et al., 1984). These results are also in agreement with faunal suggestions.

The Belohdelie frontoparietal (BEL VP-1Il) Seven fragments of a hominid cranial vault were discovered by Krishtalka during

a survey of the region in 1981 and were briefly described by Clark et al. (1984) and White (1984). A more comprehensive analysis has been provided by Asfaw (19871, so the specimen will not be treated in detail here. Three of the fragments have been shown to join to form most of an adult frontal. They come from a level 11 m below the CT horizon and consequently have been dated at “greater than 4.0 my” (Clark et al., 1984). According to Clark et al. (1984), and White (1984), the specimen shows a complex of generalized and primitive features in the topography of the orbital rim, postorbital region, and the temporal lines. Asfaw’s more recent assessment (1987) revealed that the Belohdelie frontal was not strongly constricted postorbitally, unlike later Australopithecus crania from east and southern Africa. The upper face appears to have been broad, with a frontofacial index of 72% (Asfaw, 1987). The supraorbital margin is reported as being thick, but there is no supratoral sulcus. Finally, the temporal lines are strongly inflected medially, but the temporal fossa itself is not deeply excavated. Asfaw (1987) notes that the pattern preserved in the Belohdelie frontal reflects a mix of primitive and derived elements. Of interest are differences between BEL-VPM and the juvenile A ustralopithecus afarensis cranium AL 333-105 involving the postorbital region. To the extent that one can use juvenile hominoids to predict adult topography, Asfaw (1987) shows that the juvenile cranium probably would have had a greater degree of postorbital constriction as an adult than does the Belohdelie specimen. In these and several other features it appears that this frontal bone and associated parietal fragments differ slightly from the morphological pattern previously defined for A ustralopithecus afarensis, but when all elements are considered, it is more similar to the latter taxon than it is to any other known hominid. As Asfaw (1987) points out, it is quite possible that the Belohdelie frontal represents a population of early Australopithecus afarensis that was present in the Middle Awash about 4 my.

Hill and Ward] ORIGIN OF THE HOMINIDAE I1

The Maka femur (MAK-VP-1Il) The other Pliocene hominid from the Middle Awash was found by White in 1981

and is briefly described in Clark et al. (1984) and White (1984). It is a proximal femur fragment coming from 7 m above the projected CT horizon in the Maka drainage about 700 m SW of the Belohdelie specimens. It is also separated from the CT level by an erosional disconformity. The fauna is compatible with that of the Sidi Hakoma member of the Hadar Formation, Ethiopia, and with the Upper Laetoli Beds in Tanzania, and on this basis Clark et al. (1984) suggest an age of 3.5 my-4.0 my. Our own work in the Tugen Hills indicates that the fauna is younger than that of most sites in the Chemeron Formation, which supports this age estimate.

According to the description provided by Clark et al. (1984) and White (19841, the Maka specimen is a proximal femur of a subadult hominid, with a Homo sapiens developmental age of 16-17 years. The specimen is clearly a hominid and not a pongid, and it shows a complex of features that characterize the proximal femora of later Australopithecus samples, including a low necklshaft angle, flattened neck and proximal shaft, minimal flare of the greater trochanter, and a relatively long neck. A convincing case is made by these authors that the specimen is similar in all preserved elements to the Hadar hominid sample attributed to Australopithecus afarensis.

EAST AFRICAN ENVIRONMENTS 14 MY-4 MY

One of the fundamental questions about the origin of the Hominidae alluded to in the introduction involved causes. Why did those particular changes which led to the divergence of the hominid lineage occur when they did? Any answers to this question involve more inference than do those concerning the nature of the earliest hominid or where it evolved. We have just demonstrated that the relevant data concerning these more straightforward questions are so sparse as to preclude definite or definitive responses. This applies even more forcibly to the reasons for hominid speciation. We may never have the necessary data to answer such a question, but it is still fruitful to discuss the range of factors that may plausibly have been involved.

Changes in the environment have been implicated in speciation and evolutionary change to varying degrees. In the context of human evolution, some such as Vrba (1985a,b) have recently been advocating a strong environmentally deterministic approach, with faunal change forced by possibly extraterrestrial factors mediated through global climatic change. She has articulated a “turnover pulse hypothesis” which suggests that faunal change should be expected to be synchronous in separate lineages.

Major changes in world conditions over this time are becoming better documented. The beginning of this period more or less coincides with the last of Raup and Sepkoski’s (1984) 26-my periodic major extinctions. Periodicities of climate on various scales are now well documented. There is the origin and expansion of the Antarctic ice sheets to be considered, and the Mediterranean Messinian salinity crisis. It would be attractive if the origin of some of the distinctive human adaptations could be linked to one or another of these events. However, connecting terrestrial faunal turnover to such occurrences is rather difficult. Behrensmeyer and Cooke (1985) indicate some of the problems. Barry et al. (1985, in press) treat the excellent Pakistan Siwalik record in this light; the African data are discussed in Hill (1987).

Traditionally and loosely the origin of hominids has been seen in the light of changes in vegetation. Consequently it is worth reviewing beliefs and information about vegetation in the later Miocene and early Pliocene. Darwin (1871) saw bipedalism arising through a hominid moving from trees to ground provoked by “a change in its manner of procuring subsistence, or to a change in the conditions of its native country.” Similar ideas have persisted, and a transition from pervasive forest to predominant grassland has been thought to accompany the origins of hominids. However, other than for the later Pleistocene, paleobotanical evidence is generally not good for sub-Saharan Africa.


