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A New Species of Varanus (Reptilia: Sauria) from theMiocene of KenyaLynne M. Clos aa 1185 Claremont Drive, Boulder, Colorado, 80303

Available online: 24 Aug 2010

To cite this article: Lynne M. Clos (1995): A New Species of Varanus (Reptilia: Sauria) from the Miocene of Kenya, Journalof Vertebrate Paleontology, 15:2, 254-267

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Journal of Vertebrate Paleontology 15(2):254-267, June 1995© 1995 by the Society of Vertebrate Paleontology

A NEW SPECIES OF VARANUS (REPTILIA: SAURIA) FROM THEMIOCENE OF KENYA

LYNNE M. CLOS1185 Claremont Drive, Boulder, Colorado 80303

ABSTRACT-A new species of Varanus is described from the early Miocene (17.8 Ma) of RusingaIsland, Kenya. This is the earliest described appearance of the Varanidae in Africa and the oldestcertain occurrence of the genus Varanus in the fossil record. Varanus rusingensis was a one to twometer-long lizard that probably favored riparian habitats in the lowland evergreen forest that coveredmuch of western Kenya during the early Miocene. Tooth structure suggests that the Rusinga monitorfed extensively on molluscs as do several living species of Varanus.

INTRODUCTION

The fossils described in this paper come from theearly Miocene (17.8 Ma) of Rusinga Island, Kenya(latitude 0025'S, longitude 34°21'E), in northeast LakeVictoria at the mouth of the Nyanza Gulf. They rep­resent the earliest described appearance of the familyVaranidae on the African continent, and the oldestcertain occurrence of the genus Varanus in the fossilrecord. A faunal list for a site in the former USSRincludes mention of "Lacertilia (?Varanus sp.)" in amid-Eocene layer, but no description of the materialis given (Reshetov et aI., 1978; Lungu et aI., 1983).

The holotype of Varanus rusingensis is a small, prob­ably young, adult individual approximately one meterlong. It is assumed that the type specimen is an adult,because the recent monitors that exhibit a similar du­rophagous dentition do not acquire it until adulthood.Bones of the holotype are comparable in size to thoseof a meter-long specimen of V. niloticus (AMNH10499) , and some of the hypodigm material is ap­proximately twice this size. Thus, adult Rusinga mon­itors ranged from about one to at least two meters inlength. Except for the lower jaw, right pes, and a setof nine caudal vertebrae, the bones are disarticulated,but are not abraded and probably did not undergomuch, if any, transport prior to burial. They are, inmost cases, well preserved. The presence of twelvecomplete and fragmentary femora indicates that a min­imum of six individuals are included in the materialreferred to V. rusingensis.

The bones of V. rusingensis are found in a matrixof grey tuffaceous siltstone derived from the Kisingirivolcano which lay between the incipient Eastern andWestern Rifts. Volcaniclastic sediments in the area arethought to have been reworked by shallow, sluggishstreams and redeposited in a floodplain environment(Andrews and Van Couvering, 1975; Pickford, 1981,1986; Van Couvering, 1972). A fuller discussion of thestratigraphy and dating of the Rusinga Island sedi­ments can be found in Drake et aI. (1988) .

254

All of the material described in this paper was col­lected between 1947 and 1972 and is in the collectionsof the Kenya National Museum. The following ma­terial was available for comparative study: Varanusniloticus , skeletons UCM OS-1186 and AMNH 10499;Varanus bengalensis, skeleton USNM 220281; Sani­wa, vertebrae UCM 38114, UCM41157, UCM41159,UCM 41275, DMNH 2510, and DMNH 2838; Pa­laeosaniwa, vertebra UCM 37868.

Institutional abbreviations used are AMNH­American Museum ofNatural History; DMNH-Den­ver Museum of Natural History; KNM-Kenya Na­tional Museum; UCM- University of Colorado Mu­seum; USNM-National Museum of Natural History(formerly United States National Museum).

SYSTEMATIC PALEONTOLOGY

Class REPTILIAOrder SAURIA

Family VARANIDAE

Genus VARANUS

VARANUS RUSINGENSIS, sp, nov.

Ho1otype-A partial, disarticulated and partly artic­ulated skeleton contained in three separate blocks andconsisting of a mandible (KNM 24319-a); parietal(KNM 24319-c); scapula (KNM 24319-d); cervicalvertebrae (KNM 24319-g, KNM 24321-c); dorsal ver­tebrae (KNM 24319-e, f, h, KNM 24321-a); caudalvertebrae (KNM 24320-r 9ct .); ribs (KNM 24319-i, j,k, 1, m, n); radius (KNM 24319-b); ulna (KNM 24321­b); and partial femur (KNM 24320-q). An articulatedtibia fragment (KNM 24320-a); astragalus (KNM24320-b); calcaneum (KNM 24320-c); fourth distaltarsal (KNM 24320-d); metatarsals (KNM 24320-e, f,g); and phalanges (KNM 24320-h, i, j, k, 1, m, n, 0, p).

Hypodigm-Maxilla (KNM RU 3404-F); maxillafragments (KNM 24307, KNM MAB 161 '49, KNM795 '56, KNM 171 '51, KNM 327 '47, KNM 697 '51) ;dentary fragments (KNM R 269 '71 3ct., KNM RU

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CLOS-NEWVARANUS FROM KENYA 255

3313, KNM MW 66 '52, KNM 1333 '50, KNM 24308,KNM 13 '56, KNM 1747 '50); parietal (KNM 24338­a); coracoid (KNM 24323-A, B); ilia (KNM RU 3414,KNM 24333-d, KNM 24325-A, B); ischia (KNM24325-C, D, KNM RU 3404-C, K, KNM 24338-c);cervical vertebra (KNM 24337-a); dorsal vertebrae(KNM RU 3405-A, B, D, E, E', G, H, P, KNM 24311,KNM 24312, KNM 24313, KNM 24314, KNM RU3417 , KNM 24333-a, c, e, g, KNM R1948 G74, KNM24336-b, KNM RU 3282C); sacral vertebrae (KNMRU 3408, KNM 24333-b, KNM 24324, KNM 24336­a); caudal vertebra (KNM 24333-f); ribs (KNM 243103ct., KNM 24335 4ct., KNM 24309-a, b, c, KNM24334, KNM 24337-b, KNM 24336-c, d); humeri(KNM RU 3404-A, B); humerus fragments (KNM24316, KNM RU 3410, KNM 24330-a, b); ulna frag­ment (KNM RU 3412); femora (KNM RU 3406, KNMRU 3407, KNM 24326-A, B, KNM 24327); femurfragments (KNM 24328-a, b, KNM 24329, KNM24331, KNM 24339-a, b); tibiae (KNM 24318, KNM24322); fibula (KNM RU 3404-G); metapodials (KNMRU 3404-H, I, KNM 24309-d, KNM 24332 2ct.) ; pha­langes (KNM RU 3404-J, L, M, N, 0). Hypodigmmaterials referred to V. rusingensis differ significantlyfrom the holotype elements only in size, completeness,and lack of articulation.

Type Locality and Age-Locality #Rl14 (Whit­worth's pothole), Kiakanga Hill; Grit Member of theHiwegi Formation of Rusinga Island, Kenya. LowerMiocene, 17.8 ± 0.5 Ma (Drake et al. , 1988).

Diagnosis- Varanus rusingensis can be recognizedby its possession of a unique combination ofprimitiveand derived characters. It shares with the modern mol­luscivorous monitors V niloticus, V. exanthematicus,and V. olivaceus (= V. grayi) the following derived char­acters: blunt posterior teeth, robust mandible, and con­stricted parietal plate; yet it differs from those modernspecies in exhibiting a lesser degree of development ofthe latter two features. Additionally, the precondylarconstriction of the vertebrae is less pronounced in V.rusingensis than in modern species of Varanus.

Etymology-The specific name, rusingensis, refersto the type area.

