Xenothrix Mcgregori (Xenotrichini, Callicebinae, Pitheciidae), with a Reconsideration of the Aotus Hypothesis 1

New Craniodental Remains of the Quaternary Jamaican Monkey Xenothrix mcgregori (Xenotrichini, Callicebinae, Pitheciidae), with a Reconsideration of the Aotus Hypothesis 1

Authors: MACPHEE, R.D.E., and HOROVITZ, INÉS Source: American Museum Novitates, 2004(3434) : 1-51 Published By: American Museum of Natural History URL: https://doi.org/10.1206/0003- 0082(2004)434<0001:NCROTQ>2.0.CO;2

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Downloaded From: https://bioone.org/journals/American-Museum-Novitates on 01 Apr 2020 Terms of Use: https://bioone.org/terms-of-use Access provided by American Museum of Natural History PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024 Number 3434, 51 pp., 17 ®gures, 13 tables May 14, 2004

New Craniodental Remains of the Quaternary Jamaican Monkey Xenothrix mcgregori (Xenotrichini, Callicebinae, Pitheciidae), with a Reconsideration of the Aotus Hypothesis1

R.D.E. MACPHEE2 AND INEÂ S HOROVITZ3

ABSTRACT

The Jamaican monkey Xenothrix mcgregori is one of several extinct endemic platyrrhines known from the late Quaternary of the Greater Antilles. Until recently, the hypodigm of Xenothrix was limited to the holotype partial mandible and a handful of tentatively referred postcranial elements. Here we describe several additional fossils attributable to Xenothrix, including the ®rst cranial remains, all of which were recovered in cave deposits in the Jackson's Bay region of southern Jamaica. In addition to a partial face from Lloyd's Cave and a maxillary fragment of a different individual from the same site, the craniodental collection includes two incomplete mandibles with poorly preserved cheekteeth from nearby Skeleton Cave. The new specimens con®rm a distinctive derived feature of Xenothrix, i.e., reduced dental formula in both jaws (2/2 1/1 3/3 2/2). Although no examples of the maxillary canine are yet known, its alveolus is notably small. Similarly, although the upper face of Xenothrix is also unknown, it is clear that the maxillary sinuses were large enough to encroach signi®cantly on the bases of the zygomatic processes. The nasal fossa is also very large and wider than the palate at the latter's widest point. A similar condition is seen in the extinct Cuban monkey Paralouatta varonai. Xenothrix continues to generate disputes among platyrrhine specialists because its unusual

1 Contribution 7 to the series ``Origin of the Antillean Land Mammal Fauna''. 2 Division of Vertebrate Zoology (Mammalogy), American Museum of Natural History. e-mail: macphee@amnh. org 3 Department of Organismal Biology, Ecology and Evolution, University of California, Los Angeles; Research Associate, Department of Vertebrate Paleontology, American Museum of Natural History. e-mail: [email protected]

combination of apomorphies complicates its systematic placement. Rosenberger's recent ``Aotus hypothesis'' stipulates that Xenothrix is a close relative of the living owl monkey (Aotus) and is not a pitheciid sensu stricto. Two fundamental characters used to support this hypothesisÐhypertrophied orbits and enlarged central incisorsÐcan be shown to be inapplicable or uninterpretable on the basis of the existing hypodigm of Xenothrix. The new craniodental evidence con®rms our earlier cladistic results showing that the Antillean monkeys (Xenothrix mcgregori, Paralouatta varonai, and Antillothrix bernensis) are closely related and that Callicebus is their closest joint extant mainland relative. This may be expressed system- atically by placing the three Antillean taxa in Xenotrichini, new tribe, adjacent to Callicebini, their sister-group within subfamily Callicebinae (Pitheciidae).

RESUMEN El mono jamaiquino Xenothrix mcgregori es una de las varias especies endeÂmicas de monos platirrinos extintos conocidos del Cuaternario tardõÂo de las Antillas Mayores. Hasta recientemente, el hipodigma de Xenothrix estaba limitado al holotipo, que consiste en una mandõÂbula, y a unos pocos elementos postcraneanos tentativamente referidos a esta especie. Describimos aquõÂ varios restos foÂsiles adicionales atribuibles a Xenothrix incluyendo los primeros restos craneanos, todos los cuales fueron encontrados en depoÂsitos cavernarios en la zona de la bahõÂa de Jackson en el sur de Jamaica. AdemaÂs de un resto facial parcial de la cueva de Lloyd y un fragmento de maxilar de otro individuo de la misma localidad, la coleccioÂn de restos craneodentales incluye dos mandõÂbulas incompletas provenientes de la cueva cercana de Skel- eton, con premolares y molares pobremente preservados. Los especõÂmenes nuevos con®rman un caraÂcter derivado distintivo de Xenothrix, i.e., una foÂrmula dentaria maxilar y mandibular reducida (2/2 1/1 3/3 2/2). A pesar de que no se conoce ninguÂn ejemplar de canino superior, el alveÂolo correspondiente es notablemente pequenÄo. Asimismo, a pesar de que la parte superior de la cara no se conoce, estaÂ claro que los senos maxilares eran lo su®cientemente grandes como para invadir las bases de los procesos cigomaÂticos en forma signi®cativa. La fosa nasal era muy grande tambieÂnymaÂs ancha que el paladar en su punto maÂs ancho. Se puede apreciar una condicioÂn similar en el mono cubano extinto Paralouatta varonai. Xenothrix continuÂa generando discusiones entre los especialistas en platirrinos porque su inusual combinacioÂn de apomorfõÂas complica su posicioÂn sistemaÂtica. La ``hipoÂtesis Aotus'' recientemente propuesta por Rosenberger estipula que Xenothrix estaÂ cercanamente empar- entado con el mono almiquõÂ(Aotus)maÂs que un pitecido en sentido estricto. Dos caracteres fundamentales usados para apoyar esta hipoÂtesisÐoÂrbitas hipertro®adas e incisivos centrales grandesÐno se pueden codi®car o no pueden ser interpretados en base al hipodigma existente de Xenothrix. La nueva evidencia craneodental con®rma nuestros resultados cladõÂsticos anter- iores indicando que los monos antillanos (Xenothrix mcgregori, Paralouatta varonai, and Antillothrix bernensis), estaÂn cercanamente emparentados entre sõÂ y que Callicebus es su par- iente maÂs cercano en tierra ®rme. Esto se puede expresar en forma sistemaÂtica ubicando a los tres taxones antillanos en Xenotrichini, tribu nueva, adyacente a Callicebini, su grupo hermano dentro de la subfamilia Callicebinae (Pitheciidae).

INTRODUCTION chine-like dental formula (/2 /1 /3 /2). In their original report, Williams and Koopman Until recently, virtually nothing was (1952) brie¯y noted the existence of poorly known about Xenothrix mcgregori Williams preserved but rather primatelike postcranial and Koopman (1952) beyond the bare facts remains in the same bone collection from that this extinct platyrrhine monkey lived in Long Mile Cave that yielded the type jaw Jamaica during the latest part of the Quater- (for historical details, see MacPhee, 1996). nary and possessed unusual dental features. However, they refrained from describing this For several decades after its initial descrip- material on the ground that its allocation tion, the only item in the Xenothrix hypo- would be uncertain. Forty years later, the digm was the holotype itself, a partial Long Mile postcranials were ®nally de- mandible chie¯y remarkable for its callitri- scribed and mostly allocated to Xenothrix, al-

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Fig. 1. Map of Jamaica and Xenothrix localities: Caves on the eastern ¯ank of Portland Ridge near Jackson's Bay in southern Clarendon Parish have produced several new specimens of Xenothrix mcgregori (plans after Fincham, 1997; see also table 1). Three other localities (Long Mile Cave, Sheep Pen, and Coco Ree Cave) elsewhere on the island are also known as ``primate caves'', although Long Mile is the only one that has de®nitely yielded Xenothrix material.

though not without a question mark in some place. These specimens are abundantly illus- cases (MacPhee and Fleagle, 1991). trated in ®gures 3±6 and 9±11. In the 1990s, joint expeditions of the Several more recent expeditions to the American Museum of Natural History and Jackson's Bay caves, including those of other Claremont-McKenna College recovered sev- teams, have failed to turn up additional fos- eral cranial and postcranial specimens refer- sils of the Jamaican monkey. This is not sur- able to Xenothrix mcgregori from a number prising. Most living primates have little or of cave localities in the Jackson's Bay area nothing to do with caves as such, and Xen- on the island's south coast (®gs. 1, 2). The othrix was probably no exception: individu- hypodigm of this very rare primate now als who accidentally fell in probably had lit- stands at 17 specimens, no two of which are tle trouble getting outÐmost of the time. known to be from the same individual. In this None of the craniodental fossils so far recov- paper we describe two new partial mandibles ered shows any appreciable degree of min- and the ®rst cranial remains attributable to eralization, although a thin incrustation of this species (table 1), including a partial face calcium carbonate occurs on some bones. All (AMNHM 268006) preserving the entire pal- specimens are presumably latest Pleistocene ate and most cheekteeth in situ, the ¯oor of to late Holocene (see below), although some- the nasal fossa, and portions of the orbits and what greater ages have been reported for pos- nasal septum; and a left maxillary fragment sible primate fossils found elsewhere on the (AMNHM 268007) with PM3±M2 still in island (cf. Ford and Morgan, 1988).

Fig. 2. Jackson's Bay caves and environment: (A) Typical Caribbean dry forest formation on lime- stone substrate, en route to Drum Cave. (B) Mantrap Pit entrance to Lloyd's Cave: skylight or pitfall entrances, acting as natural traps, are common in Jackson's Bay caves. (C) Inside Lloyd's Cave near Mantrap Pit: the new partial face and maxillary fragment of Xenothrix (AMNHM 268006, 268007) were recovered in surface debris just inside the chamber (Xenothrix Hall) that opens along the north wall (see ®g. 1 and Fincham, 1997: 230).