This change from forest to grassland has been seen as already having happened by the times of Fort Ternan, a t about 14 my. Possibly this was largely motivated by the belief that Kenyapithecus wickeri was a hominid. Faunal indications of forest conditions were usually explained as being derived from the slopes of the Tinderet volcano, which were no doubt forested. Of course, Kenyapithecus, too, could have been part of this forest fauna, which posed problems. More recently paleoanthropologists have accepted that Kenyapithecus is not a hominid, and consequently the environment of Fort Ternan became less pressing a concern. However, Bonnefille (1984) has shown that there is a predominance of grasses a t Fort Ternan, suggesting to her a well-developed grassland habitat.

This should not be seen as indicating that a transition has been made in the east African environment from forest to grass. From slightly later in time BPRP work in the Ngorora Formation shows indications of forest in the Rift Valley (Kabuye and Jacobs, 1986; Jacobs and Kabuye, 19871, and at about 8 my in Ethiopia there is also evidence of forest conditions (Yemane et al., 1985). In the period just after the time span being discussed here there are grassland conditions at Laetoli a t 3.4 my (Bonnefille and Riollet, 1987). Yet a t this same time there is a suggestion from both botanical work (Bonnefille and Letouzey, 1976) and molluscs (Williamson, 1985) of rain forest around Lake Turkana.

The overall suggestion is one of much greater diversity than has been formerly imagined. We should not think in terms of a unique forest-grassland transition but of a much more patchy structure in both time and space. This opens up the possibilty of new reasons for the origins of hominid bipedalism. Some ideas (Wrangham, 1980) have emphasised bipedalism as an adaptation to feeding rather than locomotion in a new habitat. It may be an exaptation for locomotion, in traversing what were initially unusable grasslands, to get from one patch of woodland to another.

Whatever the forces that favored the development of bipedal gait in the early hominids may have been, it seems clear that they must be sought within the context of east African paleoenvironments during the period between 14 my and 4 my. It is also clear that only postcranial remains-particularly the pelvis, hip and knee joints, and the foot-can provide definitive evidence of bipedal locomotion, be it kinemati- cally modern or otherwise. We hope that future fieldwork in the Tugen Hills area, the Middle Awash, and elsewhere will produce such fossils.

ACKNOWLEDGMENTS

This paper is part of the research program of the Baringo Paleontological Research Project (BPRP), which was set up primarily to investigate the course and context of African hominoid evolution in the Tugen Hills succession. BPRP is based at Yale University, directed by A.H., and carried out jointly with the National Museums of Kenya. Our most immediate debt of gratitude is to our colleague Kiptalam Cheboi of the National Museums of Kenya. In working with various research projects in the Kenya Rift Valley since 1967, he has discovered most of the hominoid specimens referred to here. We thank other members of the project for their contributions: John Barry, Kay Behrensmeyer, Barbara Brown, Garniss Curtis, A1 Deino, Robert Drake, Bonnie Fine Jacobs, Louis Jacobs, John Kimengich, Sally McBrearty, Marc Mon- aghan, David Pilbeam, Michael Rose, and Lisa Tauxe. We thank Harvey Herr for his help in Nairobi. The project has been funded by an NSF grant to David Pilbeam, John Barry, and A.H. (BNS 84-07575) and is continued by NSF grant BNS-8802629 to A.H. In addition we acknowledge support from the Louise Brown Foundation, the LSB Leakey Foundation, and the Yale University Social Science Faculty Research Fund. S.W. also received support for this project from NSF grants BNS 84-08126 and BNS 87-18856. Richard Leakey and the National Museums of Kenya provided much logistical assistance, and we thank the Government of the Republic of Kenya for research permission. Noel Boaz kindly provided casts of Sahabi specimens. The figures were prepared by Larry Rubens and Linda Budinoff. We thank Barbara Brown, Hidemi Ishida, David Pilbeam, and Richard Sherwood for their comments on the manuscript.

Hill and Ward] ORIGIN OF THE HOMINIDAE

LITERATURE CITED

79

Aguirre E, and Leakey P (1974) Nakali: Nueva fauna de Hipparion del Rift Valley de Kenya. Es- tudios Geol. 3Ot219-227.

Andrews P (1985) Family group systematics and evolution among catarrhine primates. In E Delson (ed.): Ancestors: The Hard Evidence. New York: Alan R. Liss, Inc., pp. 14-22.

Andrews P (1986) Molecular evidence for catarrhine evolution. In B Wood, L Martin, and P An- drews (eds.): Major Topics in Primate and Human Evolution. Cambridge: Cambridge University Press, pp. 107-129.

Andrews P, and Cronin JE (1982) The relationships of Siuapithecus and Rarnapithecus and the evolution of the orang-utan. Nature 297t541-546.

Andrews P, Harrison T, Martin L, and Pickford M 119811 Hominoid Drimates from a new Miocene locality named Meswa Bridge in Kenya. J. Hum. Evol. 1Ot123-128.

Andrews P, and Martin L (1987) Cladistic relationships of extant and fossil hominoids. J. Hum. Evol. 16t101-118.

