Reprinted from: EVOLUTIONARY BIOLOGY OF THE NEW WORLD MONKEYS

AND CONTINENTAL DRIFT (1980) E d i t e d by Russell L. Ciochon and A. Brunetto Chiarelli Book available from: Plenum Publishing Corporation 233 Spring Street, New York, N . Y . 10013

Phyletic Perspectives on Platyrrhine Origins and Anthropoid Relationships

E. DELSON and A. L. ROSENBERGER

Introduction

As the editors of this volume describe in their preface (Ciochon and Chiarelli, 1980), the preceding papers were solicited from researchers in various disci- plines so that we could coIlectively examine a set of interrelated questions: ( 1) What are the paIeorltological origins of the New World monkeys?, (2) what is rhe nature of the phylogenetic affinity between the catarrhine and platyrrhirle primates ?, and (3) what is the signiQcance of these questions, and their resr~lu- twn, for ut~det.standing the influence of continental drift upon the moderu distr~buticjtlal patterns of' the anthropoid primates? We hate been askrd to evaiuatc 111c status of Questions 1 and 2, which are essentiall) ph~logenetic pl-ubletns, 011 rhe basis of the foregoing contributior~s as wcll as vur own respective rescarcllcs. We have a t tempted to do so by reiterating svme of the more salienr arguments in capsule form and pointing out what we feel a re their strengths atld weaknesses (see summary in Tables 1-1 1 I ) . Our con- clusion-in brief-is that a substantial set of first steps has been taken, largely due to the multi-disciplinary persuasion of the contributors to this volume, but many important prr~blems remain: the data on living platyrrhine comparative morpholop is still meager; the fossil record of phcyrrhines is sparse but tantalizing; comparisons of early catarrhines a n d platyrrhines have

E . L)F.LSON Department of Verrrbratr Pdleuntology, American Muscum of Natural History, New York, New York 10024, ant1 Drpar~mrnt 01 .4nrhrupalagy, Lehrnan College, CUNY, Rror~x . New York 10468. A. L ROSENBEKCER Department of Anthropol- r)F, LJnive~.sity nf Illinois at Chicago C;II-clc. Box 4348. (:hi< ago. Ill~nois fiOfi80.

PLATYWHINE ORIGINS AND ANI-HROPOID RtLA'I-IC)KSHIPS

hardly begun: too little is still known of ornomyid (and adapid) crania and postcrania; [he stbmewhat herter-known adapids (not to mention the rarer c~mornyids) are still pmrlv u tlderstood phvlet ically ; and, especially, without a clear genealogical picture of platyrrhine, catarrhine, and interanthrnpoid re- lationships, n o scientific model of their deploy men t can be svnthesized.

The papers in this volume reflect a diversity of methods that is bjth healthy and indicarive of the breadth of the attack on these problems, artd we dot1 bt that procedu t a l and philosophical differences are significantly respon- sible for the lack of a consensus on a number of fundamental issues. However, much of the data that has been generated comes in the wake of the featured debates o f the last decade. contrasting the strepsirhine-haplorhine, simio- lemuriform and prosimian-anthropoid dichotorr~ous models of primate evolution. 11 seems timeIy now to recast our questions, and perhaps our search for fossils, if we are to make more rapid progress toward solving the prohlert~s of platy rrhine origins and platyrrhine4atarrhine relationships.

C:uusideration of these two questions began in the late 19th Century. Anatomists early recognized some major distinctions between New and Old World monkeys, reconciling t h ~ m as examples of convergent evt rlution. Tar- .raw was also seen to have closer tier to the anthropoids than to Lemuriformes on the basis of placentation and cerebral arteries. Meanwhile, some paleon- rt~logists proposed that the " lemur-like" Nrtthrctus was ancestral to platvr- rhines. Later, this view was extended to view tarsiiforms as catarrhine ances- tors, irnply~ug anthropoid polyphyly. 'Thus, both the approaches and [he hypotheses of this volume are rooted in the earliest interpretive works on primate evolution.

Platyrrhine Relationships

The primary orientation of this volume, which focuscs on issues of an- thropoid origns from the perspective of the New World monkeys, is appro- priate for a number of reasons. Not only are the platyrrhines more conserva- tive than catarrhines in marly aspects of their morphology, but they have also been shown to represent actual. rather than purely hypothetical, anaIogs of early ca tarrhine behaviors and adaptations (e.g., Fleagle, 1980). Nevertheless, fundamenta1 to their heuristic utilization as models of the extinct early catar- rhinus is the development of a coherent picture of platyrrhine genealogy, which seems far fram achieving a uniformity of opinion. For example, the prolonged debate over the ancestral or derived nature of marmoset rnoryhc~lom. has important implications for understanding the evolutionary transition marking the rise of the anthropoids. Were primitive platyrrhines, and yrotnanthropoids. small-bodied, scansorial, claw-bearing frugivore- insectivores (i. e., mar moset-like) or nut? If not, what taxon or phyletic group does most closely apprrkmate our expectations af the kind of animal that was an early anthropoid? Perhaps even more important is an appreciation of the

murp hological pattern thought to have characterized the earliest New World monkeys, for that suite of features is prerequisite to the establishment 01 the phylogeneric relationships of the ratarrhines and platyrrhines.