Description

Parietal-The only skull roof bone of Varanus ru­singensis which is preserved is the parietal (KNM24319-c, Fig. 1A; KNM 24338-a). Except as notedbelow, the parietal of V. rusingensis is shaped like thatof V. niloticus (the Nile monitor or qamu), V. benga­lensis (the Bengal monitor) and V. olivaceus (the butaanor Gray's monitor), with a clearly visible pineal fora­men set well back from the frontoparietal suture. It isvery like the parietal of V. indicus figured by Mertens(1942). The pineal foramen is slightly more posteriorlypositioned in V. bengalensis than it is in V. niloticus,and its position in V. rusingensis is intermediate be­tween the two. A foramen is present in all living andfossil varanids for which the parietal bone is known,

except the earless monitor Lanthanotus (McDowell andBogert, 1954; Estes et al. , 1988).

The contact between the parietal and the postorbi­tofrontal, while somewhat sinuous, is straighter in V.rusingensis than it is in either V. olivaceus or V. nilo­ticus; in the latter it is a distinctly bilobate or W-shapedsuture. In addition, the narrowest portion of the pa­rietal plate (between the external parietal crests) is rel­atively wider in V. rusingensis than it is in either ofthe aforementioned recent species. The ratio of thenarrowest portion of the parietal plate to the width ofthe parietal bone where it meets the prootic is about0.40 in V. exanthematicus (the Cape or savannah mon­itor) , 0.35 in V. niloticus, 0.20 in V. olivaceus, and 0.60in V. rusingensis. In the subfossil V. hooijeri, anotherblunt-toothed form, the parietal plate is so constrictedthat there is only a midline crest forming the skull roof(Brongersma, 1958). Very old individuals of V. nilo­ticus and V. olivaceus figured by Mertens (1942) showthe same condition. Although there is an ontogenetictrend toward narrowing of the parietal plate as theanimal grows older in many (but not all) species ofVaranus (Auffenberg, 1988; Mertens, 1942), the ho­lotype of Varanus rusingensis is a young adult com­parable in size to one of the V. niloticus specimensexamined (AMNH 10499), and the difference in thedegree of constriction persists. In contrast, the parietalplate is relatively narrower in V. rusingensis than it isin the earlier varanids Saniwa, Cherminotus, Sani­wides and Telmasaurus (Gilmore, 1928, 1943; Stritzke,1983; Borsuk-Bialynicka, 1984). In general non-mol­luscivorous species of Varanus also show less constric­tion of the parietal plate than do the aforementionedblunt-toothed forms (see Table I). Narrowing of theparietal plate is due to a proportional increase in sizeofthe masseter muscle complex (Lonnberg, 1903; Auf­fenberg, 1988). Since the dorsolateral surface of theparietal, on which originates the pseudotemporalis su­perficialis muscle (Smith, 1982; Estes et al., 1988) , isexpanded as the parietal roof narrows, this results inthere being less area for attachment of that muscle inV. rusingensis than in those lizards with a greater con­striction of the parietal. In V. exanthematicus, thepseudotemporalis is an important muscle in the de­velopment of a strong bite force (Smith, 1982). Thismay indicate a trend toward strengthening of the jawmuscles concurrent with the shift to a diet which in­cludes hard-shelled prey items.

Maxilla-A nearly complete maxilla (KNM RU3404-F, Fig. 1B) and six tooth-bearing fragments arepresent. The maxilla is shaped much the same as inVaranus niloticus, and both are considerably more ro­bust than the maxilla of V. bengalensis. The excavationfor the external naris is more distinct in V. bengalensisthan it is in either V. rusingensis or V. niloticus.

The almost complete maxilla of V. rusingensis (KNMRU 3404-F) bears a full row of teeth; there are ten , ascompared to nine or ten teeth on the maxilla of adultV. niloticus and V. exanthematicus. Saniwa is reported(Gilmore, 1922) to have possessed at least 15 maxillary

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256 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 15, NO. 2,1995

FIGURE 1. Varanusrusingensis. A-parietal bone (KNM 24319-c). B-maxilla (KNM RU 3404-F). C-first sacral vertebra(KNM 24324). D-right coracoid (KNM 24323-A). E-Ieft ilium (KNM 24325-A). F-right ischium (KNM 24325-C). G­lower jaw in left lateral view (KNM 24319-a). The jaw has broken at the mandibular symphysis and the left ramus shifted tolie above the right ramus. Abbreviations used : de, dentary; sa , surangular; an, angular; ar, articular. Scale bars are I em.

teeth, and possibly more. In the adult V. niloticus thepremaxillary teeth are small, trenchant, and recurved,while the maxillary teeth are all blunted, almost bul­bous, but for the final posterior tooth which is reducedin size and somewhat pointed. The tooth series in V.exanthematicus is very similar to that of V. niloticusexcept that it lacks the reduction of the ultimate tooth.All of the teeth of V. bengalensis, on the other hand,are trenchant, recurved, and labiolingually flattened,as are the teeth ofmost living Varanus (Mertens, 1942),V. marathonensis (Fejervary, 1918) , and those ofSan­iwa (Gilmore, 1922), Saniwides, Telmasaurus (Bor­suk-Bialynicka, 1984), and Megalania (Hecht, 1975).All teeth of both the fossil and recent Varanus arestriated at their bases by a labyrinthine infolding ofthedentine characteristic of varanoids. The anterior max­illary teeth of V. rusingensis are somewhat more point­ed than those of V. niloticus and V. exanthematicus,though much less so than those of V. bengalensis. Theteeth of V. rusingensis gradually become larger and

more peglike posteriorly (Fig. 1B), as do those of V.olivaceus (Auffenberg, 1988).

Blunt, cylindrical teeth are present in three livingspecies (V. niloticus, V. olivaceus, and V. exanthema­ticus ; Mertens, 1942), and have been reported in thesubfossil V. hooijeri from the Pleistocene of Indonesia(Brongersma, 1958). Such tooth form in lizards hasbeen correlated with omnivorous feeding (Estes andWilliams, 1984) or, in Vara nus, with a diet high inland or freshwater snails or crabs (Lonnberg, 1903;McDowell and Bogert, 1954; Auffenberg, 1988). Mol­luscivory has also been suggested for fossil glypto­saurine anguids with enlarged posterior teeth (Gau­thier, 1982). However, the correspondence betweenblunted teeth and consumption of hard-shelled preyitems is not a strict one , as V. indicus occasionally feedson crabs (Rieppel and Labhardt, 1979), and V. ben­galensis is known to include some molluscs in its diet(Auffenberg, 1988), and both retain a trenchant den­tition. V. olivaceus eats fruits as well as molluscs, but

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CLOS-NEWVARANUS FROM KENYA 257

TABLE 1. Comparisons of some recent Varanus .

(a) ratio of narrowest portion of parietal roof, between ex­ternal parietal crests, to width of parietal where it meetsprootic. (b) dorsoventral height of lower jaw at coronoidprocess divided by anteroposterior length oflower jaw. Mea­surements for (a) for V. olivaceus from Auffenberg (1988);other data taken from Mertens (1942).

eral typically have a deep jaw build (Romer, 1956) .Increasing robustness develops with maturation in V.niloticus (Lonnberg, 1903; Rieppel and Labhardt, 1979)concurrent with the shift to a molluscivorous diet andthe eruption of durophagous teeth; V. exanthematicusshows a similar trend during ontogeny (Mertens, 1942).Trenchant-toothed monitors usually show no suchchange in jaw proportions during growth (e.g., V. sal­vator, V. bengalensis, and V. indicus; Mertens, 1942) .A numerical ratio comparable to those presented inTable 1 cannot be determined for V. rusingensis sincethe coronoid is missing, but as described above, itsmandible falls between the robust form seen in V. nil­oticus, V. olivaceus, and V. exanthematicus and themore gracile shapes seen in the trenchant-toothedmonitors. Since a sturdier jaw can better resist the largeforces generated in crushing hard food items, this sug­gests that the modern blunt-toothed monitors may bemore specialized for such a diet than was V. rusingen­sis.

