Phocinae and Phylogenetic Affinities of the Monk Seals

AMERICAN MUSEUM

Norntates

PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, N.Y. 10024 Number 2924, pp. 1-38, figs. 1-10, tables 1, 2 October 3, 1988

On "Retrogression" in the Evolution of the Phocinae and Phylogenetic Affinities of the Monk Seals

ANDRFE R. WYSS' CONTENTS Abstract ...... 1 Introduction ...... 2 Acknowledgments. 3 Phocid Monophyly and Historical Considerations ...... 3 Comparative Morphology and Phylogenetics ...... 6 "Monachus" Affinities ...... 6 Characters Pertinent to the Placement of "Monachus" ...... 6 Affinities of the "Monachinae" ...... 15 "Monachine" Characters and the "Monachine"/Phocine Division ...... 16 Systematic Conclusions and Implied Patterns of Character Evolution ...... 30 References ...... 36

ABSTRACT The origin of the phocine seals appears to have corroborated hypothesis of the monophyly of the been associated with a pattern of massive char- Phocinae, it is concluded that the monophyly of acter reversal, particularly as concerns features of the "Monachinae" remains significantly more the postcranial skeleton. To establish that the doubtful. Monk seals have been placed within this primitive features occurring in phocines do in fact latter subfamily in all recent phylogenetic treat- represent reversals and not simply retentions from ments of the Phocidae. Analysis here reveals that an ancestral phocid condition, a reexamination of this arrangement is less strongly supported than is the two currently recognized subdivisions of the generally assumed. Moreover, the genus compris- Phocidae is undertaken. In contrast to the strongly ing monk seals, "Monachus," does not itself ap- Department of Vertebrate Paleontology, American Museum of Natural History.

Copyright American Museum of Natural History 1988 ISSN 0003-0082 / Price $3.75 2 AMERICAN MUSEUM NOVITATES NO. 2924 pear to be monophyletic. Thus, in the preferred Phocinae must therefore be postulated. This pat- branching arrangement presented here both the tern of character transformation is corroborated "Monachinae" and "Monachus" are portrayed as whether or not "monachine" paraphyly is accept- paraphyletic, with the monk seals placed as se- ed. Moreover, these reversals can be substantiated quential sister-taxa to the remaining phocids. whether or not one ascribes to the multiple origin Certain aspects of the phocine postcranium, of pinnipeds. Acceptance of either "monachine" which may be considered primitive, are not prim- paraphyly or pinniped monophyly, however, ac- itive for phocids as a whole, and an exceptional centuates the pattern of reversal seen among pho- series ofreversals within the clade comprising the cines.

INTRODUCTION The so-called "true" or "earless" seals of focus ofthis paper. If other characters can be the family Phocidae are undoubtedly among recruited to support the placement of pho- the most highly specialized members of the cines as the sister-group of other phocids, it eutherian order Carnivora. It is well known might then become judicious to suggest that that in many aspects of the postcranial skel- the postcranial features ofphocines are prim- eton members of the phocid subfamily Pho- itive for phocids. Alternatively, if phocines cinae differ markedly from other phocids. can be shown to be removed from a sister- Hitherto ignored is the observation that many group position, then the unusual primitive ofthe features in which phocines depart from phocine postcr-anial attributes may reason- the conditions typical of other phocids are ably be interpreted as reversals. The appar- decidedly primitive. Also overlooked is the ently conservative aspects of phocine mor- fact that these primitive traits not only set phology include features associated with the phocines apart from other phocids, but serve architecture of the fore- and hind-flippers, as well to distinguish phocines from all other and the more proximal appendicular skele- pinnipeds. From a phylogenetic standpoint, ton, as well as a lesser number of soft ana- then, the situation seen in phocines is com- tomical and cranial traits. patible with two interpretations; either (1) Phocids are currently divided into the these characters represent primitive hold- postcranially plesiomorphic Phocinae and the overs from the ancestral phocid condition, or "Monachinae,"2 which are more typically (2) they represent reversals to more primitive pinniped in many postcranial aspects. One states that have occurred subsequent to the means of establishing that phocines (assum- early diversification of phocids. Preference ing for the moment their monophyly) are not for one ofthese transformational hypotheses the sister-group of other phocids is a dem- necessarily depends on the acceptance of a onstration of the paraphyly of the presumed particular notion of phocid phylogeny and phocine sister-group the "monachines." thus the remarks presented below are pri- Therefore I first examine the presumed basal marily aimed at an examination of some of ("monachine"/phocine) phocid dichotomy, the more general aspects ofthe interrelation- dealing specifically with the monophyly of ships of these highly aquatic carnivorans. "Monachus"-a taxon widely recognized as The greatly divergent morphology of pho- representing an early offshoot in the evolu- cids, coupled with their scant fossil record tion of phocids-and a consideration of the and a general historical lack of detailed ex- affinities of its three Recent species to other amination, has resulted in both a poor un- phocids. This leads to an evaluation of the derstanding of the origin of the group as a evidence bearing on the monophyly of the whole and considerable uncertainty regard- higher taxonomic group of which "Mona- of its ing the mutual phylogenetic affinites 2 Because the monophyly of the "Monachinae" and members. Higher-level intra-phocid rela- its type genus "Monachus" has yet to be securely dem- tionships are crucial to deciding between the onstrated and is in fact called into question by this anal- two alternative sequences of transformation ysis, these nomena are included in quotes throughout outlined above, and thus form the principal this paper. 1988 WYSS: PHOCINE SEALS 3 chus" is widely held as being a member, the are monophyletic. Advanced features com- "Monachinae." This phylogenetic frame- mon to members ofthis highly modified group work then permits the central objective of are many, including: the inability to draw the this paper, a more detailed consideration of hind limbs forward during terrestrial loco- the occurrence ofwide-scale character rever- motion, the lack of a lesser trochanter on the sal in the evolution of phocine seals, a pos- femur, the lack of an alisphenoid canal, a sibility suggested above. transversely directed basal cochlear whorl, an The present account is not intended as an opening of the cochlear fenestra outside the exhaustive treatment ofintraphocid relation- tympanic cavity to form a cochlear foramen, ships; it merely represents a preliminary ex- the lack of an internal auditory meatus and amination of these affinities as they pertain prefacial commissure, strongly everted ilia, a specifically to the questions outlined above. massively developed posterior astragalar I make no claim to either the originality of process and greatly reduced calcaneal tuber, any ofthe observations made or to any ofthe heavily pachyostotic mastoid region, ptery- characters considered. My efforts are aimed goids reaching the auditory bulla, pit for in- simply at putting into a phylogenetic context sertion oftympanohyal anterior to stylomas- one particular-and highly peculiar-char- toid foramen, greatly inflated heavily ossified acter distribution. caudal entotympanics, and an ilial psoas major insertion (Weber, 1904; Gray, 1905; Faw- ACKNOWLEDGMENTS cett, 1918; Howell, 1929; Kummer and NeiB3, Chester Tarka is gratefully acknowledged 1957; Burns and Fay, 1970; Repenning, 1972; for sharing with a most recalcitrant pupil what Hunt, 1974; deMuizon, 1981a, 1981b; King, he could ofhis prodigious photographic skills. 1983). Features common to phocids that also I thank Lorraine Meeker for her ever patient are approached or matched in Odobenus, its tutelage with the figures and for her pains- close fossil allies, and/or the Miocene allo- taking "heroics" with figure 10. I have ben- desmine and dematophocine "otarioids" in- efited greatly from discussions with, and the clude: greatly expanded cochlear fenestra, continued encouragement of, Dr. Richard H. greatly expanded basal whorl of the scala Tedford. Drs. Tedford, Sydney Anderson, tympani, separation of the entrances of cra- Annalisa Berta, Francis H. Fay, John J. Flynn, nial nerves VII and VIII, inguinal testes, dark Malcolm C. McKenna, Michael J. Novacek, epidermis, hind limb propulsion, greatly en- and Randall T. Schuh read and provided larged incus, malleus and epitympanic recess, valuable comments on the manuscript. I prof- mortised jugal-squamosal contact, nasals ited enormously from a particularly detailed wedging deeply between the frontals, short and incisive critique by Dr. Fay; I am deeply premaxillary-nasal contact, absence of pin- appreciative ofhis generous efforts and freely nae, nonmedulated primary hairs, lack ofsu- shared expertise. Through the courtesy of praorbital processes, lack of fusion between Charles A. Repenning I was able to study and exoccipital and mastoid, and merging of ca- photograph the Hawaiian monk seal tem- nal for cochlear aqueduct with cochlear fe- poral region (figured herein) in his care. Guy nestra (citations above and Scheffer, 1964; G. Musser and M. J. Novacek are thanked Mitchell, 1966; Barnes, 1972, Fleischer, 1973; for access to collections under their super- Gordon, 1981; Fay, 1982). Most ofthese and vision. This work was supported by a faculty other characters are discussed at length else- fellowship from Columbia University and by where (Wyss, 1987). Therein these features the Frick are argued to represent evidence of the kin- Laboratory Endowment Fund, ship ofphocids to the abovementioned groups AMNH. (see also remarks below). PHOCID Given such an apparently robust diagnosis MONOPHYLY AND of the Phocidae, it is not surprising that his- HISTORICAL CONSIDERATIONS torically there has been little debate about its If any statement about the higher-level re- genealogical reality. Following Illiger's 1811 lationships among arctoid carnivorans is be- recognition of pinnipeds as a group distinct yond reasonable doubt, it is that the Phocidae from other aquatic mammals, Gray (1825) 4 AMERICAN MUSEUM NOVITATES NO. 2924 erected the grouping Phocidae to include what "Otarioidea" appears to consist largely of would today be regarded as phocids, otariids primitive characters, that is, characters of a (sea lions and fur seals), and Enhydra. Cur- distribution much more general than simply iously, Gray's arrangement excluded the wal- "otarioids" (e.g., retention of an alisphenoid rus, Odobenus (= Trichecus rosmarus), rele- canal, an internal auditory meatus, and the gating it instead to isolated familial status ability to draw the hind limbs forward during within an order encompassing cetaceans and terrestrial locomotion). Thus the morpholog- sirenians. It was Brookes (1828) who first rec- ical basis ofthe conventionally accepted phy- ognized the phocid grouping as it is presently logenetic unity of "otarioids" consists in large conceived. Subsequently, in Allen's (1880) measure of the shared absence of the apo- well-known subdivision of the pinnipeds, morphies common to phocids, leading one phocids came to be termed "wrigglers," while to conclude that this collocation has been their terrestrially more nimble brethren the based largely on the nonphocid status of its otariids and Odobenus (which maintain the constituents. In keeping with this assessment, use oftheir hind limbs in locomoting on land) and on the basis of the features listed above, were dubbed "walkers." I have elsewhere presented the admittedly Beyond universal agreement on the ques- controversial argument that some "otari- tion ofphocid monophyly, however, there is oids" share a more recent common ancestry little consensus regarding other aspects of with phocids than they do with other sup- phocid relationships. Disagreement centers posed "otarioids" (Wyss, 1987). on two areas, identification ofa phocid sister- While higher-level relationships among the group and the establishment of major phy- major pinniped lineages have attracted much logenetic subdivisions within the family. With detailed discussion -and are likely to contin- respect to the former, "Which carnivoran lin- ue to do so as several recent, not always con- eage is most closely allied to phocids?" there gruent, considerations ofthe subject indicate are two widely divergent schools of thought. (e.g., Flynn et al., 1988; Wozencraft, 1988)- One view held by many comparative anat- many other interesting phylogenetic prob- omists earlier this century (e.g., Weber, 1904; lems among pinnipeds remain. The interre- Winge, 1923, 1941) and shared almost unan- lationships among phocids is one area war- imously among molecular and karyological ranting further attention. Naturally the two systematists (e.g., Deuel, 1955; Fay et al., areas of inquiry, higher-level pinniped rela- 1967; Sarich, 1969a, 1969b; Arnason, 1974, tionships and the relationships within one of 1977; de Jong, 1982; Arnason and Widegren, its subgroups, are to a large degree inter- 1986), places phocids within a monophyletic twined. Pinnipedia as the sister to a group comprising Before considering relationships among otariids and odobenids. An alternative view phocids, the phylogenetic position ofphocids establishes pinnipeds as diphyletic in origin among other pinnipeds and among other car- with phocids representing an independently nivorans must be discussed as this influences derived aquatic lineage closely allied to mus- decisions about character generality. It is telids (e.g., McClaren, 1960, Tedford, 1976; widely recognized that for systematic inves- de Muizon, 1982a, 1982b). As noted above, tigations to yield phylogenetic results (i.e., to evidence has been presented elsewhere (Wyss, reflect genealogy), proposed relationships 1987) supporting yet a third arrangement, must be supported on the basis ofshared pos- namely that phocids are members of a clade session of derived attributes (Hennig, 1966). including Odobenus, Allodesmus, and Des- One useful means of establishing character matophoca, with this grouping in turn em- polarity is outgroup comparison. Any anal- braced within a monophyletic Pinnipedia. ysis should specify its operating assumptions, Allodesmus and Desmatophoca traditionally including the selection of reference taxa. In have been allocated to the "Otarioidea" -a the present case, the choice of outgroups is group essentially equivalent to Allen's inseparable from the question of pinniped "walkers" plus their subsequently described monophyly. Although the debate is not set- presumed fossil allies. It should be pointed tled, space is not taken here to provide a de- out, however, that evidence supporting the tailed assessment of the dual versus single 1988 WYSS: PHOCINE SEALS 5 origin issue. For the moment it suffices sim- scheme admits a monophyletic "Monachus," ply to state that the monophyly hypothesis "Monachinae," and Phocinae. Other ar- remains by far the least contradicted of pres- rangements shown in figure 1 are discussed ently available alternatives. The present anal- in succeeding sections but are briefly sum- ysis thus proceeds from the premise that ota- marized here. Class II hypotheses place riids and Odobenus (and not mustelids) "Monachus" as the sister-group ofother pho- represent appropriate nearest phocid out- cids, with the "Monachinae" recognized as groups, with Odobenus (among living pin- paraphyletic. In class III hypotheses "Mon- nipeds) being the most immediate sister- achus" is recognized as paraphyletic but the group. It should be emphasized, however, that monophyly of "monachines" exclusive of in a certain general sense these assumptions "Monachus" is preserved. In class IV ar- are not critical. For most of the characters rangements only the subfamily Phocinae is examined, the character states in question recognized as monophyletic with other would be unambiguously regarded as derived "monachines" and "Monachus" represent- even if mustelids were used as an outgroup. ing successively more distant paraphyletic Potential conflicts that would arise if mus- outgroups. telids were recognized as the phocid sister- The "Monachinae" traditionally include group are noted in the discussion. How the (in addition to "Monachus" and Mirounga) phylogenetic results accepted here would be the almost certainly monophyletic tribe Lo- altered under an assumption of pinniped di- bodontini, comprising among living forms phyly, is considered in the conclusions. Ref- the Antarctic Leptonychotes, Lobodon, Hy- erence to the diphyly argument is included drurga, and Ommatophoca. As the phylo- to show that the conclusions drawn here are genetic arrangement of phocids has been in- not strictly dependent on the rejection of di- terpreted by de Muizon (1982a), Mirounga phyly. The pattern of primitive character is the sister-group of the lobodontines, with reacquisition identified among phocines, al- "Monachus" in turn representing the out- though mildly sensitive in the degree to which group to Mirounga + lobodontines. As will it is expressed, holds true whether or not be discussed below, however, the monophyly monophyly is assumed. of this subfamily is not as strongly founded Historically phocids have been variously as might be desired, particularly as regards divided into two to four major subgroupings. the inclusion of "Monachus." In her insightful 1966 study, King collapsed A third phocid subfamily, the "Cystopho- earlier, more highly split arrangements, ad- rinae," was formerly recognized (e.g., Schef- vocating instead a two-part division of the fer, 1958) for the two taxa with an inflatable Phocidae into the so-called northern (Erig- proboscis, Mirounga and Cystophora. Since nathus, Cystophora, Halichoerus, Phoca, King's (1966) contribution, this group is no Pusa, Histriophoca, Pagophilus) and south- longer regarded as monophyletic, Mirounga ern lineages ("Monachus," Mirounga, Lep- being dispatched to the "monachines" and tonychotes, Lobodon, Hydrurga, Ommato- the Cystophora to the phocines. phoca). At the same time King suggested that As concerns the status of the genera rec- Erignathus and "Monachus" may represent ognized in this analysis, it is necessary to point forms linking these two broad groups. This out the recommendation that the phocines split has been formalized with the recognition Pusa, Histriophoca, and Pagophilus be as- of two phocid subfamilies, the "Monachi- signed to subgeneric rank under the genus nae" and the Phocinae in numerous subse- Phoca (Burns and Fay, 1970). Other authors quent classifications (e.g., King, 1983; de (see de Muizon, 1982a: 188) have also pro- Muizon, 1 982a). Presented in figure 1 are what posed Pusa as a subgenus of Phoca. I have I consider the four most important alterna- chosen to sidestep this issue. A matter ofmore tives for the phylogenetic arrangement of pressing concern is how the various taxa and phocids. The most widely held current view monophyletic groups of taxa we elect to rec- of a phocid division into two monophyletic ognize are interrelated. The monophyly of subfamilies (e.g., de Muizon, 1982a) is re- Phoca in the broad sense (including Pusa, garded as a class I hypothesis; this branching Histriophoca, and Pagophilus) has not been 6 AMERICAN MUSEUM NOVITATES NO. 2924 upheld by one recent study (de Muizon, conservative members of the Phocidae and 1982a). Thus I regard the matter as unsettled to probably represent an early split in the and simply recognize all ofthese four as gen- evolution of the group (e.g., Repenning and era. Similar reasoning applies to the question Ray, 1977; Repenning et al. 1979; de Mui- of the appropriate rank for the group com- zon, 1982a). In their important study of the prising all phocids. This is not an objectively Hawaiian monk seal, Repenning and Ray resolvable matter and consequently there ex- (1977) reviewed several lines ofevidence sug- ists a considerable diversity of opinion (e.g., gesting that in many respects species of Barnes et al., 1985). For the purpose of in- "Monachus" appear to be more primitive ternal consistency and in the interest of con- than other phocids. Furthermore, these au- venience I arbitrarily regard phocids as a thors highlighted several morphologic differ- family. ences between the three Recent taxa and not- Most published studies agree on the mono- ed that "M." schauinslandi (ibid.: 684) "ap- phyletic grouping of Pusa, Histriophoca, pears to be the modern representative of the Pagophilus, Halichoerus, and Phoca, typical- most ancient of living phocid lineages." ly given the tribal designation Phocini (e.g., Translating these remarks into the terminol- Burns and Fay, 1970; de Muizon, 1982a), a ogy of phylogenetic systematics, Repenning concept also supported by this analysis. and Ray hinted at, but did not advocate explicitly, a phylogeny conforming to a class II COMPARATIVE MORPHOLOGY or III arrangement of figure 1, where "M." AND PHYLOGENETICS schauinslandi represents the sister-taxon of We are now in a position to attempt a de- other phocids. Later, however, Repenning et tailed character analysis. First, characters al. (1979: fig. 1) modified this opinion, de- bearing on the question of the placement of picting the "Hawaiian Island Group" as an "Monachus" within the Phocidae will be early offshoot of the monachine (rather than considered, then features that have been mar- phocid) lineage, thus preserving the tradi- shalled in support ofa "monachine"-phocine tional monachine-phocine division of the division. It will be primarily in review ofthis family (a class I hypothesis of fig. 1). If this second set ofcharacters that the "primitive" second interpretation is accepted and if "M." attributes of phocines will become apparent. schauinslandi is more conservative in several Once the characters have been considered and respects than are other phocids, we may infer a phylogenetic framework of phocids estab- that the advanced characters ofphocids other lished, patterns of character transformation than the Hawaiian monk seal must have orig- within the phocines will be open to inspec- inated at least twice, once within a clade em- tion. Detailed consideration is given to the bracing the "monachines" exclusive of "M." derivation of the proposed phylogeny since shauinslandi, and once within phocines. Al- such an analysis necessarily forms the back- ternatively, "M." shauinslandi, and perhaps bone of any of character evolution. other species of "Monachus," may have sec- study ondarily reacquired some primitive features "MoNAcHus" not found in other phocids. AFFINITIES Much of the present paper, therefore, is a As currently conceived, the genus "Mon- review of the alternative character transfor- achus" includes three Recent species, the mations implied by these phylogenies. Hawaiian "M." schauinslandi, the Mediter- Throughout the discussion that follows, char- ranean "M." monachus, and the recently ex- acters are numbered as in tables 1 and 2, tinct Caribbean "M." tropicalis. The ques- where polarity decisions are summarized and tion of the mutual affinities of these three the distribution ofthese features is provided. seals has attracted only limited attention. However, in view of their singularly impor- TO THE tant phyletic position as the potential sister- CHARACTERS PERTINENT group(s) of other phocids, a consideration of PLACEMENT OF "MONACHUS" their phylogenetic affinities seems advisable. Repenning and Ray (1977) pointed to sev- Monk seals are said to be among the most eral features of the "Monachus" ear region 1988 WYSS: PHOCINE SEALS 7