Whereas a tlurnber of contributors to this volume have concluded that the claw-bearing marmosets, Callitrichinae, are quite derived in aspect (e, g.. Luc- kett, 1980; Bugge, 1980; Maier, 1980; Kav. 1980; Hoffstetter, 1980; Gantt, 1980; Martin and Could. 1980; see also Rosenherger, 1977, 1979), marking somewhat of' a transition from the prevaili~lg opinion o f prerreding decades (e.g., Le Cros Clark, 1959; Napier and Ndpier, 1967; Hrrshkovitz, 1977 and before), the details rjf marmoset alld nonnlarmoset interrelationships a re not agreed upon or evcn well estab1isht.d in certain cases. Tn some extent, this is due to a genuine lack of information and the sti l l ut>derdeveloped ~nterest in platyrrhine biology. Iln the other hand, it seems true also that most current students continue to employ the conventional marmoset VS. nonmarmoset perspe~tivt. for framing thcir questions and inrerprering their data. Rosen- berger ( 1 977, 1979) and snme others {e. g., Egozcue and Perkins, 197 1: Romero-Herrera et at., 1976, 1978: Dene aL, 1976) IIWP contested the phylogenutic accuracy of that distinct~on, arid we have attempted to documerlt (e. g., Szalay and Iklsr~n. 1979) an alternative dichotomy based upon a cladis- t i t split between a telids ( Aotw, Callic~bw, sakl-uakaris, atelines) and rebids (cebines and callitrichines), Thus far, this notion has received little support f rom immunological efforts. although the DNA sequencing data of Romero- Herrera and colleagues up hold the major outlines of this interpreta- tion as a parsimonius possibili~ y . T h e hiomolccular-based con1 ributions of' this volume (Sarich and Cronin, 1980; Baba ~t ul., 1980) are not mu~ually consis- tent and present a number of significant problems. I t seems especially impor- tant, for example, to determine why the albumin and transferrin data seen1 to have low restllving power bevond a few almost universally accepted phylet~c groupings (Pitheck +Caca~ao; At~ le3 +Lnguthrtx +Alomt[n : Callitrichinae), alld why the CroninSarich estimates of divergence times predict that no relatives of' the living forms would exist prior to 15-20 millirm years ago. T h e tossil record establishes almost uneqivocdlly that platyrrhines were prescrlt as early as 35 million ycars ago and that species exceedirlglp like, i f not ances~rai r , , ! 11e living squirrel monkey (Dnhrhoivhs) and the owl monkey ( Tremaccbus) existed 20-25 million years ago. Give11 our limited knowledge in this area, we note only that the validity 01' the molecular clock must continue t o be seriousl) questioned, especially slnce internal anatyses have show^^ that trlany of the ma~romolecules used in clock constructic~n d o not evolve dt mutually consis- tcrlt rates (Corrucciri~ rt al., 1979).

Platyrrhine Origins

As several authors state or imply, the question of p la tyr rh i~~r origir~s rnay be evaluated within the L'ramcwork of rither of two alternative phyletic ap-

448 PLATYRRHINE ORIGINS A N D ANTHR0PC)ID RELATIONSIllPS

proaches: (1 ) ancestor descendant, lirlrage h ypntheses or (2) sistrr-taxon, cladistic hypotheses. The latter, of course. is a n irldirecl apprwch ta) thr issue of origzns, but represents a less complex first stcp n hich ma, remain the nnly course when the nature of the data so dictales (e. g.. in neon~ologiral work) or when ancestor descendant hypotheses are nullified. 11 is wa~rth painting out

in this regard that except for amino acid sequeo~ing, whi~h dSSeSSe5 the trans- formation of specific, unit character states from une ~onditic>n 10 antbther, none of the molecular evidence is truly comparable to the esserlre of cladist~c analysis, the inference of shared, homologous derived features. Thus, al- though couched in cladistic terminology in that clusters of taxa are recognized as "clades" (implying a unique common ancestry) the foundation of such analyses (e . g., Sarich and Cronin, 1980) is esse~ltially phenetit. We do no1 wish to minimize the significance of phenetic studies, but merely point our that we prefer them to play an auxiliary role in the establishment of genealog- ical relationships.