Axial Skeleton - Many well preserved dorsal ver­tebrae are present, but only poorly preserved cervicalvertebrae are available. An excellent specimen of thefirst sacral vertebra exists (KNM 24324), and there areseveral caudals, including one with the neural spineintact (KNM 24333-f). The articular surface of thecondyle faces upwards and back, to meet the cotyle ofthe next vertebra which faces forward and somewhatdown; the same condition seen in modern Varanus.As in all varanids, the vertebrae are procoelous.

All vertebrae of V. rusingensis have the precondylarconstriction characteristic ofva ranids , although this ismost marked on the dorsal vertebrae. Both V. niloticusand V. bengalensis also show a more distinct precon-

0.220.250.20

0.150.160.170.120.160.16

Robustnessof jaw (b)

0.630.430.520.520.710.64

Constric­tion ofparietal

(a)Species

Significantly molluscivorous speciesV. niloticus 0.35V. exanthematicus 0.40V. olivaceus 0.20

Non-molluscivorous speciesV. sa/vatorV. indicusV. griseusV. prasinusV. timorensisV. bengalensis

the teeth are not involved in frugivory as the fruits areswallowed whole (Auffenberg, 1988) . Interestingly, thejuveniles of modern molluscivorous and cancrivorousVaranus species have a fully trenchant dentition andonly acquire the durophagous morphology once theswitch from an insectivorous to an adult diet (con­taining a substantial component of hard-shelled prey)is made (Lonnberg, 1903; McDowell and Bogert, 1954;Auffenberg, 1988) . The blunted teeth of the holotypeand other referred material indicate that the fossilsprobably represent adult lizards.

The maxilla (KNM RU 3404-F) also has a dorso­ventrally compressed anterior region similar to thatseen in V. niloticus. The ascending process, where themaxilla meets the supraorbital, is broken in the fossilspecimen.

Mandible-A nearly complete lower jaw (KNM243l9-a) and nine tooth-bearing dentary fragments arepreserved. The jaw (KNM 243l9-a, Figs. 1G, 2) isbroken at the intramandibular joint and has furthersplit at the mandibular symphysis in such a mannerthat the left ramus lies above the right ramus, so thatthe inner wall of the right and the outer wall of the leftmandible can be seen . The coronoid is missing, butthe surangular and articular are well preserved. Theangular bone is present but is disarticulated and frac­tured.

In general form the jaw resembles that of V. niloticus,but is somewhat longer and more slender; it is, how­ever, more robust than that of V. bengalensis. Thiselongation is seen in the shapes of the dentary, sur­angular, and articular bones, which otherwise lookmuch like those of V. niloticus. The dentary is a slender,anteriorly blunted, conical bone which is slightly con­cave dorsally, and exhibits a row of distinct pits alongits length (foramina dento-facialia of Mertens, 1942) .The surangular approximates an elongated rectangle,with an anteriorly convex surface at the intramandib­ular joint and an irregular posterior border where thebone is incompletely preserved. The dentary and sur­angular bones are of the same shape in V. niloticus, V.rusingensis, and V. bengalensis, but form a series fromrobust (V. niloticus) to more gracile ( V. bengalensis),with V. rusingensis exhibiting an intermediate condi­tion. The broken angular bone of V. rusingensis is slen­der and semicylindrical. The articular bone is gentlyconcave ventrally and has a relatively long, slenderretroarticular process like that of V. bengalensis, incontrast to the shorter, stouter process seen in V. oli­vaceus (Auffenberg, 1988) . The articular of V. rusin ­gensis is less robust than that of either V. niloticus orV. olivaceus; that of V. niloticus is thicker both la­biolingually and dorsoventrally than that of V. rusin­gensis, and the articular of V. bengalensis is more grac­ile still .

As indicated in Table 1, the robustness of the lowerjaw (given by its heigh t/length ratio) is greater in themodern significantly molluscivorous forms than inother modern Varanus (this correlation was also notedby Auffenberg, 1988). Molluscivorous reptiles in gen-

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258 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. IS , NO.2, 1995

FIGURE 2. Holotype of Varanus rusingensis. Block containing mandible, radius, parietal, scapula, and ribs (KNM 24319).Scale bar is 1 em .

dylar constriction of the dorsals than of either the sa­crals or the caudals (see Table 2).

The neural canal is almost circular in cross-section,not tripartite as in Megalania (Fejervary, 1935). Also ,V. rusingensis has a much smaller adult size than Hecht(1975) reports for Megalania. V. rusingensis possessesa relatively larger neural canal than the fossil speciesV. marathonensis, V. hofmanni (Estes , 1983b), V. bol­ka yi (Fejervary, 1935), and V. tyrasiensis (Lungu etaI., 1983).

There are no indications that V. rusingensis pos­sessed the rudimentary pseudozygosphene seen in Pa­laeosaniwa. A pseudozygosphene is also present inSaniwa (Gilmore, 1928 ; Stritzke, 1983) and Telma­saurus (Gilmore, 1943). Fejervary (1918 , 1935) andHecht (1975) have reported a vestigial pseudozygos­phene in Megalania , but this has been questioned byHoffstetter (1943), who interprets it as a ligamentousattachment site.

Cervical Vertebrae - Three badly broken cervicalvertebrae of V. rusingensis are present (KNM 24319­g, KNM 24321-c, KNM 24337-a). Notable featuresare difficult to discern due to the poor state of pres-

ervation, but the anteroposterior elongation charac­teristic of varanids is evident. In general form theyappear to resemble the neck vertebrae of both V. nil­oticus and V. bengalensis.

Dorsal Vertebrae-Twenty-four dorsal vertebrae,perhaps from several individuals, are included in thefossil material. The pronounced precondylar constric­tion is evident, as is the well developed collar on thecondyle (see KNM R 1948 G74, Fig. 3C, and KNM24321-a, Figs. 3A, B, D). Iberovaranus catalunicus,from the Miocene of Spain, possesses a less distinctcollar than the modern Varanus (Hoffstetter, 1969). Inthis character the vertebrae of Varanus rusingensis mostclosely resemble those of V. niloticus. V. bengalensishas a more distinct collar than either V. rusingensis orV. niloticus.

The degree of precondylar constriction of the dorsalvertebrae, as measured by the ratio of the width at thenarrowest part of the constriction to the width of thecondyle, averaged 0.78 in V. rusingensis. This ratioaveraged 0.72 and 0.70 in the measured dorsal ver­tebrae of V. niloticus and V. bengalensis respectively,less than the average ratio of 0.93 seen in the Saniwa

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CLOS-NEWVARANUS FROM KENYA 259

TABLE 2. Vertebral measurements.

f-

*Vertebrae are listed in caudad order but determination ofsequence numbers was not possible because spinal columnwas incomplete.**Disarticulated; sequence numbers unknown.

dorsals examined (see Table 2), or the average ratio of0.90 calculated from the data given by Gilmore (1928)for dorsal vertebrae of Saniwa. Thus, V. rusingensisexhibits a condition closest to the modem Varanusspecies measured, but intermediate between them andSaniwa.

The ventral surface of the dorsal vertebrae issmoothly convex, as it is in Saniwa and other Varanusspecies. There is no trace of the longitudinal channelseen in the vertebrae of Palaeosaniwa figured by Gil­more (1928) .

Sacral Vertebrae - The first sacral vertebra of V. ru­singensis, represented by one excellent (KNM 24324)and three reasonably complete specimens (KNM RU3408, KNM 24333-b, KNM 24336-a), is very similarto that of V. niloticus, with the following notable ex­ceptions (see KNM 24324, Fig. 1C).