Monachinae ^Monachinae'

I II

'Monachinae' 'Monachinae' 'Monachus' "Monachus' '

,+ .4 I Phocinae Phocinae

III IV

Fig. 1. The four general hypotheses of phocid interrelationships discussed in text. Most commonly debated arrangements represent one of these patterns or slight permutations thereof. These possibilities do not subsume all possible branching arrangements; others include a nonmonophyletic Phocinae, or the placement of phocines as the sister-group of other phocids, but these are not among the most likely alternatives. For example, since King (1966) phocine monophyly has not been questioned. Likewise, the placement of phocines as the sister-group of other phocids has no precedent in the literature nor is such an arrangement given credence by the present analysis. that are clearly plesiomorphic among pho- diving (Repenning, 1972). Unlike the other cids. The following five auditory features seem "monachines" and phocines that have been to be primitive (except as noted) among Pin- examined, the distribution pattern ofthis tis- nipedia and their alternative derived condi- sue within the epitympanic recesses of "M." tions may be diagnostic of a monophyletic shauinslandi "appears to parallel that of group of phocids exclusive of "Monachus." otarioid pinnipeds" (Repenning and Ray, 1977: 672). They added, however (recogniz- 1. "Otarioid"-like distribution of cavern- ing that this does not necessarily imply par- ous tissue lining middle ear cavity. The pin- allelism), that they were inclined to the view niped middle ear cavity is filled by distensible that this pattern "reflected some unknown tissue thought to inflate with blood in re- primitive condition" (ibid.). Due to its great- sponse to increasing external pressure during er economy I would similarly favor this sec- 8 AMERICAN MUSEUM NOVITATES NO. 2924

TABLE 1 Selected Phocid Features and Polarity Determinations Discussed in Text Feature Primitive Derived 1) tissue lining middle ear "otarioid"-like thick near floor and roof cavity 2) dorsal region of petrosal unexpanded expanded 3) petrosal apex unexpanded, pointed dorsoventrally thickened, blunter in outline 4) internal auditory meatus remnant of roof present roof completely absent 5) pericardial plexus poorly developed well developed 6) tibia and fibula unfused proximally fused proximally 7) innominate, obturator present uniformly absent nerve foramen 8) teres major process caudal scapular angle square hooklike 9) mastoid swelling not visible in dorsal view visible in dorsal view 10) auditory bulla does not cover petrosal, widely sepa- essentially covers petrosal, nearly con- rate from exoccipital tacts exoccipital 11) posterior lacerate fora- circular, basioccipital abuts auditory coalesces with petrobasilar fissure medi- men region al to auditory region 12) atlas vertebrarterial foramen visible in pos- visible in dorsal view terior view 13) scapular spine prominent markedly reduced 14) entepicondylar foramen absent present 15) cuneiform distally projecting ledge absent present 16) metacarpals I and II, I greatly enlarged approximately equal comparative size 17) intermediate phalanx V greatly reduced comparable in size to its counterparts of carpus 18) metacarpal head, phalan- smooth head, phalanges flat, articula- heads with palmar ridges, phalanges geal articulations tions hingelike round, articulations trochleated 19) ilium straight, flat strongly everted, lateral excavation 20) astragalus sustentacular facet long facet short 21) metatarsal III, posterior short, margin concave long, margin straight flipper margin 22) foreflipper claws reduced long 23) hind-flipper claws long reduced 24) premaxilla ascending process visible laterally ascending process dips into nasal aper- along entire length ture 25) upper incisors six four 26) natal coat black gray or white 27) secondary hairs absent present 28) molt cornified tissue and hair do not form cornified tissue and hair form sheets sheets during molt 29) mystacial whiskers smooth beaded 30) mammary teats four two 31) chromosomes 2N = 34 2N = 32 32) upper incisors round in cross section compressed laterally 33) carotid canal, postero- posterior opening visible in ventral not visible in ventral view, process ab- medial process of audi- view, process present sent tory bulla 34) interorbital width least in posterior half of interorbital least in anterior half septum 35) basioccipital-basisphe- ventral surface strongly concave flat to convex noid area 36) mastoid lip does not cover external cochlear fora- covers or partially covers foramen men 1988 WYSS: PHOCINE SEALS 9

TABLE 1-(Continued)

