Geography of phocid evolution

Geography of Phocid Evolution

Clayton E. Ray

Systematic Zoology, Vol. 25, No. 4. (Dec., 1976), pp. 391-406.

Stable URL:

http://links.jstor.org/sici?sici=0039-7989%28197612%2925%3A4%3C391%3AGOPE%3E2.0.CO%3B2-8

Systematic Zoology is currently published by Society of Systematic Biologists.

Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available athttp://www.jstor.org/about/terms.html. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtainedprior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content inthe JSTOR archive only for your personal, non-commercial use.

Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained athttp://www.jstor.org/journals/ssbiol.html.

Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printedpage of such transmission.

The JSTOR Archive is a trusted digital repository providing for long-term preservation and access to leading academicjournals and scholarly literature from around the world. The Archive is supported by libraries, scholarly societies, publishers,and foundations. It is an initiative of JSTOR, a not-for-profit organization with a mission to help the scholarly community takeadvantage of advances in technology. For more information regarding JSTOR, please contact [email protected].

http://www.jstor.orgMon Sep 10 15:46:46 2007

http://links.jstor.org/sici?sici=0039-7989%28197612%2925%3A4%3C391%3AGOPE%3E2.0.CO%3B2-8

http://www.jstor.org/about/terms.html

http://www.jstor.org/journals/ssbiol.html

GEOGRAPHY OF PHOCID EVOLUTION

Abstract Ray, C . E. (Department of Paleobiology, Smithsonian Institution, Washington, D. C .

20560) 1976. Geography of Phocid Euolution. Syst. 2002.25:391406.-Phocid distribu-tion suggests origin in and primary radiation from the North Atlantic-Paratethyan region. Phocines and monachines are equally old groups, known first from the lower middle Miocene Calvert Formation. Phocines dominated Paratethys in semi-isolation. Both groups dispersed freely around the margins of the North Atlantic in Miocene and Pliocene time. Phocines entered the North Pacific, probably from the north, in Pliocene time, and have modernized and radiated in latest Cenozoic time, exclusively in the cold waters of the northern hemisphere. Monachine distribution receded southward in the North Atlantic during latest Cenozoic time, and in the Pliocene they spread into both the southern hemisphere, where they radiated in the empty Antarctic, and into the Pacific via the middle American seaway.

At least four forces acting independently over the past decade or so combine now to make a fresh look at the geography of marine mammals and its interplay with their systematics rewarding:

1. The revitalization of paleogeography resulting from the new dynamism in concepts of crustal evolution. Plate tectonics and sea floor spreading are a general theme in geology today, but most of us in the United States who finished our formal schooling as little as 15 years ago were reared scholasti- cally on the supposedly solid foundation of stable continents, with at most a dutiful if not derisive bow toward continental drift, followed by quick dismissal. The impact of colliding continents is now being felt through- out geology.

2. The development of a cosmopolitan time frame for the Cenozoic Era, through long distance correlation by planktonic foraminifera and nanno-plankton, and by magnetic and radio- metric techniques. The integration of these lines of evidence, with increasingly rigorous application of stratigraphic principles, has provided a comprehensive working hypothesis against which the fit of patterns of marine mammal relationships may be tested.

3. Intensified and broadened interest in the biology, distribution, and systematics of modern marine mammals, as a direct outgrowth of the burgeoning environmentalist, conservationist, and protectionist movements. Public con- cern for and numbers of researchers of marine mammals are at all-time peaks.

4. The spectacular increase, for some groups by orders of magnitude, in quantity and quality of raw materials, in the form of available specimens of fossil marine mammals.

This increase in fossil specimens has been less spectacular for seals of the fam- ily Phocidae than for any other major group of marine mammals. The rapid accumula- tion of significant material, including good skulls, skeletons, and in some instances even series of specimens, representing otarioid pinnipeds, cetaceans, desmos-tylians, and sirenians has been truly re-markable. Of Tertiary phocids on the contrary there has been not a single complete skull (new material from South Africa under study by Hendey and Repenning provides the first exception to this rule, Repenning, personal communication), very few fragmentary ones (cf. Guiscardi, 1871; McLaren, 1960a; Tavani, 1941), few good mandibles, and mostly dissociated, fragmentary postcranial material. Nevertheless,

--

392 S Y S T E ~ ~ A T I CZOOLOGY

CENOZOIC SOME WDlOlAETRIC NORTH M'ERICAN

EUROPEAN SOME

PINNIPED - BEARINGP L ~ N ~ T O N I C PINNIPED- BEARING&++ L4ND MAMMAL REMARKS,,CALE BEDS OF -STAGES FORAMNIFERAL BEDS OF THE IN IMYA 5"' AGES

ZOkES EASTERNU.S. WESTERN EUROPE

- RANCHOLABREAN 23 K E N P s Y I L L E ' PLEISTOCENE IRLINGTONIAN . CALABRIAN h 22 ----Tr"-- POEDERLIAN --OCCTANAPRISTIPHOCA

=ASTIAN 'H ICROATAN GL4CIATION.$' LnBRADOR CURRENT PIACENZAN

PLIOCENE 20 zz7_7---7nn_ -7- PIDDLE AND SOUTH AMERICA JOIN

ZANCLIAN lP I- y O R K ~ ~ ~ h , SCALDISIAN FM. PHOCINEETC. ~ Y A K A T A G A 5 , _ L / _ _ u - i i d i 1PRIONODELPHIS CAPENSIS 5 -

' \ N l 8 ,r-MESSINAN MODERNIZED MtD1:ERRANEAh

HEMPHILLIAN I MESSINAN EYAPORITES IN

2_

TORTOhlAN

N 17 ;:I; COBHAP I;;: -INEDITERRANEAN , PARATETHYS ISOLATED

? DIESTIAN MIOPHOCA YETUSTA 10 - CL4REMONT ~/ 10-

7 GAY HEAD GREEN SAND PARATETHY8 ISOL4TED FROM C ~ R E N D O N I A N I' S T . NARYS NORTH ATL4NTIC 7

0 SERRALALLIAN LITTLE COkE POINT UNIT CLOSURE OF WESTERN TETHYS - z 2 N 12 Nip.ii :"-CHOPTANK- -/r- ANLERSIAPI '%A LINDOBONENSIS

LANGHIAN- G -

*P

,,\, - , N D O B O N I A N . ~ -'.::c4~t'~~;'::; j -EARLIEST PHOCOIDS, 15 - 2 N 8 P ~ G OR I ~ E R '5':: I NORTH ATLnNTlC

BURDGALIAN N 7

2 N 6

HEMINGFORDIAN 20 - '