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TABLE 1 Xenothrix mcgregori: Cranial Remains

Preliminary notes on some of these spec- MacPhee and Fleagle (1991) concluded that imens have already been published (Horovitz the femora were of the wrong size and shape et al., 1997; MacPhee, 1997; MacPhee and to belong to Xenothrix, for which they had a Horovitz, 2002). The purpose of this paper better candidate. Since then no additional is to synthesize and extend these descriptions fossils attributable to the taxon represented and to respond to a recent reevaluation of the by the Coco Ree and Sheep Pen femora have phylogenetic position of Xenothrix and its al- been recognized, and its af®nities remain lies. Descriptions of the new postcranial moot (but see also MacPhee and Flemming, ®nds, which amplify and corroborate conclu- 2003). sions previously reached by MacPhee and Rosenberger (e.g., 1977, 2002; Rosenber- Fleagle (1991), will be presented elsewhere. ger et al., 1990) has argued on a number of The varied opinions regarding the phylo- occasions that the Jamaican monkey is phy- genetic af®nities of Xenothrix mcgregori and letically closest to titi monkeys (Callicebus) its relatives have been summarized on sev- among living platyrrhines. In modern sys- eral occasions (e.g., Rosenberger, 1977; tematic treatments titis are usually placed Ford, 1986a, 1990; MacPhee, 1996; Horov- close to sakis and uakaris in Pitheciidae.4 Ro- itz, 1999; Horovitz and MacPhee, 1999; senberger (e.g., 1977) has also remarked on MacPhee and Horovitz, 2002). Williams and certain resemblances between Xenothrix and Koopman (1952) classi®ed the Jamaican other platyrrhines (particularly Aotus), al- monkey rather vaguely as ``cebid incertae though until recently without drawing any sedis'', essentially equivalent to ``non-calli- particular phylogenetic implications there- trichid platyrrhine'' in their systematics. from. Features originally cited by Rosenber- Hershkovitz (1977) thought that Xenothrix ger (1977; Rosenberger et al., 1990) in favor was not very closely related to any existing of an association between Xenothrix and Pi- lineage and placed it in its own family, Xen- theciidae (in our sense) include: presence of otrichidae, a solution brie¯y endorsed by an offset entoconid and a posttalonid exten- MacPhee and Fleagle (1991). Ford (1986a, sion, together with low cusp relief, short cris- 1986b, 1990) has remained persistently ag- tid obliqua, and differentiated postprotocris- nostic about the position of Xenothrix, al- tid. In favor of a speci®c association with though she regarded it as possibly cebid in Callicebus are: small canine socket, posteri- af®nity. More radically, she theorized on oth- orly broadening premolar alveoli, parabolic er grounds that the Greater Antilles had been dental arcade, and jaw that markedly deepens colonized by callitrichines as well, basing her argument on a relatively large primate tibia 4 In this paper Pitheciinae (saki and uakari monkeys: from SamanaÂ Bay, western Hispaniola (now Pithecia, Chiropotes, and Cacajao) and Callicebinae (titi included within the hypodigm of Antillothrix monkey: Callicebus) are grouped as family Pitheciidae, bernensis by MacPhee et al. [1995]) and un- superfamily Ateloidea. Although there is some overlap in body size among pitheciid taxa, species of Chiropotes usual femoral specimens from the sites of and Cacajao can be considered ``large-bodied''; those of Coco Ree Cave and Sheep Pen, central Ja- Pithecia are ``mid-sized'', and those of Callicebus maica (Ford and Morgan, 1986, 1988). ``small-bodied''.

posteriorly. Rosenberger also correctly in- be part of such a group because it is ``a howl- ferred from the morphology and wear of the er relative, based on a comprehensive series ecto¯exid that Xenothrix must have had a rel- of derived cranial features seen nowhere else atively well developed paracone and meta- but in Alouatta, in spite of differences in den- cone, as in Callicebus (see Description of tal anatomy''. In Rosenberger's assessment, New Specimens, Cranial Remains). As to the Antillean monkeys must have originated callitrichid hypothesis, Rosenberger (1977; from at least two different sources within Rosenberger et al., 1990) argued that the loss Platyrrhini (Antillothrix was not explicitly re- of the last molar was an independent event viewed). Consequently, the MacPhee-Horov- in callitrichines and Xenothrix because their itz Antillean clade must be judged para- or dental proportions and morphology other- polyphyletic, depending on how one chooses wise differ markedly. We agree, but on the to redistribute its contents. basis of tree topology and parsimony (Ho- The only way to test phylogenetic hypoth- rovitz and MacPhee, 1999) rather than on eses meaningfully is with character evidence. those differences per se. Since no new material of Antillothrix or Par- Recently, Rosenberger (2002: 157) has al- alouatta has been reported since our latest tered his views somewhat and now holds that reviews of these taxa (MacPhee et al., 1995; ``Xenothrix is a Jamaican owl monkey most Horovitz and MacPhee, 1999), and since Ro- closely related to Aotus and Tremacebus, senberger (2002) did not otherwise identify which I believe are sister taxa to the Calli- the ``comprehensive series of derived fea- cebus lineage''. From the standpoint of Ro- tures'' that challenges our concept of the senberger's original hypothesis concerning proper placement of Paralouatta, as far as the relationships of Xenothrix, this is not a these taxa are concerned there is little to test radical departure. While sister-group rela- that is novel. The new craniodental material tionships have been rearranged, all men- described here, however, offers precisely tioned taxa (including Aotus) are considered such an opportunity for reassessing the po- by Rosenberger to be pitheciids or pitheciid sition of Xenothrix, using the tools that are collaterals. Rosenberger's (2002: 157) asser- most appropriate for this purpose: detailed tion concerning the position of Xenothrix is description, character de®nition, and parsi- based chie¯y on his assessment of two char- mony analysis (see Phylogenetic Analysis acters, orbital enlargement and central incisor and appendices 1±3). hypertrophy. These features are considered to be of great signi®cance because ``[e]nlarged ABBREVIATIONS orbits and eyeballs are the [emphasis in orig- ANATOMICAL inal] fundamental adaptive breakthrough of owl monkeys.... [T]he inferred size of I1 a., aa. artery (arteries) . . . may be linked with how a taxon exploits AD apical depth (of tooth root alveolus), an adaptive zone. In the Aotus lineage these measured from alveolar apex to or- i®ce involve harvesting adaptations ...''. Guid- AIOF anterolateral section of IOF ance in making phylogenetic assessments in art. articular this case is offered in the form of a proba- BL buccolingual(ly) bility statement: ``we must weigh the likeli- C/c maxillary/mandibular canine (ϩ hood that two regionally grouped taxa shar- conventional locus number) ing unique morphological patterns with other can. canal adaptively specialized platyrrhines living cav. cavity elsewhere are anything but their cousins''. chi. chiasma Rosenberger (2002: 159) also contested choan. choana, -ae our larger conclusion (Horovitz and Mac- coron. coronoid cran. cranial Phee, 1999; MacPhee and Horovitz, 2002) ETH ethmoid bone that the three known Antillean monkeys fac. facial (Xenothrix, Paralouatta, and Antillothrix) ϩ ®s. ®ssure Callicebus form a monophyletic group, ar- for. foramen guing in particular that Paralouatta cannot fos. fossa

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FRO frontal bone AMNHM Division of Vertebrate Zoology gen. geniohyal/genioglossal mm. (Mammalogy), American Muse- gr, grt. great, greater um of Natural History I1/i1 maxillary/mandibular incisor (ϩ BP radiocarbon years before ``pre- conventional locus number) sent'' (i.e., radiocarbon datum, inc. incisor, incisive A.D. 1950) inf. inferior, infra ch. character innom. innominatum, innominate CI consistency index IOF inferior orbital ®ssure LACM Natural History Museum of Los LAC lacrimal bone Angeles County lac. lacrimal ln natural logarithm less. lesser Ma millions of years (ago) M/m maxillary/mandibular molar (ϩ con- MNHNCu Museo Nacional de Historia Nat- ventional locus number) ural, La Habana, Cuba m., mm. muscle, muscles MPT(s) most parsimonious tree(s) mand. mandibular N sample size MAX maxillary bone POD proxy eyeball diameter max. maxillary RC rescaled consistency index MD mesiodistal(ly) RI retention index meas. measurement TBR tree bisection-reconnection med. medial TL tree length n., nn. nerve, nerves nas. nasal LOCALITIES opt. optic, optical orb. orbit, orbital New fossils attributable to the Jamaican PAL palatine bone monkey have been discovered in a number palat. palatine of cave sites situated along the western end PAR parietal bone PIOF posteromedial section of IOF of Portland Ridge, southernmost Clarendon PM/pm maxillary/mandibular premolar (ϩ Parish (Fincham, 1997; ®gs. 1, 2). Paleoeco- conventional locus number) logical investigations of the caves in question postgl. postglenoid (Somerville, Drum, Skeleton, and Lloyd's pr. process Caves) have recently been conducted by preinc. preincisive McFarlane et al. (2002). As currently PTER pterygoid bone mapped (Fincham, 1997), the Jackson's Bay pter. pterygoid, pterygoidal caves consist of some 7000 m of passage- rot. rotundum ways located less than 40 m below the pre- sin. sinus sent surface. The so-called ``upper'' caves, sph. sphenoid, spheno- sphenpal. sphenopalatine which include the Xenothrix sites just men- SPH sphenoid bone tioned, are dry but contain a distinctive se- SQU squamosal bone quence of secondary deposits (see McFarlane surf. surface et al., 2002). sut. suture The environs of Portland Ridge support a temp. temporal low, xerophylic, sclerophyllous scrub vege- trans. transverse tation (®g. 2A). Regional precipitation aver- tub. tuberosity ages 1014 mm/year with a pronounced dry v., vv. vein, veins season of 6±10 months according to infor- VOM vomer bone mation compiled by McFarlane et al. (2002). w. wing ZYG zygomatic bone Although this is clearly a dry environment, zyg. zygomatic, zygomatico- some populations of Callicebus moloch and Aotus azarae are able to survive today at low densities in areas that are even more arid and INSTITUTIONAL AND OTHER seasonal than southern Jamaica, but always AMNH/CMC American Museum of Natural within high forest or more diverse habitat in History/Claremont-McKenna relation to permanent or ephemeral water- College joint expeditions ways (Stallings et al., 1989: 431). McFarlane

et al. (2002) presented various kinds of evi- not ``orbitosphenoid''), unless there is no ap- dence to support the conclusion that condi- propriate term in human anatomy. However, tions along this part of Jamaica's south coast numerical designations for premolar and mo- were rather more mesic between 16,500 BP lar loci follow the usual mammalogical con- and 700 BP, becoming drier thereafter. ventions.5 Finally, it should be noted that, to Archaeological remains are common in ensure good photographic results, the teeth Jackson's Bay caves, and include human of the fossil specimens were coated in order bones, cassava griddles, and petroglyphs (see to reduce irregularities in coloration due to Fincham, 1997). These remains are almost damage or soil pigments. always super®cial and are either unaffected or occasionally thinly veneered by calcite MANDIBULAR REMAINS sinter. Some of the Xenothrix fossils were Rosenberger's (1977) descriptions of the also found in completely super®cial settings, type jaw and its dentition are generally ex- but others were found buried or encrusted cellent, and in this section we con®ne our- with matrix, suggesting that this primate en- selves mostly to describing features not rep- joyed a lengthy tenure in southern Jamaica. resented on the type. McFarlane et al. (2002) attempted to use 14C dates on gastropod shells and bat guano to Two left mandibular fragments (AMNHM establish proxy chronologies for the Jack- 268001, 268004; ®gs. 3±6; table 1) were dis- son's Bay area during the late Quaternary. covered in the course of excavations in 1995 Although none of their dates is directly based in the Map Room, a small chamber within on the platyrrhine fossils, it is reasonable to Skeleton Cave (®g. 1; Fincham, 1997: 333). conclude that most or all of the bones come On entry the Map Room was found to be 1 m of dry silts and clays, as from contexts that are latest Pleistocene or ®lled with Ͼ well as a considerable amount of breakdown Holocene (possibly even mid- to late Holo- and localized areas of induration. Soft sedi- cene). It should be noted, however, that the ments were taken by bucket into the main uncorrected age estimate of 6730 Ϯ 110 BP, quoted by McFarlane et al. (2002) for gas- chamber for screening; excavation continued tropod shell from the ``Xenothrix level'' at in the rear of the cave until the slope of the Skeleton Cave, does not date either of the roof and sediment induration prevented fur- jaws from this site, even by association, be- ther work. Coney and bat bones were recov- cause the cave's ®ll appears to have been cat- ered in abundance, but the monkey mandi- astrophically emplaced. bles were the only vertebrate fossils of major Other organic remains (including bones of paleontological signi®cance recovered at this birds, lizards, snakes, bats, and the endemic site. Although incomplete, AMNHM 268001 capromyid rodent or coney, Geocapromys and 268004 preserve certain structures lost brownii) were also sampled. These are or damaged on the holotype and therefore housed in uncataloged faunal collections at add substantially to our knowledge of Xen- the AMNH and are available for study by othrix mandibular anatomy. Both jaws rep- interested specialists. resent adult animals. The new fossils con®rm that, in the intact state, the jaw of Xenothrix would have re- DESCRIPTION OF NEW SPECIMENS sembled that of living pitheciids (and to a In this and following sections, we make lesser degree, atelids and Aotus) in exhibiting continuing reference to the ``comparative set'' of taxa selected for this paper (Aotus, 5 The ®rst and second molars of Xenothrix are usually homologized with the ®rst and second molars of other Callicebus, Pithecia, Chiropotes, Cacajao), platyrrhines, although in the absence of ontogenetic data relevant features of which are illustrated in on dental development in the Jamaican monkey this in- ®gures 7±8 and 12±16. For the list of modern ference is speculative. Similarly, although we use the specimens utilized in this study, see appendix convention pm/PM2±4 to refer, respectively, to anterior, middle, and posterior premolars, there is no decisive ev- 3. English equivalents of anatomical names idence regarding which of the four premolar loci of the accepted by Nomina anatomica are preferred primitive primate dentition is the one that has been lost throughout (thus ``lesser wing of sphenoid'', in platyrrhines.