Feature Primitive Derived 37) humerus, supinator ridge poorly developed well developed 38) humerus, deltoid pectoral long, merges with shaft smoothly short, ends more abruptly crest 39) post-tibial fossa develop- weak strong ment

ond interpretation. Regrettably the disposi- appears to be "the most primitive of known tion of this tissue for the other two living phocoid seals." The possibility might there- species of "Monachus" is not known and fore be considered that other phocids are apo- hence is marked in table 2 by a query. Never- morphically united by a greater enlargement theless, phocids exclusive of at least "M." of the basal turn of the cochlea. schauinslandi show a unique (at least among 3. Unenlarged V-shaped petrosal apex. As pinnipeds) pattern ofdistribution ofthe cav- has been carefully observed and discussed by ernous tissue lining middle ear wherein it is Ray (1976) a considerable diversity in the thickest near the floor and roofofthe middle form of the temporal region exists within ear cavity, thinning near the eustachian tube, phocids. Although as Ray noted, the exceed- across the tympanic membrane, and in the ingly complex morphology of the region is epitympanic recess (Repenning, 1972). not readily broken down into "key" com- 2. Unexpanded dorsal petrosal region ponent characters, some potentially system- (primitive character distinguishing "AM." atically useful features do seem to be exhib- schauinslandi from other phocids). Repen- ited. Most conspicuous perhaps is the swelling ning and Ray (1977) made the important ob- ofthe dorsal petrosal surface, resulting in the servation that among all known phocids (fos- development ofa dense globular mass of bone sil and Recent) the dorsal part ofthe petrosal near the dorsal petrosal apex, a condition seen (defined as the region above a horizontal plane particularly in phocines (except Erignathus) extending from the vestibular aqueduct, for- and in Mirounga (ibid.). Thus in these forms ward across the cochlear aqueduct to the the highest point on the intracranial surface anterodorsal surface of the petrosal apex) is of the petrosal is on this swollen apex which the least developed among "M." shauin- is seen in anterior view to extend above the slandi. Thus, unlike that in other phocids (in- level of the entrance of the facial canal. cluding "M." tropicalis and "M." mona- Another feature of potential significance is chus), the ventral part ofthe petrosal in "M." the general form-aside from the swellingjust schauinslandi protrudes medially and api- noted-ofthis apical region. Relative to those cally from beneath the unexpanded dorsal of other pinnipeds, the petrosal apex of all portion. Typically in phocids, the derived ex- phocids is massive, but in comparison to those pansion of the dorsal part of the petrosal re- in other members of the family the petrosal sults (in dorsal view) in the ventral portion apices of all three Recent species of "Mon- largely being covered (fig. 2) (see also Repen- achus" remain relatively unexpanded (fig. 2). ning and Ray, 1977: pl. 1). Not only is "M." In carnivorans in general, including otariids schauinslandi the most conservative of liv- and particularly Odobenus, the petrosal apex ing phocids in its relatively unenlarged dorsal assumes a distinctly V-shaped outline in dor- petrosal region, it appears to be less advanced sal view. This appearance is modified some- than all known fossil phocids as well (ibid.). what in most phocids either by the apical Also pertinent here is the observation of Re- hypertrophy noted above or by medial and penning and Ray (1977: 675) who noted that lateral outgrowths near the apical region, both the petrosal in "M." shauinslandi, by virtue of which contribute to a generally blunter, of its relatively small basal cochlear whorl sometimes almost square, outline (fig. 2). The AMERICAN MUSEUM NOVITATES NO. 2924 10

TABLE 2 Distribution of Phocid Features Discussed in Text Features correspond to those listed in table 1. Symbols in the matrix denote the following: + derived character, 0 primitive character, ? not known, * features ofphocines which although derived for phocids, are, or approach, the primitive camnivoran (or mammalian) condition. Mona- chus schauins- M. M. Lepto- landi monachus tropicalis Mirounga nychotes Lobodon 1) tissue lining middle ear cavity 0 + + + 2) dorsal region of petrosal 0 + + + + + 3) petrosal apex 0 0 0 + + + 4) internal auditory meatus 0 0 0 + + + 5) pericardial plexus 0 ? ? + + + 6) tibia and fibula 0 + + + + + 7) innominate, obturator nerve foramen 0 + + + + + 8) teres major process 0 0 0 0 + + 9) mastoid swelling 0 0 0 0 0 0 10) auditory bulla 0 0 0 + + + 11) posterior lacerate foramen 0 0 0 0 0 0 12) atlas 0 0 0 + + + 13) scapular spine 0 0 0 0 + + 14) entepicondylar foramen 0 0 0 0 0 0 15) cuneiform 0 0 0 0 0 0 16) metacarpals I and II, comparative size 0 0 0 0 0 0 17) intermediate phalanx V of carpus 0 + 0 0 0 0 18) metacarpal head, phalangeal articulations 0 0 0 0 0 0 19) ilium 0 0 0 0 0 0 20) astragalusc 0 0 0 0 0 0 21) metatarsal III, posterior flipper margin + + + + + + 22) foreflipper claws 0 0 0 0 0 0 23) hind-flipper claws + + + + + + 24) premaxilla + + 0 + + + 25) upper incisors + + + + + + 26) natal coat 0 0 0 0 + + 27) seconary hairs 0 0 0 0 + + 28) molt + ? ? + 0 0 29) mystacial whiskers 0 0 0 + + + 30) mammary teats 0 0 0 + + + 31) chromosomes 0 0 0 0 0 0 32) upper incisor shape 0 0 0 0 0 0 33) carotid canal, posteromedial process of auditory bulla 0 0 0 0 0 0 34) interorbital width 0 0 0 0 0 0 35) basioccipital-basisphenoid area 0 0 0 0 0 0 36) mastoid lip 0 0 0 0 + + 37) humerus, supinator ridge 0 0 0 0 0 0 38) humerus, deltoid pectoral crest 0 0 0 0 0 0 39) post-tibial fossa 0 0 0 0 0 0 a The phocine scapula more resembles the terrestrial camivoran form than that of other phocids in its exaggerated hooklike teres major process and strong reduction of the supraspinous fossa. b Very strong scapular spine in phocines. c See text. d Among phocids this feature more closely approaches the primitive camivoran conditions in phocines. e See text. 1988 WYSS: PHOCINE SEALS 11

TABLE 2-(Continued)

Ommato- Erig- Cys- Hali- Histrio- Pago- Hydrurga phoca nathus tophora Phoca Pusa choerus phoca philus

0 0

+ + 0 0 0 0 0 0 0 0

+ + 0 0 0 0 0 0

0 0 0 0 *b

0 0 + 0 0 + + 0 0 + + + * 0 0 + 0 0 0

0 0 0 0 0 0 *e + + 0 0 * + + + *e + + + + + + +

+ + +

+ + + + + + + + +

* + + + +

* +

fAlthough the "monachine" condition is here coded as derived, the condition common to most phocines nevertheless approaches the terrestrial carnivoran form. g As indicated, apparent reversal is not restricted to the Phocinae. 12 AMERICAN MUSEUM NOVITATES NO. 2924

A B

ac ac

C D sf

ac , ac

pa sf pC vc pa vc PC Fig. 2. Dorsomedial views of selected phocid temporal regions (right side, anterior toward left): A, "Monachus" schauinslandi; B, "Monachus" tropicalis, AMNH 35354; C, Lobodon carcinophagus, AMNH 88535; D, Phoca sp., AMNH 2195 CA. Note relatively unexpanded dorsal petrosal region in A, the pointed petrosal apices and remnant of the auditory meatal roof in A and B. Abbreviations: ac, anterior opening ofcarotid canal; ca, opening ofcochlear aqueduct; cf, facial (VII) nerve canal; pa, petrosal apex; pc, posterior carotid foramen; r, remnant of roof of internal auditory meatus; sf, subarcuate fossa; vc, fossa accommodating vestibulocochlear nerve. Scale approximately 0.85 x for A, B, D, and 0.70 x for C.

exception to this trend is "Monachus" where- 4. Remnant of roof of internal auditory in the apex remains both dorsoventrally thin meatus. All pinnipeds except phocids retain and V-shaped in outline. a true mammalian internal auditory meatus. 1988 WYSS: PHOCINE SEALS 13

Typically in mammals this depression on the 6. Lack of proximal fusion of tibia and dorsal (cerebellar) surface of the petrosal is fibula. The tibia and fibula fuse proximally roofed by an anteriorly projecting petrosal lip in all phocids except "M." schauinslandi (Re- and serves as the common entrance for the penning and Ray, 1977). An additional ex- seventh and eighth cranial nerves. In phocids ception was noted by these authors, a then these nerves have separate entrances, a me- undescribed fossil form from Sacaco, Peru. dial fossa accommodating passage ofthe ves- This taxon remains undescribed but has since tibulocochlear nerve, and a laterally placed been referred to as a small "monachine" from canal for the facial nerve (Gray, 1905). In all the Pisco formation (de Muizon and Hendey, phocids, therefore, a true internal auditory 1980: 118). The tibia and fibula are proxi- meatus is lacking and, with the exception of mally fused in all living otariids but unfused the monk seals, the petrosal lip roofing the in what has been proposed as a sister-taxon internal auditory meatus is completely ab- ofthis group, the Miocene form Thalassoleon sent. In all three species of"Monachus," ves- mexicanus (Berta and Demere, 1986). The tiges of the former roof of the true meatus condition in Pithanotaria starri, another ear- can clearly be seen as a thin bony spur pro- ly and cladistically "basal" otariid, may not jecting dorsally between the vestibulocochle- be unambiguously determined from Kel- ar fossa and the canal for passage for the facial logg's (1925) description or figures. Never- nerve (fig. 2) (see also Repenning and Ray, theless, the unfused condition in Thalasso- 1977: pls. 1, 3). Therefore, it stands to reason leon mexicanus, a taxon considered the that the complete absence of the lip roofing nearest sister of a group including living ota- the internal auditory meatus may represent riids plus the Pliocene taxon Hydrarctos (Ber- a synapomorphy of all living and known fos- ta and Demere, 1986) and ancestral to living sil phocids exclusive ofthe three living species otariids (Repenning and Tedford, 1977), is of "Monachus." well established and likely represents the primitive condition for the group. These ele- 5. Pericardial plexus. The presence of a ments are only rarely fused in Odobenus well-developed pericardial plexus has been (King, 1983), unfused in Allodesmus (Mitch- reported as typical of phocids but has been ell, 1966), and unfused in Enaliarctos (Berta found to be absent in "M." schauinslandi and Demere, 1986), a taxon considered the (Harrison and Tomlinson, 1956; King and sister-group of all other pinnipeds (Wyss, Harrison, 1961). Because this venous struc- 1987). Given this distribution in phocid out- ture is not known to occur in otariids or Odo- groups, proximal fusion ofthe tibia and fibula benus (King, 1977; Fay, 1981), its presence is here regarded as an apomorphic resem- in most phocids is reasonably interpreted as blance ofphocids exclusive of"M." shauins- derived. In this connection it is also of in- landi. As a result of the condition in Thal- terest to note one of the summing remarks assoleon, the ancestral otariid condition is offered by King and Harrison (1961: 292) in considered in this analysis to be unfused; con- their important anatomical consideration of sistent fusion of the tibia and fibula has ap- "M." schauinslandi: "It could be argued that parently been independently achieved once the monk seal shows less vascular (venous) otari- specialization than Phoca, Mirounga, Lep- within the group encompassing living tonychotes, Lobodon, Halichoerus, and Hy- ids and once within phocids. drurga, but more than Zalophus." The con- 7. Separate foramen for obturator nerve in dition of the pericardial plexus in "M." innominate (fig. 3). In contrast to those of monachus and "M." tropicalis is known but other phocids, the innominate bone of "M." naturally would be ofgreat interest (distress- schauinslandi presents a separate foramen for ingly, for the latter such knowledge is now passage of the obturator nerve midway be- irrevocably lost). tween the acetabulum and the obturator fe- Repenning and Ray (1977) also drew at- nestra (King and Harrison, 1961; Ray, 1976; tention to two postcranial features which Repenning and Ray, 1977). A separate fo- might imply the remote placement of "Mon- ramen is rarely present in "M." tropicalis (e.g., achus" relative to other phocids (numbers 6 those specimens noted by Repenning and Ray, and 7 below). 1977: 679-680 and AMNH 10421; see fig. 3 14 AMERICAN MUSEUM NOVITATES NO. 2924

.%Oppp

. : v ,.. _/ ^ a Ps' r II 'sviiE__> I .". - , . 1-4w

Fig. 3. Lateral view of left innominate bones of "Monachus" tropicalis AMNH 77741 (top) and Phoca vitulina AMNH 80195 (bottom), contrasting the general form of the bone in "monachines" plus Erignathus and in phocines exclusive ofErignathus. Note presence of nearly complete obturator nerve foramen in the Caribbean monk seal and hollowing of anterior ilial region in Phoca. where this foramen is nearly complete). A (not shown in fig. 3): "[it] is nearly of the separate foramen occurs variably among form more often encountered in the Otari- "otarioids" (Repenning and Ray, 1977) ap- idae and the supraspinous space is several pearing most consistently among the arcto- times as extreme as the infraspinous." The cephaline otariids. A distinct foramen is pres- shape of the caudal angle is nearly identical ent in Thalassoleon mexicanus (Repenning to that seen in "Monachus," and agrees closely and Tedford, 1977) and it appears occasion- with the form seen in Odobenus, fossil odo- ally in Odobenus (bilaterally present in benids, otariids, and Allodesmus (ibid.; AMNH 73304, unilaterally present in AMNH Mitchell, 1966; Repenning and Tedford, 90784, 14071) and therefore its absence in 1977; King 1983). Thus it would seem safe phocids (exclusive of "M." schauinslandi, to conjecture that the shape of the posterior where it occurs uniformly) may reasonably scapular termination seen in these taxa rep- be interpreted as apomorphic. resents the ancestral phocid configuration and that its more hooklike form in phocids ex- 8. Presence of hooklike teres major pro- clusive of"Monachus" and Mirounga is apo- cess (common to all phocids except Mirounga morphic (this hooked form is especially pro- and "Monachus") (fig. 4). As King (1956) has nounced among the Phocini; see fig. 4F). reported, in "Monachus" the posterior and Related to the scapular form, it may be dorsal edges ofthe scapula meet to form near- mentioned that in "monachines" the supra- ly a right angle and thus, in contrast to the spinous fossa is generally quite large, most condition seen in most phocids, thisjunction extremely so in Mirounga (see also, King, (the caudal angle) is not hook-shaped. Howell 1969; Pierard, 1971, 1979). King (1956) has (1929: 26) has commented on the essentially noted the square shape of the anterior scap- primitive form of the scapula in Mirounga ular border in the lobodontines and its short- 1988 WYSS: PHOCINE SEALS 15

zve' (

11 " .IA.