N 5 20-AGUlTANlAN

N 4

L EARLIEST CTARODS,

ARIKAREEAN NORTH PACIFIC N 3

25 --- L" WHITNEYAN CHATTIAN

N 2

30 - ORELMN 30-

N 1 rUUIIu

FIG,1.-Correlation of some geologic deposits and events of importance in phocid history with some relevant time scales, primarily after Berggren and \'an Cowering, 1974, and Black\velder and Ward, 1976.

compared to what was available a decade ago, there has been a massive increase in available material, however fragmental, notably from the middle Pliocene of South Africa (Prionodelphis capensis, described by Hendey and Repenning in 1972, and the first well-founded phocid from the Ter- tiary of the southern hemisphere); from the Sarmatian of Romania and elsewhere in Paratethys ( Grigorescu, this volume ) ; from the Miocene and Pliocene of the Atlantic Coastal Plain of the United States. Most of this last comes from the lower Pliocene Yorktown Formation of Virginia and North Carolina. No phocid has yet been reported in the literature from this formation (Ray, 1976), but we now have more than 1500 specimens (mostly fragments) represent-ing five or more species of seals, as well as one walrus, mostly from the Lee Creek Mine, North Carolina. Figure 1will serve to put the temporal relationships into perspective.

Of an importance at least equal to that

of the new collections is the restudy of the classic collections after a century of almost total neglect. The obsolescence of the primary literature on fossil phocids has been a stumbling block for zoogeographers and neozoologists. Misconceptions perpetuated in recent literature are the fault neither of the old timers nor of the highly com-petent neopinnipediological synthesizers, as Davies (1958a, 1958b), King (1964, 1972), McLaren ( 1960a), and Scheffer ( 1958), but of we paleontologists who have failed to renovate our literature.

For example, the practice of using the genus Phoca as a receptacle for various species of fossil seals of uncertain affinities is innocuous enough and preferable to in- troduction of ill-founded new generic names if it is recognized as a temporary holding device, but it has had the unfortu- nate and understandable effect of influenc- ing taxonomic and evolutionary interpretation through the power of nomenclature. A single example of good work harmed by

PHOCID EVOLUTION

reliance on poor paleontology will suffice:

It is even more notable that seals of the modern genus Phoca, and only slightly distinguishable from the modern species Plzoca vitulina, are re-corded from the Miocene. The evi-dence, although small in bulk, clearly shows that there was comparatively rapid evolution up to the Miocene but that since then rates have been ex-tremely slow, at least in the Northern Hemisphere. (Davies, 1958b, p. 491).

Just as with the centennial restudy of Prorastomus sirenoides (Savage, this issue), it turns out that much can be learned from the old collections of fossil phocids to which one must turn, however imperfect they are in quality and data, for names to apply to new material. Of course the nine- teenth century workers made their share of outright errors, but more to the point, they were working with meager compara- tive collections, and under concepts of biology, evolution, systematics, and geologic correlation of their time, all largely irrele- vant today (just as one hopes ours will be in 2076) and not yet updated.

The growing collections from the eastern United States stimulated my review of the classic collections from the Miocene and Pliocene of the Antwerp Basin, from which Van Beneden (1877, and earlier works) described thirteen species of phocids, the largest source of phocid paleotaxa. In the first two columns of Table 1are listed Van Beneden's taxa with their affinities according to him, both carried forward more or less intact into the modern literature (cf. King, 1964, pp. 130-132). In succeeding columns are my most conservative altera- tions of the taxa, my interpretation of affinities, and status on the west side of the North Atlantic. This fauna is introduced here as a demonstration of the importance and fruitfulness of critical reexamination of original collections, whether new material is involved or not. We will return to it below, but at this point it should be noted that the Belgian material was col-

lected mostly as spoil, essentially without stratigraphic data. The ages indicated in the table were deduced after the fact by Mourlon ( 1877), and were called in question by some later Belgian stratigraphers. However, our western North Atlantic forms, collected in part with better stratigraphic control, reassuringly arrange them- selves in similar stratigraphic sequence.

Similar restudy is in progress of other old collections, including that from Kishinev near the Russian-Romanian bor- der on the northwest corner of the Black Sea, which Nordmann (1860) described in part. Examination of this collection has already revealed that most of the lectotype femur of Monotherium maeoticum, desig- nated from the literature ( McLaren, 1960a), is missing, and has raised serious doubt as to the validity of assignment of the species to Monotherium and indeed of any Paratethyan Tertiary seal material to the Monachinae. The study of fossil phocids is beset by many practical and procedural problems, mostly traceable directly or indirectly to the paucity of good quality material in the past and continuing in large measure to the present. The fact that many types or lectotypes are isolated femora creates problems because of the generally low diagnostic value of femora. Among postcranial elements, humeri offer much greater promise, and have been used by myself (Antwerp collections, ms.) and others (True, 1906). Much basic alpha taxonomy remains to be done. Compre-hensive description and illustration of the Russian collections is a particularly urgent priority.

My purpose here is to attempt to ra-tionalize the major features of the history of the Phocidae by testing the fit of the known, guessed, or suggested relationships and distribution of fossil and modern phocids against the patterns of paleogeography, paleoclimatology, paleoecology, and correlation developed independently of phocid considerations through decades of research along varied lines by numerous individuals. For phocid purposes, this

394 SYSTEMATIC ZOOLOGY

SEALS DESCRIBED BY VAN BENEDEN AFFINITIES ACCORDING REVISED FROM VICINITY OF ANTWERP, BELGIUM TO VAN BENEDEN (1877) NOMENCLATURE

SCALDISIAN, EARLY PLIOCENE

Mesotaria ambigua Otariid Callophoca ambigua

Callophoca obscura Phoca groenlandica Callophoca obscura

Paleophoca nystii Monachus Paleophoca nystii

Platyphoca vulgaris Erignathus Platgphoca vulgaris

Gryphoca similis Halichoerus G ~ y p h o c asimilis

Phocanella pumila Phoca hispida Phocanella pumila

Phocanella minor Phoca hispida Phocanella minor

Phoca vitulinoides Phoca vitulina Phoca vitulinoides

DIESTIAN, LATE MIOCENE

Monotherium delognii Monachus Monotherium delognii

Monotherium affine Monachus Monotherium a f f ine

Monotherium aberratum Monachus Monotherium aberratum

ANVERSIAN, MIDDLE MIOCENE

Prophoca rousseaui Primitive Prophoca rousseaui

Prophoca proxima Primitive Leptophoca proximu

vast field of study has been synthesized the skimpy phocid record, it should con-admirably and recently (Berggren and Van form to and reflect the more broadly and Couvering, 1974; Berggren and Hollister, securely based features of earth history. 1974). I had independently reviewed much of the literature as it seemed to bear on ORIGIN

the seals prior to publication of these We still lack the critical fossils to address works, and I find my conclusions drawn the problems of origin directly, but enough from the literature in such harmony with of a pattern seems to be emerging in fossil these authors, and their covergge of the phocids to venture some tentative com-literature so thorough, that one need only ments on the essential questions of when, cite their papers for present purposes. My where, and whence. usage of epochal terms and ages in millions Contrary to past widely expressed opinion of years ago follows that of Berggren and (as Davies, 1958b) that would put the co-authors in these and earlier papers. origin of pinnipeds back to Eocene or even