While a number of' authors have suggested definite scenarios of platyr- rhine origins, we consider all of these as highly speculative or lacking in robusticity. Proponents of a polyphyletic origination model (e.g., Lhiarelli, 1980; Perkins and Meyer, 1980) bear the burden of refuting the contradictory morphological evidence which implies that platyrrhines are in fact monophyletic (see Table I). This objection stands irrespective of' the ancestral stock(s) from which these workers would derive the N e w World monkeys. In advocating a dual origin involving both adapids and omomy ids, Perkins and Meyer have essentially resurrected the early 20th century hypotheses noted above. In this form, however, it is based on neontological rather than paleon- tological evidence, thus having little resolution as far as descent is cotlcerned.

Hoffstetter's (1 980 and before) argument for the descent o f platyrrhines from catarrhines via the Parapithecidae has been specifi~ally considered by a number of workers (Rosenberger, 1979; Szalay and Llelsun, 1979; Kay. 1980). All of' these are firmly in opposition, citing the uniquely derived attributes of parapithecids (relative to eucatarrhines) or platy rrhines (rekative to catar- rhines) which militate against Hoffstetter's hypothesis (see Table I). Although Parapithecus and Apidium may resemble some platy rrhines in sutnr Kcat i~res. these appear to be conservative retentions trom the last cornnlorl arlcestclr of anthropoids and thus do not signify a special relatiot~ship betwren parapithecids and New (ot Old) World monkeys. Furthermore, it is becoming increasingly well established (Szalay and Delson, 1979; Fleagle and Simons. 1979) that parapithecids are dentally derived by comparison to othe t F~VLIIII catarrhines but are mure ~trnservative than cercopithecids and pongines in lacking ischial callosities and it1 retaining P2. In sum, the evidence suggests that parapithecids are a collateral branch of the catarrhines which did uot give rise tu any of the living anthropo~rls.

A similar set of' anatomical features and phyleric arguments are applica- ble to any hypo1 hesis which postula~es the descent of platyrrhines from a bona fide catarrhine stock (e.g.. Falk, 1980,). Even the most basic of catarrhine

Table 1. Some Characters of Selected Higher Primate Morphotypes"

Platyrrt~incs I ) Hylx>coni~lid atwent on M J Kay ( I !#HI)) 1) Me~rr~)n~r l t . s highlv r rd~tccd with ~ ) a r ~ t r l ~ , r ~ l e s prob- Rr ) se i~ tx r~e r (1979)

ably ahsclir U Zygnn~atico-par~rtdlptrriotl with la~cra lorh~ta l i~ssilrc Ko\enbcrgcr (1977) I 1 tritraplaccnialn~a~rr~la~iesselspresent;~~lat-ental Lu~Lrtl(l!)HO)

hcrnato[~)iesis ],rrscnt 1) kdi ic t i r l t~ of nasal wing cart~lages; enlarged cmbry- Maler (I9801

o t ~ x n a ~ a l tapsule Catarrhines

D Prrwr~r r ( > I i a ~ c t "X" I)II I r~wtr molars Kay ( 1980) I1 Preserlr t. ~ r i hypotonulid rrn .M ,,, S/.ala?- and Dclstm ( 1 Y7!#) D Llss r j f lateral nrbital fissure Cartmill (1980) Il Retluc-~ior~ ut' presphcnc>pala~~r~e lamina ot- palatine Citrt~ll~ll ( 1980) D PIacclltaI disk villorls: cytntrt>pl~oklastic shcll well de- 1.uchect ( 1980)

\ rlol)ed Il h'arror*, ir~lernarial septum with r ~ d u c t i r ~ r ~ oi' wing Malcr ( 1 980)

carti1agr.r arid crll~ctor): scrolls: loss (11 bon~eronasal orEan nl J a ~ u h w n

A~~t t l r t q~ l i r l s C) 12 rt~niral and robust Rosenbcrgel. alld Sralay ( 1 980)

I Thickened enamel on 1owc1- arilrrtur premolar Kay (1980) P lms at F I , mesiotiistatly "rrowdrcl" prenlulars Kay (19M1) D Sy ~ ~ q ' h > s t ~ l f usiotl Kay (1IIHI)) (:I): and adapids) P T)pc IIB et~amcl p t i sn~ pattern Garut ( lL3Ub) U Postc~rbital sepiulll complete or ncarly 5 0 Cartmill (ISXO) (13; and

tarstcrs) I) 'rraber,ula~e h)-prh\ nipall~c sinus Kosrnberger and Srala! ( 1 9801 D l o s s c ~ t - stapedial artery BURR' ( 1'380); Krl.cenhcrgrt