Al% -1,f rfi

2V' B

A r N'NA,I

I I (. '-. ! , -,4' ..I '; I

:,, NI. E F

Fig. 4. Lateral views of representative pinniped scapulae: A, Zalophus californicus AMNH 5039 (reversed); B, Odobenus rosmarus AMNH 121; C, "Monachus" tropicalis AMNH 77741; D, Leptony- chotes weddelli AMNH 34250; E, Erignathus barbatus AMNH 19347; F, Phoca vitulina AMNH 80195. Note particularly the strong hook-shaped teres major process in F, the relatively (for a phocid) large supraspinous fossa in C, and the poor development of the spine in D. Not to scale. ness in "Monachus." A large supraspinous ing the placement of "Monachus" as the sis- fossa is a constant feature of otariids, Odo- ter-group ofother phocids; this stands in con- benus, Allodesmus, and Enaliarctos (Mitch- trast to the currently accepted phylogeny of ell, 1966; Bisaillon and Pierard, 1981; see fig. phocids which incorporates a clean "mona- 5 of Barnes et al., 1985). In relation to the chine"/phocine bifurcation. It follows, then, size of the infraspinous fossa, the supraspi- that the characters of the previous section nous fossa tends to become substantially re- should be considered against those that have duced, particularly in Erignathus and among been proposed in the past as uniting "Mon- members ofthe Phocini. As a result, the scap- achus," Mirounga, and the lobodontines into ula ofthese taxa could be interpreted as show- a monophyletic "Monachinae." To my ing a closer resemblance to the form typical knowledge there are only two such data sets, ofterrestrial carnivorans than that ofany oth- those ofKing (1966) and de Muizon (1982a). er pinnipeds. Features of the scapula will be As has already been discussed, King's considered further in the discussion of char- (1966) study of the relationships of hooded acter 13. and elephant seals marked a turning point in the consideration on higher-level relationships among phocids. King listed 17 char- AFFNITIES OF THE "MONACHINAE" acters in her study (9-23 below) said to dis- From the foregoing tabulation there would tinguish monachines from phocines: by appear to be considerable evidence support- implication, then, these would argue for 16 AMERICAN MUSEUM NOVITATES NO. 2924 membership of "Monachus" in the "Mona- concern is, as Ray points out, the fact that chinae." These features will be briefly re- generally the boundary between the petrosal viewed below-with particular consideration and the mastoid in this region is highly un- paid to polarity determination. clear if not completely obscured. As a result it becomes exceedingly difficult, if not im- "MONACHINE" CHARACTERS AND THE possible, to identify an intrusion into the pos- "MONACHINE"/PHOCINE DIVISION terior lacerate as definitively "petrosal" or 9. Mastoid visible in dorsal view of skull. "mastoid" (compare for example figs. 6 and This is almost certainly a derived character 7 of de Muizon, 1982a). A less arbitrary cri- occurring by King's accounting in "Mona- terion by which the complex morphology of chus" and in all phocines (and would con- this region may be interpreted might be the sequently seem to argue against recognition posterior extent of the auditory bulla. As of a "monachine" grouping). The mastoid is Hendey and Repenning (1972) and Ray generally not visible in dorsal aspect in most (1976) have noted, in the lobodontines and mammals including terrestrial carnivorans, Mirounga the bulla nearly covers the petrosal otariids, and Odobenus. Bums and Fay (1970: and almost contacts the exoccipital, thereby 381) reported that the mastoid was in view essentially excluding the petromastoid com- dorsally in a large percentage of specimens plex from contributing to the ventral margin of other "monachines" examined in their of the posterior lacerate foramen. In table 2, study. They emphasized, however, that: "The therefore, a bulla essentially covering the pe- value of the pars mastoidia as a diagnostic trosal and nearly contacting the exoccipital character is its form, which, in the Phocinae is regarded as a derived attribute; although ... is distinctive by reason of the lateral this condition fails to provide support for a swelling that forms an oblique ridge at an monophyletic "Monachinae," it does poten- angle of about 600 from the long axis of the tially diagnose at least a subgroup ofits mem- mastoid bone as a whole. This ridge is absent bers. or barely discernable in all of the Monachi- 11. Posterior lacerate foramen extending nae...... " Following this, the lateral swelling medially to tympanic bulla. Typically in car- of the mastoid visible in dorsal view is re- nivorans (and mammals in general) the pos- garded in table 1 as a potential synapomor- terior lacerate foramen is a roughly circular phy of the phocines. aperture situated behind the posteromedial 10. Petrosal visible in posterior lacerate corner ofthe auditory bulla. In pinnipeds this foramen. Again by King's tabulation, this foramen is greatly enlarged but usually main- condition occurs in "Monachus" and in the tains its circular form. In phocines, exclusive phocines. Since the petrosal is also visible in ofErignathus, the posterior lacerate foramen Odobenus and its fossil allies (Repenning and becomes confluent with a broad petrobasilar Tedford, 1977), and in what are here consid- fissure, forming a common opening that ex- ered close phocid allies (desmatophocines + tends between the basioccipital and the au- allodesmines) (Berta, personal commun.), this ditory complex as far anteriorly as the basi- character is most likely primitive at a level occipital basisphenoid suture. Thus although higher than the Phocidae. It follows, then, this character does not bear directly on the that the petrosal covered completely by the question of "monachine" relations, it is di- auditory bulla (occurring in Mirounga and agnostic of a phocine subgroup. This condi- lobodotines) may plausibly be regarded as a tion represents a significant departure from derived attribute. Ray (1976), however, co- the condition typical of terrestrial carnivo- gently warned against such a simplistic char- rans and other pinnipeds wherein the petro- acter demarcation, noting that although the basilar fissure is obliterated during ontogeny lobodontines and Mirounga generally do have and the bullar and basioccipital regions be- little or no petrosal exposure within the pos- come closely appressed. On the basis of this terior lacerate foramen, such exposure does distributional information the condition occur in some individuals of Ommatophoca present in Cystophora and the Phocini is here and Leptonychotes. Perhaps of more critical judged to be derived. 1988 WYSS: PHOCINE SEALS 17

12. Atlas, vertebrarterial (=transverse) fo- (Davis, 1949, 1964), Allodesmus (Mitchell, ramen faces posteriorly. As King (1966) pre- 1966), Odobenus (Bisaillon and Pierard, sented only a brief account of this character, 1981), and otariids and is therefore likely I am interpreting it here to mean the direction primitive for pinnipeds. Regarding the con- from which the transverse foramen of the dition ofthe spine, its degree ofdevelopment atlas is most clearly visible. King's distribu- is a trait much more difficult to characterize. tional table shows a posteriorly facing fora- To my mind three reasonably distinctive pat- men occurring in phocines, and a dorsally terns of scapular spine development occur facing foramen present in Mirounga and the among phocids: its strong development lobodontines. She concluded, however, that among the phocines where it may extend the position of the foramen in "Monachus" completely to the vertebral scapular border, was not convincingly like that ofother "mon- its extreme reduction to the point of serving achines." My own observations are in agree- as only a support of the acromion process in ment with King's conclusions. Regarding the lobodontines, and a somewhat intermediate condition seen in "Monachus," I would only condition in "Monachus" and Mirounga add that in "M." tropicalis the vertebrarterial wherein the spine reaches or nearly reaches foramen is exceptionally large for a phocid, the scapular margin but is generally less and is therefore at least partially visible in prominently defined than it is in phocines. dorsal view (it is, in fact, not dissimilar to The degree to which the spine is developed the condition found in Odobenus, see below). in otariids, Odobenus, and Allodesmus falls In "M." monachus this foramen is much more typically somewhere in between the condi- typical in size and is visible only in posterior tions seen in phocines and the monk and el- view, so that in this respect it much more ephant seals. Within this spectrum of pin- closely approximates the phocine rather than niped scapular spine development, the form the Mirounga + lobodontine condition. In seen in the lobodontines (where it is almost most terrestrial carnivorans, except canids, entirely absent) is by far the most distinctive. the transverse foramen is visible only in pos- The condition obtaining in "Monachus" and terior view. The same appears to apply to Mirounga is not sufficiently reduced so as to otariids although there is a certain degree of be closely compared to the unique lobodon- variation. The transverse foramen in Odo- tine condition and therefore convincingly ally benus, owing to its extremely large size, is all "monachines." Extreme reduction of the visible in both dorsal and posterior views, scapular spine is here regarded as a derived therefore not falling neatly into either cate- condition restricted to the lobodontines; re- gory; but in the Miocene odobenid Imago- duction of the acromion may therefore rep- taria this foramen is small and clearly faces resent a potential synapomorphy ofphocines. posteriorly [personal observ. from cast of SBMNH (Santa Barbara Museum ofNatural 14. Humerus, supracondylar (=entepi- History) 342]. In Allodesmus the foramen is condylar) foramen present. An entepicon- also posteriorly directed (see Kellogg, 1931: dylar foramen is common to phocines; it is fig. 10; Mitchell, 1966: pl. 6). From this out- unfortunate, however, that interpretation of group information it would appear, then, that the polarity of this character among phocids the two in hinges directly on the choice of outgroups. of conditions occurring phocids, De Muizon (1982a) considered the trend to- the condition pertaining to Mirounga and lo- ward absence of this foramen in "mona- bodontines is more likely the derived one. chines" as the apomorphic phocid condition, Thus as concerns the affinities of "Mona- basing thisjudgment on his phocid outgroups chus" the significance ofthis character would Potamotherium (an enigmatic late Oligocene appear to be moot. through Miocene otterlike arctoid) and other 13. Scapular spine reduced, knoblike mustelids. Given my acceptance of the close acromion (fig. 4). These characters have been alliance of phocids to other pinnipeds and cited (King, 1966) as common to "mona- recalling the absence ofan entepicondylar fo- chines." The latter feature may be dealt with ramen in otariids, odobenids, and Allodes- easily; a knoblike acromion occurs in ursids mus, the presence of this foramen is here 18 AMERICAN MUSEUM NOVITATES NO. 2924 judged to be a potential synapomorphy of in Zalophus), occurs in "M." tropicalis, "M." phocines; hence its absence in "monachines" schauinslandi, Mirounga, and the lobodon- is regarded as plesiomorphous. The foramen tines. Again, this character is almost certainly is also present in some fossil "monachines," primitive for pinnipeds as a group, as it oc- e.g., some species ofMonotherium and Hom- curs in otariids and Odobenus as well. In ter- iphoca capensis (formerly Prionodelphis) restrial carnivorans the intermediate phalanx (Hendey and Repenning, 1972; Ray, 1976; forms a significant element of digit V of the de Muizon, 1982a). Additional humeral fea- manus, being-proportional to digit length- tures will be considered in the discussions of comparable in size to its counterparts on dig- characters 37 and 38. its II through IV. projecting ledge Establishment ofthe polarity ofthis feature 15. Carpus with distally at the level ofPhocidae poses some difficulty, on cuneiform. A distally projecting process however, because ofuncertainty regarding the (palmar process) of the cuneiform arcs over condition in Allodesmus. The carpus of the the palmar surface ofthe fifth metacarpal head holotype ofA. kelloggi LACM 4320 (=A. ker- in all phocines (King, 1966). This broad pro- nensis fide Barnes, 1972) depicted in plates cess is absent in otariids, Odobenus [although 15 and 17 of Mitchell (1966) shows an un- it is salient in the Miocene odobenid Ima- reduced intermediate phalanx on digit V, the gotaria (Repenning and Tedford, 1977)], Al- intermediate element being approximately 70 lodemus (Mitchell, 1966), and "monachines" percent of the length of the proximal (from and thus its presence likely represents a syn- pl. 15). IfMitchell's reconstruction is correct, apomorphy for phocines. and if Allodesmus is regarded as the sister- this raises a conundrum for 16. Metacarpals I and II ofapproximately taxon ofphocids, equal size (fig. 5). This relationship of meta- establishing the ancestral phocid condition carpal size occurs among all phocine seals. for this character. Until the phylogenetic ar- Although this pattern is undoubtedly prim- rangement of the monk seals is firmly estab- itive for carnivorans, within phocids it must lished, the polarity ofthis feature, at the level be considered a secondarily derived reversal of the Phocidae, cannot be unambiguously or, at least, a departure from the typical pin- determined. At present it can equally force- niped condition. This follows from the ob- fully be argued that (1) the reduced condition servation that relative to the second, the first is primitive for phocids and that the resem- metacarpals of otariids, Odobenus, and Al- blance betweenAllodesmus, "M." monachus, lodesmus are all greatly elongated and con- and the phocines is derived (even if it might spicuously more robust. On this basis, there- be due to convergence), or (2) that the con- fore, King's ninth character "1st metacarpal dition seen in Allodesmus is primitive and noticeably longer and thicker than the oth- the resemblance seen in "M." tropicalis, "M." ers" would appear to be an apomorphic fea- shauinslandi, Mirounga, and the lobodon- ture, uniting pinnipeds with the exception of tines is derived. phocines where a reversal toward a closer There is, however, reason to question the approximation of the primitive carnivoran Allodesmus phalangeal arrangement suggest- condition has apparently occurred. The pho- ed by Mitchell. As is indicated in his discus- cine condition may only be regarded as an sion, the position of some of the phalanges incomplete reversal, however: although the figured in the plates cited above are uncer- on two elements are ofapproximately equal size, tain, their placement being based purely metacarpal I remains slightly longer than size and curvature. Downs (1956) described and articu- metacarpal II, whereas ofcourse the opposite the remarkably complete largely applies in terrestrial carnivorans. lated skeleton of Atopotarus courseni [=Al- lodesmus courseni, Barnes, 1972] and al- 17. Intermediate phalanx of digit V of though he noted the generally poor quality of foreflipper very reduced (fig. 5). Marked re- preservation, gave the lengths of the median duction of this phalanx, to the point that it and proximal phalanges ofdigit V as 8.0 and is but a small fraction of the length of its 38.0 mm, respectively (table 1, ibid.). There- proximal neighbor (e.g., approximately 17% fore at least one specimen of Allodesmus, 1988 WYSS: PHOCINE SEALS 19