Thus, after a brief look at the still open Cretaceous time, I see no reason to look question of origin, I will attempt a broad- beyond the Oligocene, and for phocids at brush sketch of phocid history through least, conceivably beyond the beginning Miocene, Pliocene, and Quaternary time. of the Miocene. The earliest authenticated If there is any objectivity to be found in phocids are of early middle Miocene age,

395 PHOCID EVOLUTION

TABLE1. ( C o n t i n u e d )

IIEVISED AFFlNITIES

Monachine, near Monachus ( and Mirounga?), possibly male C. obscura

Same as C. ambigua, possibly female; includes material originally referred to Paleophoca nystii

Odontocete cetacean, near Scaldicetus

Large aberrant phocine

Phocine, possibly close to Phocanella pumila

Phocine

Small phocine, possibly conspecific with Phoca vitulinoides

Small phocine

Large primitive monachine, possibly conspecific with M . affine

Primitive monachine, possibly conspecific with M . delognii

Small primitive monachine; originally referred material

STATUS I N WESTERN NORTH ATLANTIC

YORKTOWN FORMATION

Present

Present

Present (cetacean)

Present

Uncertain

Present

Unknown

Uncertain

ST. MARYS FORMATION AND GAY HEAD GREENSAND

Genus and at least two species present; number of species and trans- Atlantic status uncertain

CALVERT FORMATION

Probably present

Present or represented by L . lenis

includes undescribed phocine

Primitive phocine

Primitive phocine, close to Leptophoca lenis

perhaps 14 million years old at the oldest and certainly not more than 16. This leaves some 6-8 million years of prior Miocene time, ample for origin from a non-marine aquatic ancestor.

These earliest phocids are the phocine Leptophoca lenis and monachine Mono-therium? wymani from the Calvert Forma- tion of Maryland and Virginia (Ray, 1976), the probably somewhat younger Lepto-phoca proxima and Prophoca rousseaui from the Anversian black sands of Belgium, and "Phoca" vindobonensis (possibly referable to Leptophoca) from the Vienna Basin, at that time (perhaps 12-14 million years ago) probably still indirectly confluent with the North Atlantic. Thus the margins of the North Atlantic or its appendages appear to be the most probable locale for phocid entry into the marine

environment. I do not agree with the argu- ments for pinniped origin in the Arctic Basin advanced by Davies (1958b, p. 478) and in part already countered by McLaren ( 1960b) and Chapski ( 1970).

Considerable thought has been devoted to problems of pinniped ancestry, particularly to diphyletic vs. monophyletic origin, based on evidence from diverse sources. Since we still lack truly intermediate fossil phocids, I have only two minor observations to add to what has been well presented by several recent authors (Mitchell, 1967, McLaren, 1960b, 1975, Sarich, 1969, Amason, 1974). First, assumptions to the contrary, some of the more recent ap-proaches, as karyology and serology, may well be subject to limitations and pitfalls (variable rates, convergence, parallelism, etc.) at least as severe as those encountered


FIG. 2.-Phoca vi t t~l ina,harbor seal, two adults and a pup, left, and an adult Alopex lagopus, Arctic Fox, right; photographed in Pribilof Islands by E. H, hliller.

in classical disciplines, and in any case, for the foreseeable future, only the fossils can tell us what has lived and when and where. Second, the disparate adaptation and morphology of phocoids and otarioids have not been accorded sufficient weight. Other-wise, I will confine my remarks here primarily to historical zoogeography, and the known fossils.

First, any presumptive explanation of origin(s) must take into account that otarioid and phocoid first appearances are sepa- rated by some 8 million years and by the North American continent. The absence of phocoids from the Pacific coast of con-terminous United States and Mexico prior to the Pleistocene (Barnes and Mitchell, 1975) is difficult to explain if monophyly is accepted, especially in view of the enor- mously rich and varied marine vertebrate faunas known from the late Oligocene on- ward. Concealing the ancestral phocoid in high latitudes during its early evolution

is not an attractive option. Pre-Pliocene invasion of the North Pacific should have been feasible from an Arctic source. Also later phocid evolution recommends a middle latitude, warmer water origin, with high latitude adaptation a latest Cenozoic phenomenon, phocine in the northern hemisphere, and monachine in the southern.

From the otarioid side there is no evi-dence to recommend a common Arctic Basin origin: the Pacific coast of North America, represented as unsuitable for marine invasion by pinnipeds (Davies, 1958b, p. 478), is the most prolific source of fossil otarioids, including the most primitive forms known; otariids never invaded the North Atlantic which they surely would have done from the Arctic Basin; otariids today are not pagophilic; mounting paleon- tological evidence indicates that Arctic adaptation of the living walrus is excep- tional, if not unique, among odobenids

PHOCID EVOLUTION

FIG. 3.-Right humeri of some phocine seals in lateral aspect. A. Leptophoca lenis, USNM 5359, holotype, Calvert Formation, lower middle Mio-cene. B. Phocanella pumila, USNM 171151, re-ferred, Yorktown Formation, lower Pliocene. C. Plzoca groenlandica, USNM 396625, modern.

(Repenning, this volume) and is a latest Cenozoic, probably Pleistocene, develop-ment.

As regards the morphology of known fossils. the usual assertions, that we lack the critical fossils and that phocids are full-fledged at first appearance in the record, are not entirely accurate. True, there is indeed a wide gulf between an advanced, highly terrestrial arctoid carni- vore and an advanced highly marine one ( Figure 2) , and we do not have real intermediate forms between land and sea adaptations, except possibly in the form of Potamotherium or the problematical Se-mantor. However, further analysis of available material, and discovery of better material, of known forms, as Leptophoca lenis, will certainly shed light on early evolution. The full modernization of phocines and Antarctic monachines took place almost certainly no more than 4 million years ago, probably concomitant with climatic deterioration and high latitude adaptation. Phocine modernization apparently had to do importantly with achievement of present locomotor adaptations, judging from the contrast in morphology and pro-

FIG. 4.-Left innominate bones of some modern phocids in lateral aspect. A. Monachus schauinslandi, USNM 395999. B. Monachus monachus, USNM 219059. C. Phoca groenlandica, USNM 188766.

portions between the appendicular skeletons as far as known of Mio-Pliocene phocine seals and advanced living phocines. For example, modern phocines have

robust, curved humeri with strongly developed crests and rugosities, whereas Leptophoca lenis (middle Miocene) and Phocanella pumih (early Pliocene) have relatively slender, straight humeri with subdued crests and rugosities (Figure 3) ; modern phocines (excepting Erignathus, sometimes implied to be "monachine" in some characters, but in my opinion a conservative and in part aberrant phocine) have the anterior end of the ilium highly everted and excavated laterally to a thin blade except for marginal buttresses, whereas all Tertiary phocines and Esig-nathus have comparatively straight, thick ilia, more as in monachines (Figure 4). A skull or associated skeleton of Lepto-phoca lenis when found undoubtedly will tell us a lot about its origin.