A prominent ridge connects the pre-zygapophyseswith the neural spine in V. rusingensis; this feature isnot present in V. niloticus, although it is seen to a lesserdegree in V. bengalensis. While in the Nile monitor,the condyle of the first sacral vertebra and the cotyleof the second are modified to restrict motion betweenthem, this feature is practically nonexistent in the fossil(the condyle being smoothly ellipsoidal, as in V. ben­galensis). Gilmore (1922) reported that the two sacralvertebrae in Saniwa are firmly ankylosed. This doesnot appear to be the case in V. rusingensis, as there areno articulated pairs among the fossil remains.

Caudal Vertebrae-Ten caudal vertebrae are pres­ent, including a series of nine in articulation (KNM24320-r, Fig. 3E), but only one is preserved such thata complete neural spine can be seen (KNM 24333-f,Fig. 3F). Unlike the condition seen in Saniwa (Gil­more, 1922), the spine is tall (height = 22.6 mm) andslender, like that of V. niloticus, indicating some degreeofdorsoventral elongation ofthe animal's tail, a featurecorrelated with aquatic habits (Romer, 1956). The neu­ral spine runs about three-quarters of the length of thecentrum ("elongated neural arch" ofHoffstetter, 1969),whereas that of V. niloticus and V. bengalensis is car­ried only on the posterior half of the centrum. In thisfeature the vertebrae of V. rusingensis are intermediatebetween those of V. niloticus and those of Iberovar­anus, which carries the spine on almost the full cen­trum length (dimensions given by Hoffstetter, 1969).In size and shape the vertebrae generally resemble thoseof V. niloticus. Chevrons are broken from all caudalvertebrae.

Ribs-Six slender, curving, nearly complete ribs(KNM 243l9-i, j, k, 1, m, n) are exposed in the blockwhich contains the lower jaw (Fig. 2). All other pre-

0.9390.9270.9170.9490.9160.9470.9090.945

0.9380.8750.8420.873

0.6660.6980.7310.6760.7940.7100.7090.7660.6550.6490.674

0.7620.7880.7590.7890.7760.7790.796

0.7260.7490.7420.7410.7550.7590.7490.7430.9980.9590.9930.9030.8500.826

0.6210.6860.6910.7450.771

7.627.205.565.84

6,428.058.208.238.138.638.878.95

8.348.608.048.668.729.028.958.968.948.618.90

9.799,409.008.354.72

10.309.009,45

10.3010.509.659.11

10.0010.5014.0213.6413.2513.5513.8413.6613.0013.5113.9211.259.719.19

WidthWidth of ratio con­condyle, strictionl

mm condyle

7.857.097.178.138.157.527.25

7.156.304.685.10

6.037,467.527.817,458.178.068,46

6.086,456.226.223.64

7.267.86

10,4010.1110.0010.2910.3610.1512.9812.9613.8210.168.257.59

Width atconstric­tion, mm

V. rusingensis, dorsals**KNM 24311KNM 24312KNM 24313KNM 24314KNM 24336KNM RU 3282CKNM RU 3405H

Specimen

V. niloticus UCM OS-11863rd cervical6th cervical9th cervicall st dorsal3rd dorsal5th dorsal7th dorsal18th dorsal1st sacral2nd sacrall st caudal6th caudall Oth caudal15th caudal

V. bengalensis USNM 220281 *dorsal 5.56dorsal 6.00dorsal 5.88dorsal 5.85dorsal 6.92dorsal 6,40dorsal 6.35dorsal 6.86dorsal 5.86dorsal 5.59dorsal 6.00

Saniwa DMNH 2838**dorsaldorsaldorsaldorsaldorsaldorsaldorsaldorsal

Saniwa, other**UCM 38114 dorsalUCM 41275a dorsalUCM 41275b caudalUCM 41275c caudal

V. niloticus AMNH 104999th dorsall Oth dorsal11th dorsal14th dorsalcaudal

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260 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 15, NO.2, 1995

FIGURE 3. Varanus rusingensis . A-D, dorsal vertebrae: A-KNM 24321-a, caudal view ; B-KNM 24321-a, dorsal view ;C - KNM R 1948 G74, ventral view; D- KNM 24321-a, left lateral view . E - block containing caudal vertebrae and articulatedright pes (KNM 24320). F -caudal vertebra with intact neural spine (KNM 24333-f). Scale bars are I em .

served ribs are fragmentary. They have single headswith elliptical proximal articular surfaces, as do theribs of V. niloticus and V. bengalensis. The ribs of V.rusingensis are somewhat flattened in cross-section,but not as much as those of either of the aforemen­tioned recent species.

Coracoid-A nearly complete right (KNM 24323­A) and fragmentary left coracoid (KNM 24323-B) arepresent in the fossil material. There are two deep notch­es or emarginations on the forward border of the cor­acoid (KNM 24323-A, Fig. ID), and it is essentiallyidentical in shape to that of both V. niloticus and V.bengalensis. In contrast, the coracoid of Saniwa ensi­dens figured by Gilmore (1922 , 1928) has only a single(anterior) notch. Estes et al. (1988) note that the sec­ondary (posterior) emargination is very small or absentin Lanthanotus, considered among living lizards to bethe sister group of the genus Varanus (Pregill et al.,1986; Estes et al., 1988), and it is also lacking in themosasaur Clidastes (Romer, 1956), which is a varanoidbut not a varanid. Thus the presence of two stronglydeveloped coracoid notches in Varanus is likely a de­rived feature . Coracoids of other fossil varanid generaare unknown.

Scapula-The right scapula of V. rusingensis, theonly one preserved, is essentially indistinguishable fromthose of V. niloticus and V. bengalensis (KNM 24319­d, far right in Fig. 2). It is an hourglass-shaped bonewith a greater flare at its posterior than anterior (gle­noid) end, and a smooth surface.

Ilium - Two right and two left ilia (KNM RU 3414,KNM 24333-d, KNM 24325-A, B) are included amongthe Rusinga fossils. The ilium of V. rusingensis showsa stronger development of the excavation which liesbetween the dorsal protuberance and the medial ridge,on the inner surface of the bone (see KNM 24325-A,Fig. 1E), than do those of V. niloticus and V. benga­lensis. Otherwise, the ilia of V. rusingensis and V. nil­oticus are identical; both are more robust than that ofV. bengalensis.

Ischium-A good right ischium (KNM 24325-C) andfour fragmentary ischia are included in the study ma­terial. The ischium of V. rusingensis has a stronglycurved forward margin and is essentially indistinguish­able from that of V. niloticus (KNM 24325-C, Fig. 1F);the ischium of V. bengalensis is slightly more gracile.

Humerus-One complete right humerus (lacking theepiphyses; KNM RU 3404-A, Fig. 4A) and five less

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FIGURE 4. Limb bones of Varanus rusingensis. A-right humerus (KNM RU 3404-A); B-ulna (KNM 2432 l-b); C-rightfemur (KNM 24327); D-right tibia (KNM 24322); E-Ieft fibula (KNM RU 3404-G). Scale bar is 1 em.

complete humeri of V. rusingensis are represented inthe fossil material. In general aspect the bone is verysimilar to that of V. niloticus. The following differencesmay be noted.

The foramen just proximal to the capitellum issmaller and less conspicuous on the fossil bone thanit is on the humerus of V. niloticus. In this feature V.rusingensis most closely resembles V. bengalensis. V.rusingensis also exhibits a larger tuberosity for attach­ment of the pectoralis muscle than does V. niloticus;and the supinator process is slightly more prominentin V. rusingensis than in V. niloticus.

Radius-A single radius is preserved (KNM 24319­b, far left in Fig. 2). It is flared at the ends, but notquite as much in relation to its midpoint diameter asis the radius of V. niloticus; otherwise the two bonesappear identical.

Ulna-One relatively complete ulna (KNM 24321-b) and one fragment are included in the Rusinga ma­terial (see KNM 24321-b, Fig. 4B). The ulna of V.rusingensis is more robust in proportion to its length,and also presents a rounder (less mediolaterally flat­tened) cross-section midway along the shaft, than doesthat of V. bengalensis; it is very similar to that of V.niloticus. The shaft ofthe Rusinga monitor's ulna showsless curvature or bowing away from the radius thandoes the ulna of V. bengalensis or V. niloticus. Thereis a prominent fossa on the medial surface of the ulnae

of V. bengalensis and V. niloticus, near the proximalend, for the origin of the flexor palmaris profundusmuscle (Romer, 1956). This is not quite as stronglydeveloped in V. rusingensis.