Andrews P, and Walker A (1976) The primate and other fauna from Fort Ternan, Kenya. In G Isaac and ER McCown (eds.): Human Origins: Louis Leakey and the African Evidence. Menlo Park: W.A. Benjamin Inc., pp. 279-304.

Asfaw B (1987) The Belohdelie frontal: New evidence of early hominid cranial morphology from the Afar of Ethiopia. J. Hum. Evol. 16t612-624.

Baker BH (1963) The geology of the Baragoi area. Rep. Geol. Sum. Kenya 53:l-74.

Barry J, Flynn L, and Pilbeam DR (in press) Diver- sity and turnover in a Miocene terrestrial com- munity. In R Ross and W Allmon (eds.): Biotic and Abiotic Factors in Evolution. Chicago: University of Chicago Press.

Barry J, Hill A, and Flynn L (1985a) Variation de la faune au Miocene inferieur et moyen de I’Afri- que de I’est. L’Anthropologie (Paris) 89t271-273.

Barry J, Johnson NM, Raza SM, and Jacobs LL (198513) Neogene mammalian faunal change in southern Asia: Correlations with climatic, tectonic, and eustatic events. Geology 13t637-640.

Behrensmeyer AK (1976) Lothagam Hill, Kanapoi, and Ekora: A general summary of stratigraphy and faunas. In Y Coppens, FC Howell, GL Isaac, and RE Leakey (eds.): Earliest Man and Environ- ments in the Lake Rudolf Basin: Stratigraphy, Paleoecology, and Evolution. Chicago: University of Chicago Press, pp. 163-170.

Behrensmeyer AK, and Cooke HBS (1985) Paleoen- vironments, stratigraphy, and taphonomy in the African Pliocene and early Pleistocene. In E Del- son (ed.): Ancestors: The Hard Evidence. New York: Alan R. Liss, Inc., pp. 60-62.

Benefi‘i B, and Pickford M (1986) Miocene fossil cercopithecoids from Kenya. Am. J. Phys. Anthro- pol. 69t441-464.

Bernor RL (1982) A preliminary assessment of the mammalian biochronology and zoogeographic relationships of Sahabi, Libya. Garyounis Sci. Bull. Spec. Issue 4t133-139.

Bernor RL, and Pavlakis PP (1987) Zoogeographic relationships of the Sahabi large mammal fauna (Early Pliocene, Libya). In NT Boaz, A El-Arnauti, AW Gaziry, J de Heinzelin, and DD Boaz (eds.): Neogene Paleontology and Geology of Sahabi. New York: Alan R. Liss, Inc., pp. 349-383.

Bishop WW, and Chapman GR (1970) Early pliocene sediments and fossils from the northern Kenya Rift Valley. Nature 226t914-918.

Bishop WW, Chapman GR, Hill A, and Miller JA (1971) Succession of Cainozoic vertebrate assem- blages from the northern Kenya Rift Valley. Na- ture 233t389-394.

Bishop WW, Hill A, and Pickford M (1978) Cheso- wanja: A revised geological interpretation. In WW Bishop (ed.): Geological Background to Fossil Man. Edinburgh: Scottish Academic Press; Geological Society of London, pp. 309-327.

Bishop WW, Miller JA , and Fitch FJ (1969) New potassium-argon age determinations relevant to the Miocene fossil mammal sequence in east Af- rica. Am. J. Sci. 267t669-699.

Bishop WW, and Pickford M (1975) Geology, fauna and palaeoenvironments of the Ngorora Forma- tion, Kenya Rift Valley. Nature 254t185-192.

Bishop WW, Pickford M, and Hill A (1975) New evidence regarding the Quaternary geology, archaeology, and hominids of Chesowanja, Kenya. Nature 258~204-208.

Boaz NT (1980) A hominoid clavicle from the Mio- Pliocene of Sahabi, Libya. Am. J. Phys. Anthro-

Boaz NT (1987) Sahabi and neogene hominoid evolution. In NT Boaz, A El-Arnauti, AW Gaziry, J de Heinzelin, and DD Boaz (eds.): Neogene Paleon- tology and Geology of Sahabi. New York: Alan R. Liss, Inc., pp. 129-134.

Boaz NT and Meikle WE (1982) Fossil remains of primates from the Sahabi Formation. Garyounis Sci. Bull. Spec. Issue 4t1-48.

Boaz NT, Gaziry AW, and El-Arnauti A (1979) New fossil finds from the Libyan upper Neogene site of Sahabi. Nature 280t137-140.

Bonnefille R (1984) Cenozoic vegetation and environments of early hominids in east Africa. In RO Whyte (ed.): The Evolution of the East Asian En- vironment. Hong Kong: Centre of Asian Studies, University of Hong Kong, pp 579-612.

Bonnefille R, and Letouzey R (1976) Fruits fossiles d’Antrocaryon dans la Vallee de I’Omo (Ethiope). Adansonia 265-82.

Bonnefille R, and Riollet G (1987) Palynological spectra from the Upper Laetolil Beds. In MD Leakey and JM Harris (eds.): Laetoli: A Pliocene Site in Northern Tanzania. Oxford: Oxford Uni- versity Press, pp. 52-61.

Carney J, Hill A, Miller J, and Walker A (1971) Late australopithecine from Baringo District, Kenya. Nature 23Ot509-514.