SYSTEMATIC ZOOLOGY

In short, I believe that phocids entered the marine environment independently of otarioids, from a Potamotherium-like an-cestor, somewhere around the margins of the North Atlantic no more than 22, and perhaps as little as 18-20, million years ago.

MIOCENE

At about 18-20 million years ago, long prior to the first appearance of phocids, the breakup of Tethys had progressed to the point of closure at the eastern end of the present Mediterranean Sea by collision of Africa and Asia Minor. There seems to be no evidence of marine interchange between western Tethys and the Indian Ocean after this time (Burdigalian), precluding dis-persal of seals into the Indian Ocean, and, along with other evidence, militating against arrival of the progenitors of Mon- achus schauinslandi in the mid-Pacific via this route (contrary to Rice, 1973).

By early middle Miocene time, perhaps 14 million years ago, the phocids had differentiated into phocine and monachine lineages and the species probably were distributed linearly around the rim of the North Atlantic at least from North Caro- lina, Virginia, and Maryland on the west to Belgium on the east. Prophoca was present on both sides, as was Leptophoca, similar but for the larger size of Prophoca. A monachine, Monotherium? wymani, was present at least on the west side (Ray, 1976).

It is only fair to point out how skimpy is the evidence on which the above assertions are made. Leptophoca lenis of the U.S. is known from the holotype humerus plus a few dozen largely undescribed specimens; L. proxima of Belgium from the humerus, radius, and ulna, all incomplete. Prophoca rousseaui of Belgium is known from less than 10 bones, all incomplete. The best evidence for it in the western Atlantic is a partial innominate bone from Maryland. Monotherium? wymani was known originally in 1850 from a partial skull consisting of at least a well preserved

braincase, subsequently lost or destroyed except for parti-a1 temporal bones, plus a few fragments, to which a few more fragments have been added recently, all from Richmond, Virginia (Ray, 1976).

At the same time or slightly later, a smaller form close to Leptophoca lenis, "Phoca" vindobonensis, was present in the Vienna Basin, which was at that time still confluent with the North Atlantic via the perialpine trough and the western Mediterranean or across northwestern Germany to the North Sea (Gignoux, 1955, pp. 555,569,588, 592- 593). "Phoca" vindobonensis probably gave rise to the phocine radiation in the Para- tethys (Grigorescu, this issue).

In the middle Miocene (Choptank For- mation) of Maryland and Virginia there are a few undescribed monachine bones.

In the Vienna Basin and elsewhere in Europe there are a few poorly understood forms whose relationships and relative ages are unclear, including Miophoca vetusta (not referable to Pristiphoca, and phocine, not monachine) ,Monotherium gaudini, and "Phoca" rugosidens.

The late Miocene (Diestian) genus Monotherium was erected on the basis of reasonably adequate material from the Antwerp Basin of Belgium, including three nominal species which exhibit a size range suggestive of at least two species, or one sexually dimorphic species. The same taxa are probably present on the western shore of the Atlantic, judging primarily from a small humerus from Martha's Vineyard (Ray, 1976) and a large one from Mary- land (St. Marys Formation). There is as well an undescribed phocine in the Diestian deposits of the Antwerp Basin, represented by an associated hind foot referred previ- ously to Monotherium aberratum (Van Beneden, 1877).

By this time Paratethys was isolated from the North Atlantic as a brackish inland sea at various times subdivided into isolated or semi-isolated basins. Here there de-veloped a peculiar and in part aberrant phocine fauna, represented by forms such as Phoca pontica, P. bessarabica, and

PHOCID EVOLUTION

"Monotherium" maeoticum (see Grigor-escu, this volume). In fact, the evidence for assignment of any Paratethyan seal to Monotherium or to the Monachinae is not compelling. Some of the humeri in the Nordmann Collection (most of the collection was not illustrated or described by Nordmann) are conceivably monachine, but all other bones are equivocal, or clearly diagnostically phocine, including those assigned to "Phoca" mueotica by Nord-mann. I do not feel that the presence of monachines in Paratethys prior to the Pleistocene invasion of the Black Sea (rem- nant of Paratethys) by Monachus has been demonstrated.

Paratethyan seals continued to evolve, perhaps in complete isolation, through late Miocene ( Messinian) and Pliocene time. A direct seaway to the Arctic from Par- atethys has been suggested but not proven. A plausible case can be made for evolution of the Pusa group in Paratethys, perhaps explaining the origin and distribution of the Caspian and Baikal seals, and the pro- pensity of Pusa seals for freshwater, as in the lake populations of northern Europe. McLaren (1960a, 1960b) has presented a persuasive argument along these lines, excepting that he has regarded the Parate- thyan representatives of the Pusa group as reflecting a southern extension from the Arctic, whereas I would suggest that the group originated in Paratethys and sub-sequently invaded the Arctic.

In the latest Miocene ( Messinian) the Mediterranean may have dried up com-pletely (see Sonnenfeld, 1975, for recent discussion of the problem), but whether it did or became reduced to isolated salt lakes cut off from the Atlantic by closure of Tethys on the west as a result of Africa and the Iberian Peninsula swinging to-gether is immaterial to phocid evolution. The supposition of authors (as Davies, 195813, p. 488) that monachines somehow had to survive continuously in the Medi- terranean is wholly unnecessary, as the Mediterranean was in Mio-Pliocene time at most an appendage to monachine dis-

tribution. The monachines were the dominant seals in the Mio-Pliocene of the North Atlantic, and would if necessary have re- populated the Mediterranean immediately following the Messinian salinity crisis. Even in Recent time Monachus monachus has occupied, and continues to occupy a broad area outside the Mediterranean. Our thinking perhaps has been captive to the modern time plane, to our nomenclature ("Mediterranean" monk seal), and to the history of European acquaintance with the animal in the Mediterranean since classical times. In fact I am aware of no evidence to demonstrate that the Mediterranean has been a major theater of phocid evolution.

Apparently the affinity of phocines for the middle latitudes prevented their entering the Pacific during the Miocene via the wide-open Middle American seaway. The relationship of the monachines to the Mid- dle American seaway is discussed below under the Pliocene. If the Arctic Ocean existed in Miocene time ( cf. MacNeil, 1965, pp. G6-7), there is no evidence that any phocids used it as a route to the Pacific.