Femur-Twelve complete and fragmentary femoraof V. rusingensis are present (see KNM 24327, Fig.4C). The femur closely resembles those of V. benga­lensis and V. niloticus. The femur of V. rusingen sis hasa slightly more prominent ridge running from the distalmedial (anterior) condyle toward the femoral head,extending for approximately one-fourth of the bone'slength, than is seen in either V. bengalensis or V. nil­oticus. Also, the area of attachment of the adductorfemoris , just distal to the fourth trochanter, is betterdeveloped (as a slightly flattened area) in V. rusingensisthan in V. nilot icus.

Tibia-One right (KNM 24322), one left (KNM24318), and one fragmentary right tibia (KNM 24320­a) are included in the fossil material. The larger of thetwo complete tibiae (KNM 24322, Fig. 4D) possessesa slightly better developed cnemial crest than does thecomparable bone of V. niloticus, but this may be anallometric feature, because it is not so obvious on thesmaller complete bone (KNM 24318). In all other re­spects the tibia of V. rusingensis is indistinguishablefrom that of V. niloticus.

Fibula-The fibula of V. rusingensis, represented bya single specimen (KNM RU 3404-0, Fig. 4E), differs

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in several respects from those of recent Varanus. Thedistal end of the fibula in both V. niloticus and V.bengalensis has a slight sigmoid curve on its lateralsurface where it articulates with the calcaneum, where­as in the Rusinga monitor, the profile of this surfaceis almost straight. The fibulae of V. nilot icus and V.bengalensis are flared at their distal ends (with respectto the smallest shaft diameter) to a much greater degreethan is that of V. rusingensis. The attachment scar forthe iliofibularis muscle is a distinct tuberosity in V.niloticus, while in V. rusingensis it is a mere nubbinon a ridge which spirals the length of the bone, fromthe proximomedial to the distolateral end.

Pes-The pes is represented by a nearly complete,articulated right foot (Fig. 3E). The distal end of thetibia (KNM 24320-a) is present, as are the astragalus(KNM 24320-b) and calcaneum (KNM 24320-c). Thefourth distal tarsal is also preserved (KNM 24320-d).These bones are very like those ofthe modem Varanus.Three metapodials (KNM 24320-e, f, g), probably rep­resenting digits II, III, and IV, articulate with phalanges(KNM 24320-h, i, j, k, 1, m, n, 0 , p). The foot bears aclose resemblance to that of V. niloticus. The astragalusand calcaneum of V. rusingensis are fused, but themedially convex suture between them is clearly visible,showing the calcaneum to be roughly triangular, andthe astragalus to be an irregularly rectangular bone, indorsal view.

The metapodials of V. rusingensis are flared anddorsoventrally flattened at their proximal ends, as arethose ofboth V. bengalensis and V. niloticus. The cross­section is almost round at the midpoint of the shaft'slength in all three species . The metapodials of V. ben­galensis and V. niloticus are slightly more gracile thanthose of V. rusingensis. The only metapodial of V.rusingensis which differs in any other way from thatof either of the aforementioned recent species is thefourth , which is flared slightly more at its proximalend relative to the midpoint diameter, than is that ofV. niloticus or V. bengalensis.

The phalanges of V. rusingensis are slightly morerobust than are those of either V. niloticus or V. ben ­galensis, and they are not quite as flared at both endswith respect to the midpoint shaft diameter as are thoseof the two recent species. That is, they are a little morecylindrical and not quite as hourglass-shaped in dorsalview. The average ratio ofthe narrowest shaft diameterto the phalangeal length is 0.21 in V. rusingensis, 0.18in V. niloticus, and 0.14 in V. bengalensis. The cross­section of the phalanges in all three lizards is approx­imately D-shaped, being flattened on the ventral sur­face.

Discussion

Although almost 18 million years separate V. rusin­gensis and the modem members of the genus Varanus,the resemblances between them are considerable, in­dicating that varanid evolution has been relatively con­servative from the Miocene to the present.

In its tooth morphology, V. rusingensis most closelyresembles the modem species V. niloticus, V. exan­thematicus, and V. olivaceus. The blunted teeth areknown to correlate in those species with an adult dietcontaining a significant element of hard-shelled prey(Lonnberg, 1903; McDowell and Bogert, 1954; Rieppeland Labhardt, 1979; Auffenberg, 1988). Such a den­tition is also reported in the Pleistocene V. hooijeri(Brongersma, 1958), and presumably indicates a sim­ilar diet. In contrast, all other species of Varanus pos­sess a trenchant dentition.

The narrowing of the parietal plate and the robust­ness of the bones of the lower jaw are indicators ofjawadductor muscle size and strength, which in tum cor­relate with a molluscivorousdiet (Lonnberg, 1903; Auf­fenberg, 1988). These features are better developed inthe modem blunt-toothed monitors than they are inV. rusingensis, suggesting that the Rusinga monitormay have been less specialized for such a diet than arethe modern forms.

The height of the neural spines of the caudal ver­tebrae, which indicates the degree ofdorsoventral elon­gation ofthe tail, correlates with a semiaquatic lifestyle(Cowles, 1930; Romer, 1956; Auffenberg, 1988). Inthis feature, V. rusingensis more closely resembles V.niloticus than V. olivaceus or V. exanthematicus, bothofwhich are primarily terrestrial forms . Nile monitorsare expert swimmers and are often found in or nearwater (Cowles, 1930), and V. rusingensis probably hadsimilar habits. Rusinga Island during the Miocene wascovered by a mosaic of lowland evergreen forest , gal­lery forest, and more open country (Andrews, 1973;Andrews and Van Couvering, 1975; Axelrod and Ra­ven, 1978), which included riparian habitats similarto those occupied by V. niloticus today (Chesters, 1957).V. rusingensis may have fed on land snails, but that isinconsistent with the aquatic habit which is indicatedby the relatively deep tail. It is likely, therefore, thatfreshwater molluscs or other aquatic creatures formeda significant part of its diet. Fossil snails and clams,including representatives of six modern genera, havebeen found in the Miocene sediments ofthe Kavirondorift (Nyanza gulf) region (Verdcourt, 1963, 1972); ap­proximately 16% of the known species are freshwatertypes (Verdcourt, 1972).

Songhor material- Fossils similar to those found atRusinga have been collected from zeolitized tuffaceoussediments at the Songhor locality, about 120 km east­northeast of Rusinga Island. The Songhor fossils areslightly older than those at Rusinga, between 19.5 and19.9 million years old (Bishop et aI., 1969). Varanidvertebrae and tooth-bearing jaw fragments are amongthe fossils found at Songhor. The vertebrae are muchsmaller than those referred to V. rusingensis, and havenot been studied in detail. They may represent anothermolluscivorous species of Varanus, or alternatively,younger individuals of V. rusingensis. The teeth showthe same striated tooth bases and blunted shape seenin the Rusinga monitor.

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CLOS-NEWVARANUS FROM KENYA 263

PHYLOGENETIC RELATIONSHIPSWITHIN THE VARANIDAE

Lizards assigned to the family Varanidae (monitorlizards or goannas) are known since the Late Creta­ceous, where they are represented by good skulls fromeastern Asia and fragmentary, somewhat questionablematerial from North America (Gilmore, 1928 , 1943;Estes , 1983a, b; Borsuk-Bialynicka, 1984). By far themajority ofspecies belong to the genus Varanus, whichincludes 32 living monitors as well as several extinctones (Mertens, 1942; Estes, 1983b). Today they inhabitthe tropical and subtropical regions ofAfrica, Asia, theEast Indies, and Australia.