and h a l a y (I%-ii)j ?A Ilphthalrr~~c artery arises Llorrl ir~~t-rnal carotid tlugge (1 9803 (U) n Presence I ~ C ~ r ~ l ~ s v e r s e crntral tcrrbral *ulct~s Falk ( I '380) D Expandrd t~sua l r-orlex and asociated sulr-i h l k (1980) D Reduc-etl levper rrochanter ol i e n ~ u r Ford (1980) I?D; ?I') D Loss of lemoral third rmrhnrlrer kprd (1980) (?D; 7P) D Ililtal femoral epiphjsis arlwrop,steriorly c-cttnprewed bqrrd ( 19HOI OD; ?P) I' K a r ~ t ~ ~ r pic similarit!: C111al-rlli ( I 980) L) Prl~nt>r.ctial amniotic cdvlt J. present : an~r~icrgcnesis by Lut L r ~ i ( 1930)

cat ~ ~ a ~ i c ~ n : bidisc ~ t l a l tiernochorial plat rnra: hlasto- cyst attachnlcrlr br emhqonit polc: pri~naa-v a r d sect~ndary vulk sac present; tralwci~lar dtsk Ltlerus simplcx; rudinlen~ary villous a t~thor ing; n o hcad- to-head qnrrrn aggluti~lalic~r~, sk~hlingua absrtu

a 0")- n l t ~ r p r ~ ~ ~ ~ l ~ , r l (at ~ I I V ~ W I J I - ~ I ~ or 5ta1\1: 1 s t ~ . Rtnw111wrger (19791 lcnr 11iv1 Iltxl$] 14 e*~<l, I C A ~ U I Y 15 i~~<li~;itcd in the lei t ~oltrn>u .I,< ~I IXI I I IK to the tr)llourn~ I unvet~tiuiis: A. a l i r r ~ l ~ ~ l . slldretl m-ith A srslcr. I ~ L O I I ; I), tl~lic~uely c i r~~\vd 1))- L [ > I ~ ~ ~ I S , I I I la r s i+~<-~ I ~ I X O I I ; L;. cmnerKc11t. I I I U I ~ U I I I C ~ ~ < ~ ~ ~ I U S q111111~irit) : P, p l ~ t ~ > t ~ ~ i <~11111,1iit) whew ph!lelir ~i#llli I( , I I I L C A C C a l J l l w I I I I C ~ . '['he right iall~rrl~~r h w a [he rnmrtrs f i )~ t..~ih chal.at IV: d r u l (11v1r i11tr1-pret a1ic71) m-IICII (lilferr~~i 1 1 G ~ I I I I I U I - IIWII. AItI~otigIi uc I I A I 1. 11111 ittt~rlipted I I I a s r s 5 c ~ I ' I ~ ~ I ( tel- 1111 i v l ~ [ l 4 1 1 1

111 rliis t , ~ t~~~ la t~a l~ ) . sc\pii%l \el5 1 2 1 L I I J I ~ L ~ C I . S I ~ I T P S tl;l\e lwcn gruupr.ri hlr ro~~\enic.nt t:.

molar patterns (excluding the t w o poorly-known forms Oligopitk~rus-which w e consider probably nonanthropoid-and Pondaunp) is too derived lo have been ancestral to that of the platyrrhines unless a number of reversals can be documented (see Table 1). This irt~plics that any presumptive platyrrhine ancestor inhabiting the Old World would not be regarded as a catarrhine (even on the basis of the Atlantic Ocean as a major diagnostic feature), but rather as a prr~toanthropoid.

Anthropoid Origins

Given tha t none of the known anthropoids is ancestral to platyrrhines (or to catarrhines), the next questions for consideration relate to the monophyly c ~ f anthropoids and their relationships to other primates. The majority of authors in this volunle have accepted the concept that anthropoids are manophyletic (Table l ) , thus implying the prior existence of an ancestral species which displayed at least some of the characteristic anthropoid morphology. On the other hand, no authoritative response has yet been coun- terposed to widespread dou hts as to anthropoid monophyly (e.g., Simpson, 1945; Gazin, 1958; Simons, 1972; Cache], 1979). Other than brief' reviews such as this one, there i s still no published, detailed objective analysis of the anthropoid morphotvpe which goes beyond conventional wisdatn and the scah ~ I U W C , such as chat provided by Le Gros Clark (1959). T h e concern over rnonoph y ly has largely been based upon the supposition that the postorbital sept urn evolved cor~vergerltly among platyrrhines and catarrhines, coupled with a healthy mistrust of the zoogeographic requirements engendered by the monvphyly hypothesis. The ontogenetic and distributional patterning of the bony mosaic at the pterion among all primates is a topic worthy of detailed analysis. Major distinctions do contrast platyrrhines and catarrhines (see also ~ o s d n h e r ~ e r , 1977; Car~mill, 1980), and these probably do bear on the evolu- tion of postorbital closure.