PLIOCENE

This is the epoch of best and richest evidence in phocid paleontology-in the eastern U.S., Belgium, southern France, Italy, Romania, Alaska, and South Africa- with hints of material from Peru, Argentina, and elsewhere.

A rich early Pliocene North Atlantic fauna of 4 5 genera and 4-7 species is known, primarily from the Antwerp Basin (Scaldisian) and eastern North Carolina (Yorktown Formation), of which mon-achines are the dominant element in terms of number of bones though doubtfully in number of species. By far the most common morphologic group consists of two species or one sexually dimorphic species, the smaller, Callophoca obscura, about the size of Monachus, and the larger, C. ambigua, the size of Hydrurga. Further sub- stantiation of evidence for sexual di-morphism would strengthen the case for Callophoca as a possible ancestor of the

SYSTEMATIC ZOOLOGY

elephant seals. Morphologically the Cal-lophoca group seems to be a permissible ancestor for either Monachus or Mircuunga or both. This or these fossil forms, plus at least two (probably more) phocines, Platyphoca vulgaris and Phocanella pumila, and at least one walrus, are known on both sides of the North Atlantic at this time, perhaps 4.5 million years ago.

Known thus far only from a few bones and only on the west side of the North Atlantic, also from the Yorktown Forma- tion, is a form very similar to Prionodelphis capensis of the South African middle Plio- cene. A single humerus, collected recently as float along the lower Potomac River and probably derived from the Cobham Forma- tion (in any case not younger), closely re- sembles humeri of Prionodelphis, and ex-tends the range of this group in the western North Atlantic back to late Miocene time (Table 1 ) . Monotherium almost certainly gave rise to this form. The distribution patterns of Monotherium and other phocids in the North Atlantic during Miocene and Pliocene time suggest that Prionodelphis should have occurred in the eastern North Atlantic as well, in which case its trans- equatorial dispersal could have been along the west coast of Africa, to give rise to Prionodelphis capensis in South Africa. However, southward dispersal along the east or west coast of South America from a Caribbean center open to the Pacific now seems more probable, giving rise in Argen- tina to Prionodelphis rovereti (whose status requires clarification through redis- covery and restudy of referred material and discovery of new material), and to P. capensis by west-to-east dispersal across the South Atlantic. The modern Antarctic monachines (especially Leptonychotes, Repenning, personal communication) must have arisen at least in part (almost certainly excepting Mirounga) from this invasion of the southern hemisphere, although their diversity and in part dissimilarity to P. capensis (cf. Hendey, 1972, p. 105) strongly recommend multiple ancestry.

Rather than disjunct populations in the

early Pliocene I think it more reasonable to suppose that monachine species then as earlier shared an amphi-North Atlantic distribution pattern with phocines, just as all phocine species continue to do today, with the essential difference of more equable, probably ice-free, climates prior to the Pleistocene. In the North Atlantic the monachines and phocines responded dif-ferently to the drastically deteriorating climates of post-early Pliocene times. Mon- achines retreated southward with their receding ancestral habitats, and the Mona- chus lineage changed little, excepting that interruption of gene flow around the northern perimeter of the Atlantic led to diver- gence and speciation into Monachus monachus on the east, with Pristiphoca occitana of southern France and Pliophoca etrusca of Italy its immediate ancestors, and M. tropicalis on the west. Speciation of Mona- chus on opposite sides of the southern North Atlantic in this manner seems much more probable than waif dispersal directly westward across the widest part of the Atlantic to the Caribbean via the route of Columbus (contrast Davies, 1958b, and Hendey, 1972). Similarly, there seems no need to move Prionodelphis or its ancestor directly across the Atlantic in low latitudes; its probable ancestor, Monotherium, was present on both sides, and whether Priono- delphis is found eventually on the Euro- pean side or not, it certainly was in position for southerly dispersal in the western hemisphere.

Did Prionodelphis move southward along the east or the west coast of South America? When did monachines enter the eastern Pacific? What was the history of dispersal of Mirounga, of Monachus schauinslandi? The solutions to all of these problems hinge upon the date of effective closure to monachine passage of the Mid- dle American seaway, and upon fossil evidence from low latitudes and from South America in general.

The dominant view among vertebrate paleontologists, based on the evidence of terrestrial mammals, has been that the land

PHOCID EVOLUTION

bridge was completed only in latest Plio- cene or early Pleistocene time, in seeming conflict with evidence from multiple sources pointing toward much earlier interruption of free marine interchange. This conflict may be more apparent than real in view of differing concepts of the beginning of the Pleistocene (1-3 million years ago) and of the possibility that an effective, ecologically broad land bridge may not have existed for purposes of general land mammal dispersal until long after emer-gence had progressed to the point of major deflection of currents (such as that enhanc- ing the Gulf Stream), leading to development of contrasting environments, and hence an ecological barrier, on opposite sides of middle America (warm Caribbean vs. cold Pacific). In any case the evidence now seems to point strongly toward cessa- tion of marine interchange by middle Plio- cene time (3.5-4 million years ago) at latest, and possibly by early Pliocene or even late Miocene time (Berggren and Hol- lister, 1974, p. 175; Emiliani, Gartner, and Lidz, 1972; Savage, 1974; Weyl, 1974).

The continuing dearth of monachine fossils in low latitudes and in South Amer- ica generally impedes solution of these problems of monachine dispersal and evolution. The rich Miocene and Pliocene pinniped faunas of the Pacific coast of the United States, and even those of Cedros Island and Baja California (the last poorly known as yet) may well represent waters too cold for monachines, and in any event have produced none as yet. The supposed Pliocene record of Mirounga (Hendey, 1972) is based on a pair of tusks from the San Diego Formation that I believe to be odobenid on the basis of their continuous tubular core of fine-grained globular osteo- dentine. There seems to be no record as yet for Mirounga on the Pacific coast prior to the late Pleistocene (Barnes and Mitchell, 1975). The best hope at present for critical fossils in a strategic location is from the Sacaco fauna in the Pisco Forma- tion at 15' south in Peru. These deposits are of uncertain Mio-Pliocene age, but con-

tain otariids and phocids (Hoffstetter, 1968). The character of 'these phocids (surely monachines) should aid greatly in answering questions of distribution in the eastern Pacific and dispersal to the southern hemisphere.

Until the key fossil evidence is available, some speculative interpretations may be made on the basis of modern distribution, of morphology and of fossil evidence from elsewhere and from other groups.