Chapman GR (1971) The Geological Evolution of the Northern Kamasia Hills, Baringo District, Kenya. Unpublished Ph.D. thesis, University of London.

Chapman GR, and Brook M (1978) Chronostratig- raphy of the Baringo Basin, Kenya Rift Valley. In WW Bishop (ed.): Geological Background to Fossil Man. London: Geological Society of London, Scot- tish Academic Press, pp. 207-223.

Chapman GR, Lippard SJ, and Martyn JE (1978) The stratigraphy and structure of the Kamasia Range, Kenya Rift Valley. J. Geol. SOC. Lond.

pol. 53t49-54.

135r265-281. Clark JD, Asfaw B, Assefa G, Harris JWK. Ku- rashina H, Walter RC, White TD, and Williams MAJ (1984) Palaeoanthropological discoveries in


the Middle Awash Valley, Ethiopia. Nature 307:423-428.

Conroy G, Jolly CJ, Cramer D, and Kalb JE (1978) Newly discovered fossil hominid skull from the Afar Depression, Ethiopia. Nature 275:67-70.

Cooke HBS (1987) Fossil suidae from Sahabi, Li- bya. In NT Boaz, A El-Arnauti, AW Gaziry, J de Heinzelin, and DD Boaz (eds.): Neogene Paleontol- ogy and Geology of Sahabi. New York: Alan R. Liss, Inc., pp. 255-266.

Cooke HBS, and Ewer RF (1972) Fossil suidae from Kanapoi and Lothagam, north-western Kenya. Bull. Mus. Comp. Zool. Harvard 143r149-296.

Corruccini RS (1975) A Metrical Study of Crown Component Variation in the Hominoid Dentition. Ph.D. dissertation, University of California, Berkeley.

Corruccini RS, and McHenry HM (1980) Cladomet- ric analysis of Pliocene hominoids. 3 . Hum. Evol. 9:209-221.

Dagley P, Mussett AE, and Palmer HC (1978) Pre- liminary observations on the pal aeomagnetic stratigraphy of the area west of Lake Baringo, Kenya. In WW Bishop (ed.): Geological Back- ground to Fossil Man. London: Geological Society of London, Scottish Academic press, pp. 225-235.

Darwin C (1871) The Descent of Man, and Selection in Relation to Sex. London; John Murray.

de Heinzelin J, and El-Arnauti A (1982) Stratigra- phy and geological history of the Sahabi and related formations. Garyounis Sci. Bull. Spec. Issue 4:5-12.

de Heinzelin J, and El-Arnauti A (1987) The Sahabi Formation and related deposits, In N T Boaz, A El- Arnauti, AW Gaziry, J de Heinzelin, and DD Boaz (eds.): Neogene Paleontology and Gcology of Sa- habi. New York: Alan R. Liss, Inc., pp. 1-21.

Desio A (1931) Osservationi geologiche e geograf- iche compiute durante un viaggio nella Sirtica. Boll. Reale. SOC. Geogr. Ital. Ser. 6 3:275-299.

Ekhardt RB (1977) Hominid origins: The Lothagam problem. Curr. Anthropol. 18:356.

Fitch F, and Miller JA (1976) Conventional potas- siudargon and argon 40iargon 39 dating of volcanic rocks from East Rudolf. In Y Coppens, FC Howell, GL Isaac, and RE Leakey (eds.): Earliest Man and Environments in the Lake Rudolf Basin: Stratigraphy, Paleoecology, and Evolution. Chi- cago: University of Chicago press, pp. 123-147.

Franzen JL (1985) Asian australopithecines?: In PV Tobias (ed.): Hominid Evolution: Past, Present and Future. New York: Alan R. Liss, lnc., pp. 255- 263.

Fuchs VE (1934) The geological work of the Cam- bridge Expedition to the East African Lakes, 1930-31. Geol. Magazine 7Zr97-112.

Fuchs VE (1950) Pleistocene events in the Baringo Basin. Geol. Magazine 87r149-174.

Gaziry AW (1982) Proboscidea from the Sahabi formation. Garyounis Sci. Bull. Spec. Issue 4:lOl- 108.

Gaziry AW (1987) Remains of Proboscidea from the early Pliocene of Sahabi, Libya. In N T Boaz, A El- Arnauti, AW Gaziry, J de Heinzelin, and DD Boaz (eds.): Neogene Paleontology and Geology of Sahbi. New York: Alan R. Liss, Inc., pp. 183~-203.

Gregory JW (1896) The Great Rift Valley. London: John Murray.

Gregory JW (1921) The Rift Valleys and Geology of East Africa. London: Seeley Service and Co.

Hall CM, Walter RC, Westgate JA, and York, D (1984) Geochronology, stratigraphy and geochem-

istry of Cindery Tuff in the Pliocene hominid- bearing sediments of the Middle Awash, Ethiopia. Nature 308t26-31.

Harris JM, and White TD (1979) Evolution of the Plio-pleistocene Suidae. Trans. Am. Philos. SOC. 69: 1-128.

Hill A (1985a) Les variations de la faune du Mio- cene recent et du Pliocene d’Afrique de l’est. L’An- thropologie (Paris) 89r275-279.

Hill A (198513) Early hominid from Baringo, Kenya. Nature 315.222-224.