The Varanidae is herein considered to consist of themodem genera Varanus and Lanthanotus (Pregill etaI., 1986; Estes et aI., 1988), plus the fossil forms Cher­minotus, Saniwides, and Telmasaurus from the Cre­taceous of Mongolia (Borsuk-Bialynicka, 1984), Pa­laeosaniwa from the Cretaceous of western NorthAmerica (Gilmore, 1928), Saniwa from the Paleocenethrough Oligocene of North America and Europe (Gil­more, 1922, 1928; McDowell and Bogert, 1954; Estes,1983a, b; Stritzke, 1983), Iberovaranus from the Mio­cene of Spain (Hoffstetter, 1969), and Megalania fromthe Pleistocene of Australia (Fejervary 1918 , 1935;Hecht, 1975). Fossil species referred to Varanus arealso known from the mid-Miocene through Pleistoceneofeastern Europe, southern Asia, and Australia (Estes,1983b); the remains in most cases limited to a fewvertebrae. There is a questionable report of an EoceneVaranus from the former USSR (Reshetov et aI., 1978;Lungu et aI., 1983), but no description of the materialhas been given. The Helodermatidae, whose living rep­resentatives are the gila monster and beaded lizard ofthe genus Heloderma, is generally considered to be thesister-group of the Varanidae as defined herein (Pregillet aI., 1986; Estes et aI., 1988).

A comprehensive cladistic analysis ofthe entire fam­ily Varanidae, including all 32 living members of thegenus Varanus, is beyond the scope ofthis paper. How­ever, a more limited analysis has been undertaken inan attempt to clarify the position of V. rusingensis withrespect to other members of the family. Iberovaranus ,Palaeosaniwa, and Megalania have not been included,because available information regarding comparablecharacters is insufficient to place them with any con­fidence. The same is true ofother fossil species referredto Varanus.

Based on their extensive studies ofboth skeletal andsoft characters, both Mertens (1942) and Auffenberg(1988) believe that each of the modem blunt-toothedVaranus species is separately descended from a gen­eralized, V. salvator-like ancestor, and that many ofthe similarities between them are due to convergenceresulting from the independent adoption of mollusci­vorous habits. If this is the case, the affinities of V.rusingensis most likely lie with one or the other of theAfrican species (V. niloticus or V. exanthematicus),rather than with the Philippine V. olivaceus. In this

analysis, the generalized form is represented by V. ben­galensis, a close relative of the water monitor V. sal­vator (Mertens, 1942) .

Characters Used in Cladistic Analysis

1. Palatine and pterygoid teeth. O-present; I-ab­sent. Small teeth are present on the palatine and pter­ygoid bones of Lanthanotus (McDowell and Bogert,1954; Estes et aI., 1988), Saniwides and Telmasaurus(Borsuk-Bialynicka, 1984), and Saniwa (Gilmore,1928). They are absent in all recent species of Varanus(Mertens, 1942; Estes et aI., 1988). Palates of fossilVaranus species are unknown (Brongersma, 1958; Estes,1983b; Lungu et aI., 1983), including V. rusingensis.Presence of palatine and pterygoid teeth is the primi­tive condition, and loss of them derived (McDowelland Bogert, 1954; Estes et aI., 1988) .

2. Precondylar constriction of vertebrae. O-none;1-weak (average ratio ofconstriction width to condylewidth between 0.8 and 1.0); 2-strong (ratio :s 0.8).All members of the family Varanidae possess somedegree of precondylar constriction. The amount variesamong species; measurements taken of the dorsal ver­tebrae are most diagnostic, and have been used in th isanalysis (see Table 2 for representative values). Thevertebrae of Heloderma are not constricted anterior tothe condyle (Estes et aI., 1988). A weakly developedconstriction is seen in Lanthanotus (McDowell andBogert, 1954; Estes et aI., 1988), Saniwa (Gilmore,1922), and Telmasaurus (Gilmore, 1943); dorsal ver­tebrae of Saniwides and Cherminotus are unknown(Borsuk-Bialynicka, 1984). A stronger constriction isseen in members of the genus Varanus. Lack of anyprecondylar constriction is thought to be primitive(Estes et aI., 1988), so it is inferred that a strongerconstriction represents an increasingly derived con­dition.

3. Thickening of lower jaw bones. O-absent (ratioof mandible height at coronoid to overall mandiblelength < 0.2); I-present (ratio ~ 0.2) . Increasing ro­bustness is seen in the modem molluscivorous Var­anus species (Mertens, 1942; Auffenberg, 1988; seeTable 1), and is a derived feature related to the adop­tion of such a diet and the large crushing forces gen­erated thereby (Lonnberg, 1903). It was not directlymeasurable in V. rusingensis (see description). Jawthickening is not present in the Cretaceous varanoidEstesia (Norell et aI., 1992), Lanthanotus (McDowelland Bogert, 1954; Estes et aI., 1988), Saniwa (Gilmore,1922), or V. bengalensis. Material sufficient to deter­mine this ratio is not available for Cherminotus, San­iwides and Telmasaurus (Borsuk-Bialynicka, 1984).

4. Vestigial pseudozygosphene. O-absent; I-pres­ent. Presence of a pseudozygosphene, but no pseudo­zygantrum, is noted in Telmasaurus (Gilmore, 1943)and Saniwa ensidens (Gilmore, 1928) . This feature islacking in Iberovaranus (Hoffstetter, 1969), Heloder­ma , Lanthanotus, and all Varanus species (Mertens,1942; Estes et aI., 1988). Saniwa feisti (Stritzke, 1983)

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U)::::lU

en en ..--U) en en en ro

::J en ECtl ::::l ::J ~C C..-- en ~ Q) U) Q)

E 0 0 ::J Q)Q) ro ro ::J .c~ c -a c 0> o ..--Q) E ~~

ro en ro 0> C :;::; C-a ..c ro .~ c "00 0 ro0 ~

~ E Q) xQ) c c C .0 ::JC Q)Q) .c ro ttl Q) ro '-

I 0 (f) ~ .- (f) > >= > >

"~ 8(0) -~ 5(2)

. - 9(2)

2(1), 11

4, 9(1)

10

3,5(1),6

.~ 1,2(2),7,8(1)

FIGURE 5. Phylogenetic relationships within the Varanidae (see text). Position of character number indicateschange fromstate 0 to state I for binary characters; multistate character changes indicated by parenthetical notation.

has both a pseudozygosphene and a pseudozygantrum.Vertebrae ofSaniwides and Cherminotus have not beendescribed (Borsuk-Bialynicka, 1984). Romer (1956)notes the presence ofa pseudozygosphene in most fos­sil varanoids. However, given the absence of this fea­ture in Lanthanotus, Heloderma (Estes et aI., 1988)and the fossil helodermatid Lowesaurus (Pregill et aI.,1986), it is likely that the most recent common ancestorof all varanids lacked a pseudozygosphene, and thefeature is secondarily derived in Telmasaurus and San­iwa, rather than being the retention ofa plesiomorphiccondition. Estes et aI. (1988) note that the polarity ofthis character within the wider context ofthe Squamatais difficult to determine with certainty. Lack ofa pseu­dozygosphene is tentatively considered to be the ple­siomorphic state for the clade consisting of the Hel­odermatidae + Varanidae.

5. Degree of constriction of parietal plate. O-little(ratio of narrowest portion of parietal plate to width

ofparietal where it meets prootic > 0.6); I-moderate(0.4 :5 ratio :5 0.6); 2-strong (ratio < 0.4). See de­scription section for discussion of this ratio in modernVaranus. Primitive varanoids (Carroll and DeBraga,1992; Norell et al., 1992), Heloderma and Lanthanotus(Estes et aI., 1988), Saniwides and Telmasaurus (Bor­suk-Bialynicka, 1984), and Saniwa (Gilmore, 1928;Stritzke, 1983) all show little narrowing of the parietalplate, while species of Varanus, especially V. niloticus,V. olivaceus, and V. hooijeri, show more. This may bea morphocline related to the development of mollus­civory, at least within the genus Varanus; if so, state2 is the most derived.