Sometime within late Miocene and/or early Pliocene time the common ancestor of Monachus tropicalk and M. schauinslandi, perhaps a form not very different from Monotherium? wymuni or Callophoca obscura, must have been distributed through the Caribbean-Pacific Middle American seas, along with the ancestor of Mirounga, probably from the same stock, and probably Prionodelphis. Odobenine walruses certainly occupied the same seas, as evidenced by a much better southerly fossil record (Ray, unpublished; Repen-ning, this volume). With disruption of the seaway, the walruses ultimately became extinct on the Pacific side and continued their evolution in the North Atlantic, re-entering the Pacific from the north only in the Pleistocene (Repenning, this volume); the ancestor of Mirounga became extinct on the Caribbean side but gave rise to Mirounga on the Pacific side and at some stage dispersed southward along the South American coast to give rise to M. leonina; Primodelphis ultimately disappeared from the middle latitudes in both oceans but not before dispersing into the southern hemisphere; ancestral Monachus continued in the Caribbean, evolving into M. tropi-calk.

Another isolate may have survived on the Pacific side for an unknown length of time, and either it or its Caribbean-Pacific ancestor have given rise to M. schuuinslandi by waif dispersal to Hawaii. M. schauinslandi is a well differentiated species, with certain distinctive morphological charac-ters such as its free fibula, not coossified proximally with the tibia, a (primitive?)

402

FIG.5.-Left tibias and fibulas of monk seals in posterior aspect. A. Monachus schauinslandi, USNM 395996, with fibula rolled aside to show proximal articular facets. B. Monachus monachus, U S N M 219059, with tibia and fibula coossified proximally.

feature unique among phocids (Figure 5 ) , and a wide separation in the innominate between the acetabulum and the obturator foramen, pierced by a foramen unique among phocids ( Figure 4).

Phocines responded to deteriorating climates of the North Atlantic after the early Pliocene perhaps in part by retreating southward but also by adaptation. The early Pliocene Yorktown-Scaldisian pho-cines were still conservative osteologically. Sometime between then and the late Pleistocene when the living species appear, the modernization of the phocine skeleton occurred, in my opinion coincident with increasingly severe extremes of seasonal climate and expansion of the icy Arctic. The modern adaptive radiation of the Phocinae was a post-early Pliocene and/or Pleisto-cene phenomenon, quite the contrary to the supposed presence of modernized

SYSTEMATIC ZOOLOGY

Phoca in Miocene times, a misimpression created in part undoubtedly by the ten-dency of past workers to refer a variety of species, mostly poorly known, to Phoca. This late radiation of phocines would help to explain the taxonomic difficulty, vari- ability, and plasticity of the group (see Burns and Fay, 1970, for the best discussion of these problems).

By middle Pliocene time a small Pusa- like form was present in southern Alaska as evidenced by a single radius (Barnes and Mitchell, 1975). This may represent the first entry of Pusa into the high latitudes, possibly from Paratethys. There is no persuasive evidence of phocines farther south in the Pacific until early Pleistocene time (Barnes and Mitchell, 1975).

The Pleistocene history of phocines is clearly complex, though in part one of alternate southward and northward vacil- lation of ranges in response to cooling and warming, of response to changing local conditions (Fred&. 1975: Forsten and Alhonen, 1*5; and Sergeant, 1972), and of greater or lesser ease of inter-change across the Arctic. Each species and species group undoubtedly has a distinctive history only very incompletely analyzed and understood at present but provoca-tively discussed by Davies ( 1958a, 1958b), McLaren (1960a, 1966), and others. Some stocks have been thought to represent highly differentiated species pairs, as Phoca groenlandica and P. fasc.iata (Davies, 1958a; cast in doubt by Burns and Fay, 1970, but supported by McLaren, 1975); Erignathus barbatus has differentiated weakly into two subspecies (Manning, 1974); P. hispida is little differentiated but apparently distinguishable into localized populations, as is P. groenlandica (Yablo- kov and Sergeant, 1963) although interchange must occur (Sergeant, 1973) ;Phoca vitulina seems to be still actively differen- tiating if not in process of developing a species swarm (Fay, 1974; Naito and Nishiwaki, 1975) ; Cystophma surprisingly seems never to have established itself on the Pacific side, although strays, apparently

PHOCID EVOLUTION

usually young males, are common enough in the Beaufort Sea for the Eskimos to have a name for them (Burns, pers. comm.) which seems to point up the chancy nature of such invasions; apparently Halichoerus has always preferred middle latitudes, too southerly for movement into the Pacific via the Arctic, and too northerly and too young geologically for invasion via the Middle American seaway.

The role of ice in the evolution of pinnipeds, especially phocines, and especially in terms of the white lanugo, its presence or absence in utero and/or post partum and its adaptive and/or evolutionary significance, has been much discussed in the literature (for example, McLaren, 1966, 1975; Burns, 1970; Fay, 1974). Its tra-ditional interpretation as protective coloration against predators now seems to be at best an incomplete explanation of its oc-currence. I am unable to accept the occur- rence of a white coat alone, either embryonal or neonatal, as conclusive evidence of special relationship or of ances-tral pupping on ice, but believe instead that it could have developed (and did) independently and repeatedly in a geo-logically short time (as white coloration surely did in other northern mammals and birds) and that pinnipeds had massive ex- posure to ice only within Pleistocene time. The ecological and evolutionary significance of ice for pinnipeds is only beginning to be investigated and understood (Fay, 1974). Stirling (1975) has discussed interestingly the possible role of ice in developing phocid breeding patterns, es-pecially polygyny, which would suggest that evidence for polygyny should not be expected in pre-Pleistocene phocids, and that the gross sexual dimorphism in Mirounga for example is a very late evolutionary development. However, the role of ice seems doubtful for Mirounga, in view of the geologically late, and in my opinion, secondary, contact of Mirounga with ice, in the southern hemisphere only. With regard to Halichoerus, its meager fossil record suggests southerly displacement away from

the ice (Ray, et al., 1968); perhaps a case could even be made that the modern ice- breeding populations represent utilization of marginal reproductive habitat left to the species by usurpation of most of its (possibly preferred) land breeding territory by man.

CONCLUSIONS

The shores of the North Atlantic Ocean, not the Arctic, have been the site of the origin, the longest part of the discovered history, and the reservoir of successive dis- persals and radiations of phocids.

Monachines were apparently the dominant phocids in the Mio-Pliocene North Atlantic, changing relatively little and slowly from first appearance in the early middle Miocene, but retreating southward following their ancestral habitat, and thereby abandoning the north temperate and Arctic seas to the more adaptive phocines as the climate cooled and developed toward its patterns of Pleistocene fluctuations and modern seasonal extremes. The monachines invaded, and radiated in, high latitudes only in the Antarctic in the absence of phocines.