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Fig. 3. Mandibular fossils of Xenothrix mcgregori, occlusal views and locality of recovery: (A) AMNHM 148198 (holotype), Long Mile Cave (Trelawny Parish); (B) AMNHM 268001, Skeleton Cave (Jackson's Bay, Clarendon Parish); and (C) AMNHM 268004, Skeleton Cave (Jackson's Bay, Clarendon Parish). Teeth in new specimens are poorly preserved due to desiccation cracking. All to scale in panel A.

a very broad ascending ramus hafted onto an likely con®gurations of the reconstructed anteriorly tapering corpus (``posteriorly horizontal rami yield a jaw with subparallel deepening'' mandible as de®ned by Rosen- cheektooth rows. With no canines or incisors berger, 1977; cf. ®gs. 7, 8). Furthermore, the to help establish a silhouette, it is dif®cult to large size of the individual teeth and short determine the likely appearance of the ante- absolute length of the dental battery in Xen- rior toothrow. However, there can be no othrix would have given its mandible a ros- question that the individual members of the trally abbreviated or foreshortened appear- row were relatively narrow-crowned (see ance, rather as in extant Chiropotes and Ca- Discussion). cajao (®g. 8D). Average toothrow length in the two jaws that can be measured for this CORPUS AND RAMUS feature is 28.9 mmÐessentially identical to extant Pithecia and Chiropotes, despite the AMNHM 268001 (®gs. 3B, 4B, 5B) con- fact that these latter taxa retain the third mo- sists of the left ascending ramus and body as lar. well as both sides of the symphyseal region. Reconstructions of the mandible of Xen- The entire inferior edge of the mandible has othrix in occlusal and left lateral views are spalled off except for a small area close to depicted in ®gure 6A and B. Because each the symphysis. Although the posterior border fossil jaw possesses some anatomical details of the ramus is missing from condyle to an- that the others lack, it is possible to recon- gle, as a whole this part of the mandible is struct, within limits, essentially all of the cor- better preserved than it is in the type speci- pus and ramus except for the coronoid pro- men (®gs. 3A, 4A, 5A). The lateral surface cess and the condylar and gonial areas. All of the ramus bears a shallow triangular fossa,

Fig. 4. Mandibular fossils of Xenothrix mcgregori, medial views (see ®g. 3 for details): (A) AMNHM 148198 (holotype), (B) AMNHM 268001, and (C) AMNHM 268004. Orientation based on position of jaws as seen in pitheciid skulls placed in Frankfurt plane. *, recently attached fragment of inferior border of type mandible (see text). **, small section of mandibular notch preserved in AMNHM 268001. All to scale in panel C.

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Fig. 5. Mandibular fossils of Xenothrix mcgregori, lateral views (see ®g. 3 for details): (A) AMNHM 148198 (holotype), (B) AMNHM 268001, and (C) AMNHM 268004. All to scale in panel C.

available, and the reconstruction (®g. 6B) is noncommittal. On the medial side of the ramus, behind the last molar, is a large and very excavated mandibular foramen (not ``mylohyoid foramen'' of Rosenberger [1977: 470], a lapsus). Above the foramen a thick pillar of bone runs from the body of the mandible backward and slightly upward. In the intact state this pillar would have ter- minated as the neck of the condyle. Remarkably, a tiny piece of cortical bone de®ning the inferior margin of the mandibular notch is still preserved (double asterisk, ®g. 4B). This is of some interest because it gives a qualitative idea of the length of the mandibular load arm, assuming that the mandibular condyle of Xenothrix resembled that of other platyrrhines (i.e., in norma lateralis, superior surface of condyle situated only slightly higher than inferiormost point on mandibular notch). If this inference is correct, the effective length of the ramus (occlusal plane to condyle) in Xenothrix would have been rather short, as in larger-bodied pitheciids (®g. 8B±D). As is typical for platyrrhines other than Paralouatta, the symphyseal region slopes sharply away beneath the incisor sockets and there is no mental eminence. By contrast, on the oral side there is a strong retromental but- tress, underneath which are two deep pits for genioglossus/geniohyoid mm. As in the type, the mental foramen is located at the level of pm3. Because the canine was unquestionably small (see Dentition), the apical end of its Fig. 6. Composite reconstructions of the man- alveolus does not swell the symphyseal pla- dible of Xenothrix mcgregori:(A) occlusal view, num laterally nor interrupt the smooth line of based on AMNHM 148198 (proper and mirror images); and (B) left lateral view, based on the the inferior margin of the horizontal ramus, three available jaws (AMNHM 148198, 268001, as it does in all extant noncallitrichines ex- and 268004) and oriented approximately in recon- cept Aotus and Callicebus (which likewise structed norma lateralis (Frankfurt plane). Dashed have small canines). lines indicate features and borders still unknown. The second mandible from Skeleton Cave, Cf. ®gures 7 and 8. AMNH 268004 (®gs. 3C, 4C, 5C), consists of a small section of the corpus preserving both molars. Although the specimen as a presumably for the insertion of part of the whole is severely damaged, the inferior edge super®cial masseter m. (area not represented of the mandible beneath the cheekteeth is on type jaw). This fossa is continued upward well preserved, giving a much ®rmer idea of onto the broken root of the coronoid process, the contour of this border than previously which, judging from what remains, must known. This specimen shows that the inferior have been quite large. Whether the coronoid border of the mandible in Xenothrix was con- ended as a spike or was strongly recurved spicuously in¯ected medially, as in many cannot be determined from the material other platyrrhines (including Callicebus and

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Fig. 7. Mandibles of comparative set, occlusal view: (A) Aotus azarae AMNHM 211463, (B) Cal- licebus cupreus AMNHM 34636, (C) Pithecia pithecia AMNHM 94133, and (D) Cacajao calvus AMNHM 73720.

Pithecia). Large ridges de®ne the limit of an men, making it dif®cult to quantify the extensive, multicompartmental fossa in the amount of gonial ¯are. Rosenberger (1977: gonial region for the insertion of fascicles of 468, ®g. 3) attempted to design a mandibular the medial pterygoid m. (area not represented pro®le index, but noted that because the in- on type jaw because of breakage). ferior border of the Xenothrix type specimen Although it is clear that the jaw of Xen- was completely broken away, only ``a mini- othrix exhibited a deep gonial region, very mal estimate'' could be made. Thanks to the little of this area remains on any one speci- recent discovery of a small piece of the

Fig. 8. Mandibles of comparative set, left lateral view: (A) Aotus azarae AMNHM 211463, (B) Callicebus cupreus AMNHM 34636, (C) Pithecia pithecia AMNHM 94133, and (D) Cacajao calvus AMNHM 73720. Specimens approximately oriented to modi®ed Frankfurt plane.

type's inferior border (single asterisk, ®g. than, that of Callicebus and Lagothrix.By 4A), found during recuration of H.E. An- contrast, according to our results, Xenothrix thony's 1920 faunal collection from Long places closer to midsized pitheciids than to Mile Cave, it is now possible to gain a better Callicebus for this feature. From this we con- (if still imperfect) idea of gonial ¯are in the clude that Xenothrix possessed posterior Jamaican monkey. Although the area of the deepening, but not in the exaggerated form jaw's maximum ¯are is probably not repre- seen in the titi monkey or woolly spider sented, enough remains to allow the taking monkey (or, for that matter, Aotus). Some of the two measurements (symphyseal height published photographs of the type jaw (e.g., and modi®ed gonial height) presented in ta- Rosenberger, 1977: pl. 2A) make it seem as ble 2. These measurements are not identical though Xenothrix possessed a greatly deep- to Rosenberger's (1977), as we had dif®culty ened gonial region, but this is due to misori- in ascertaining the position of ``minimum entation of the specimen (symphyseal end depth'' according to his criteria. Neverthe- raised excessively, thereby overemphasizing less, except in one crucial area our results are the degree of posterior deepening). in broad agreement. According to Rosenber- ger's (1977) measurements, Xenothrix would DENTITION have expressed a degree of posterior deep- The teeth remaining in the new mandibles ening comparable to, if not more extreme are not in good condition, most having lost

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TABLE 2 Xenothrix mcgregori and Comparative Set: Symphyseal Height and Gonial Height (in mm)

signi®cant sections of their crowns (®gs. 3± AMNHM 268001 preserves on the left 5). They are also extensively worn, both oc- side parts of pm3±m2 and sockets for i1± clusally and interproximally, indicating that pm2 (®gs. 3B, 4B, 5B). On the right side, the new jaws came from animals that were sockets (but no teeth) are partially preserved ontogenetically somewhat older than the one for i1±pm1. AMNHM 268004 retains only represented by the holotype (the molars of the two left molars and the distal wall of the which show virtually no wear). Although left pm4 socket (®gs. 3C, 4C, 5C). A notice- dental measurements for these specimens are able gap, not present in the holotype, exists provided in tables 3 and 4, most should be between the distal margin of the m2 and the regarded as minimum estimates due to break- edge of the ascending ramus in both age and loss of material. AMNHM 268001 and 268004. To con®rm

TABLE 3 Xenothrix mcgregori and Comparative Set: Toothrow Length (TRL) (in mm)a

TABLE 4 TABLE 5 Xenothrix mcgregori: Callicebus and Cacajao: Dental Measurements (in mm)a Comparative Dental Measurements (in mm)a

that this gap is not due to the presence of an have remained stable or to have increased unerupted m3, AMNHM 268001 was radio- [compared to the primitive condition], the graphed. No evidence of a crypt was found absolute number of components notwith- (cf. Williams and Koopman, 1952), and we standing.'' conclude that the difference between jaws in The molars of Xenothrix mcgregori and this respect is probably due to intraspeci®c Cebus apella are also similar in size (cf. variation or is a function of age. Swindler, 2002). However, despite evident Despite damage to the molars, it is obvi- bunodonty in Xenothrix, its crown enamel is ous that their occlusal surfaces were com- not relatively thickened (L. Martin, personal paratively large. The few linear measure- commun.), in contrast to C. apella in which ments that can be taken indicate that the oc- extremely thick enamel apparently facilitates clusal area (BL ϫ MD) of each molar is the mastication of palm nuts and other very more than two times the size of individual hard foods. It is tempting to speculate that m1s and m2s of Callicebus (table 5). Fur- Xenothrix may have been chie¯y a ``seed thermore, summed m1±m2 occlusal area predator'' in the manner of the large living (based on mean dimensions) in Xenothrix is pitheciines (Kinzey, 1992), although we can- 54.2 mm2, which is effectively identical to not offer any morphological support for this the average for the entire molar row in a argument at present. Even within Pitheciinae, sample (N ϭ 3) of Cacajao (52.7 mm2; see a morphologically homogeneous group, there also table 5). This comparison is of some in- is some dietary plasticity with regard to the terest, inasmuch as Xenothrix was probably intake of ripe fruits, leaves, and insects, similar to uakaris in body size (see Discus- which should make one cautious about inter- sion). This ®nding supports Rosenberger's preting the fossil monkey's preferences too (1977: 474) contention that ``in Xenothrix the narrowly. total relative length of the molars appears to The middle and posterior premolar crowns