Hill A (1987) Causes of perceived faunal change in the later Neogene of east Africa. J. Hum. Evol. 16:583-596.

Hill A, Drake R, Tauxe L, Monaghan M, Barry JC, Behrensmeyer AK, Curtis G, Fine Jacobs B, Ja- cobs L, Johnson N, and Pilbeam D (1985) Neogene palaeontology and geochronology of the Baringo Basin, Kenya. J. Hum. Evol. 14:749-773.

Hill A, Curtis G, and Drake R (1986) Sedimentary stratigraphy of the Tugen Hills, Baringo District, Kenya. In LE Frostick, RW Renaut, I Reid, and JJ Tiercelin (eds.): Sedimentation in the African Rifts. Oxford: Blackwell, Geological Society of London Special Publication # 25, pp. 285-295.

Hill A, and Ward S (in MS) Hominid mandible from Tabarin, Kenya. L’Anthropologie.

Hill A, Ward S, and Brown B (in MS) The Lotha- gam mandible. To be submitted to American Jour- nal of Physical Anthropology.

Howell FC (1978) Hominidae. In VJ Maglio and HBS Cooke (eds.): Evolution of African Mammals. Cambridge: Harvard University Press, pp. 154- 248.

Ishida H (1984) Outline of the 1982 survey in Sam- buru Hills and Nachola area, northern Kenya. Afr. Study Monogr. Suppl. Issue 2.1-14.

Ishida H, Ishida S, Torii M, Matsuda T, Kawamura Y, and Koizumi K (1982) Report of field survey in Kirimum, Kenya, 1980. Study of the Tertiary Hominoids and their Palaeoenvironments in East Africa. Vol. 1. Osaka: Osaka University, pp. 1- 181.

Ishida H, Pickford M, Nakaya H, and Nakano Y (1984) Fossil anthropoids from Nachola and Sam- buru Hills, Samburu District, Kenya. Afr. Study Monogr. Suppl. Issue 2t76-85.

Jacobs BF, and Kabuye CBS (1987) A middle Mio- cene (12. 2 my old) forest In the East African Rift Valley, Kenya. J. Hum. Evol. 16:147-155.

Johanson DC, Taieb M, and Coppens Y (1982) Pli- ocene hominids from the Hadar Formation Ethio- pia (1973-1977): Stratigraphic, chronologic, and paleoenvironmental contexts, with notes on hominid morphology and systematics. Am. J. Phys. Anthropol. 57r373-402.

Johanson DC, and White T (1980) On the status of A ustralopithecus afarenszs. Science 207: 1104-1105.

Johanson DC, White T, and Coppens Y (1978) a new species of the genus A ustralopithecus (Primates: Hominidae) from the Pliocene of eastern Africa. Kirtlandia 28:l-14.

Johnson NM. and McGee VE (1983) Magnetic polarity stratigraphy: Stochastic properties of data, sampling problems and the evaluation of interpretations. J. Geophys. Res. 88:1213-1221.

Kabuye CHS, and Jacobs BF (1986) An interesting record of the genus Leptaspis, Bambusoideae from Middle Miocene Flora Deposits in Kenya, East Africa. Abstracts: International Symposium on Grass Systematics and Evolution. Washington D.C.: Smithsonian Institution, p. 32.


Kalb JE, Jolly CJ, Mebrate A, Tebedge S, Smart C Oswald EB, Cramer D, Whitehead P, Wood CB; Conroy GC, Adefris T, Sperling L, and Kana B (1982a) Fossil mammals and artefacts from the Middle Awash Valley, Ethiopia. Nature 298t17- 25.

Kalb JE, Jolly CJ, Oswald E, and Whitehead P (1984) Early hominid habitation in Ethiopia. Am. Sci. 72t168-178.

Kalb JE, Jolly CJ, Tebedge S, Mebrate A, Smart C, Oswald EB, Whitehead P, Wood CB, Adefris T, and Rawn-Schatzinger V (198213) Vertebrate faunas from the Middle Awash Valley, Afar, Ethiopia. J. Vertebrate Paleontol. 2:237-258.

Kalb JE, Oswald EB, Mebrate A, Tebedge S, and Jolly CJ (1982~) Stratigraphy of the Awash Group, Middle Awash Valley, Afar, Ethiopia. Newslett. Stratigr. 11t95-127.

Kalb JE, Oswald EB, Tebedge S, Mebrate A, Tala E, and Peak D (1982d) Geology and stratigraphy of Neogene deuosits. Middle Awash Vallev. Afar. ” , I

Ethiopia. NatGre 298:25-29. Kalb JE, Wood CB, Smart C, Oswald EB. Mebrate A, Tebedge S, and Whitehead P (1980) Prelimi- nary geology and paleontology of the Bod0 D’ar hominid site, Afar, Ethiopia. Paleogeogr. Paleocli- matol. Paleoecol. 30:107-120.

Kappleman J (1985a) Changement climatique au cours du Plio-Pleistocene dans la Gorge d’olduvai, Tanzanie. L’Anthopologie (Paris) 89t281-283.

Kappleman J (1985b) Climatic change during the _ _ Plio-pleistocene a t Olduvai Gorge,-Tanzan&. S. Afri. 1. Sci. 81.255.