Phocines were present in the North At- lantic continuously with monachines from their joint first appearance in early middle Miocene time, and apparently entered the Paratethyan region early and radiated there in isolation, but possibly ultimately con-tributed the Pusa lineage to the northern phocine fauna. The evidence for mon-achines in Paratethys is not persuasive as yet. The great radiation, modernization, spread to the Pacific, and dominance of phocines in northerly latitudes is a latest Cenozoic, largely Quaternary, phenomenon, probably stimulated by extreme cooling and climatic fluctuations of the Pleistocene, and is still in progress. Modernized phocines are unknown with certainty prior to the Pleistocene; reference of poorly known earlier phocines to the genus Phoca has been misleading.

There are many seeming anomalies in the patterns of phocid evolution. Why did


FIG.6.-The North Atlantic Ocean and environs 5howing paleogeography and sugge5ted phocid and odobenine dispersal dnring late Miocene-early Pliocene time; the Lee Creek Mine and Antwerp fossil localities; Sable Island and the Orkney Idands, probable southern breeding limits of walru, in Recent time; the Recent distribution of Pl~oca citulinu and Monachus within the mapped area. Dotted circles and arro\r7s denote les, probable event,. The possible intermittent land barrier between Enrope and Greenland, after Leh~nann (1973), is improbable for the Neogene, but if present could have con-tributed to the continnity of phocid distribution. Map compiled from many sources.

the ancestors of hlonachus do so little with summarize the North Atlantic-centered the apparent opportunities for radiation history of the Phocidae (and Odobeninae) in the eastern Atlantic and Mediterranean, in late Miocene-early Pliocene time, a phase and in the Caribbean and eastern Pacific? of major importance to their subsequent Why should we have only hlonachus distribution and evolution. It must be schauimlandi in the mid-Pacific, and not strongly emaphasized that we are still at several species more widely distributed? the stage in phocid paleontology at which What factors have limited monachines for a single well preserved, well documented the most part to high latitudes in the south- bone say from the late Tertiary of Alaska, ern hemisphere after having crossed the Peru, New Zealand, Argentina, or even equator to get there? Are they that uni- from the "well known" beds in the Para- versally incompatible with the southern tethyan region, western Europe, or either otariids? coast of North America, could radically

Figure 6 represents primarily an effort to alter basic understanding of phocid geog-

PHOCID EVOLUTION

raphy. It must be equally emphasized that conditions of distribution of seals in life, body size, social structure, deposition, and coincidences of human activity such as location of population and scientific centers, inevitably have profound impact upon the revealed record of phocid paleontology. Until 1972 there were no significant records of fossil phocids in the south-ern hemisphere, whereas Prionodelphis capensis is now the best known fossil phocid; until now there has been no seal fauna known for the Yorktown Formation, which when published will be the richest Ter- tiary seal fauna. Both the South African and North Carolinian faunas are by-products of phosphate mining. Further, it was not until more than 1000 pinniped bones had been collected at the Lee Creek Mine, North Carolina, that the first recog- nizable bone of Prionodelphis turned up. Undoubtedly there are many more sur-prises in store for us, some of which almost certainly will alter drastically the outline of the geography of phocid evolution sketched here.

ACKNOWLEDGMENTS

I wish to thank Jane Knapp for translation of Russian literature; Edward H. Miller for permission to use the photograph reproduced in Figure 2; Lawrence B. Isham and Jeffrey Lund for preparation of the illustrations; John J. Burns and Dan Grigorescu for unpublished information on seals; and especially Charles A. Repenning for many stimulating discussions on pinnipeds and for constructive criticism of a draft of this paper. Financial support for the research on which this paper is based and for participation in the syrn- posium was provided by the Smithsonian Institu- tion through the Walcott and Kellogg Funds and the Smithsonian Research Foundation.

REFERENCES

ARNASON,0. 1974. Phylogeny and speciation in Pinnipedia and Cetacea-A cytogenetic study. Lund, Carl Bloms Boktryckeri A,-B.

BARNES,L. G., AND E. D. MITCHELL. 1975. Late Cenozoic northeast Pacific Phocidae. In K. Ronald and A. W. Mansfield (eds.), Biology of the seal. Conseil International pour I'Explora- tion de la Mer, Charlottenlund Slot, Denmark, Rapports et proc8s-verbaux des RBunions 169: 34-42.

BERGGREN,W. A,, AND C. D. HOLLISTER. 1974. Paleogeography, paleobiogeography and the history of circulation in the Atlantic Ocean. In W. W. Hay, (ed.), Studies in paleo-oceanography. Soc. Econ. Paleont. Min. Spec. Publ. 20: 126-186.

BERGGREN,W. A,, AND J. A. VAN COUVERING. 1974. The late Neogene. Biostratigraphy, geo- chronology and paleoclimatology of the last 15 million years in marine and continental sequences. Palaeogeogr., Palaeoclimatol., Palaeo- ecol. 16:l-216.

BLACKWELDER,B. W., AND L. W. WARD. 1976. Stratigraphy of the Chesapeake Group of Maryland and Virginia. Geol. Soc. Amer. NE- SE Sections joint mtg., Guidebook field trip 7b.

BURNS, J. J. 1970. Remarks on the distribution and natural history of pagophilic pinnipeds in the Bering and Chukchi Seas. J. Mammalogy 51 :445-454.

BURNS, J. J., AND F. H. FAY. 1970. Compara-tive morphology of the skull of the ribbon seal, Histriophoca fasciata, with remarks on system-atics of Phocidae. J. Zool., London 161:363-394.

CHAPSKI, K. K. 1970. [The concept of the Arctic origin of pinnipeds and another solution to this problem.] I n A. I. Tolmachev, (ed.), The Arctic Ocean and its coastline in the Ceno- zoic. Hydrometeorological Publishers, Lenin-grad:166-173 [in Russian, translated by Jane K ~ ~ P PI .

DAVIES, J. L. 1958a. Pleistocene geography and the distribution of northern pinnipeds. Ecology 39:97-113.

DAVIES, J. L. , 1958b. The Pinnipedia: an essay in zoogeography. Geogr. Rev. 48:474-493.

EMILIANI, C., S. GARTNER, AND B. LIDZ. 1972. Neogene sedimentation on the Blake Plateau and the emergence of the Central American Isthmus. Palaeogeogr., Palaeoclimatol., Palaeo-ecol. 11:1-10.

FAY, F. H. 1974. The role of ice in the ecology of marine mammals of the Bering Sea. In D. W. Hood and E. J. Kelley, eds., Oceanography of the Bering Sea. Inst. Marine Sci. Univ. Alaska, Fairbanks :383-399.

FORST~N, P. ALHONEN. 1975. The sub- A., AND '

fossil seals of Finland and their relation to the history of the Baltic Sea' Boreas 4:143-155.