6. Durophagous teeth. O-absent; I-present. Theseare found only in the species of Varanus which aremolluscivorous to a significant degree . All other var­anids possess a trenchant dentition, which is consid­ered to be the primitive condition (McDowell and Bo­gert, 1954).

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CLOS-NEWVARANUS FROM KENYA 265

7. Secondary (posterior) coracoid emargination. 0­absent; 1-present. A strongly developed posterior cor­acoid notch is found only in members of the genusVaranus, although a small one is sometimes seen inLanthanotus (Estes et aI., 1988). Saniwa lacks this fea­ture (Gilmore, 1922), and coracoids ofSaniwides, Tel­masaurus, and Cherminotus are unknown. Lack of asecondary notch is the primitive state (Estes et aI.,1988).

8. Length of neural spine relative to centrum. 0­spine more than 60% ofcentrum length; I-carried onposterior halfofcentrum only. Saniwa (Gilmore, 1922)and V. rusingensis possess a longer neural arch, as doprimitive varanoids (Carroll and DeBraga, 1992) andIberovaranus (Hoffstetter, 1969). Modern Varanusvertebrae examined carry the spine only on the pos­terior half of the centrum, representing the derivedcondition.

9. Frontoparietal suture morphology. O-tightly me­andering; I-broadly curved; 2-smoothly sinuous tonearly straight. A straight or smoothly sinuous suture,indicating significant mesokinetic mobility, is seen inCherminotus and Saniwides (Borsuk-Bialynicka, 1984).Telmasaurus possesses a broadly curving one (Borsuk­Bialynicka, 1984), like that ofSaniwa (Stritzke, 1983).Lanthanotus (McDowell and Bogert, 1954), Heloder­ma (Estes et aI., 1988) and all modern Varanus (Mer­tens , 1942) have sutures composed of many small in­terlocking fingers; this represents the primitive con­dition.

10. Ontogenetic fusion of nasals. O-not fused; 1­fused. The nasal bones remain distinct in Heloderma(Estes et aI., 1988), Cherminotus, and Saniwides (Bor­suk-Bialynicka, 1984), while they fuse into a singlenasal bone in Saniwa (Gilmore, 1928), Lanthanotus,and Varanus (Estes et aI., 1988). The anterior portionof the skull of Telmasaurus is unknown, so this char­acter cannot be assessed (Gilmore, 1943; Borsuk-Bi­alynicka, 1984). Fusion represents the derived condi­tion (Pregill et aI., 1986).

11. Venom canals. O-present; I-absent. The mod­ern and fossil Helodermatidae possess canals on theirteeth for the delivery of venom (Pregill et aI., 1986;Estes et aI., 1988); none of the other lizards in thisstudy do. Such canals are also found in the Cretaceousvaranoid Estesia, and Norell et aI. (1992) suggest thata venom delivery system may be primitive for theVaranoidea.

Results of Cladistic Analysis

The cladogram shown in Figure 5 was generated byPAUP (version 3.0) using the branch-and-bound al­gorithm and the character data given in Table 3. Char­acter polarities were established by consulting pub­lished studies by Pregill et aI. (1986) and Estes et aI.(1988); by comparison with character states found inother varanoids such as agialosaurs (Carroll andDeBraga, 1992) and Estesia (Norell et aI., 1992); andby using the Helodermatidae as an outgroup. Character

TABLE 3. Character matrix.

Character number

Taxon 2 3 4 5 6 7 8 9 10 11

Heloderma 0 0 o 0 0 0 0 ? 000Cherminotus ? ? ? ? 0 0 ? ? 2 0Lanthanotus 0 1 o 0 o 0 (01)* ? 0 1San iwides 0 ? ? ? 0 0 ? ? 2 0Telmasaurus 0 1 ? 0 ? ? ? 1 ?Saniwa 0 1 0 1 0 0 0 0 1 1Varanus bengalensis 1 2 0 o 0 0 1 1 0 1V. rusingensis ? 2 ? 0 1 1 1 0 ? ?V. niloticus 2 o 2 1 1 1 0V. exanthematicus ? 0 1 1 1 ? 0

*Variable

states were obtained from the various published stud­ies cited in the previous section as well as by exami­nation of the comparative material listed earlier in thispaper. The analysis was first run using the a prioricharacter polarizations listed in the previous section.A set of six equally parsimonious trees was obtained,each having 72 steps and a consistency index of 0.917.By leaving the two trichotomies unresolved, these werecondensed into the single consensus tree presented inFigure 5. The data were then reanalyzed using onlyunpolarized characters (see Swofford , 1990) and thetrees rooted using Heloderma as the outgroup accord­ing to the preferred method of Lundberg (1972) andMeacham (1984). This resulted in the same character­state changes and consensus tree, lending confidenceto the results of the initial analysis.

Although it was hoped that this exercise might clarifywhether V. rusingensis was more closely related to oneor the other ofthe modern African blunt-toothed mon­itors, in the absence of better skull material of theRusinga monitor this did not turn out to be possible.Such an analysis might also best be done within thecontext of a full revision of the genus Varanus, whichis, however, beyond the scope of this paper.

The phylogeny presented in Figure 5 supports thehypothesis of Estes (1983a) that, subsequent to a Cre­taceous origin in eastern Asia, varanid lizards split intotwo groups; the lineage leading to Saniwa crossed intoNorth America via Beringia, where unnamed varanidvertebrae from Ellesmere Island (Estes and Hutchin­son, 1980) attest to the far northerly extent reached bythe family during a period of peak tropicality in theEocene. Migration eastward into Europe occurred atthis time (Estes, 1983a). Estes believes that the re­maining varanids dispersed throughout southeast Asia(where the most primitive members of the family arefound today (McDowell and Bogert, 1954; Mertens,1942)) and subsequently westward to colonize southcentral Asia and Africa. V. rusingensis indicates thatvaranids had reached Africa by the Early Miocene,although unfortunately there are no Paleogene fossils

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documenting the route, as the early Cenozoic recordin Asia is poor (Estes, 1983a).

ACKNOWLEDGMENTS

I would like to thank Judith Harris for her guidanceduring the early stages of this project, and I am infi­nitely grateful to Richard Stucky for offering encour­agement and feedback on later versions of the paper.I would also like to thank Hans-Dieter Sues for hishelpful suggestions, Peter Robinson and Don Eicherfor reading early versions ofthe manuscript, and LoganIvy for enduring my endless questions. Olivier Rieppeland an anonymous reviewer made many importantcomments on the manuscript which substantially im­proved the revision. I am indebted to Ken Tighe, RonHeyer, and Darrel Frost for the loan of Varanus skel­etons for comparison. Jose Rosado was most helpfulregarding the teeth of some modem Varanus species .Robert Hoffstetter offered much appreciated clarifi­cation regarding Iberovaranus. The Walker Van RiperFund provided financial support for translating someforeign language papers. Finally, without the endlesshours ofbabysitting for my daughters Allison and Mat­tie that my parents, Teddie and Ralph Mobley, pro­vided, this project would never have been brought tocompletion.

LITERATURE CITED

Andrews, P. 1973. Vegetation of Rusinga Island. Journalofthe East African Natural History Society and NationalMuseum 142:1-8.

--- and J. A. H . Van Couvering. 1975. Paleoenviron­ments in the East African Miocene; pp . 62-103 in F.Szalay (ed.), Approaches to Primate Paleobiology. S.Karger, New York.

Auffenberg, W. 1988. Gray's Monitor Lizard. Universityof Florida Press, Gainesville, 419 pp .

Axelrod, D., and P. Raven. 1978. Late Cretaceous andTertiary Vegetation History of Africa; pp. 79-119 in M.Werger (ed.), Biogeography and Ecology ofSouthern Af­rica. Dr. W. Junk, the Hague.