Fig. 5. Dorsal views ofwalrus and phocid foreflipper osteology: A, Odobenus rosmarus; B, Monachus tropicalis; C, Ommatophoca rossi; D, Phoca vitulina. The great reduction of intermediate phalanx V is displayed in all but D, the strong disparity in size between metacarpals I and II in A, B, and C (lessened in D), the extremely reduced claws in C, and their very strong development in D. Not to scale. where the association ofphalangeal elements Whatever the primitive condition for Al- appears to be reasonably certain, demon- lodesmus eventually proves to be, and hence strates a strongly reduced fifth medial ele- whatever polarity of this feature at the level ment. ofPhocidae might then be accepted, the con- One additional line of evidence might call dition seen in phocines and "M." monachus into question Mitchell's identification ofthis represents a reversal ofan ancestral pinniped element in LACM 4320. Typically, in mam- condition to a primitive carnivoran (or mammals, including all pinnipeds, there is a de- malian) condition. This discussion suggests, crease in size ofthe intermediate phalanx from therefore, a moderately complex series of the third digit of the carpus to the fifth. As transformations of this element during the identified in LACM 4320 (in pl. 15 but not evolution of phocoids (if Allodesmus indeed 17, ibid.) the intermediate phalanx ofdigit V exhibits the derived condition) and the early is considerably longer than its counterpart on diversification ofphocids (originating appar- digit IV, which if true is clearly not what ently at least twice, once in "M." monachus would normally be expected. In short, I pres- and once in phocines). ently find it more reasonable to conclude that Allodesmus maintained a phalangeal arrange- 18. Metacarpal heads with well-developed ment similar to that found in all pinnipeds palmar ridge (fig. 6). In phocines (as in most exclusive of phocine phocids and the Medi- terrestrial mammals) a strong longitudinal terranean monk seal. From this interpreta- ridge divides the distal and palmar surface of tion it follows that the reduced condition of the metacarpal head, separating the points of intermediate phalanx V in "M." tropicalis, articulation ofthe two sesamoid bones. Coin- "M." schauinslandi, Mirounga, and the lo- cident with this arrangement, the proximal bodontines should be considered primitive articulation surfaces of the proximal pha- for phocids. But the best that can be said at langes are marked by a deep notch on their our current state ofknowledge is that the na- palmar margins accommodating these meta- ture of this character in Allodesmus remains podial ridges. These features-widespread unsettled. Such being the case, one is forced among terrestrial carnivorans and undoubt- to examine the next most proximal available edly primitive at a taxonomic level much outgroups- Odobenus and otariids -and as a higher than the Carnivora-do not occur in result, for the moment at least, favor the no- "monachines" where these ridges are scarcely tion that a reduced intermediate fifth phalanx visible and the proximal surfaces ofthe prox- is primitive for phocids. imal phalanges are only weakly indented along 20 AMERICAN MUSEUM NOVITATES NO. 2924

langes in "monachines" correspond closely

b. ,: ,IA to those seen in otariids, odobenids, and Al- lodesmus, strongly suggesting that the arrangement common to "monachines" represents also the ancestral pinniped condition. Thus the "monachine" condition holds little valence in diagnosing a phocid subgroup; the phocine condition alone represents a derived character (for a pinniped), and so in yet another respect this group appears to have I,!, , i- .-.f2 regressed to a more general carnivoran con- It. -.,1 @, , .;al .,i. .' dition. 19. Ilium everted, excavated laterally (fig. 3). Lateral eversion of the ilium is common to all phocids. This lateral twisting of the anterior ilial arm is more markedly developed, however, and is accompanied by a deep Fig. 6. Palmar views ofphocid phalanges con- lateral excavation in all living phocines save trasting the trochleated form of interphalangeal Erignathus (King, 1966). Lateral excavation articulations in phocines with their more hingelike and strong eversion are not present in ota- form in "monachines": left, Phoca vitulina AMNH riids, Odobenus, Allodesmus, or "mona- 232416 (proximal phalanx II, manus); right, Mon- achus tropicalis AMNH 77741 (intermediate pha- chines" and the occurrence of these features lanx II, manus). Actual lengths: Phoca, 29 mm; may therefore be judged to represent pro- Monachus, 47 mm. gressive conditions in phocines. 20. Lower astragalus-calcaneum articula- their palmar borders. The metacarpopha- tion very long. The lower articulation on the langeal and interphalangeal articulations (and plantar astragalar surface (the sustentacular their counterparts in the pes) are strongly facet) is generally long among members of trochlear in phocines but flatter, broader, and the Phocini and Cystophora (King, 1966). But markedly less trochlear in "monachines." because this feature seems to display a con- Furthermore, the phalangeal bones them- siderable degree of variation and is difficult selves assume a much more dorsoventrally to polarize, a few comments are pertinent flattened form in "monachines," which stands here. Turning first to a consideration of out- in contrast to their primitive, cross-section- groups, otariids are characterized by a long ally more rounded form in phocines. Any sustentacular facet which stretches the length indication of flattening of these elements in ofthe astragalar neck, contacting proximally the phocine carpus appears to occur only in the medial tubercle which lies directly inter- the pollex (Howell, 1929) while these bones nal to the upper (ectal) facet. Thus in otariids of the other digits maintain a more typically the sustentacular and ectal facets nearly meet primitive form. In the phocine pes, flattening in this region of the tubercle at the proxi- is relatively pronounced in the first and fifth mointemal angle ofthe plantar astragalar sur- proximal and the fifth intermediate pha- face much as they do in most terrestrial car- langes, but otherwise their counterparts are nivorans. A markedly different situation is of a more typical mammalian form. As a re- met in Odobenus, Allodesmus, and in phocids sult of these skeletal modifications, the ball where the sustentacular and ectal facets are and socket metapodial phalangeal articula- broadly divided by a deep furrow (interartic- tions and the strongly trochlear interphalan- ular sulcus) running across the length of the geal articulations typical of terrestrial carni- distal margin ofthe ectal facet and extending vorans (and most mammals) are found in to the medial margin of the astragalar neck. "monachines" to be weakly interlocking hinge As a result, the sustentacular facet nowhere joints. Importantly, the form of these artic- closely approaches the medial tubercle or the ulations and the flattened shape of the pha- sustentacular facet but remains broadly iso- 1988 WYSS: PHOCINE SEALS 21 lated; in relation to the condition seen in ota- the others (fig. 7). Based on the observation riids it would thus be considered "short." that the third metatarsal is approximately as King's (1966) categorization of the phocid long as are its four counterparts in otariids sustentacular facet as either long or short and odobenids, and that it is only slightly therefore refers to the subdivision of the ar- shortened in Allodesmus (Mitchell, 1966), the rangement wherein, relative to other car- development of a marked shortening of this nivorans, the facet is already short. As King element may plausibly be regarded as a noted, the sustentacular facet is generally quite "monachine" synapomorphy. King's (1966: short and a wide gap separates it from the 395) table shows that the length of the third ectal facet in Mirounga and the lobodontines. metatarsal, as a percentage of the length of This distribution is not without exceptions, the first metatarsal, ranges between 63.1 and however; for example, I have observed a fair- 72.7 in phocines and between 43.2 and 57.7 ly long condition in some specimens of Lo- in "monachines." This table does not include bodon. In "Monachus," King pointed out that measurements ofthe third metatarsal of Cys- the articular surface is longer than is usual tophora, however; AMNH 100135 demon- among "monachines" and is in this respect- strates surprisingly that the third metatarsal as was the case with the atlar character pre- is also relatively short (MT III is approxi- viously mentioned-not assuredly "south- matley 55% the length of MT I) and that ern." In fact in "M." tropicalis this facet, in therefore Cystophora does not cluster with addition to being quite long, is extremely other phocines as would be expected but rath- broad and is not unlike that seen in Allodes- er with "monachines." This raises the pos- mus and Odobenus. On the other hand, in sibility that third metatarsal shortening may "M." monachus the long, thin form of the be viewed as primitive for phocids (judging facet is reminiscent of the condition seen in from what might be construed as the rela- the Phocini. Furthermore, Hendey and Re- tively secure placement of "Monachus" as penning (1972) found the sustentacular to be the phocid "sister-group"), so that the length- short in some specimens of Cystophora and ening in phocines (exclusive of Cystophora) long in some presumed fossil "monachines" might represent another reversal associated (Homiphoca and Monotherium). On this ba- with what appears to be the prevailing pattern sis they questioned the utility of this char- of character regression associated with the acter at the subfamilial level. In view of the development of the phocine pes. Obviously variability observed, a detailed survey ofthe this assertion is contingent upon the prior form and variation of this character in large acceptance of "Monachus" as the sister- samples ofall phocids is required, a task outgroup(s) of other phocids. But because this side the scope of this paper. Whatever such relationship is in fact being tested in the pres- a study may eventually show, it seems un- ent analysis, this character has been coded in likely that this character, given its atypical table 1 as a potential "monachine" synapo- "southern" manifestations in "Monachus," morphy that has been independently ac- will ever be used to argue for the monophy- quired in Cystophora. letic association of monk seals and other Naturally, metatarsal shortening is mani- "monachines." Pending such an inquiry I fest externally in the form ofthe distal margin have provisionally coded this character in ta- of the hind flipper. Although the third digit ble 1 as primitive throughout the family. That is also clearly the shortest in members of the is not to suggest that all the forms represented Phocini, it tends not to be as short as in in this diversity are necessarily primitive; "monachines" and Cystophora. Thus in rather, I do not have sufficient comparative "monachines" and Cystophora (where the material at hand to reach any broad conclu- toes are the most highly unequal) there is a sions. Nevertheless, on the narrower question strongly concave arrangement of the poste- at hand, my observations indicate that this rior flipper border. Conversely, the pedal dig- character does not persuasively unify the its in members of the Phocini, although they "Monachinae." vary to a certain extent in length, are more uniform than in "monachines" and Cys- 21. Third metatarsal much shorter than tophora: in Erignathus the digits of the pes 22 AMERICAN MUSEUM NOVITATES NO. 2924