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TABLE 6 bulbous than the teeth on either side of it, Xenothrix mcgregori: Measurements of but it probably did not project above them to Anterior Premolar and Canine Alveoli (in mm) any signi®cant extent. None of the mandibular incisors is preserved, but the close packing and parallel walls of their highly compressed alveoli suggest relatively narrow crowns (see Discus- sion). In the available specimens, incisor alveoli are too incomplete to determine whether the roots of the centrals were larger than those of the laterals. In Pitheciidae generally (including Callicebus), lateral incisor crowns are appreciably larger than those of the centrals, but roots are only slightly larger. In Aotus, laterals are subequal to very slightly larger than centrals for both features. Wheth- er lower incisor crowns were relatively ``heightened'' (a diagnostic feature of Pithe- ciinae originally noted by Kinzey [1992]) are also large and stoutly built. As Rosen- cannot be decided in the absence of the teeth berger (1977) noted, BL widths of the molars themselves. of Xenothrix are broad compared to those of extant platyrrhines. This also applies to the CRANIAL REMAINS premolars: for example, the broken left pm4 of AMNHM 268001 has a BL width of ϳ5.2 Complementing the new jaws are two cra- mm, as compared to a mean of 4.4 mm for nial specimens recovered in a side chamber the homologous tooth in the Cacajao sample (Xenothrix Hall) opening from Mantrap Pit, (tables 4, 5). The condition of the anterior Lloyd's Cave (®gs. 1, 2). Both specimens premolar has to be inferred from alveolar were found in cave-¯oor surface debris dur- measurements (table 6), as the tooth is not ing ®eldwork conducted in September 1996. preserved in any specimen. Interestingly, the Unlike the mandibular specimens, which dis- right pm2 alveolus in AMNHM 268001 play desiccation cracks and pigment uptake seems to be unusually shallow (?anomalous consistent with lengthy burial, the cranial retention of deciduous tooth), although so lit- specimens appear similar in apparent fresh- tle is left of this feature that it is hard to be ness to the numerous remains of goats and certain (®g. 4B). In any case, no crypt for an other domestic animals which litter the ¯oor unerupted successor is in evidence. The left of this and other Portland Ridge caves. Lack pm2 alveolus appears normal (®g. 5B). In of staining is consistent with the possibility larger pitheciines the equivalent of the curve that the skull remains from this site are not of Spee is quite pronounced, the premolars particularly old. showing a steady forward increase in crown AMNHM 268006 is a partial face preserv- height (®g. 7C, D). In Callicebus and prob- ing the lower parts of the orbits and nasal ably also Xenothrix the curve is ¯atter, in complex, together with the entire palate and keeping with the imputed small size of the PM4±M2 on both sides (®gs. 9, 10). canine (cf. ®gs. 6B and 7B). AMNHM 268007 consists of a left maxillary Although the condition of the c1 in Xen- fragment only, retaining PM3±M2 still in po- othrix is not known, because there are no os- sition and the alveolus of PM2 (®g. 11). Di- teological indications of diastemata in the rect comparison of these specimens with available jaws we agree with Rosenberger skulls of other platyrrhines indicates that, that it seems unlikely that the c1 crown could contra Rosenberger (1977: 475), skull size in have ¯ared either mesially or distally to any Xenothrix is signi®cantly larger than in Aotus important degree. Our reconstruction (®g. or Callicebus (see below). 6B) suggests that c1 may have been more Not unexpectedly, the new material con-

Fig. 9A. Xenothrix mcgregori AMNHM 268006, partial face and palate (Lloyd's Cave, Clarendon Parish). Stereopair views (with keys) on this and following pages: (A) ventral (occlusal), (B) dorsal, (C) rostral, (D) caudal, and (E) right lateral. *, aperture in presphenoid (?natural); **, anterior portion of zygomaticomaxillary suture; ***, groove marking the anterior end of the infraorbital ®ssure; ****, eminence marking the medial border of the optic canal. All to scale in panel A.

®rms that only two molar loci occur in the FACIAL SKELETON AND ORBITS maxillary dentition of Xenothrix mcgregori, As preserved, AMNHM 268006 is reason- whose dental formula (2/2 1/1 3/3 2/2) is ably intact (®gs. 9, 10; table 6): the alveolar unique within noncallitrichine Anthropoidea. process of the maxilla and palate are com-

Fig. 9B.

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Fig. 9A Continued.

plete except for minor abrasions, and sub- idently broken away some time ago, as no stantial portions of the sphenoid, palatines, fresh breaks can be seen in the relevant areas. vomer, lacrimal, and interorbital septum re- Morphological evaluations of the midfa- main. Other parts of the face, including the cial, nasal, and palatal regions are provided upper orbits and most of the orbital ¯oors, in subsequent sections of this paper. It is un- zygomatics, and upper nasal cavity were ev- fortunate that so little is left of the orbital

Fig. 9B Continued.

Fig. 9C.

skeleton in AMNHM 268006, since the plau- extant pitheciids, which may display excep- sibility of Rosenberger's Aotus hypothesis tional protrusion of the premaxillae and in- largely turns on his interpretation of its mor- cisor row (Hershkovitz, 1977; Rosenberger, phology. Features connected with the eye 1992). The partial face of Xenothrix (®g. 9B, and orbit of Xenothrix are reserved for sep- E) can only be roughly aligned along the arate treatment (see Discussion). Frankfurt plane, but its degree of midfacial MIDFACIAL REGION: The midfacial region prominence is clearly greater than that of is a relatively smooth, undulating surface be- Aotus. tween the inferior rims of the orbits and max- The canine fossa, a feature found in most illary alveolar process (®g. 9C). The infra- noncallitrichines and all pitheciids except nasal planumÐthe zone on the premaxillae Callicebus (in which it is indistinct), is ab- below the nasal sillÐvaries greatly in mor- sent or barely indicated in Xenothrix. The in- phology among platyrrhines, especially in re- distinct/absent condition is obviously corre- gard to prognathism. This can best be appre- lated with the small size of the canine root ciated by viewing skulls in norma dorsalis (in (see Dentition). Double infraorbital foramina modi®ed Frankfurt plane, as de®ned in ap- occur bilaterally in AMNHM 268006 (®g. pendix 1, ch. 85). Seen from above, midfa- 9C); the more posterior of the two is larger cial prognathism in Aotus (®g. 12E) is no- and situated vertically above the PM3 alve- tably less than that of any other member of olus. Multiple infraorbital foramina are the comparative set (®g. 12F±H). Callicebus found in many species of New World mon- (®g. 12F) is less prognathic than the other keys, and foraminal number can vary be-

Fig. 9D.

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lary fragment of Antillothrix does not retain the arch; cf. MacPhee and Horovitz [2002].) A complication in scoring this character is that in some large males of Pithecia and Ca- cajao the origin of masseter m. (which springs from the lowest point on the zygomatic arch) is hypertrophied into a down- wardly projecting crest, thus mimicking to some degree the condition in platyrrhines with depressed arches (®g. 13D). However, with careful inspection these conditions can be distinguished. Fig. 9C Continued. In AMNHM 268006 the relatively dorsal position of the suture between the zygomatic bone and the anterior part of the maxillary tween and even within individuals (Hersh- root of the zygomatic arch indicates that the kovitz, 1977). former's contribution to the lateral orbital New World monkeys display differences wall was less extensive than in some extant in the vertical positioning of the maxillary pitheciids, but much more so than in Aotus. root of the zygomatic arch. In some, includ- It is critical to note that a small portion of ing living pitheciids and atelids, the zygo- the orbital wing of the zygomatic bone is matic arches have a high root, whereas in preserved on the right side of this specimen others (e.g., Callicebus, Cebupithecia, Par- (®g. 9B, E). Equally important is the small alouatta, Aotus) the root is much lower. notch that de®nes the posterior edge of this Among living platyrrhines, Aotus (®g. 14A) process (triple asterisk, ®g. 9D), as it repre- and Callicebus (®g. 14B) show an extreme sents the anterior limit of the inferior orbital condition in which the lowest part of the zy- ®ssure (IOF). The conformation of this area gomatic arch extends below the horizontal indicates that this part of the ®ssure could not level of the alveolar process in norma later- have been widely dehiscent, as it is in Aotus, alis. In Callicebus the arch actually extends but instead resembled that of most New to a level below the occlusal plane of M3 World monkeys. We reserve further remarks (®g. 14B). In Xenothrix a less extreme con- on these matters until the Discussion, as they dition is seen, in which the lowest point on bear on orbital size in Xenothrix and alleged the arch extends slightly below the level of resemblances to conditions in Aotus. the M2 alveolar margin. In the photographs A small groove on the upper, broken side this feature is best seen in ®gure 9E. (This of the maxillary root near the track of the feature is not complete enough in Paral- zygomaticofacial suture (double asterisk, ®g. ouatta to permit evaluation, and the maxil- 9B) may mark the track of the zygomaticofacial nerve and accompanying vasculature. The zygomaticofacial foramen, which pene- trates the body of the orbital surface of the zygomatic, is sometimes large in platyrrhines (e.g., Callicebus) and is often multiple. Zy- gomaticotemporal foramina (regarded here as equivalent to ``lateral orbital ®ssure'' of Hershkovitz, 1977) typically occur high on the lateral orbital wall and are not preserved in the Xenothrix material. NASAL CAVITY AND PARANASAL SINUSES:In Xenothrix the nasal aperture was apparently wide in comparison to the breadth of the face, as in pitheciids generally. Because the Fig. 9D Continued. nasals and most of the nasal processes of the

Fig. 9E.

maxillae are missing (®g. 9B, C), it is not breaks in AMNHM 268006, it can be seen possible to reconstruct in detail the shape of that air spaces deeply invade the base of the this opening when the skull was intact. How- zygomatic arch and the body of the maxillae, ever, indications are that it was probably di- thereby in¯ating much of the lateral part of amond shaped with a notched upper margin the lower face (®gs. 9B, 10). Even the ana- (as in most extant pitheciines) rather than tri- tomical nasal cavity is relatively widened: angular with a broad, straight upper margin Xenothrix and also Paralouatta seem to be (as in Pithecia speci®cally). unique among known platyrrhines (including The skull of Xenothrix was evidently high- Alouatta) in having nasal cavity ¯oors that ly pneumatized, although existing fossils are are posteriorly wider than the distance be- not well enough preserved to give a complete tween the lingual walls of the left and right picture of the degree of in¯ation in the upper M1s. More anteriorly, the rim of the inferior face and central stem. Thanks to fortuitous meatus intersects a parasagittal plane that lies

Fig. 10. Xenothrix mcgregori AMNHM 268006, partial face and palate (Lloyd's Cave, Clarendon Parish). Stereopair, oblique left lateral view, to show pneumatization of nasal ¯oor and zygomatic process of maxilla. *, grooves for optic nerve (position of optic chiasma). Same scale as ®gure 9.