Bishop, W. W., J . A. Miller, and F. J. Fitch. 1969. Newpotassium-argon age determinations relevant to theMiocene fossil mammal sequence in East Africa. Amer­ican Journal of Science 267 :669-699.

Borsuk-Bialynicka, M. 1984. Anguimorphans and relatedlizards from the Late Cretaceous of the Gobi Desert,Mongolia. Palaeontologia Polonica 46:5-106.

Brongersma, L. 1958. On an extinct species of the genusVaranus (Reptilia, Sauria) from the Island of Flores.Zoologische Mededelingen Rijksmuseum von Natuur­lijke Historie te Leiden 36:113-125.

Carroll, R., and M. DeBraga. 1992. Aigialosaurs: mid-Cre­taceous varanoid lizards. Journal of Vertebrate Pale­ontology 12:66-86.

Chesters, K. 1957 . The Miocene flora of Rusinga Island,Kenya. Palaeontographica B, 101:30-71.

Cowles, R. B. 1930. The life history of Varanus niloticusas observed in Natal, South Africa. Journal of Ento­mology and Zoology 22:3-31 .

Drake, R. E., J. A. Van Couvering, M. Pickford, G. H. Curtis,and J. A. Harris. 1988. New chronology for the earlyMiocene mammalian faunas of Kisingiri , Western Ke­nya. Journal of the Geological Society of London 145:479-491.

Estes , R. 1983a. The fossil record and early distribution oflizards; pp. 365-398 in A. Rhodin and K. Miyata (eds.),Advances in Herpetology and Evolutionary Biology.Museum of Comparative Zoology , Harvard University,Cambridge, Massachusetts.

--- 1983b . Sauria terrestria, Amphisbaenia. O. Kuhn(ed.), Handbuch der Palaoherpetologie lOA. Gustav Fi­scher Verlag, Stuttgart, 249 pp.

---, K. de Queiroz, and J. Gauthier. 1988. Phylogeneticrelationships within the Squamata; pp . 119-270 in R.Estes and G. Pregill (eds.), Phylogenetic Relationshipsof the Lizard Families. Stanford University Press, PaloAlto , California.

--- and J. H. Hutchinson. 1980. Eocene lower verte­brates from Ellesmere Island, Canadian Arctic Archi­pelago . Palaeogeography, Palaeoclimatology, Palaeo­ecology 30:325-347.

---and E. Williams. 1984. Ontogenetic variation in themolariform teeth of lizards. Journal of Vertebrate Pa­leontology 4:96-107.

Fejervary, G. 1918. Contributions to a monography onfossil Varanidae and on Megalanidae. Annales MuseiNationales Hungarici 16:341-467.

--- 1935. Further contributions to a monograph of theMegalanidae and Fossil Varanidae, with notes on recentvaranians. Annales Musei Nationales Hungarici, ParsZoologica 29:1-130.

Gauthier, J. 1982. Fossil xenosaurid and anguid lizardsfrom the early Eocene Wasatch Formation, southeastWyoming, and a revision of the Anguoidea. Universityof Wyoming Contributions to Geology 21:7- 54.

Gilmore, C. 1922. A new description of Saniwa ensidensLeidy, an extinct varanid lizard from Wyoming. Pro­ceedings ofU. S. National Museum 60:1-27.

--- 1928. Fossil lizards of North America. Memoirs ofthe National Academy of Sciences , 22. U.S. Govern­ment Printing Office, Washington, D.C., 201 pp.

--- 1943. Fossil lizards of Mongolia. Bulletin of theAmerican Museum of Natural History 81:361- 384.

Hecht, M. 1975. The morphology and relationships of thelargest known terrestrial lizard, Megalania prisca Owen,from the Pleistocene of Australia. Proceedings of theRoyal Society of Victoria 87:239-251.

Hoffstetter, R. 1943. Varanidae et Necrosauridae fossiles.Bulletin du Museum National d'Histoire Naturelle, Par­is 15(3):134-141.

--- 1969. Presence de Varanidae (Reptilia, Sauria) dansIe Miocene de Catalogne. Considerations sur l'histoirede la famille. Bulletin du Museum National d'HistoireNaturelle, Paris 40(5): 1051-1064.

Lonnberg, E. 1903. On the adaptation to molluscivorousdiet in Varanus niloticus. Arkiv for Zoologi I: 67-83.

Lundberg, J. 1972. Wagner networks and ancestors. Sys­tematic Zoology 21:398-413.

Lungu, A. N., G. A. Zirova, and V. M. Tchikvadze. 1983.[First information on Miocene Varanus in the northernBlack Sea basin.] Soobshcheniia Akademiia Nauk Gru­zinskoi SSR, Tiflis 110(2):417-420. [Russian]

McDowell, S. R, and C. Bogert. 1954. The systematic po­sition of Lanthanotus and the affinities of the anguino-

Dow

nloa

ded

by [

Cor

nell

Uni

vers

ity]

at 1

2:38

07

June

201

2

CLOS-NEWVARANUS FROM KENYA 267

morphan lizards. Bulletin of the American Museum ofNatural History 105:1-142.

Meacham, C. 1984. The role of hypothesized direction ofcharacters in the estimation of evolutionary history.Taxon 33:26-38.

Mertens, R. 1942 . Die Familie der Warane (Varanidae).Abhandlungen der Senckenbergischen Naturforschen­den Gesellschaft. Part I (Allgemeines), 462: 1-116. PartII (Schadel), 465: 117-234.

Norell, M., M. McKenna, and M. Novacek. 1992. Estesiamongoliensis, a new fossil varanoid from the Late Cre­taceous Baron Goyot Formation ofMongolia. AmericanMuseum Novitates 3045: 1-24.

Pickford, M. 1981. Preliminary Miocene mammalian bio­stratigraphy for western Kenya. Journal of Human Evo­lution 10:73-97.

--- 1986. Sedimentation and fossil preservation in theNyanza Rift system, Kenya; pp . 345-362 in L. E. Fros­tick et al. (eds.) , Sedimentation in the African Rifts.Geological Society of America Special Publication 25.

Pregill, G. K., J. A. Gauthier, and H. W. Greene. 1986. Theevolution of helodermatid squamates, with descriptionof a new taxon and an overview of Varanoidea. Trans­actions of the San Diego Society of Natural History21(11):167-202.

Reshetov, V. U. , N. S. Shevireva, B. A. Trofimov, and V.M. Tchikvadze. 1978. [Vertebrate Site Andarak II.]

Moskovskoe Obshchestvo Ispytatele i Prirody, en, Biul­leten Otdel Geologischeskii, n. s. 51(5):156. [Russian]

Rieppel, 0 ., and L. Labhardt. 1979. Mandibular mechanicsin Varanus niloticus (Reptilia: Lacertilia). Herpetologica35:158-163.

Romer, A. S. 1956. Osteology of the Reptiles. Universityof Chicago Press, Chicago, 772 pp.

Smith, K. K. 1982. An electromyographic study of the jawadducting muscles in Varanus exanthematicus (Varan­idae). Journal of Morphology 173: 137-158.

Stritzke, R. 1983. Saniwa feisti n. sp., ein Varanide (Lac­ertilia, Reptilia) aus dem Mittel-Eozan von Messel beiDarmstadt. Senckenbergiana Lethaea 64:497-508.

Swofford, D. L. 1990. PAUP: Phylogenetic Analysis UsingParsimony, Version 3.0. Illinois Natural History Survey,Champaign, Illinois.

Van Couvering, J. A. 1972 . Geology of Rusinga Island andcorrelation of the Kenya mid-Tertiary fauna. Ph .D . dis­sertation, Cambridge University, 208 pp.

Verdcourt, B. 1963. The Miocene non-marine Mollusca ofRusinga Island, Lake Victoria, and other localities inKenya. Palaeontographica A, 121:1-37.

--- 1972. The zoogeography of the non-marine Mol­lusca ofEast Africa. Journal ofConchology 27:291-348.

Received 5 October 1992; accepted 14 February 1994.

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