Fig. 7. Dorsal views ofwalrus and phocid hind-flipper osteology: A, Odobenus rosmarus; B, Monachus tropicalis; C, Ommatophoca rossi; D, Phoca vitulina. Note shortening ofdigit III in B and C, particularly ofthe metatarsal. With respect to the relative length ofdigit III, phocines (represented by D) more closely resemble the walrus (A) and otariids (not shown) than they do "monachines." Note also the strong development of ungual processes (indicative of claw size) in D and the lack of same in C. Attention is called to the derived Odobenus-phocid similarites of fifth digit enlargement (in particular the fifth metatarsal) and the degree ofthird digit reduction, conditions not found or expressed to the same degree in otanids. Not to scale. are ofapproximately equal length. Thus typ- large claws on the manus may safely be as- ically in phocines (excluding Cystophora) the sumed to represent an advanced condition posterior flipper margin is more nearly for phocines (if, of course, pinniped mono- straight than in "monachines." An exception phyly is admitted). Likewise, enlarged claws to this generality, as kindly pointed out to me on the pes must be viewed as derived for by Fay (personal commun.), is Histriophoca, phocines (at least for digits I and V, see below) a member ofthe Phocini with a strongly con- as the outer claws are greatly reduced in the cave posterior flipper margin. Nevertheless, outgroups mentioned. Both of these phocine metatarsal measurements taken from AMNH apomorphies, then, would appear to be re- 180274 indicate that the length of MT III in versals from the primitive pinniped condi- Histriophoca, as a percentage ofMT I (63%), tion. falls within the phocine (sans Cystophora) range specified by King (1966) (metatarsal length data for this taxon was not presented 23. Reduced claws on hind flippers (fig. 7). in In Hind flipper claw reduction is common to her study). short, the shape ofposterior "monachines." Since claws are present on the flipper border in the Phocini and Erignathus central three digits ofboth otariids and Odo- more closely approaches that seen in other benus, on first consideration this character pinnipeds than that in other phocids. would appear to represent a potential "mon- 22. Large claws on foreflippers (fig. 5). The achine" synapomorphy. It should be kept in fore- and hind flippers of phocines are char- mind, however, that relative to otariids these acterized by the presence of well-developed claws are markedly reduced in Odobenus. claws in contrast to "monachines" where Judging, therefore, from the apparent prev- claws tend to be more poorly produced. In alence reversal among other characters dur- otariids and Odobenus the claws ofthe manus ing the evolution of the phocine flippers, it are reduced to small nodules as they were (if might reasonably be presumed that phocids they were present at all) in Allodesmus were characterized primitively by reduced (Mitchell, 1966: 15). Thus the presence of claws on the hind flippers and that the pho- 198818WYSS: PHOCINE SEALS 23 cine condition also represents such a rever- 25. Tendency toward reduction of the sion. Nevertheless, as with third metatarsal number of upper incisors. Living and fossil shortening, this hypothetical transformation "monachines" and the phocine Cystophora is necessarily a secondary hypothesis and re- have only four upper incisors instead of the duced claws on the hind flippers has been typical pinniped number ofsix. Again, judged regarded as a potential "monachine" syn- against living pinnipeds this feature within apomorphy in tables 1 and 2. phocids would appear to represent a potential "monachine" synapomorphy. Taking into De Muizon (1982a) proposed three char- account fossils, Allodesmus packardi was acters as diagnosing the monophyly of the originally described as having four upper in- "Monachinae." One of these, the loss of the cisors but is now described as having had six entepicondylar foramen, has been discussed (Barnes, 1979: 9). To judge from the cross- above in the coverage of character 14; the sectional area ofthe incisor alveoli, in A. kel- remaining two are reviewed as characters 24 loggi the tooth occupying the first position and 25 below. was appreciably reduced, however (see Mitchell, 1966: pl. 2). The only fossil known 24. Premaxilla-maxilla suture located in- to stand in exception to the "monachine" side nasal aperture. As Hendey and Repen- pattern is Monotherium? gaudini from the ning (1972) first noted, in lateral view the Italian middle Miocene which retains a full "monachine" premaxilla is not visible along complement of six upper incisors (de Mui- its entire length as it is in most mammals; zon, 1 982a). It is relevant to point out, though, rather, it dips along its midsection into the that living forms display a considerably de- nasal aperture and is therefore obscured by gree ofvariability in this feature. Judging from the maxilla. Exceptions to this characteriza- King's (1956) data, supernumerary incisors tion are "M." monachus and Homiphoca are not uncommon among the three Recent (ibid., see pl. 3; de Muizon, 1982a) where the species of "Monachus." Burns and Fay (1970) primitive condition occurs. In addition, the found that four upper incisors occurred in "monachine" condition ofthe premaxilla oc- approximately 2 percent of their sample of curs in the phocines Histriophoca and Pa- the phocines Erignathus, Histriophoca, and gophilus (de Muizon, 1982a). Despite this Pagophilus (in fact, in Erignathus the incisor variation, among living phocids such an ar- formula 3-3/2-2 occurred in only 60% oftheir rangement would appear to be apomorphic sample) and, as mentioned, Cystophora for "monachines." It is worth pointing out, (which is almost assuredly allied to phocines) however, that Allodesmus shows a closely has only four upper incisors. The dentition similar condition (Barnes, 1972: 12): "The of Odobenus is highly aberrant and perhaps premaxillary-maxillary suture is only slightly of little relevance here. Nonetheless it is worth lateral to the margin of the nares, so that noting that Fay (1982: 84) found the first up- unlike the condition in most ofthe Otariinae per incisor to be present in none ofthe adults [=Otariidae in the sense employed here], very of his sample of 136, and the second upper little ofthe ascending portion ofthe premax- incisor to be present in less than 50 percent. illa is visible in lateral view. . ." (see Barnes, These observations together with the appar- 1972: fig. 5 and Barnes et al., 1985: fig. 7). ent reduction of the first upper incisor in Al- Barnes (1987, fig. 1) illustrated a rostrum of lodesmus (Barnes et al., 1985: fig. 7) may in- Desmatophoca which also clearly depicts the dicate a trend toward incisor reduction early "monachine" premaxillary condition de- in phocoid evolution. It is also apparent from scribed above. It becomes possible to argue, these observations that incisor number dis- therefore, that the "monachine" configura- plays a fair degree oflability among phocids. tion of the premaxilla may well be primitive Nevertheless, four upper incisors is scored as for phocids. Nevertheless, in the interest of a derived character and is thus considered conservatism and of giving the proposition supportive of, but not unique to, a mono- of "monachine" monophyly every possible "monachine" grouping. benefit, this character has been- scored in ta- phyletic bles 1 and 2 as a potential synapomorphy of To the list of characters reviewed above this assemblage. may be added a consideration of several ad- 24 AMERICAN MUSEUM NOVITATES NO. 2924 ditional features well known in the pinniped hairs appear to be almost totally absent. Ling literature. and Bryden (1981) have reported the absence 26. First pelage color. Monk and elephant of secondary hairs in Mirounga leonina. seals are born with black pelage (King, 1966; Regarding the systematic interpretation of Ling and Button, 1975). This is peculiar this character, then, it could be suggested that among phocids where white natal coats the presence of secondary hairs is primitive (members of the Phocini) or various shades for phocids and that loss occurs at least three of gray (Lobodontines, Erignathus, Cys- times within pinniped phylogeny, once in tophora, some Phoca; King, 1983; Fay, per- Odobenus, once in "Monachus" (assuming sonal commun.) are the norm. First coats in its monophyly), and once in Mirounga. De- otariids are dark brown to black (King, 1983; pending on the phylogenetic arrangement of Ling and Button, 1975) and so the condition these taxa specified by other characters, it seen in "Monachus" and Mirounga is likely may equally be argued (with the potential primitive although this assessment is tem- savings of a minimum of one evolutionary pered somewhat by the presence ofwhite la- step) that the lack ofsecondary hairs is prim- in itive for the group Odobenus + phocids and nugo the walrus (Fay, 1982). Granting this that these hairs have been regained by the qualification, phocids exclusive of these two lobodontines and phocines. Obviously nei- genera ("Monachus" and Mirounga) may be ther interpretation is entirely compelling but considered progressive in having more lightly in the context of the phylogeny advocated colored first pelage. here (fig. 9) the hypothesis of single loss and 27. Loss of secondary hairs. Although a single regain is more economical. Acceptance good deal ofinformation is available, in phy- ofpinniped diphyly would noticeably change logenetic considerations of the Pinnipedia, the interpretation offered above. With mus- aspects of the morphology and distribution telids placed as the phocid sister-group, the of hair have been used only to a limited ex- sparse secondary hair in "Monachus" and tent. Nonetheless, some variation ofhair pat- Mirounga would be viewed as apomorphic tern has proven to be of systematic impor- (and therefore supportive of the pairing of tance (e.g., Ling, 1978) and these data would these taxa, a relationship that to my knowl- seem to invite further consideration. Gen- edge is without precedent and likely, in my erally in carnivorans, hairs are arranged in estimation, to remain so) with the condition groups (units) consisting of a central coarse in Odobenus considered an independent loss. primary hair surrounded by a number offiner secondary hairs. These individual hair units 28. Cornifed layer and hair form sheets assume what appear to be rather conservative during molting. Associated perhaps with this patterns ofspacing (de Meijere, 1894). Note- loss of secondary hairs is an unusual pattern worthy of phocids is the absence of a pith or of molting that occurs in Mirounga, and the medulla of the primary hairs, an apparently single species of "Monachus" so far exam- derived condition known to occur elsewhere ined, "M." schauinslandi. In both the north- in the Carnivora only in Odobenus (Scheffer, ern and southern elephant seals and the 1964). Of further interest is the absence of Hawaiian monk seal the primary hairs be- secondary hairs in some pinnipeds. Second- come fused to the stratum corneum so that ary hairs occur in all otariids and the majority when the pelage is shed it forms large con- ofphocids but are virtually absent (occurring tinuous patches held together by this thin lay- in about 1 of every 50 units) in "Monachus" er ofcornified epidermal tissue (Kenyon and schauinslandi, Mirounga angustirostris (ibid.), Rice, 1959; Ling and Thomas, 1967). This and (in about 1 out of 10 units) Odobenus pattern has not been reported elsewhere (Fay, 1982). The occurrence or nonoccur- among pinnipeds and is therefore provision- rence of secondary hairs in the other species ally coded as derived for these two taxa in of "Monachus" has not previously been re- tables 1 and 2. From the topology ofthe phy- ported. On the several skins housed in the logeny derived from other characters consid- AMNH of "M." monachus and "M." tropi- ered in this analysis (see systematic conclu- calis I have examined, however, secondary sions section), the cohesion of hair and the 1988 WYSS: PHOCINE SEALS 25 cornified layer during molting could be in- plement (Arnason, 1974, 1977). There exists terpreted as a primitive phocid feature which direct evidence, then, that the 32 chromo- is lost at the node Lobodontini plus Phocinae. some karyotype ofthe Phocini is apomorphic Clearly, however, the validity of this inter- and that the 34 chromosome condition of pretation is dependent upon prior acceptance "monachines," Erignathus, and Cystophora ofa cladogram similar in geometry to the one is (for phocids) plesiomorphic. presented in figure 9. It should also be noted that Erignathus dis- 29. Beaded mystacial whiskers. Beaded plays several karyotypic features not found mystacial whiskers occur in all phocids ex- elsewhere in the Phocidae (ibid.). Arnason cept "Monachus" and Erignathus (King, concluded that the Erignathus karyotype 1956, 1983). Inasmuch as these whiskers are probably represents a separate line ofphocid smooth in otariids, Odobenus, and other car- chromosomal evolution which effectively bars nivorans it stands to reason that the peculiar it from being ancestral to the 32 chromosome beaded condition typical of the majority of type. This statement, however, is equivalent phocids may reasonably be regarded as apo- to the observation that the Erignathus karyo- morphic. In this way, beaded mystacial whis- type is autapomorphic. This in no way influ- kers may serve to diagnose a group ofphocids ences the acceptance of the 2N = 32 karyo- exclusive of "Monachus" with an apparent type as an apomorphy diagnostic of the retention of, or reversion to, the primitive Phocini; while this information fails to sup- smooth conditions occurring in Erignathus. port a phocine placement of Erignathus, it does not contradict it either. 30. Mammary teats. Otariids and Odo- In their consideration of the phylogenetic benus have two pairs ofnipples situated near placement of Histriophoca, Burns and Fay the umbilicus, a condition taken here to be (1970) provided a thorough distributional primitive for pinnipeds. By contrast, all pho- analysis ofcranial characters previously used cids except (in a distribution mimicking that for the diagnosis of subfamilial and tribal of the previous character) "Monachus" and phocid groupings. This consideration includ- Erignathus retain only the two nipples thought ed an appraisal of characters discussed by to correspond to the posterior pair of other Chapski (1955) and Scheffer (1958) as per- pinnipeds, an evidently advanced condition. taining to the tribe Phocini; two of these are "Monachus" and Erignathus maintain the briefly reviewed below under characters 32 primitive full pinniped complement of four and 33. nipples (King, 1983; see also references in Kenyon, 198 1). 32. Compression of upper incisor roots. The roots of the upper incisors, particularly 31. Chromosomes. Pinnipeds (as do other ofthe first two, are generally extremely trans- groups of marine mammals) display, in re- versely compressed among carnivorans (in- lation to comparably diverse terrestrial cluding otariids). Judging from the condition groups, a remarkable karyotypic uniformity. seen in "monachines" and Erignathus, pho- Otariids are characterized by karyotypes of cids would appear to have been characterized 2N = 36 and the walrus 2N = 32 (Fay et al., primitively by roots that are much rounder 1967; Arnason, 1974, 1977). It is well estab- in cross section. Burns and Fay (1970) re- lished that members of the Phocini (Phoca, ported the strong lateral compression of the Pusa, Halichoerus, Histriophoca, and Pago- upper incisors of Halichoerus, Pusa, Phoca, philus) have karyotypes of 2N = 32 whereas Pagophilus, Cystophora, and (in 94% of their all other phocids have karyotypes of 2N = sample) Histriophoca. Thus in this respect 34 (ibid.). Further, it has been determined most phocines display the more generalized through G- and C-band studies, that the ml carnivoran condition that is likely not prim- chromosome, characteristic of the 32 chro- itive for phocids. mosome karyotype ofthe Phocini, has arisen from a fusion between the short arm of the t 33. "Process from posteromedial edge of chromosome and the small satellite ofthe sat the bulla absent" (Burns and Fay, 1970). The chromosome of the 34 chromosome com- hallmark feature of arctoid carnivorans is a 26 AMERICAN MUSEUM NOVITATES NO. 2924