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The maxillary tuberosity of the maxilla, the area posterior and superior to the last molar locus, is at least marginally in¯ated by the maxillary sinus in all platyrrhines (Hersh- kovitz, 1977). In Xenothrix, the degree of in¯ation is notable, in keeping with the pneumatization of the rest of the paranasal complex (®gs. 9B, 10). Pitheciids as a group (including Callicebus) display well pneumatized maxillary tuberosities (®g. 16B±D). In Aotus (®g. 16A), by contrast, this area is ¯at- tened and the interior is spongiform or only slightly pneumatized by very small cellules (as opposed to the large chambers in pitheciids and Xenothrix as well as many other platyrrhines). It is worth remarking in this context that the maxillary sinus of the Mio- Fig. 9E Continued. cene Patagonian species Tremacebus harringtoni has been described as being both external (buccal) to the canine alveolus, an- ``poorly developed'' and ``as in Aotus'' by other evocation of the same unique feature. Fleagle and Rosenberger (1983: 144) as well The maxillary paranasal sinuses seem to as ``probably . . . large, more like Xenothrix have been single, very large spaces with little perhaps'' by Rosenberger (2002: 157). In or no subdivision. Mental reconstruction of view of the comparative size of the maxillary their volume suggests that together they excavations in Aotus and Xenothrix,asde- would have enclosed a space larger than the tailed here, these statements must be regard- anatomical nasal cavity per se. Cheektooth ed as mutually contradictory. roots can be seen emerging within the lateral PALATE AND ADJACENT REGIONS: The max- parts of the sinuses in both cranial fossils illary dental arcade of Xenothrix may be de- (®gs. 9B, 11A) as far as the coronal plane of scribed as roughly U-shaped (®g. 9A), as in PM3. In AMNHM 268007, the bone tissue Aotus (®g. 12A), Callicebus (®g. 12B), Sai- draping cheektooth roots is even more ex- miri, and most other noncallitrichine platyr- cavated than in AMNHM 268006, suggest- rhines. The maxillae are in contact along the ing that in the former individual sinus de- palatal midline up to the level of the last pre- velopment was very marked. molar, at which point the palatine bones are interposed. A large greater palatine foramen perforates each leg of the palatomaxillary suture, which is shaped like an inverted V. The palatal surfaces of the premaxillomaxillary sutures have been completely resorbed, although externally a remnant of the midline suture between the right and left premaxillae (premaxillopremaxillary suture) is still in evidence (®g. 9B). Palatal length (prosthion± staphylion) is 28.4 mm, compared to 19.5 mm in Callicebus (N ϭ 3) and 31.0 mm in Cacajao (N ϭ 3). The incisive fossa and incisive foramina together form one large, undivided hole due to the loss of the delicate spines that generally subdivide these apertures in platyrrhines (®g. 9B). Nevertheless, the large size of both Fig. 10. Continued. the nasal cavity and the incisive ``foramen''

1980), hypertrophy of these features in Xen- othrix is a distinct possibility. Two rather large preincisive foramina pen- etrate the remnant premaxillopremaxillary suture (®g. 9A±C). They may have carried an anastomotic link between the superior la- bial a. (of the facial a.) and the greater palatine a. (of the maxillary a.). Foramina in this position seem to be common in platyrrhines, although to our knowledge their homologies have not been addressed. Because of breakage, the central part of the sphenoid complex of AMNHM 268006 has been reduced to a narrow cube consisting of the body of the presphenoid and portions of the orbital surfaces (plates) of the sphenoidal greater wings (®g. 9B, E). The orbital plates are separated by two large sphenoidal sinuses (®g. 9C), divided by a septum that would have originally connected with the superior meatus of the nasal cavity. The septum is in turn continuous inferiorly with the blade of the vomer. It is doubtful that any part of the ethmoid is still present on this specimen. Although the optic canal is not preserved as such on either side, its position can be readily located by reference to the sella turcica, optic chiasma, and a small eminence on the sphenoidal orbital plate that acted as the canal's medial wall (®g. 9E). Reconstructing the position of the optic canal is helpful in trying to estimate orbital depth (see ®g. 15 and Dis- cussion). Caudally, a large aperture opens onto the presphenoid's synchondral surface (at the Fig. 11. Xenothrix mcgregori AMNHM presphenoid±basisphenoid synchondrosis) 268007, cast of partial left maxilla (Lloyd's Cave, and communicates with the sphenoidal si- Clarendon Parish): (A) dorsal, (B) lateral, and (C) nuses (®g. 9A, D). There are several other ventral (occlusal) views. All to scale in panel A. holes in the body of the presphenoid of AMNHM 268006, but these are de®nitely ar- tifacts. If the aperture in the synchondral surface is real, its existence indicates that para- in Xenothrix may be structurally and func- nasal pneumatization extended into the cor- tionally linked. In living mammals, the in- pus of the basisphenoid. cisive foramina give passage to the nasopal- Two canals can be detected in the trian- atine duct and its associated cartilage. The gular slot that represents one wall of the orig- duct connects the oral cavity with the vom- inal pterygopalatine fossa (®gs. 9D, 10). The eronasal organ (Jacobson's organ), which larger, the sphenopalatine foramen, passes contains specialized sensory cells related to anteriorly through the lateral wall of the na- the ®rst cranial (olfactory) nerve. Since the sal cavity. It would have accommodated the cartilages of the nasal ¯oor are highly de- sphenopalatine a. and the superior nasal and veloped in all platyrrhine taxa and the vom- nasopalatine nn. The other canal passes in- eronasal organ is universally present (Maier, feriorly through the sidewalls of the choanae,

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Fig. 12. Skulls of comparative set in modi®ed Frankfurt plane (see text), ventral and dorsal views: (A, E) Aotus azarae AMNHM 211463, (B, F) Callicebus cupreus AMNHM 34636, (C, G) Pithecia pithecia AMNHM 94133, and (D, H) Cacajao calvus AMNHM 73720. In norma ventralis, interptery- goid region to level of basisphenoid±basioccipital synchondrosis also illustrated. Apparent degree of prognathism as seen in norma dorsalis should be compared to conditions in norma lateralis (®g. 14).

to terminate as noted above as the greater preventing contact between the posterior palatine foramen on the palate. As in Homo, parts of the palatine and the body of the pre- the canals run in part along the sutural con- sphenoid. Cebus and Alouatta are distinctive tact between the sphenoid and palatine in that the alae reach the position of the pter- bones. ygoid and thereby completely exclude ven- Part of the lacrimal area is preserved on tral palatopresphenoid contact. Conditions in the right side of the skull, in relation to the Xenothrix are ambiguous because of break- orbital rim of the nasal process of the maxilla age. (®g. 9C). Because neither the posterior lac- The pterygoid bones are not preserved, but rimal crest nor the related portion of the eth- each palatine bone terminates posteriorly in moid is preserved, the lumen of the osseous a distinct spine and sutural surface which canal of the nasolacrimal duct is exposed would have braced the pterygoid plates dur- (®g. 9B). In life the lacrimal groove, which ing life (®g. 9D). is only partly preserved, would have been entirely encased within the lacrimal bone. DENTITION The vomer is well preserved except along its anterior edge where it made contact with As in the case of the mandibles, the cranial the nasal septal cartilage (®g. 9C, E). In the fossils preserve only molars and some pre- comparative set, each ala vomeris extends molars (®gs. 9, 11). However, unlike the posteriorly as a thin sheath along the sides teeth in the jaws, the maxillary cheektooth of the presphenoid, variably restricting or crowns are beautifully preserved except in

Fig. 12. Continued.

one instance (right M1 of AMNHM 268006). are noteworthy: (1) Principal cusps and gen- Alveoli of missing teeth are also largely in- eral crown outlines are puf®er in Xenothrix. tact in AMNHM 268006, providing some (2) M1 of Xenothrix is very large and ex- idea of the relative sizes of the roots of the presses unusual development of buccal moi- anterior teeth. ety. (3) M2 is quite reduced, like M3 in liv- Like the mandibular cheekteeth, the max- ing pitheciids (Kinzey, 1992). (4) Premolars illary molars and premolars of Xenothrix are are very large and similar in BL and MD large and ovoid to quadrangular in outline. dimensions to those of Cacajao (tables 4, 5). Principal cusps are swollen, with puffed-out (5) PM4 is premolariform as in Callicebus, shoulders that obscure the presence of cris- not distinctly molariform as in pitheciines. tae. Buccal cingula are absent, and lingual (6) Roots of cheekteeth are strongly divari- cingula are inconspicuous or absent. In size cating, as in Cacajao and to a lesser degree and to some degree in shape the upper cheek- in other pitheciids. (7) Arrangement of prin- teeth of Xenothrix strongly resemble those of cipal cusps and other small-scale features is larger pitheciines (Chiropotes and Cacajao) very similar, except that whereas the cheek- rather than Callicebus. Indeed, in most met- teeth of Chiropotes and Cacajao wear into rical regards the cheekteeth of Xenothrix can what may be described as an aligned series be described as super®cially uakarilike (ta- of troughs, the main cusps and principal bles 4, 5), although of course there are dif- blades of Xenothrix tend to retain more def- ferences in detail. In comparison to Cacajao inition, as in Callicebus (®g. 12B) or Pithe- (®g. 12D) the following features of Xenothrix cia (®g. 12C). (8) Xenothrix is distinctively

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Fig. 13. Skulls of comparative set in modi®ed Frankfurt plane (see text), anterior view: (A) Aotus azarae AMNHM 211463, (B) Callicebus cupreus AMNHM 34636, (C) Pithecia pithecia AMNHM 94133, and (D) Cacajao calvus AMNHM 73720. Arrows in B and D identify inferior margin of zygomatic process. In Callicebus (B) the inferior margin extends below alveolar border of molars. Other extant pitheciids do not show this character, although in some individuals the origin of masseter m. is sometimes built out into a separate dependent process, as in the specimen of Cacajao (D) illustrated here.

different in lacking the intense pitting, cren- Xenothrix; in our examples, the protocone ulation, and slight polycuspidation which and hypocone are less well de®ned than the uniquely distinguish cheektooth occlusal sur- paracone and metacone. The trigon and talon faces of living pitheciines. In Callicebus are indistinctly separated by a vaguely de- crenulation is much weaker than in pitheci- ®ned postprotocrista running from metacone ines. Regarding this last feature, Rosenberger to protocone. The hypocone is worn ¯at in (1977) came to a different conclusion, argu- both specimens and is associated buccodis- ing that there was some evidence of ``enamel tally with a small fossette (®g. 11C). The re- papillation'' on lower molars of Xenothrix. sult of this con®guration is a large distal Slight crevices and ripples can be detected shelf or wear surface, as seen in pitheciids under magni®cation, but they are no more generally (especially in larger species, cf. ®g. frequent or obvious than in many nonpithe- 12C, D). The paracone bulges outward (buc- ciids. Similar remarks apply to the upper mo- cally) to a greater extent than does the meta- lars of Xenothrix. cone (®gs. 9A, 11C), with the result that the There are four cusps present on the M1 of tooth is markedly wider proximally than dis-

Fig. 14. Skulls of comparative set in modi®ed Frankfurt plane (see text), left lateral view: (A) Aotus azarae AMNHM 211463, (B) Callicebus cupreus AMNHM 34636, (C) Pithecia pithecia AMNHM 94133, and (D) Cacajao calvus AMNHM 73720. In panel B, superimposed angle illustrates parietal measurement (see ch. 85, appendix 2): 1, inner surface of dorsal rim of external acoustic meatus; 2, anteroinferiormost point on parietal.

tally. This feature is present but less marked (®gs. 9A, C; 11B, C), paracone and proto- in Paralouatta and Antillothrix (cf. illustra- cone are heavily worn; with dif®culty mesial tions in Horovitz and MacPhee [1999] and and distal parastyles can be discriminated on MacPhee and Horovitz [2002]). In other pi- either side of the paracone. PM3 and PM4 theciids the two principal buccal cusps are possess two roots; PM2, represented by its mesiodistally aligned and similar in size (®g. alveolus only, seems to have had only one 12B±D). root. M2 is reduced distally, with the hypocone Although canine crowns of Xenothrix re- and metacone being barely distinguishable as main unknown, root sizes can be accurately separate cusps. The paracone is the best de- gauged from alveolar dimensions. As may be ®ned feature on the tooth, and like the M1 seen in table 6, BL and MD measurements protocone, presents a prominent buccal of alveolar ori®ces of the pm2 and PM2 (ϭ bulge. The protocone area is slightly raised maximum inside dimensions of opening) are and worn ¯at. Each molar has three roots, similar to those of the canine alveoli in the two buccal and one lingual (®g. 11A, B). same jaws. (This character is to be distin- PM3 and PM4 are bicuspid and almost guished from ch. 37, appendix 1, which com- identical morphologically, although PM3 is pares the size of the fourth premolar's alve- slightly smaller overall. In both specimens olar ori®ce to that of the canine.)