Nonetheless, following the consensus of this volume, we may turn to an assessment of the ancestry of thr earliest at~tt~ropoid, a problem much de- bated of late as a result of the prominent cotltroversy among primate sys- te tnatists during the past decade. Most of the morphological and biochemical evidence seems to support the view that the haplorhine primates (anthropoids plus tarsiiforms) are also monophy letic (Table 1 I and below; see Rosenberger and Szalay, 1980; Kay, 1980; Hoffstetter, 1980). Gingerich (1 980). however, argues that this interpretation is incorrect. He suggests, alternative ty, chat the living lemuriforms are more closely related to anthropoids than is Tar~iilu, and that Eurasian adapids were ancestral to both the living strepsirhines and the anthropoids. Cartmill and Kay (1978) have provided a shred of indirect sup- port for Gingerich's thesis by questioning the traditional acceptance of a close relationship between lernuriforms and adapids and hinting that the larter

Table 11. Some Characlers Common to Tarsiiforms and Anthropoids"

I'ar<iiforms and anthropoids 1 P Semispatulate inc~ulrs variably present

2. P Mesiodistally "crowded" premolars 3. P Nannopirhex-C<)ld replaced by postprotocriwa

(rariahlv) 4. P Premeractis~ld well developed on M ,,, (vari-

abl\ ) 5. P Tr~gon id low, talonid basin expanded (vari-

ahlvl 6. P Reduced lower third molars {variably) 7. D Short, deep, low-hafted tacial skull 8. L) Apical interorbital seplum 9 Ll l)itr~iriished nasal iossa; PI-obable l a ~ k of 01-

factory recess 10. n Reduced stapedial artery; prllarged prooiotl-

tory artery I I n Mcdiallv plsiliorleri r a ro t~d loramen 12. I3 ~ n t e r o m e d i a l l ~ enlarged hyporympanic sinus 13. ?L) Downturned hurneral t n ~ h l e a 14. D Enlarged urripital lobes: reduced r)lfactor?-

I ~ l k s 15. ?D [ m s . ~ 01 roronolateral sulr-ua

Tarsius and Antllrrl;n*irl~, 1. ?D* naired rliinarlum: Eitsrd nasal processes 2. n* No choriovi~rlline plarrrlta; rudin~entary al-

lantois: well-drveloped botly stalk; o r a r ~ a n bursa rerluced ur ahstnr; primordial anlni- otic carily transitory; invasive atrachment: monodiscoidal hemochorial plat enta

3. C Polrorbital septum 4. P* Pre rnce of fovea centralis 5 C: At~teriur position of carotid foramen fi A Lruipient enlargement of internal taroud

artcry

Clrlosky (l9Ri)); Rosen- berger atld Szalau (1'380)

Kay 11980) (01 Ka? (1980) (Dl

Kay (1980) (D)

Kay ( I YHO) (D)

Kay (1980) (D) Rosenberger and Szalay ( 1981)) Luckett (1980) Rosenberger and Sralay ( 1 !)HI))

Rosenberger and Szalay ( 1980)

Rosmherger and Szalar ( 1980) Ruwnkrqer and Szalav (1980) Rownberqer and Sralay (1980) Rosenkrger and Szala~ (1YHO)

C?itrtmill (1980) (D) C:ar~nlill (1980) (D) Canmill (1980) (D) Buggc (1980) (D)

' "Variablt" Cealures are tlot present III all ldxullolnic groups: asterisked tta1urt.r r~vt vbe~ ; th l c in ~ F I Y I I I J t111

kr\ I ( > q ~ i ~ l u > l \ we nfhtes to [-able 1,

group may be closer to rhe haplorhine clade, with the lemurifornrs a n d plesiadapiforms being somewhat further removed. We regard bvt h 01' t hesr as less likely hypotheses (see also Rosenberger and Szalay, 1980). further suggesting that other resemblances hetrveen adapids and Iemuriforms (e .g . , the freely suspended ectuty-mpanic and the lack of an ossifieri annulus mem- brane [=? reduced linea semicircularis]) ma): wel l turn out to be synapomor- phies.