Kappleman J (1986) Plio-Pleistocene marine-continental correlation using habitat indicators from Olduvai Gorge, Tanzania. Quaternary Res. 25t141-149.

Kelley J, and Pilbeam D (1986) The dryopithecines: Taxonomy, comparative anatomy, and phylogeny of Miocene large hominoids. In DR Swindler and J Erwin (eds.): Comparative Primate Biology, Vol- ume 1: Systematics, Evolution, and Anatomy. New York: Alan R Liss, Inc., pp. 361-411.

King BC, and Chapman GR (1972) Volcanism of the Kenya rift valley. Philos. Trans. R. Sac. Lond. Ser. A 271t185-208.

Kramer A (1986) Hominid-Pongid distinctiveness in the Miocene-Pliocene fossil record The Lotha- gam mandible. Am. J. Phys. Anthropol. 70:457- 473.

Leakey LSB (1967) An early Miocene member of the Hominidae. Nature 213:155-163.

Leakey MD, Hay RL, Curtis G, Drake RE, Jackes MK, and White TD (1976) Fossil hominids from the Laetolil Beds at Laetoli, northern Tanzania. Nature 262r460-466.

Leakey RE, and Leakey MG (1986) A new Miocene bominoid from Kenya. Nature 324t143-146.

Leakey RE, and Walker A (1985) New higher primates from the early Miocene of Buluk, Kenya. Nature 318t173-175.

Lovejoy CO, Johanson DC, and Coppens Y (1982) Hominid upper limb bones recovered from the Hadar Formation: 1974-1977 collections. Am. J. Phys. Anthropol. 57t637-650.

Maglio VJ (1970) Early Elephantidae of Africa and a tentative correlation of African Plio-Pleistocene deposits. Nature 225t328-332.

Maglio VJ (1973) Origin and evolution of the Ele- phantidae. Trans. Am. Philos. Sac. 63t1-149.

Makinouchi T, Koyaguchi T, Matsuda T, Mitsushio H, and Ishida S (1984) Geology of the Nachola area and the Samburu Hills, west of Baragoi, Northern Kenya. Afr. Study Monogr. Suppl. Issue 2.15544.

Mankinen EA, and Dalrymple GB (1979) Revised magnetic polarity time scale for the interval 0-5 m.y. B.P. J . Geophys. Res. 84:615-626.

Martyn JE (1967) Pleistocene deposits and new fossil localities in Kenya. Nature 215:476-477.

Martyn JE (1969) The Geological History of the Country Between Lake Baringo and the Kerio River, Baringo District, Kenya. Unpublished Ph.D. thesis, University of London.

Matsuda T, Torii M, Koyaguchi T, Makinouchi T, Mitsushio H, and Ishida S (1984) Fission-track, K- Ar age determinations and palaeomagnetic mea- surements of Miocene volcanic rocks in the western area of Baragoi, northern Kenya: Ages of hominoids. Afr. Study Monogr. Suppl. Issue 2r57- 66.

Matsuda T, Torii M, Koyaguchi T, Makinouchi T, Mitsushio H, and Ishida S (1986) Geochronology of Miocene hominoids east of the Kenya Rift Val- ley. In JG Else and PC Lee (eds.): Primate Evolu- tion. Cambridge: Cambridge University Press, pp. 35-45.

McCall GJH, Baker BH, and Walsh J (1967) Late Tertiary and Quaternary sediments of the Kenya Rift Valley. In WW Bishop and JD Clark (eds.): Background to Evolution in Africa. Chicago: Uni- versity of Chicago Press: pp, 191-220.

McClenaghan MP (1971) Geology of the Ribkwo Area, Baringo District, Kenya. Unpublished Ph.D. thesis, University of London.

McHenry HM (1976) Multivariate analysis of early hominid humeri. In E Giles and JS Friedlaender (eds.): The Measures of Man. Cambridge: Peabody Museum Press, Harvard University, pp. 338-371.

McHenry HM (1984) The common ancestor: A study of the postcranium of Pun puniscus, Australopithe- cus, and other hominoids. In RL Sussman (ed.): The Pygmy Chimpanzee. New York: Plenum, pp. 201-230.

McHenrv HM. and Corruccini RS (1975) Distal humerus “in hominoid evolution. Folia Primatol. (Basel) 23:227-244.

McHenrv HM, and Corruccini RS (1980) Late Ter- tiary Lominoids and human origins. Nature 285r397-398.

Nakaya H, Pickford M, Nakano Y, and Ishida H (1984) The late Miocene large mammal fauna from the Namurungule Formation, Samburu Hills, northern Kenya. Afr. Study Monogr Suppl. Issue 2237-131.

Ness G, Levi S, and Crouch R (1980) Marine magnetic anomaly time scales for the Cenozoic and late Cretaceous: A precis, critique, and synthesis. Rev. Geopbys. Space Phys. 18:753-770.

Patterson B (1966) A new locality for early Pleisto- cene fossils in north-western Kenya. Nature 212t577-581.

Patterson B, and Howells WW (1967) Hominid humeral fragment from early Pleistocene of north- west Kenya. Science 156:64-66.

Patterson B, Behrensmeyer AK, and Sill WD (1970) Geology and fauna of a new Pliocene locality in north-western Kenya. Nature 226t918-921.

Petrocchi C (1934) I ritrovamenti faunistici di es- Sahabi. Riv. Colonie Ital. 8(9):733-742.