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Greater discrimination can be gained by the view that this monkey was mainly her- multiplying BL and MD measurements by bivorous, like the other members of its clade. AD (root length) in order to generate a vol- In this connection it is interesting that Xen- ume modulus as a proxy for PM2/pm2 and othrix evidently lacked substantial midfacial C1/c1 root size. As may be seen in table 6, prognathism, large canines/diastemata, and at least for the two specimens of Xenothrix highly procumbent lower incisorsÐall fea- that could be measured adequately, the root tures of larger extant Pitheciinae. Without volume modulus for C1 is about 30% larger these specializations, the feeding maneuvers than that for c1. This is to be expected, as of Xenothrix doubtless differed from those of the usual condition in platyrrhines is one in pitheciine ``sclerocarp foragers'' as described which the maxillary canine is appreciably in detail by Kinzey (1992) and Rosenberger larger than the mandibular. However, the size (1992). In sum, the dental evidence suggests relationship of the premolars is the reverse: that Xenothrix was a rather unspecialized fru- pm2 root volume is about 20% larger than givore, probably not unlike its closest living that of PM2. The same situation obtains in relative, Callicebus. the comparative set, indicating that this relationship of premolar to root size is proba- DISCUSSION: ORBITAL bly primitive. HYPERTROPHY, SPATULATE Alveolar data cannot be used directly to INCISORS, AND THE AOTUS infer whether the crowns of the canines pro- HYPOTHESIS jected past the occlusal level of adjacent teeth in Xenothrix, although on the basis of In this section we focus on issues in cran- conditions in platyrrhines generally and in iodental morphological assessment raised by pitheciids speci®cally we consider this prob- Rosenberger's (2002) Aotus hypothesis, or able (®gs. 6, 8, 14). At the same time, the the argument that Aotus, not Callicebus,is degree of projection was probably quite the sister group of Xenothrix. This is neces- small, along the lines seen in extant Calli- sary in any event because the de®nition and cebus and Aotus rather than Pithecia or any scoring of several of the characters used in of the larger pitheciines (or other ceboids and the phylogenetic analysis in the next section ateloids generally). Inspection of a range of are directly dependent on the accuracy of his skulls of extant pitheciines lacking anterior assessments. teeth indicates that the C1 socket is typically As outlined in the Introduction, Rosenber- about two to three times deeper than that of ger's long-standing view is that Xenothrix, PM2. By contrast, if AMNHM 268006 is Callicebus, and Aotus are related as pitheci- representative, in Xenothrix (table 6) the up- ines (pitheciids in our taxonomy) because per canine socket is only about 60% longer they share several derived features, among than that of the anterior premolar. In which are small canines and a deep jaw. To AMNHM 268001, c1 and pm2 roots are sub- resolve their closer af®nities, however, Ro- equal. senberger (2002) has recently emphasized Although within the comparative set only the signi®cance of two features which he Aotus (®g. 13A) has truly spatulate upper in- identi®es as ``high weight'' apomorphiesÐ cisor crowns, in owl monkeys as well as pi- (1) enlarged orbits and (2) large, spatulate theciids I1 crowns are larger than those of I1s. These features, he claimed, occur in the I2s (®g. 13B±D). In AMNHM 268006 Aotus and Xenothrix but not in Callicebus, there is no question that I1 roots were more thus settling in his opinion the question of substantial than those of I2s, but there is no sister-group relationships. We note in passing independent evidence that the crowns were that, as Rosenberger's methodology is not spatulate (see Discussion). based on parsimony analysis, he does not Living ceboids (which include Aotus in mention or even consider the possibility that our view) differ from ateloids in that the for- one might ®nd countervailing ``high weight'' mer rely to a much greater degree on insects apomorphies that uniquely link Callicebus (Horovitz and Meyer, 1997). The known and Xenothrix and the other Antillean mon- morphology of Xenothrix is consistent with keys. Be that as it may, the issue here is

whether the morphological evidence for orbit atomical entity, but because it is a gap rather size and central incisors in Xenothrix has than a structure this approach may obscure been correctly interpreted. more than it reveals. For morphological pur- poses we ®nd it convenient to divide the in- SIZE AND CONSTITUTION OF BONY ORBIT ferior orbital ®ssure into anterolateral (AIOF) and posteromedial (PIOF) sections (®gs. 15, On the basis of conditions in AMNHM 16). In platyrrhines the AIOF is de®ned by 268006, Rosenberger (2002: 157) claimed the orbital surfaces of the maxilla and zy- that the orbital morphology of Xenothrix re- gomatic which grow together in various sembled that of Aotus ``in all important re- complex ways, ranging from widely open (as spects''. In particular, Rosenberger pointed to in Aotus; ®gs. 15A, 16A; table 7) to almost (1) the Aotus-like condition of the IOF and completely obliterated due to the approxi- (2) the ``wide arc'' described by the right or- mation of bone territories (as in most Calli- bital sill in this specimen, which he took to cebus; ®gs. 15B, 16B; table 7). be evidence of ocular hypertrophy. Inspec- In pitheciids generally (®g. 15B±D), zy- tion of the views comprising ®gure 9 shows gomatic/maxillary contact tends to be broad: that there is virtually nothing left of the ¯oor these two bone territories often grow togeth- or sill of either orbit. Therefore, the degree er in such a way that the anteriormost part to which they can be described as Aotus-like of the AIOF is pinched off as a separate fo- cannot be inferred merely from casual in- ramen or slit, here identi®ed as foramen inspection. Nevertheless, Rosenberger's inter- nominatum.6 In Aotus, the orbital surfaces of pretations of Xenothrix could be of great sig- the zygomatic and maxillary are oriented dif- ni®cance if correct, because a widely dehis- ferently than in pitheciids because of the lat- cent IOF and large orbit are derived traits of erad bulging of the orbits (®gs. 13A, 15A). Aotus that contrast sharply with conditions in There is a signi®cant gap between these bone Callicebus (and indeed all other pitheciids). territories not only medially but also later- To evaluate this possibility we examined sev- ally, where the lateral part of the AIOF eral morphological indicators which might be yawns especially widely because the zygo- expected to provide some reliable informa- matic's orbital surface is pushed out, as it tion on the size and constitution of the bony were, onto the root of the zygomatic process. orbit, even in a skull as damaged as There is no question of a narrowly con®ned AMNHM 268006. (Although we shall use foramen innominatum being formed under the conventional terminology, we note that these circumstances. in platyrrhines it is often not meaningful The PIOF is ventrally de®ned by the or- morphologically to distinguish the superior orbital ®ssure as an entity distinct from the 6 What this foramen transmits is uncertain, although spheno-orbital foramen. The inferior orbital by default the likeliest candidate on the basis of condi- ®ssure, however, is always well marked even tions in Homo (cf. Warwick and Williams, 1978) is a when nearly closed over.) venous branch communicating between the ophthalmic v. and pterygoid venous plexus (of the external jugular v.). It is unlikely to be the infraorbital artery of the max- CONSTRUCTION OF THE INFERIOR ORBITAL illary a., which normally enters through the posterior FISSURE part of the IOF to course along with the infraorbital neurovascular bundle (cf. Bugge, 1974; Warwick and Wil- As a ®rst approximation it could be argued liams, 1978). A separate orbital foramen for this vessel that a widely dehiscent IOF is characteristic has never been reported for primates. Nor can the fora- of primates with the largest eyes, but within- men represent an aperture for branches of the zygomatic group variation in strepsirhines is actually nerve, as these originate within the orbit and run out through foramina (zygomaticofacial and zygomatico- rather inconsistent for this feature (Cartmill, temporal) located elsewhere. A brief survey of Old Word 1980). Among extant haplorhines, Tarsius anthropoids indicates that the foramen (although not and (to a lesser extent) Aotus have large necessarily the vessel) is absent in catarrhines. Even in IOFs, which of course leads to the supposi- platyrrhine taxa in which the foramen is normally complete there may only be a notch or widened slit in the tion that this feature may in fact be correlated expected location. Here we shall simply identify the fea- with ocular hypertrophy in this group. ture as a foramen innominatum (for examples, see ®gs. The IOF is usually treated as a single an- 15 and 16).

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Fig. 15. Skulls of comparative set, left orbital mosaic (slightly schematic): (A) Aotus,(B) Callicebus, (C) Pithecia, and (D) Cacajao. Arrow in panel A illustrates measurement points for AIOF character (see ch. 87, appendix 2). *, roof over part of IOF formed by medial expansion of greater wing of sphenoid. Inset in panel C illustrates POD measurement (double-headed arrow; see text).