Gingerich's (1980 and before) hypothesis o f adapid-anthropoid ties is predicated upon ( I) the presence of more than a dozen itemized poitlts of resemblance shared k ~ w e e n them (Table 111); (2) recogniticm of presumed morpholugicall y intern~ediate forms that are difficult to allocate [e.g., Pro-

Table 111. Some Characters Common to Adapids and Anthropoids

Body w e F e a l e r tharl 5(10 q Tendenrv iu fuse I Ilr rnarid~bular s) mphysls \'ertirai, spariibtc lnciwrs I , su~aller rhan I I ~ ~ r e r l o c k ~ n g canine occ lus~cir~ Carlines rrlotierately large 2nd prrrjcctu~g Canines sexi~allp dim or phi^ Canine-premolar "honing" Molari~erl P4 'I'endency toward qitadratc lower molars Nontubular [part~ally free] ectotymp.ri~c"

P Relatively short calcanr~rrn A lJ11fused ~ibia-fibula

Gingerirh ( lYHO)R Cingerich (1980); Kay (1980) (?D) Gingerir 11 (1980) Gingerich ( 1980) Gingcrich (1980) Orlosky (19HO) (PI Gingcrich (1980) G i n ~ r i c h (198CI); Kay (1980) Gin~er ich (1980) Cir~gerir tl ( 1 980) Gil~gerlq 11 ( 1 QPO)

a Nr~ne of the characters enumeraterl by (;it~gt.r~cl> uerr s i i p ~ h ~ e d a\ \hdic~l. III.II\CCJ r,md~t~cm+merelr as sirnil;triries iridicative of rlow rela~ioi~$tup. Sce also noles la, -l'al,le I ' Gln~er i rh has r-laimrd that the ectntyniptnic i s p ~ r l i a l l ) Irri- I n earl$ snthrrvplrls. See r u x ~ . 1). 453 for c~ur

I-clutation of this claim.

tuadupis (" C~rramonius ") brachyrynchu~, A rtlph tpilhuihus, #on nghoniw, 01igopatht.cw and P o d n u n p r r ] ; (3) the intermediate stratigraphic position o f these dubious taxa and thy continuous nature of' the Paleogene primatc rucord; and (4) the geographic distribirtion ut adapids and early anthropoids. As examples of' "extrins~c" nongenetic evidence, we regard the last three poirlts as h a v i n g only a secondary rrlevance to the issue. A phyIetic hypothesis should be based upon testablc statements about homologclus similarities. Other forms ul in- - formation rrlay sllarpeu the argument but cannot supersede morphology and genealogical reasoning. either positive or negative. Moreover,'the fossil rei.a,rris of adapids and omornyids are in fact replete with stratigraphic a n d mr,rphologic g a p , uncer iainty about the evolutionary significance of' i tlcom- plcte fossils should militate against their being used in grand hypotheses; atld thc ~cnlporal sequence of tma has far lcss significance than the ~empcrtal sequence of' uharaclers, which tells us little in this case.

'The morphological evirlenc-e for adapid-anthropoid links also sut'[e~.s upon close scrutiny. Many of I hc. charac~el-s i~~volved are probably correlated, a point often glossed over by most work~r s , including ourselves (e .g . , features 2-4, 5-8, and 12-13 of- Table I 1 I ) , so their shccr nuntbcr is not as impressive -as it rnight wcm. Some of' rhese resemblances are likely to represent con- vergences on the anthropoid condition (characters 2,3-4, 5-8, and 9-10: see Cartmill and Kay, 1978; K a y , 19HO; Roser~berger and Szalay, 1980) or are primitive for the euprimates ( fea t~~res 1 0 , 12, and 13) or otherwise are 01' limited genealogical value (condition 1 I . S o n - ~ e arl t hors have employed terms such as spatulate incisors. molnrlzpd prerr~olars, a11d quadrate lower mtdars in desc.rihing shared character status arrlorlg these primates. Such biologir-ally imp]-ecise terms dtr not permit clear understand it^^ of the details of ariy po- trntial similarity, s o that deturmination of homology vs, convergence is not

F.. I)EI.SON A N D A. L. ROSEKBERGER 453

possible i n these ~a5c.s. bloreovet. one feature (number 1 1 of Table 111) i s based un a specimen which we suggest may be misidentified. 'I'he only evi- dence thal an \ anthn~poids ever had a free, intrabullar ectotympanic ctjmes from a broken bone allocated by Gitlgerich (1973) lo Apzdium (in part on the basis of its I-ecovery alongside a mcrlar of that genus). Such features trf this presumed squarnuus temporal fragment as ( 1 ) the orientation o f thc "zygoma- tic prtjcess": (2) the morphology o f the "pstglenoid process" and its sur- rounding anatomy; (3) the very large size of thr bone by comparisr~n to other fragments of Apidium ; and (4) the ext remc lateral position of the "ectoty m- panic" inferred by Gingerich lead us to doubt thal this b o ~ l r derives from a primate, muuli less represents the otherwise well-known .4pirfium pluorn~~is;. Finally, Gingerich and other proponents of the adapid ancestry hypothtsis have not adequately dealt with much of the positive evidence supporting the tar~iiforrn -at~thropoid theory [although Gingerich ( 1980) has made several impor t i i~~t points in this vein]. If w e are to believe that Adayidae i s the sistur- taxon ot'anthropoids, we must he persuaded by nlorphological and systematic argument that the characters identified as haplorhine synapomorphies (Table 11) are either conservative retentions or nonhomologous [convergent) shared rraiw. T'o ignore counterargumerlts is not to refute them.