canal formed of caudal entotympanic which in relation to the presence or absence of the transmits the medial branch of the internal entepicondylar foramen (character 14). Sev- cartoid artery within the medial auditory bul- eral additional "monachine"/phocine dis- lar wall. In ventral aspect the posterior open- tinctions discussed below reside on the hu- ing of this canal is generally clearly visible, merus. and in otariids, Odobenus, and most phocids from the dorsal and/or medial margin of the 37. King (1966) noted the tendency for aperture a bony shelf may be seen to project greater development ofthe supinator ridge in toward the posterior lacerate foramen. Due phocines than in "monachines.' My own ob- primarily to prominent bullar inflation, in servations are in agreement with her sug- phocines the posterior opening is not visible gested distinction; the supinator "ridge" in in ventral view and, as Burns and Fay have southern phocids is invariably only faintly noted, the aperture is smooth and the process developed, occurring as a low rounded em- near its border absent. This would appear to inence. This condition stands in clear con- represent an advanced condition common to trast to the long, sharply defined ridge found the Phocini and Cystophora, occurring only in phocines (fig. 8). This ridge is generally rarely in Erignathus (Burns and Fay, 1970). strongly developed in terrestrial carnivorans but is absent in otariids, Odobenus, fossil 34. "Least interorbital width of adults in odobenids, and Allodesmus (Repenning and the anterior half of the interorbital septum." Tedford, 1977; Mitchell, 1966, from pls. 15 Burns and Fay (1970: 383) have noted this and 16; and personal observ.). Accordingly character as being common to members of the lack ofthis ridge may be securely consid- the Phocini and Cystophora, occurring oc- ered primitive for pinnipeds. Thus the pres- casionally in Erignathus (in 17% of the their ence of a supinator crest in a phocid repre- sample). Primitively the narrowest point in sents an advanced condition, even though the the pinniped interorbital region occurs in its character is undoubtedly primitive at a much posteriormost section (e.g., in "monachines," more general level, perhaps Carnivora. It fol- otariids, and Odobenus). lows that the appearance ofa strong supinator 35. Basioccipital-basisphenoid area flat to crest in phocines is likely just one more ex- convex. Burns and Fay (1970) also have com- ample of a reversion in this group to a more mented on the flat to convex ventral surface primitive terrestrial carnivoran condition. ofthe basioccipital-basisphenoid region in all phocines. In marked contrast, this region is 38. Hendey and Repenning (1972) have strongly concave in "monachines," otariids, discussed some additional points further dif- and Odobenus, particularly in the areas of ferentiating the "monachine" and phocine insertion of the rectus capitus musculature, humerus. In general, pinniped humeri show a condition taken here to be primitive. a distinct resemblance in the strong development ofthe deltoid/pectoral crest (Howell, 36. Mastoid lip. Several authors have 1929) but in the details of construction there commented on the unique presence among exist notable "monachine" and phocine dis- the Lobodontini ofa mastoid lip overlapping tinctions (Hendey and Repenning, 1972). Ac- the posterior bullar wall (Repenning and Ray, cording to these authors, generally in "mon- 1977; de Muizon and Hendey, 1980; de Mui- achines" insertion ofthe pectoralis is extended zon, 1 982a). There is little doubt that this lip distally down the shaft terminatingjust prox- (covering ventrally the cochlear foramen in imal to the distal articulation (although this these forms) represents a derived condition pattern of insertion does not apply to "M." (typically in phocids the cochlear foramen schauinslandi; Fay, personal commun.). The remains exposed ventrally). As it stands, then, deltoid crest also is expanded two-thirds to this character does not play a role in a "mon- three-quarters the length ofthe shaft, at which achine"-phocine demarcation, although it is point the crest and shaft merge smoothly (fig. of interest for potentially diagnosing a 8). In this respect the monachine humerus subgroup of the former. resembles that ofotariids, odobenids, and Al- The humerus has already been considered lodesmus, where a similar elongation of pec- 1988 WYSS: PHOCINE SEALS 27 toral insertion and the deltoid crest occurs character does not apply to a fossil taxon (Hendey and Repenning, 1972; Repenning amounts to little more than an argument for and Tedford, 1977; Mitchell, 1966). convergence (or reversal), or for the multiple Strengthening of the pectoralis insertion in independent appearance ofthe alternate state phocines is accomplished in quite a different of that character among that fossil's living manner. Insertion does not extend nearly as allies. In other words, suggestions ofthis kind far distally; the deltoid crest stretches less than do not more than underscore the discordant one-halfthe length ofthe shaft, where it ends distribution ofthe character in question. Such abruptly, forming a near overhang ofthe shaft reasoning, as far as it goes, is of course per- in lateral view. From the distributional in- fectly plausible provided that it is substan- formation indicated above, I conclude that tiated by the distribution of other characters. the short deltoid crest and proximally re- Returning to the character at issue here, de stricted pectoralis insertion very likely rep- Muizon and Hendey (1980) confronted the resent derived phocine attributes whereas the apparent problem of the phocine resem- condition characterizing "monachines" is es- blances of the Homiphoca humerus by sug- sentially primitive. gesting that they are primitive. Indeed an The Pliocene phocid Homiphoca is ofcon- entepicondylar foramen and strongly devel- siderable interest with respect to the features oped supinator ridge do occur in Potamoth- of the humerus just mentioned. By all pub- erium and for that matter most other arc- lished accounts Homiphoca is allied, at least toids, and from a diphyletic perspective of in a general sense, to the Antarctic lobodon- pinniped origins, de Muizon and Hendey's tines and has therefore traditionally been (1980: 116) conclusion that these two char- confidently placed within the "Monachinae." acters are "evidently primitive features" is, However, the humerus of this taxon bears a in a restricted sense, fully justified. A point striking resemblance to that of phocines, a seemingly overlooked in this interpretation, fact called to attention explicitly by its orig- however, is that the establishment of a char- inal describers (Hendey and Repenning, acter as primitive at one level-for example, 1972). Both an entepicondylar foramen and as de Muizon and Hendey would argue, the strongly developed supinator ridge are pres- primitive presence of an entepicondylar fo- ent, as is a long deltoid pectoral crest, a char- ramen at the level ofPhocidae-does not im- acter otherwise typical of "monachines" and ply that it is necessarily primitive at some other pinnipeds. Hendey and Repenning less inclusive level, e.g., the Lobodontini. Just (ibid.) did not view the phocine resemblances as the absence of limbs is primitive for the of the humerus as necessarily contradicting group Vertebrata, the lack oflimbs in a group the "monachine" allocation of Homiphoca, of tetrapods such as snakes is derived. Sim- concluding instead that King's (1966) criteria ilarly if one wishes to argue that the presence for distinguishing phocine and "monachine" ofan entepicondylar foramen is primitive for humeri (the presence of an entepicondylar phocids, the appearance of these features in foramen and a well-developed supinator a lobodontine-the taxonomic placement of ridge) appear to apply to modem species only. Homiphoca favored by de Muizon and Hen- These authors judged the pattern ofinsertion dey (1980) and de Muizon (1982a)-which of the pectoral muscle to be a character of are characterized by the lack of an entepi- greater validity in classifying phocids than condylar foramen, cannot be dismissed on the two criteria offered by King. the ground that it is primitive. Leaving aside the question ofjustification Considering this problem from the per- for the latter decision, a more general issue spective of a single pinniped origin favored concerning the treatment of fossil data may here, presence of an entepicondylar foramen be raised. While it may be tempting to argue and strong supinator ridge in Homiphoca rep- from an operational standpoint that certain resent advanced features (at a level inside the characters appear to be valid only among liv- Phocidae). Similarly, acceptance ofpinniped ing forms, the fact is that character conflicts monophyly calls into question the presence remain character conflicts whether they occur of a long deltoid/pectoral crest as represent- in fossils or not. Suggestions that a particular ing a derived condition among phocids. In 28 AMERICAN MUSEUM NOVITATES NO. 2924

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Fig. 8. Representative "monachine," phocine, walrus, and otariid humeri. Anterior (A, D, G. J), medial (B, E, H, K), and lateral (C, F, I, L) views of: Odobenus rosmarus AMNH 121 (A, B, C); Zalophus californicus AMNH 1263 CA (D, E, F); "Monachus" tropicalis AMNH 10421 (G, H, I); Erignathus barbatus AMNH 19347 (J, K, L). Attention is called to the long deltoid/pectoral crest in all except Erignathus. Note also the presence of an entepicondylar foramen and strongly pronounced supinator ridge in Erignathus. Abbreviations: dpc, deltoid/pectoral crest; sr, supinator ridge; ef, entepicondylar foramen. Not to scale. view of its widespread appearance in pin- nae" nor to the placement of Homiphoca nipeds, this last mentioned feature speaks within it. neither to the monophyly of the "Monachi- From the foregoing it should be apparent 1988 WYSS: PHOCINE SEALS 29

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;5 ' K W Fig. 8. Continued. that rather than arguing for monachine affin- .and Ray, 1977; de Muizon and Hendey, ity (by virtue of one primitive character), the 1980). I have raised the subject simply to humerus ofHomiphoca shows advanced fea- point out that if monachines are monophy- tures in which it resembles phocines. That is letic, and if on other evidence Homiphoca not to say, however, that I necessarily es- can be referred to this group, its humerus pouse a phocine placement of Homiphoca; offers a curious instance ofcharacter conflict. there is, in fact, evidence to the contrary In the context ofeither pinniped monophyly, (Hendey and Repenning, 1972; Repenning or the inclusion of Homiphoca within a 30 AMERICAN MUSEUM NOVITATES NO. 2924 monophyletic "Monachinae" or Lobodon- strongly, in the "monachines" Lobodon and tini, the phocine resemblances of the Hom- Homiphoca (de Muizon and Hendey, 1980). iphoca humerus may not simply be regarded This fossa, which is otherwise widespread as primitive but must be considered synap- among the Carnivora, is not known to occur omorphic or homoplastic. elsewhere in the Pinnipedia.

39. Tibia. King (1966) noted that the post- SYSTEMATIC CONCLUSIONS tibial (=intercondyloid) fossa is more pro- AND IMPLIED PATTERNS OF nounced among the Phocinae than in the CHARACTER EVOLUTION "Monachinae." Howell (1929: 39) indicated that the post-tibial fossa is much more deeply What phylogenetic implications may be developed in Pusa than it is in Zalophus. gleaned from the evidence here considered? Similarly the post-tibial fossa achieves only Using table 2, questions of monophyly for a shallow development in other otariids, Odo- number of groups may be addressed: First, benus, and most terrestrial carnivorans (per- is "Monachus" monophyletic? Second, are sonal observ.), and Mitchell (1966) has re- the "Monachinae" monophyletic? Third, are ported a similar shallow condition in the Phocinae monophyletic? And finally, if Allodesmus. From this it may be concluded some or all of these points of inquiry can be that the phocine condition is most probably answered with any degree of confidence, any derived. Homiphoca, as Hendey and Repen- recurring patterns of character evolution ning (1972) have pointed out, is remarkable within the Phocidae may be considered. for its "development of pronounced fossae The monophyly of a taxonomic group is a on the posterior and antero-lateral surfaces" scientific hypothesis, a notion open to testing. ofthis element (see also de Muizon and Hen- Shared derived characters are potentially in- dey, 1980). Thus, as with the humerus, the dicative of relationships and achieve synap- tibia ofHomiphoca displays an unusual oth- omorphic status (and therefore phylogenetic erwise "phocine" attribute. significance) only when they are found to be Two additional characters exhibit what ap- congruent with other derived characters in- pear to be trends toward primitive character dicating similar relationships. The phyloge- reversion in phocines, particularly among the netic status of a character is never known Phocini. These are not sufficiently constant with certainty but is itself an hypothesis sup- to be treated across all taxa considered and ported largely on the basis of its relationship therefore do not consistently differentiate all to other features. As character information is phocines; nevertheless a general pattern of increased or improved, concepts of relation- reversal is revealed by their distribution. ship are altered, resulting in turn in a mod- As suggested by Burns and Fay (1970) the ification of previously accepted notions of major palatine foramen is normally situated character support for given phylogenetic anterior to the maxillary-palatine suture groupings. Thus phylogenetic concepts re- among "monachines" while among phocines main in a constant state of flux, a context in it typically rests on or behind this suture. This which the present analysis should be viewed. foramen is situated far anterior of the suture The data of table 2 were analyzed using in otariids, and less extremely so in Odo- Swofford's (1985) PAUP (Phylogenetic Anal- benus, but it occurs on the suture in ursids, ysis Using Parsimony) software package. Ini- canids, felids, and most mustelids. This dis- tial runs were conducted using the mulpars tribution would argue, therefore, that the global branch swapping procedures; these condition typical ofphocines represents a re- yielded over 100 maximally parsimonious versal of the primitive pinniped condition. trees, with most variants simply representing Phocines differ from other phocids, as well rotations within polytomous branchpoints. as from other pinnipeds, in their marked ten- On subsequent runs, groups of taxa with in- dency to develop a distinct trochanteric fossa variant character distributions (i.e., members of the femur (King, 1966). This fossa is ex- of the Phocini and Lobodontini) were col- tremely pronounced among members of the lapsed to single terminal taxa and the result- Phocinae and occurs, but apparently not as ing data matrix then run on the exhaustive 19888WYSS: PHOCINE SEALS 31 search option branch and bound. Three achinae" are necessarily not monophyletic. equally most parsimonious trees were ob- For the sake of argument, though, the prob- tained and these were reduced to the consen- lems associated with "Monachus" mono- sus branching arrangement depicted in figure phyly may be ignored for the moment and 9 (where the "redundant" taxa have been an assessment of the relative strength of the reinserted) using the CONTREE (strict) sub- morphological evidence favoring a mono- routine of PAUP. phyletic as opposed to a paraphyletic "Mon- Returning to the specific questions posed achinae" may be carried out independently. above it may be said, respecting "Monachus" At first inspection several derived characters monophyly, that the characters reviewed here seem to support the monophyletic integrity tend not to support the naturalness of this ofthe "monachine" grouping. These include: grouping as "M." monachus and "M." trop- (21) shortening of the third metatarsal, (23) icalis seem more closely related to other pho- reduced claws on the pes, (24) configuration cids than to "M." schauinslandi. Several fea- of the premaxilla, and (25) reduced upper tures, most of which were addressed by incisor number. As detailed in the discus- Repenning and Ray (1977), indicate such a sions of characters, most of these features remote placement of "M." shauinslandi rel- have shortcomings. Of the four, only 23 (re- ative to other members of the family (see duced hind-flipper claws) occurs uniquely below). Confidence in this placement could among "monachines." In addition to prob- be significantly enhanced with knowledge of lems previously mentioned, the derived con- several structures ofthe "soft" anatomy cur- dition of 25 (four upper incisors) occurs also rently unavailable for the other two species in Cystophora. Notwithstanding the possi- of the "genus." Most helpful in this regard bility that the "monachine" premaxillary would be information concerning the pattern configuration (considered the derived state ofthe distensible tissue ofthe middle ear and for character 24) is in fact primitive for pho- the development of the pericardial plexus in cids, this feature does not occur in some "M." monachus. Even in the absence ofthese "monachines" and is present in some pho- data, however, a few skeletal characters for cines (see above). which the distribution naturally is well known These four potential "monachine" char- [such as (2) the unexpanded dorsal petrosal acters stand in opposition to those which in- region, (6) lack of proximal tibia and fibula dicate the exclusion of "Monachus" from a fusion, and (7) invariable presence ofobtura- group including all other phocids, for ex- tor nerve foramen in the innominate] point ample: (3) enlargement of the petrosal apex, to several important plesiomorphic aspects (4) complete loss of the roof of the auditory of the Hawaiian species. meatus, (8) hooklike teres major process, (26 This result raises a nomenclatural concern: and 27) features of the pelage and molt, and ifmonk seals are indeed paraphyletic it would (30) the presence offour mammary teats [(30) seem desirable to recognize this circumstance occurs also in Erignathus and (26 and 27) in their binomial appellations. At this point, serve equally to set Mirounga apart from oth- however, I think it premature to propose new er phocids]. generic assignments for members of "Mon- Preference for one of these two alterna- achus." Although such action would seem tives, if considered strictly, is based on a rel- justified, at least in the case of"M. " schauins- atively slim character margin. Ifthe character landi, until such time as the mutual relation- base is broadened, however, to include those ships of the other two species are more sat- pertinent to the question of "Monachus" isfactorily understood, the proposal of new monophyly, then support swings decidedly names would be premature. Meanwhile I in favor of a nonmonophyletic "Monachi- think it preferable to place "Monachus" nae" (fig. 1, II-IV). Consequently, one would within quotation marks to emphasize the opt, on the basis of parsimony, for the hy- questionable status of its monophyly. pothesis that the "monachine" configuration Ifthe paraphyly of monk seals and the sis- of the premaxilla, reduced claws on the pes, ter-group position of "M." shauinslandi to four upper incisors, and third metatarsal other phocids are accepted, then the "Mon- shortening are all characters primitive for the 32 AMERICAN MUSEUM NOVITATES NO. 2924