bital surface of the maxilla and the terminal ritories either never grow together or do so part of the maxillary tuberosity and dorsally only locally. For example, in large-bodied pi- by the lower margins of the the sphenoid theciines a small tongue of bone, usually de- wings, where the gap grades insensibly into rived from the zygomatic or sphenoid, is of- the superior orbital ®ssure. In contrast to the ten seen to roof over the proximal part of the AIOF, in most platyrrhines the PIOF tends to channel for the infraorbital neurovascular remain widely open, and opposing bone ter- bundle in carefully cleaned specimens (aster-

isk, ®g. 15D). In other specimens the tongue complete the postorbital plate and orbital sill. seems not to have formed or to have been Since zygomatic material is unquestionably broken off during preparation. present in the fossil, pressed up against the In a general way IOF size in adult pithe- lateral part of the maxillary tuberosity, this ciids seems to be correlated with body size: may be considered unequivocal evidence that Callicebus has relatively and absolutely the the AIOF could not have been widely dehis- narrowest IOF, while Pithecia, Chiropotes, cent as in modern Aotus. and Cacajao display progressively wider A minor point that cannot be elucidated gaps (ignoring the tongue just described). further without more complete remains is This correlation obviously does not hold for whether in Xenothrix the orbital wing of the Aotus (®g. 15A): despite this monkey's com- zygomatic was typically re¯ected back onto paratively small body size, both AIOF and the maxillary tuberosity, thereby creating a PIOF are very wide and the contribution of foramen innominatum. What is left of the or- the zygomatic to the lateral wall of the orbit bital skeleton of Xenothrix does not preclude is relatively slim. This suggests that condi- the possibility that the foramen was present, tions in the owl monkey are directed by fac- but nothing makes it particularly likely (or tors other than those controlling degree of any more likely than the moderately open ®s- closure in pitheciids. sure seen in callitrichines, cebines, and large- Turning now to the partial skull AMNHM bodied pitheciids). More positively, the mor- 268006, it is evident that, while no detailed phology seen in Alouatta, Brachyteles, La- reconstruction of the IOF is possible, it is gothrix, Ateles, and Paralouatta, in which clear nevertheless that conditions are not at the anterior end of the AIOF is reduced to a all Aotus-like. First, although most of the or- very narrow slit, cannot have been present in bital wing of the zygomatic is not represent- Xenothrix. ed, the remaining part is in sutural union with In sum, the only thing that can be conclu- the maxilla in the orbital ¯oor. Zygomatico- sively inferred about the AIOF in Xenothrix maxillary contact does not occur in the ¯oors is that it must have been much narrower and of extant Aotus in the region of the IOF. Sec- differently shaped than in Aotus. Further, IOF ondly, in the fossil the trailing margin of the size and shape are not necessarily coupled zygomatic wing de®nes a notch (®gs. 9D, with orbit size: in Paralouatta, where orbit 16E), which by virtue of its position must be size is comparable to that of Aotus, the IOF the anterior end of the AIOF, in agreement nevertheless displays the narrow condition. with conditions not only in pitheciids like We conclude from these considerations that Cacajao (®g. 16D) but also in all other plat- Rosenberger's (2002) view that Xenothrix yrrhines we have examined. The importance and Aotus are similar in IOF construction of this observation may be appreciated by garners no support from comparative anato- imagining what the orbital skeleton of an owl my. monkey would look like if the zygomatic wing were broken away along the margin of ESTIMATING THE SIZE OF THE BONY ORBIT the AIOF. Since there is no contact with the maxilla in this region, it follows that no part Rosenberger (2002) asserted that enough of the zygomatic would be represented in the remains of the orbital rim in AMNHM orbital ¯oor except anteriorly, where by ne- 268006 to permit a reasonable estimation of cessity the zygomatic meets the maxilla to eyeball size, although he did not attempt to

→ Fig. 16. Skulls of comparative set, left inferior orbital ®ssure in oblique left lateral view (slightly schematic): (A) Aotus,(B) Callicebus,(C) Pithecia,(D) Cacajao, and (E) Xenothrix (AMNHM 268006). Foramen innominatum is not always complete (i.e., not entirely closed off from rest of inferior orbital ®ssure). AIOF is dif®cult to discriminate from PIOF in this view, so only the latter is speci®cally noted. Dashed line reconstructs probable shape of anterior terminus of AIOF in Xenothrix, which did not possess a wide AIOF like that of Aotus (A).

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TABLE 7 Xenothrix mcgregori and Comparative Set: Anterior Portion of Inferior Orbital Fissure (IOF)a

quantify this. In principle an empirically almost straight in many platyrrhines (e.g., meaningful estimate of eyeball size in a fos- Cebus, Callicebus, Saimiri, Pithecia) and sil primate can be achieved by using a sub- therefore independent of orbit size (cf. ®g. stitute, such as an appropriately shaped 13B). sphere of modeling clay. A model that is just Utilization of Kay and Kirk's (2000) os- large enough to pass through the orbital teological method to derive information con- opening should be approximately equivalent cerning activity pattern and visual acuity in to the size of the original eyeball (cf. extinct primates is also precluded, because MacPhee, 1987), although this makes no al- none of the required variables (skull length, lowance for the intrinsic orbital muscles, fat, orbit diameter, optic foramen [canal] size) and other tissues that also ®ll the bony orbit can be measured on AMNHM 268006. How- (Schultz, 1940). Experience shows, however, ever, there is another method that can be ap- that this method works well only if the bony plied in the present case. Although the fo- orbit is complete or nearly so. If too little of ramina de®ned by the lesser wing of the the orbital rim and walls remain, then the sphenoid are no longer present in AMNHM diameter of the model cannot be adequately 268006, the position of the medial wall of constrained and an erroneous (or, at any rate, the optic canal can be reliably identi®ed (see an insecure) estimate of eyeball size may re- Description of New Specimens, Cranial Re- sult. This is the case with AMNHM 268006: mains). Using this landmark as one terminus primate orbital rims are rarely perfectly cir- and the point at which the zygomaticomax- cular, and a plausible arc of curvature cannot illary suture intersects the inferior margin of be derived from the few millimeters of rim the orbit (internal wall) as the other, a proxy that are still preserved on this specimen. In measurement for orbital depth (POD) can be fact, the medioventral section of the orbital taken (®g. 15C, inset). This measurement is rim that is preserved in Xenothrix is typically related to, but is obviously not the same as,

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true eyeball diameter. POD makes no allow- duction of various errors (original expression ance for eyeball sphericity, projection of the based on much wider sampling of primates, globe beyond the con®nes of the bony orbital linear measurement indirectly derived from margin, or distance between the ori®ce of the volumetric data, orbit depth and body weight optic canal and the anatomical origin of the not obtained from the same individuals/spe- optic nerve on the eyeball. Our interest is cies). Although the dataset is therefore less simply to compare taxa (specimens) of vary- clean than might be hoped, two general ob- ing body size for unit measurements that bear servations are warranted. on the size of the bony orbit, in order to test (1) With or without correction for allom- whether or not Xenothrix had orbits of a size etry, Xenothrix falls close to taxa that have larger than expected. relatively small orbits as compared to Aotus. Table 8 compares PODs and average body Indeed, Aotus stands apart from all other size (ABM) estimates for several platyrrhine platyrrhines considered here: this is surely to taxa, including Xenothrix. POD is slightly be expected for a primate whose orbital in- smaller in Xenothrix than Aotus, but this is dex as de®ned by Martin (1990) places it in not especially meaningful in view of their the top end of the range occupied by noctur- substantial difference in body size. Rough nal lorises and lemurs. No matter how one adjustment for size can be achieved by di- wishes to express relative orbital size, Xen- viding POD by ABM to generate an index, othrix emerges as different from AotusÐin- as is done in table 8 using natural log (ln) deed, so different that they lie at opposite transformations. Results indicate that the or- ends of the spectrum presented here. bits of Xenothrix are relatively small com- (2) Accordingly, the bony orbits of the Ja- pared to those of other members of the com- maican monkey are not larger than expected, parative set, especially in the case of Aotus. either in absolute terms or when compared The same conclusion obtains when suit- with taxa in the same body size range. In- able allowance is made for the effect of al- stead, orbital depth appears to scale with lometry. As Schultz (1940) showed, there is measurements of other mid- to large-sized a negative allometric relationship between pitheciines, and not with Aotus (or Callice- eye size and body size in primates. This also bus, for that matter). Even if one uses the applies to orbit size. Thus we should expect lowest body weight (2 kg) that MacPhee and that, in proportion to body size, large pri- Fleagle (1991) considered reasonable for mates will inevitably have smaller orbits than Xenothrix, the resulting index value is still small primates do (cf. Kay and Kirk, 2000). only 2.5, comparable to Pithecia of average In the present case, performing an allo- body size but quite unlike Aotus. metric correction is hindered by the fact that The case for Aotus-like orbital construc- we lack body size estimates for specimens tion in Xenothrix thus founders. At least on actually measured for POD (body size varies the evidence considered here, Rosenberger's intraspeci®cally to a substantial degree with- (2002) contentionÐthat the Jamaican mon- in Platyrrhini [Ford and Corruccini, 1985]). key followed the same ``adaptive trend'' that Since appropriate data are unlikely to be conditioned the evolution of orbital size in gathered in the foreseeable future, any cor- the owl monkeyÐappears to be without rection will have to be approximate. We uti- strong foundation. lized Schultz' (1940) data (which cover a much broader range of primate species than INCISOR WIDTH the set utilized here) to develop a linear re- gression expression relating orbital depth to Rosenberger (2002: 157) argued that ``the body size. Derivation of the expression, in ®rst upper incisor alveolus is greatly en- the form ln POD ϭ 0.19(ln ABM) Ϫ 0.21, larged in the fossil [i.e., AMNHM 268006], is explained in footnote e, table 8. It should relative to the I2 socket. This is paralleled by be noted that all values in the last column of a relatively large interalveolar distance sep- table 8 are much higher than 1 (expected ra- arating right and left I1's. I interpret the mor- tio of left and right sides of the allometry phology as an indication of a greatly broad- equation), which probably re¯ects the intro- ened I1 crown, which is a novelty of Aotus.''

TABLE 8 Xenothrix mcgregori and Comparative Set: Orbital Depth/Body Size Index

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TABLE 9 TABLE 10 Xenothrix mcgregori and Comparative Set: Xenothrix mcgregori and Comparative Set: Incisor Alveolar Row Width (IARW) (in mm)a Ratio of Areas of Alveolar Apertures of First and Second Maxillary Incisors

In the absence of incisor teeth allocatable to Xenothrix it is fruitless to enter into an extended discussion of this topic, although some brief observations on alveolar dimensions are warranted. As already noted, the mere fact that the alveoli of the maxillary central incisors in AMNH 268006 are larger than those of the lateral incisors does not indicate that the crowns were Aotus-like in their shape or proportions. In this specimen the row width of maxillary incisor alveoli is only 11.8 mm (table 9), which is little different from the equivalent measurement in large-bodied pitheciines (cf. ®gs. 9C and last-named taxa. Further, the separation of I1 13C, D). Presumably, if the upper incisors of alveoli is a highly variable feature, as is ev- Xenothrix had been broad and shovel-shaped ident by inspection of any large group of hu- like those of Aotus, row width would have mans. Even among Aotus specimens this fea- been disproportionately greater. ture is not consistent (cf. Aotus lemurinus To investigate the relationship of I1/I2 al- LACM 27258, A. lemurinus LACM 27259, veoli further, we measured representatives of A. azarae LACM 60645, all of which display all platyrrhine genera (see table 10 and Phy- unremarkable separation of I1 alveoli). By logenetic Analysis). We found that having an contrast, broad separation of I1 alveoli oc- I1 aperture much larger than that of I2 is not curs in many species, whether or not ``spat- an exclusive characteristic of Aotus and Xen- ulate'' upper incisors are present and regard- othrix: it also occurs in Callicebus and Ca- less of I1/I2 alveolar proportions (cf. Calli- cajao. Also, Pithecia, Chiropotes, and Ateles cebus sp. LACM 90817; Pithecia monachus show extensive overlap in values with these LACM 90818; Pithecia pithecia LACM