As noted above, w e believe that the tarsiiform hypothesis of' anthropoid urigins, which presumes that the protoanthropr~id was omomyid-derived, is rhe bcsr available interpretive scheme for explaining the bulk o f the evidence. 'I'hr strcngth of this hypothesis lies in the completnt.ntary nature of the results l'rotn character analyses of a variety of' data sets obtained from both extant and extinct taxa (Table 11) combined w i ~ h rhc' phenetic support from biomt)lccular studies (for example. see Baba et at., 1930). Illoreover, the in- corporation of nullifying counk1-are;l~lnents against the adapid-anthropoid alternative scheme allows us to rqjecr opposing inrerpretations based on the same anatomical systems (see above). Clearly, additional work can further sharpen this hypothesis by excludil-tg many of rhe known genera ur lineages from potential ancestral status (see Kay. I 980; Kosen herger and Szala) : 1980) and by the recovery of more informat it e cranial and postcranial remains.

Cartmill (Cartmill, 1980; Cartmill and Kay, 1978) has attempted to go br- pond this conservatively vague statement of tarsiifornl-anthropoid affinities 111

offering the intriguing hypothesis that Tarsius itself', rather than some unknown or unrecognized tarsiiform o r omomvid, is most closely related to anthropoids. Some of the cvidente against this view has been presantcd by Rosenberger aud Szalay (1980), but (:artrn~ll (15W0) has marshalled additio~ial points in rupport. I t appears ro us rhar ttic Lev t o this question lies i n comparisons between Tarsttu and rnicrochtrerinc omomyids, some of which share with Tursim such derivcd features (hv comparison to strepsirhities antllor Rooneyia) as tibio-fibular fusion and major calcancal elongation (see Gingerich, 1980; Szalay and l)elsr,n, 1979). a narrow interorbital region and somewhat en- larged orbits (Cartmill and Kay, 1!17A), aud a se~ondarily narrowed external auditory tube and rtducvd subtympanic recess of' he bulla (Rosenberger and

454 PLATYRRHINE ORIGIKS A N D ANTHROPOIU REI.ATIONSHlPS

Szalay, 1980). 1 f' these homologies and polarities are correct, the hypothesis most compatible with the many au tapomorphies of Tars2us would recognize microchoerines, rather than anthropoids, as the closest relatives of tarsiers. This concept, supported by Simtrns (1961) but rejected by Szalay (1Y76), re- quires further analysis before it will be widely accepted.

Furthermore. we remain uncorlvinccd that Cartmill's (1980) admittedlv fragile reconstruction of' orbit and eyeball evolution among the haplorhines is correct (see also Rosenberger and Szalay. 1980). The cnormtlus bony ring and flanges which make u p the tarsier eve socket resemble those of Aotus, whose ocular and orbital morphology is deri\.ed among platyrrhines (Kosenberger, 1979). Whatever advantage a postorbital enclosure might provide when a retinal fovea is present, as it is in Tar~zus (apparently) and in anthropids other than Aotus, the ana~omical association of these two structures need not be causally linked. Al~hrrugh Cartmill (1980) implied that all srrepsirhines have a tapetum lucidu~n while all haplorhines (save Aotus) possess a fovea, the litera- ture is replete with queries to this simple picture. Pariente (1979) has reported foveae in Lemur catta and Hapalemur p e w , both of which lack an anthropoid-like postorbital septum, while Wolin and Massopust (1970) indi- cate doubts about the presence of a true fovea in Tarsiw and the distribution t rf tapeta in strepsirhines. Cartmill (1980) has suggested that Tctonizls, an early ornomyid, may have possessed a tapetum on the basis of its relatively large orbital size. but w e offer an alternative interpretation. Cartmill and Kay (197H) indicated that smaller species have relatively larger orbits than do larger relatives, and most mammals do not have either a tapetum or a fovea, suggesting this lack to be the ancestral condition. If TtPtorrd~ c (and by implica- t inn other omom !ids) were diurnal animals lacking either derived feature, the eyes would have been large to gather the unconcentrated light, especially in a small animal which was vision-oriented. Such a conservative omomyid rnight give rise to diurnal foveate anthropoids, while the microchoerines and Tarsius might have evolved parallel, canalized specializatiot~s independently, involv- ing both the fovea and the postc~rhital seprum.