[Vol. 31, 1988 82 YEARBOOK OF PHYSICAL ANTHROPOLOGY

Pickford M (1975a) Stratigraphy and Palaeoecology of Five Late Cainozoic Formations in the Kenya Rift Valley. Unpublished Ph.D. thesis, University of London.

Pickford M (1975b) Late Miocene sediments and fossils from the northern Kenya Rift Valley. Na- ture 256279-284.

Pickford M (1978a) Geology, paleoenvironments and vertebrate faunas of the mid-Miocene Ngorora Formation, Kenya. In WW Bishop (ed.): Geologi- cal Background to Fossil Man. London: Geological Society of London, Scottish Academic Press, pp. 237-262.

Pickford M (1978b) Stratigraphy and mammalian paleontology of the late-Miocene Lukeino Forma- tion, Kenya. In WW Bishop (ed.): Geological Back- ground to Fossil Man. London: Geological Society of London, Scottish Academic Press, pp. 263-278.

Pickford M (1981) Preliminary Miocene mammalian biostratigraphy from western Kenya. J. Hum. Evol. 10:73-97.

Pickford M (1983) Sequence and environments of the lower and middle Miocene hominoids of western Kenya. In RL Ciochon and RS Corruccini (eds.): New Interpretations of Ape and Human Ancestry. New York: Plenum, pp. 421-439.

Pickford M (1985) Kenyupithecus: A review of its status based on newly discovered fossils from Kenya. In PV Tobias (ed.): Human Evolution: Past, Present and Future. New York: Alan R. Liss, Inc., pp. 107-112.

Pickford M (1986a) Hominoids from the Miocene of east Africa and the phyletic position of Kenyupi- thecus. Z. Morphol. Anthropol. 76r115-130.

Pickford M (198613) The geochronoloby of Miocene higher primate faunas of east Africa. In JG Else and PC Lee (eds.): Primate Evolution. Cambridge: Cambridge University Press, pp. 19--33.

Pickford M (1986~) A reappraisal of Kenyupzthecus. In JG Else and PC Lee (eds.): Primate Evolution. Cambridge: Cambridge University Press, pp, 163- 172.

Pickford M, Ishida H, Nakano Y, and Nakaya H (1984a) Fossiliferous localities of the Nachola- Samburu Hills area, northern Kenya. Afr. Study Monogr. Suppl. Issue 2t45-56.

Pickford M, Johanson DC, Lovejoy CO, White TD, and Aronson JL (1983) A hominoid humeral fragment from the Pliocene of Kenya. Am. J. Phys. Anthropol. 6Or337-346.

Pickford M, Nakaya H, Ishida H, and Nakano Y (1984b) The biostratigraphic analyses of the faunas of the Nachola area and Samburu Hills, northern Kenya. Afr. Study Monogr. Suppl. Issue 2t67-72.

Pilbeam D (1985) Patterns of hominoid evolution. In E Delson (ed.): Ancestors: The Hard Evidence. New York: Alan R Liss, Inc., pp. 51--59.

Pilbeam D (1986) Distinguished lecture: Hominoid evolution and hominoid orgins. Am. Anthropol.. 88r295-312.

Raup DM, and Sepkoski JJ (1984) Periodicity of extinctions in the geologic past. Proc. Nat. Acad. Sci. USA 81t801-805.

Senut B (1980) Nouvelles donnees sur I’hunierus et ses articulations chez les hominides plio-pleistocenes. L’Anthropologie (Paris) 84t112-118.

Senut B (1981a) Humeral outlines in some hominoid primates and in plio-pleistocene hominids. Am. J. Phys. Anthropol. 56t275-282.

Senut B (1981b) L’Humerus et ses Articulations Chez les Hominides Plio-Pleistocenes. Cahiers Pa- leoanthropologie. Paris: CNRS.

Senut B (1982) Reflexions sur la brachiatlon et l’origine des Hominides a la lumiere des Homi- noides miocenes et des Hominides plio-pleistocenes. Geobios Mem. Spec. 6335-344.

Senut B (1983) Quelques remarques a propos d’un humerus d’hominoide Pliocene provenant de Chemeron (bassin du lac Baringo, Kenya). Folia Primatol. (Basel) 41267-276.

Senut B, and Tardieu C (1985) Functional aspects of Plio-Pleistocene hominid limb bones: Implica- tions for taxonomy and phylogeny. In E Delson (ed.): Ancestors: The Hard Evidence. New York: Alan R. Liss, Inc., pp. 193-201.

Shackleton RM (1951) A review of some recent work in the rift valleys of Kenya. 18th Int. Geol. Congr. 14213.

Sibiey CG, and Ahlquist J E (1984) The phylogeny of hominoid primates, as indicated by DNA-DNA- hybridization. J . Mol. Evol. 20r2-15.

Simons EL, and Pilbeam DR (1978) Rnmupzthecus (Hominidae, Hominoidea). In, VJ Maglio, and HBS Cooke (eds.): Evolution of African Mammals. Cambridge: Harvard University Press, pp. 147- 153.

Smart C (1976) The Lothagam 1 fauna: Its phylo- genetic, ecological, and biogeographic significance. In Y Coppens, FC Howell, GL Isaac, and REF Leakey (eds.): Earliest Man and Environ- ments in the Lake Rudolf Basin: Stratigraphy, Paleoecology, and Evolution. Chicago: Chicago University Press, pp. 361-369.