'Monachinae' Phoci nae

'Monachus Lobodontini

1931,34 1 1, 19,32,33,35 9,14,15,16,17,18,22,37,38,39

28 8,26,27 3,4,29,30

1,2,5,6,7 (see text)

Fig. 9. Cladogram depicting consensus results of PAUP for Recent phocid genera: intratribal relationships ofthe Lobodontini and Phocini left unresolved. Numbers identify characters discussed in text and listed in tables 1 and 2. Minus symbols indicate postulated reversals. Broken lines identify the most severe instances of character conflict: (upper) apomorphies common to Mirounga and the Lobodontini; (middle) a character shared by "Monachus" and Mirounga; (lower) characters that potentially diagnose a monophyletic Monachinae. Note, however, that none ofthese relationships is upheld within the context of overall parsimony and the characters involved are best regarded as homoplastic. In the scheme presented, characters 21, 23, 24, and 25, for example, are more efficiently interpreted as primitive phocid features which reverse at the level of the Phocinae. In addition to these four, postulated reversals (or partial reversals) from more generalized pinniped conditions occurring at the phocine node include: 14, 16, 17, 18, 22, 37, 38, 39, and perhaps 13 (see text). Tribal designations for "Monachus," Mirounga, Erignathus, and Cystophora are unspecified. Some character distributions have equally parsimonious alternative interpretations (e.g., 21 and 25 may be primitive for phocids and have been lost independently in Erignathus and the Phocini) but these do not influence cladogram topography. Presence of characters 2 and 5 in "M." tropicalis and "M." monachus is conjectural.

Phocidae that have been secondarily modi- process on cuneiform, (16) metacarpals I and fied within the Phocinae. The feasibility of II nearly equal in size, (17) fifth intermediate this proposal (which might seem rather un- phalanx on manus not reduced, (18) meta- tenable at first) will be more apparent follow- carpal heads with strong palmar ridge, pha- ing a consideration of the "northern" langes not flat, (22) large claws on manus and subfamily. pes, (37) well-developed supinator ridge on In answer to the third question posed above, humerus, (3 8) deltoid crest short, ends it seems that the monophyly ofthe Phocinae abruptly above humeral shaft, and (39) deep (Erignathus + Cystophora + the tribe Pho- post-tibial fossa. cini) is indeed very securely founded. The Within this phocine grouping may be di- following are characters common to the group: agnosed a pairing of Cystophora and the Pho- (9) mastoid visible in dorsal view, (14) ent- cini on the basis of their shared possession epicondylar foramen present, (15) plantar of the following characters: (1 1) petrobasilar 1988 WYSS: PHOCINE SEALS 33 fissure and posterior lacerate foramen merge balance to disrupt the case for "monachine" to isolate bulla medially, (19) strongly everted paraphyly. Acceptance of the diphyly notion ilium with lateral excavation, (33) posterior alone, therefore, does not convincingly over- opening ofcarotid canal not visible in ventral turn the reversal interpretation. view and absence of process from the pos- Rejection of the reversal hypothesis de- teromedial edge of the auditory bulla, and mands also the demonstrably insecure as- (35) ventral surface of basioccipital/basi- sumption of "monachine" monophyly. Fur- sphenoid region flat to convex. Many ofthese thermore, an argument against the reversal phocine and Cystophora + Phocini features hypothesis requires yet a third unlikely prop- are uniquely derived, but these two sets of osition, namely that the derived resem- characters include some that might easily be blances of "monachines" and other pin- mistaken as primitive (e.g.: 14, presence of nipeds (such as the reduction of the fifth entepicondylar foramen; 16, metacarpals I intermediate phalanx on the carpus, the tre- and II not greatly disparate in size; 17, typical mendous enlargement ofthe first metacarpal, fifth intermediate phalanx on manus; 18, and flattened phalanges lacking trochleated trochleated interphalangeal articulations; 22, articulations, to name but a few) are the result long foreflipper claws; 32, upper incisors of convergence. In summary, the possibility flat in cross section; 37, well-developed su- that the character distribution among pho- pinator ridge; 38, relatively short deltoid pec- cines considered here represents anything but toral crest; 39, strongly developed post-tibial a suite of reversals is exceedingly unlikely. fossa). In this category would be placed also It is curious to note how reversals are par- the tendency among phocines to develop a ticularly evident in flipper structure. Here they trochanteric fossa of the femur, reduction of have occurred to such an extent that in many the supraspinous fossa of the scapula, and a respects [e.g.: reduction in size ofmetacarpal posterior position of the palatine foramen. I (16), enlargement of intermediate phalanx For reasons discussed earlier, these charac- V in the carpus (17), metacarpal heads with ters, while representing general carnivoran or palmar ridges, phalanges round in cross sec- mammalian features, may not be considered tion, and trochleated interphalangeal articu- primitive for pinnipeds (assuming monophy- lations (18), and large claws on manus (22)] ly). Suggesting otherwise implies that pho- these seals have reverted to, or approached, cines are the sister-group of all other pin- the primitive carnivoran (not simply pinnipeds, a proposal which seems hardly niped) character states. If the "Monachinae" credible in the face ofoverwhelming evidence are viewed as paraphyletic, then this pattern supporting phocid monophyly. These seem- of character reversal within the flippers also ingly "primitive" phocine characters must encompasses lengthening of the third meta- therefore have originated within the Pinni- tarsal (21) and the gain of claws on the pes pedia, more precisely within the Phocidae, (23). Reversals are by no means limited to and necessarily represent reversals. flippers but include features of the humerus To reject the proposal advanced here that [presence of entepicondylar foramen (14), the numerous "primitive" features seen in strong supinator ridge and short abruptly ter- phocines are in fact reversals, one must si- minating pectoral crest (37 and 38)], the den- multaneously accept both pinniped diphyly tition [six (25) laterally compressed incisors and "monachine" monophyly. Employing (32)], tibia (presence of a strong post-tibial mustelids as the phocid sister-group (leaving fossa) and perhaps the premaxillary config- aside the doubtful nature ofthis assumption) uration (24) as well. strengthens the evidence for "monachine" By way of a general conclusion, I offer one monophyly, shifting (14) the absence of an brief remark regarding the higher-level rela- entepicondylar foramen in its favor and re- tionships within the Phocidae. As is often the moving doubt about the possible primitive- case in systematics, when a well-defined ness of(24) the "monachine" premaxilla con- monophyletic grouping is subtracted from figuration. Nevertheless, admittance of another more inclusive group (in the case ex- mustelids as close phocid allies does not suf- amined here, the Phocinae from other Pho- ficiently redistribute the overall character cidae), agglomerating the "leftovers" (here the 34 AMERICAN MUSEUM NOVITATES NO. 2924

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(,A~ U . C 1988 WYSS: PHOCINE SEALS 35

"Monachinae") usually yields a nonmono- To be sure, this proposition amounts to phyletic result. In such instances, cohesion of little more than a descriptor, yet I think it the residual taxa is more often based simply aptly delineates some of the character trans- on the mutual exclusion ofits members from formations that likely occurred during the the more restricted monophyletic subdivi- early evolution of phocids as a group, and in sion, than it is on features intrinsic to those large measure many of the character trans- taxa. While the "monachine"-phocine split formations during the evolution ofits various may be convenient for discussing biogeog- subgroups, particularly the phocines. What- raphy (as popularity of the locutions "north- ever developmental mechanisms underlie ern" and "southern" indicates), this dichot- such wide-scale character reversal, that such omy receives less than persuasive support "retrogression" has occurred appears, at this from comparative morphology. Whatever the point, difficult to refute. merits or pitfalls of the phylogeny depicted The evolution ofthe limbs ofthe Phocinae in figure 9, this analysis raises serious doubts affords a well-founded example of broad- about seemingly unquestioned validity ofthis based character reversal. The difficulty typ- widely accepted basal phocid dichotomy. The ically posed in cases where the appearance of possibility of phylogenies conformable with atavistic characters or heterochronic onto- class III and IV hypotheses of figure 1 need genetic modifications such as neoteny are to be considered. Rather than continue to suspected, is finding sufficient additional force living and fossil taxa into a traditional characters independent of such processes for but very likely unnatural classificatory "correctly" placing a given taxon within a scheme, alternatives might profitably be en- phylogeny. In highly transformed taxa, re- tertained. versals may be so pervasive as to erase most In the conclusion of his classic "Contri- or all derived characters which might oth- bution to the comparative anatomy of the erwise have been indicative of more highly eared and earless seals," Howell (1929) puz- resolved cladistic placement. The almost cer- zled over his observation that in several retain monophyly of the Phocinae and their spects such as details of the myology, the membership within an unquestionably greater tendency toward flattening ofthe pha- monophyletic Phocidae provides a rigorously langes of the pes, and the cartilaginous ex- supported phylogenetic hypothesis, the es- tensions ofthe digits, Zalophus has "traveled sential element ofany demonstration ofchar- farther from the typical terrestrial carnivore" acter reversal. Phocine seals, therefore, pres- than has Pusa. The lack ofthese skeletal mod- ent a rare opportunity for the study of ifications struck Howell as particularly vex- extensive character reversion. This phenom- ing given that such structures would seem far enon is normally extremely difficult to iden- more "useful" to the hind-limb swimming tify, and in the case of "adaptively unified phocids-which, moreover, are generally re- functional complexes" (such as pinniped flip- garded as the most highly aquatic ofthe pin- pers) is sometimes claimed not to occur. nipeds- than to the otherwise seemingly less Finally, results presented here counter the aquatically specialized otariids. Likewise he seemingly logical notion held by most work- found perplexing the presence ofcertain spe- ers (e.g., Laws, 1959; King, 1964) that pho- cializations of the forelimb in Pusa that ap- cids have undergone a phylogenetic trend pear to be of no "real use." Thus as related toward increasing flipper "specialization" to the evolution of what are generally re- from a structurally conservative phocine ar- garded as the two major groups ofpinnipeds, rangement to an ostensibly more highly "ad- otariids (including odobenids) and phocids vanced" "monachine" form. It seems, how- (for contrary view see Wyss, 1987), Howell ever, that phocid flipper evolution has entertained (but remained far from con- progressed in a direction exactly opposite this vinced of) the possibility that this unexpect- expectation, culminating in a pattern looking ed morphology was attributable to a pattern deceptively primitive phylogenetically but of retrogressive evolution. being in fact only secondarily so. 36 AMERICAN MUSEUM NOVITATES NO. 2924

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