FRED~N, C. 1975. Subfossil finds of Arctic whales and seals in Sweden. Sveriges Geol. Undersokning, Ser. C 710, Avhandl. Uppsatser, Arsbok 69 ( 2 ) :1-62.

GIGNOUX,M. 1955. Stratigraphic geology. Free- man and Co., San Francisco, California.

GUISCARDI,G. 1871. Sopra un teschio fossile di foca. R. Accad. Scienze Fisiche Matematiche Atti, Naples, 5 ( 6 ) :1-8.

HARINGTON,C. R., AND D. E. SERGEANT. 1972.

SYSTEMATIC ZOOLOGY

Pleistocene ringed seal skeleton from Champlain Sea deposits near Hull, Quebec-a reidentifica-tion. Canadian J. Earth Sci. 9:1039-1051.

HENDEY, Q. B. 1972. The evolution and dis-persal of the Monachinae (Mammalia: Pin-nipedia). Ann. S. African Mus. 59:99-113.

HENDEY, Q. B., AND C. A. REPENNING. 1972. A Pliocene phocid from South Africa. Ann. S. African Mus. 59: 71-98.

HOFFSTETTER,R. 1968. Un gisement de vert8- brks Tertiares a Sacaco (sud-Pkrou ), tkmoin NkogBne d'une migration de faunes australes au long de la cbte occidentale Sud-Amkricaine. C. R. Acad. Sci. Paris, Ser. D, 267:1273-1276.

KING, J. E. 1964. Seals of the World. British Museum ( Natural History), London.

KING,J. E. 1972. Observations on phocid skulls. In R. J. Harrison, (ed. ), Functional anatomy of marine mammals. 1. Academic Press, London, New York:81-115.

LEHMANN, U. 1973. Zur Palaogeographie des Nordatlantiks im Tertiar. Mitt. Geo1.-Palaont. Inst. Univ. Hamburg 4257-69.

MACNEIL, F. S. 1965. Evolution and distribution of the genus Mya, and Tertiary migrations of Molluscs. U.S. Geol. Surv. Prof. Pap. 483- G:Gl-G51.

MANNING,T. H. 1974. Variations in the skull of the bearded seal. Univ. Alaska Biol. Pap. 16: 1-21.

MCLAREN, I. A. 1960a. On the origin of the Caspian and Baikal seals and the paleoclimato- logical implication. Amer. J. Sci. 258:47-65.

MCLAREN, I. A. 1960b. Are the Pinnipedia biphyletic? Syst. Zool. 9: 18-28.

MCLAREN, I. A. 1966. Taxonomy of harbor seals of the western North Pacific and evolution of certain other hair seals. J. Mammalogy 47: 466473.

MCLAREN, I. A. 1975. A speculative overview of phocid evolution. In K. Ronald and A. W. Mansfield, (eds.), Biology of the Seal. Conseil International pour l'Exploration de la Mer, Charlottenlund Slot, Denmark, Rapports et Proces-verbaux des Rkunions 169:4348.

MITCHELL, E. 1967. Controversy over diphyly in pinnipeds. Syst. Zool. 16 :350-351.

MOURLON,M. 1877. Sur le classement stratigra- phique des phoques fossiles recueillis dans les terrains d'Anvers. Bull. Acad. Roy. Sci. Belg., Ser. 2,43:603-609.

NAITO, Y., AND M. NISHIWAKI. 1975. Ecology and morphology of Phoca witulina largha and Phoca kurilensis in the southern Sea of Okhotsk and northeast of Hokkaido. In K. Ronald and A. W. Mansfield, (eds.), Biology of the seal. Conseil International pour l'Exploration de la Mer, Charlottenlund Slot, Denmark, Rapports et ProcBs-verbaux des Rkunions 169:379-386.

NORDMANN,A. VON. 1860. Palaeontologie Siid-russlands. IV. Elephas, Mastodon, Dinotherium, Phoca, Manatus, Cetotherium, Balaena, Balae-noptera und Delphinus. H. C. Friis, Helsingfors: 271-360.

RAY,C. E. 1976. Phoca wymani and other Ter- tiary seals (Mammalia: Phocidae) described from the eastern seaboard of North America. Smith-sonian Inst. Contribs. Paleobiol. 28:l-36.

RAY, C. E., A. WETMORE, D. H. DUNKLE,AND

P. DREZ. 1968. Fossil vertebrates from the marine Pleistocene of southeastern Virginia. Smithsonian Misc. Colls. 153 ( 3 ) :1-25.

RICE, D. W. 1973. Caribbean monk seal (Monachus tropicalis). Internat. Union Conserv. Nature and Nat. Res. Publ., New Ser., Suppl. Pap. 39:98-112.

SARICH, V. M. 1969. Pinniped phylogeny. Syst. Zool. 18:416-422.

SAVAGE,J. M. 1974. The isthmian link and the evolution of neotropical mammals. Nat. Hist. Mus. Los Angeles County Contribs. Sci. 260: 1-51.

SCHEFFER, V. B. 1958. Seals, sea lions, and walruses. Stanford Univ. Press, Stanford, Cali- fornia.

SERGEANT,D. E. 1973. Transatlantic migration of a harp seal, Pagophilus groenlandicus. J. Fish. Res. Bd. Canada 30:124-125.

SONNENFELD,P. 1975. The significance of up-per Miocene (Messinian) evaporites in the Mediterranean Sea. J. Geology 83:287-311.

STIRLING,I. 1975. Factors affecting the evolution of social behaviour in the Pinnipedia. In K. Ronald and A. W. Mansfield, (eds.), Biology of the seal. Conseil International pour 1'Explora- tion de la Mer, Charlottenlund Slot, Denmark, Rapports et ProcBs-verbaux des Rkunions 169: 205-212.

TAVAM, G. 1941. Revisione dei resti del pin-nipede conservato nel Museo di Geologia di Pisa. Palaeontographia Italica, Mem. Paleont. 40 (new ser. 10):97-113.

TRUE, F. W. 1906. Description of a new genus and species of fossil seal from the Miocene of Maryland. U.S. Nat. Mus. Proc. 30:835-840.

VAN BENEDEN, P.-J. 1877. Description des os-sements fossiles des environs d'Anvers. Premiere partie. PinnipBdes ou amphithkriens. Ann. Mus. Roy. Hist. Nat. Belg. 1:l-88.

WEYL, R. 1974. Die palaogeographische Ent-wicklung Mittelamerikas. Zentralbl. Geol. Palaont., Teil 1, Jg. 1973:432466.

YABLOKOV,A. V., AND D. E. SERGEANT. 1963. [Cranial variation in the harp seal (Pagophilus groenlandicus Erxleben, 1777).] Fish. Res. Bd. Canada Transl. Ser. 485: 1-9. [original in Russian, translated from Zool. Zh. 42:1857-1865.1

Documents

Geography of phocid evolution