Tauxe L, Monaghan M, Drake R, Curtis G, and Staudigel H (1985) Paleomagnetism of Miocene East African Rift sediments and the calibration of the Geomagnetic Reversal Timescale. J. Geophys. Res. 9Ot4639-4646.

Thomson J (1884) Through Masailand. London: Samson Low, 364 pp.

Tobias PV (1967) Pleistocene deposits and new fossil localities in Kenya. Nature 215r478-480.

Vrba E (1985a) Environment and evolution: Alter- native causes of the temporal distribution of evolutionary events. S. Afr. J. Sci. 81t229-236.

Vrba E (1985b) Early hominids in southern Africa: Updated observations on chronological and ecological background. In PV Tobias (ed.): Hominid Evolution: Past, Present and Future. New York: Alan R. Liss. Inc., pp. 195-200.

Ward S, and Hill A (1987) Pliocene hominid partial mandible from Tabarin, Baringo, Kenya. Am. J. Phys. Anthropol. 722 1-37.

Ward S, and Hill A (in MS) The Chemeron hominid temporal. To be submitted to the Journal of Phys- ical Anthropology.

Ward S, Johanson DC, and Coppens Y (1982) Suboc- clusal morphology and alveolar process relationships of hominid gnathic elements from the Hadar Formation: 1974-1977 collections. Am. J. Phys. Anthropol. 57t605-630.

Ward S, and Kimbel WH (1983) Subnasal alveolar morphology and the systematic position of Siuu- pithecus. Am. J. Phys. Anthropol. 61t157-171.

Ward S, and Pilbeam D (1983) Maxillofacial morphology of Miocene hominoids from Africa and Indo-Pakistan. In RL Ciochon and RS Corruccini (eds.): New Interpretations of Ape and Human Ancestry. New York: Plenum, pp. 211-238.

White TD (1977) New fossil honiinids from Laetoli, Tanzania. Am. J. Phys. Anthropol. 46t197-229.

White TD (1980) Additional fossil hominids from Laetoli, Tanzania: 1976-1979 specimens. Am. J. Phys. Anthropol. 53:487-504.


White TD (1984) Pliocene hominids from the Mid- dle Awash, Ethiopia. In P Andrews and JL Fran- Zen (eds.): The Early Evolution of Man, With Special Emphasis on Southeast Asia and Africa. Courier Forschungsinstitut Senckenberg 69t57- 68.

White TD (1986) A ustralopithecus afurensis and the Lothagam mandible. Anthropos (Brno). 23t79-90.

White TD (1987) Review of Neogene Paleontology and Geology of Sahabi. J. Hum. Evol. 16t312-315.

White TD, Johanson DC, and Kimbel WH (1981) Australopithecus africanus: Its phyletic position reconsidered. S. Afr. J. Sci. 77t445-470.

White TD, and Johanson DC (1982) Pliocene hominid mandibles from the Hadar Formation, Ethio- pia: 1974-1977 collections. Am. J. Phys. An- thropol. 57~501-544.

White TD, Suwa G, Richards G, Watters JP, and Barnes LG (1983) “Hominoid clavicle” from Sa- habi is actually a fragment of cetacean rib. Am. J. Phys. Anthropol. 61t239-244.

Williams LAJ, and Chapman GR (1986) Relation- ships between major structures, salic volcanism and sedimentation in the Kenya Rift from the equator northwards to Lake Turkana. In LE Fros- tick, RW Renaut, I Reid, and JJ Tiercelin (eds.): Sedimentation in the African Rifts. Oxford: Black- well, Geological Society of London Special Publi- cation # 25. pp. 59-74.

Williams MAJ, Getaneh A, and Adamson DA (1986) Depositional context of Plio-Pleistocene hominid- bearing formations in the Middle Awash valley, southern Afar Rift, Ethiopia. In L Frostick, RW Renaut, I Reid, and JJ Tiercelin (eds.): Sedimen- tation in the African Rifts. Oxford: Blackwell, Geological Society of London Special Publication b’ 25, pp. 241-251.

Williamson PG (1985) Evidence for an earlv Plio- Pleistocene rainforest expansion in east Africa. Nature 315t487-489.

Willis B (1936) East African Plateaus and Rift Val- leys. Washington: Carnegie Institution.

Wrangham RW (1980) Bipedal locomotion as a feeding adaptation in Gelada baboons, and its implications for hominid evolution. J. Hum. Evol. 9t329-331.

Yemane K, Bonnefille R, and Faure H (1985) Pa- laeoclimatic and tectonic implications of Neogene microflora from the northwestern Ethiopian high- lands. Nature 318t653-656.

Zhang Y (1984) The “Austrulopithecus” of West Hubei and some early Pleistocene hominids of Indonesia. Acta Anthropol. Sin. 3t92.

Zhang Y (1985) Gigantopithecus and “Australopi- thecus” in China. In R Wu and JW Olsen (eds.): Palaeoanthropology and Palaeolithic Archaeology in the People’s Republic of China. New York: Ac- ademic Press, pp. 69-78.

Documents

Origin of the hominidae: The record of african large hominoid evolution between 14 my and 4 my