Conclusion

In summation, we agrec with the majority 01' authors in this volume in supporting strict monophyly of b>th ca~arrhines a n d plaryrrhines (aIthough we offer a different internal arrangement of' the ceboids). Anthnqmids, ton, are most likely monophyletic, with rile earliest representatives presenting at least some of the synapomorphies listed in Table I . Such an early anthroplid would not have been greatly similar in dental details to any of the known Oligocene to modern platyrrhi tles or catarrhines. Comparing the several most widely accepted hypotheses of' origin for ancestral anthropoids, w e think I hat the tarsiiform genealogical tie is the most firmly established (Table 11). Not

E. DELSON AKD h L. RClSENBERGER 455

only does morphology (Table 111 and refutation a h v e ) no1 support a set of homnlogous synapomorphies be~rueen adapids and anthropoids, but there are important stratigraphic lacunae in the supposed ct)ntinuum as well. All suggested refinements of the tarsiifortn-anthropoid concept suffer from sig- nificant difficulties and appeal- to be based mainly o n negative evidence, es- sentially related to our limited knowledge of ornomyid morphology and inter- relationships. Microchoerines may be the sistcr-taxon of modern Tarsus, but it is doubtful that this clade is especially close to the protoanthropoids. On the other hand, w e suggest that features of the anterior dentition in forms such as Arapahovzur (perhaps Tetor~ius) and Ourayh, which are little if at all known cranially or postcraniall y, probably include derived homologies shared with anthropoids. Thus we take the conservative stand that the ancestral higher primate originated sorr~ewhere in c>r near the Omomyidae.

Finally, in the spirit ~Cspeculation (and of paleogeography, to which this book is dedicated), we olfer our current deployment scenario, already put forward in esserlce b) Szalay and Delson (1979). It appears that the east A s ~ a n ?adapid Lnshzui atid omomyid Altaneus have their most significant ~norphological rescrnblances to western North American anaptomorphine omornyids, lendrng priuidte support to the Bering connection as a mammalian migration route during the Eocene. Similarly, a primate connection between eastern Asia and Africa IS suggested by ( I ) the disjunct presence of Hoan- ~ h o n i z u and Olagoptth~cw, both probably nonanthropoid; and (2) a possible phyletic link between the still poorly-known Ponduungwl of Burma and the Fay urn ratarrhines (see Szalay and Delson, 1979; Gingerich, 1980; Kay, 1980). Recent studies of Mediterranean rodents (Adrover sl al., 1978), Turkish em- brithopads (Sen and Heintz, 1979) and Pakistani proboscideans and cetaceans (West, 1980) suggest further links of these regions and taxa to Fayum rela- tives. Thus, as Gingerich (1980) delineates in his Fig. 4 (but with dif Lerent taxa involved), some early euprimates could have occupied a single biotic commu- nit): spanning the circum-Pacific region and differenliated I hpre in to the pro- toanthropoid stock. With the apparent world-w ide oceanic regression duri tlg the late Eocene, the formative catarrhine branch (of which P o n h u n p nlav represent an offshoot) might have crossed the narrowing western Tcthys and entered Africa, while the protoplatyrrhines managed ro cross into South America from the north (see also Wood, 1 980).* As with all paleogeographic hypotheses, this one is not easily amenable to tesling in the precise manner applicable to morpholo~cal theories, but musl stand or fall on consensus

*Many authors in this volume have preferred a trans-Atlatlric rafting disprsal of prutuan- thropoids from Africa to South America. We reject such dispersal nut only &cause of the problelns of dehydration, salt poisoning, and exposure facing any rafted primate unable to estivate, but also on phyletir gruur~ds. N o known Old World arithtopoid is conserrativc enougll to be ancestral to platyrrhineu, even the earlielt of which lack several of the catarrhirlc derived characters found in Fayum and Pondaung Frrssils. Tlius, rafting requires pustulation of an unknown source group, a well as serendipitous paleocontinental relationships and paletnx-eanographic condittons.

456 P L A ' I - Y K K H I K E ORIGINS A N D A N T I I R ~ P C ) I I ) K F I . A ' I I O N S I ~ I P S

analyses of a variety o f data. We await thr nexr incarnation o f this vtdume (or at least of ' the questions it has posed) for such a consensual evaluation.

We thank Drs. (;it,chon and Chiarrlli for inviting us to preparc this summary, which rrprcsv1lth solely our ow11 views, and our colluagues w h o wrote stimulat- ing paptrs and permitted us to analvze them in this prepublication manner. This study w a s suypr~rted (in part) by research grants to E. D. f r o m the PSC-BH k. Fnrult) Rcsearch Award Program of' City University of New Ynrk (Nos. 121 88 and 1298.5) and the Naticlt~al Science Fuundation (BNS79-1500 1) and by a postrlocroral fclkjwship A.L.R. from the 1)epartment of Atlatomi- cal Sciences. Stale U~liversity rlf N e w Yurk, Stony Brook.

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