90822; Chiropotes satanas LACM 27276, sults indicated that the Antillean species 27277, 27279; Cebus albifrons LACM formed a monophyletic group, the sister tax- 56109, 30359; Cebus apella LACM 55233; on of which was Callicebus. Saimiri sciureus LACM 90823, 27322, In this paper we reanalyze our original 5488). data in light of three additional characters There is even less reason to think that the newly coded for this analysis (see appendix mandibular incisors of Xenothrix could have 1, chs. 85±87), as well as six other characters been shaped like those of Aotus. In the two that were coded by one of us in a previous fossil mandibles that can be measured for paper (Horovitz, 1999). Callithrix has been this feature, incisor alveolar row width (table shown to include Cebuella pygmaea (Can- 9) is extremely narrow, even after allowance avez et al., 1999a, 1999b; Porter et al., 1997, is made for damage. We therefore disagree 1999), so we eliminated C. pygmaea as a ter- with Rosenberger (1977: 470) who, citing minal taxon. Two characters exclusive to Williams and Koopman (1952), maintained these two taxa (chs. 30 and 32 in Horovitz that the lower incisors of Xenothrix could not and MacPhee [1999] and Horovitz [1999]) have been as closely packed as in pitheciines. were therefore deleted because they have be- To be sure, average row width in Aotus is come uninformative under the new arrange- metrically similar to AMNHM 148198 and ment. Thus the total number of characters 268001, but the individual teeth (as judged now included in our analysis is 87. Among by alveolar dimensions) are of course much fossil taxa, Tremacebus harringtoni and Nu- smaller, re¯ecting greater root spacing to ac- ciruptor rubricae were added because of commodate the spadelike, orthally implanted their putative relevance to the placement of incisor crowns characteristic of owl mon- Xenothrix. Scoring for these taxa is naturally keys. limited to those characters for which there is Thus, although the fossil documentation is empirical evidence. Outgroup taxa include admittedly poor, there does not currently Tarsius, a set of living catarrhines (including seem to be any persuasive evidence in favor both cercopithecoids and hominoids), and the of Rosenberger's argument that Xenothrix Oligocene Fayum anthropoid Aegyptopithe- possessed spatulate incisor crowns resem- cus zeuxis. When logically possible, multi- bling those of Aotus, while there is consid- state characters were ordered additively. erable circumstantial evidence against it. Al- Missing characters are scored as question though it is questionable whether incisor marks and inapplicables as dashes, although morphology in Xenothrix exactly replicated operationally there is no difference between that of any living species, the few measure- the two. Taxa with multiple entries for a ments that can be taken suggest that the man- character are coded as polymorphic. dibular incisor crowns in particular had to As there is discussion in the literature re- have been relatively slender, which is a prim- garding orbit size in Tremacebus, we need to itive platyrrhine feature. If Xenothrix is still explain brie¯y why this taxon has not been to be considered an aotine, it seemingly lacks scored for ch. 11 (appendix 1). Both Rusconi an important apomorphy of that group. (1933) and Hershkovitz (1974) concluded that, despite the poor condition of the type PHYLOGENETIC ANALYSIS (and only) skull, there were suf®cient grounds to infer that Tremacebus had en- MATERIALS AND METHODS larged orbits. Neither presented any mea- In a previous paper (Horovitz and Mac- surements that might have served to substan- Phee, 1999), we conducted a cladistic study tiate their statements. However, Hershkovitz that included representatives of all living (1974: 10) also remarked that the orbits of genera of platyrrhines and the fossil species Tremacebus were ``less expanded than in Paralouatta varonai, Xenothrix mcgregori, Aotus, more expanded than in Callicebus'' Antillothrix bernensis, Stirtonia victoriae, and thus somehow intermediate between and S. tatacoensis. That analysis utilized 80 these extremes. Fleagle and Rosenberger characters and included the new specimens (1983: 144) thought that this representation of Xenothrix described in this paper. Our re- was misleading: ``relative to the length of the

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maxillary tooth row . . . the orbits of Tre- TABLE 11 macebus are only slightly larger than those Xenothrix mcgregori and Comparative Set: of Callicebus, but considerably smaller than Parietal Elevation Relative to Frankfurt Plane those of the nocturnal Aotus''. As already (in degrees) noted (see Discussion), in a more recent paper Rosenberger (2002: 157) has seemingly contradicted this presumably well-founded view, ®nding instead that ``the orbit of Xen- othrix is enlarged, like [that of] Aotus and Tremacebus''. Like Hershkovitz' (1974) analysis, this statement was also made without bene®t of supporting measurements. Be- cause it is not apparent which, if any, of these relativistic, unquanti®ed statements about orbit size in Tremacebus can be accepted, we coded the relevant cell as ``data missing''. Character 85 is concerned with the extent to which the parietal participates in the pterion region of the external sidewall of the skull (see table 11). In atelids and pitheciids (including Paralouatta) the inferior edge of the parietal occupies a more ventral position in the pterion mosaic than it does in the other primates included in this analysis. We have attempted to quantify this difference (see ®g. 19 and appendix 1). This region of the skull is not preserved in Xenothrix. The remaining new characters concern as- pects of platyrrhine morphology that have been adequately introduced in the preceding morphological sections of this paper, so we shall restrict our comments here to the matter of scoring. Character 86 concerns the relative size of the alveoli for I1 and I2 (see Discus- sion). Because we wanted to include Xenoth- rix in the analysis, we de®ned our character states on the basis of alveolar rather than crown measurements. Although the distri- bution of values was found to be essentially continuous and overlapping among platyr- concerns the width of the anterior extremity rhine genera (see table 10), in de®ning two of the infraorbital ®ssure (AIOF), with mea- states we were attempting to test Rosenber- surement performed as indicated in the char- ger's (2002) judgment regarding proportional acter de®nition in appendix 1 and ®gure 16A. differences between these teeth in Aotus as Aotus and Tarsius are outliers for this fea- compared to other platyrrhines. Our results ture, having a very wide AIOF, whereas cat- reveal that Callicebus, Pithecia, Chiropotes, arrhines show an AIOF slightly larger than Cacajao, Ateles, and Leontopithecus all dis- that of most platyrrhines (the only exception play a level of difference between I1 and I2 being Aotus). that is equal to or greater than that encoun- In addition to the foregoing, hypothetical tered in Xenothrix or even some individuals characters with a scoring of ``1'' for Aotus of Aotus. and Xenothrix and of ``0'' for all other taxa Our ®nal character (ch. 87; see table 8) were created to further test how this addition

would affect the recovered phylogeny. One low mainly because of the positional volatil- character was added at a time until a change ity of the fossil specimens included in the in the topology of the phylogeny was pro- analysis: several of them have a very large duced. The goal behind this addition was to number of missing entries and can ®t any- test how many characters exclusive for Aotus where in the tree within a low range of ad- and Xenothrix would be needed before these ditional steps. A list of all unambiguous two taxa appeared as sister groups. changes is shown in table 12. We note that A maximum parsimony analysis was per- the number of apomorphies for the two formed using the program PAUP* (Phylo- clades in which Nuciruptor and Tremacebus genetic Analysis Using Parsimony), version are placed is decreased compared to those 4.0b10 (Swofford, 2002) applying a heuristic reported by Horovitz and MacPhee (1999). search with 100 replications. Wagner trees This is due to the lack of information per- were obtained with random addition se- taining to many of those characters in these quence of taxa, and they were subjected to fossil taxa, which renders character optimi- TBR. Tarsius was the designated root of the zations ambiguous at relevant nodes. trees. The clade consisting of Callicebus and the We obtained Bremer support values for Antillean species (node 42, ®g. 17) is sup- each branch (Bremer, 1988; KaÈllersjoÈ et al., ported, as previously reported (Horovitz and 1992) and inspected strict consensus trees up MacPhee, 1999), by four unambiguous char- to four steps longer than the most parsimo- acters: (1) presence of two prominences on nious trees (four separate trials, adding one the lateral wall of the promontorium (ch. 15, step per trial). The program MacClade 4 derived from presence of a ¯at surface or (Maddison and Maddison, 2000) was used to presence of a single prominence); (2) pres- change the position of Aotus and Xenothrix ence of a zygomatic arch that extends ven- and to assess the number of steps needed to trally below the level of the part of the al- implement this change relative to the most veolar process bearing the posterior cheek- parsimonious tree(s). teeth (ch. 23, derived from a higher position of the zygomatic arch); (3) a mandibular ca- RESULTS nine root that is highly compressed (ch. 32, derived from a more rounded outline); and Our data matrix is presented in appendix (4) C1 alveolar ori®ce (BL ϫ MD) that is 2. The heuristic search yielded 9 MPTs, the smaller than that of PM4 (ch. 60, derived strict consensus of which is shown in ®gure from a C1 alveolar opening larger than that 17 (tree length ϭ 293 steps; CI ϭ 0.52, RI of PM4). As noted in the descriptive section, ϭ 0.64, RC ϭ 0.33). The resulting relation- the utility of character 2 is compromised ships (except for the addition of Nuciruptor somewhat by the existence of size/sexual rubricae and Tremacebus harringtoni) are variation in the development of muscle ori- identical to the ones published by Horovitz gins on the underside of the zygomatic arch. and MacPhee (1999). Nuciruptor appears as The Antillean clade resolves as: (Xenoth- the sister group of Cebupithecia ϩ Pitheci- rix (Paralouatta, Antillothrix)). It is support- inae, in agreement with Meldrum and Kay ed by three unambiguous characters: (1) (1997) and Horovitz (1999). Tremacebus ap- presence of a wide nasal fossa, wider than pears in a trichotomy nested within the Ce- the palate at the level of M1 (ch. 25, derived boidea, in general agreement with Horovitz from a narrower palate; see Horovitz and (1999). However, the latter analysis included MacPhee, 1999: ®g. 10); (2) buccolingually a host of other fossil taxa with which Tre- small c1 alveolar ori®ce compared to that of macebus formed a group nested above Cebus pm4 (ch. 37, derived from a c1 alveolus buc- and Saimiri and more basal than the Callitri- colingually wider than that of pm4); and (3) chinae. The nine trees differ in regard to re- presence of a bulging buccal surface of the lationships detected among atelids (Brachy- M1 protoconid (ch. 51, derived from absence teles, Ateles, Lagothrix, and Alouattinae) and of this feature). the relationships among Tremacebus, Saimi- Regarding the three new features included ri, and the callitrichines. Decay values are in this analysis, the relative size of alveoli

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Fig. 17. Consensus tree of nine most parsimonious trees (87 morphological characters, TL ϭ 293, CI ϭ 0.52, RI ϭ 0.64, RC ϭ 0.33). Numbers in circles match node numbers in list of apomorphies (table 12). Numbers next to circles are Bremer support values (see Bremer, 1988). Daggers (²) identify fossil taxa.

TABLE 12 List of Apomorphiesa

for I1 and I2 (ch. 86) is large in both Aotus state) among catarrhines. Finally, the ventral and Xenothrix, but this character state is also extent of the parietal on the lateral wall of widespread among other platyrrhines. In the skull (ch. 85) is an exclusive synapo- MPTs, this character supports Pitheciidae (al- morphy of Ateloidea. None of these charac- though with two reversals within terminals) ters contradicts the position of the Antillean and it appears independently in Aotus, Ateles, species as sister group of Callicebus, and the and Leontopithecus. The character state de- last character further supports the hypothesis scribing the wide AIOF (ch. 87) is an auta- that Ateloidea does not include Aotus, as has pomorphy for Aotus and appears indepen- been repeatedly shown with morphological dently in Tarsius and (in an intermediate and molecular data (see Horovitz [1999], Ho-

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rovitz et al. [1998], and references cited owl monkeys are more closely related to the therein). clade consisting of Cebus, Saimiri, Trema- Ten additional steps are needed to move cebus (as shown in analyses involving mor- Aotus from its most parsimonious position phology), and callitrichines than to any other and place it as the sister group of Xenothrix, platyrrhines (see also ®g. 17). whereas seven steps are needed to remove MacPhee and Iturralde-Vinent (1995; Itur- Xenothrix from the Antillean clade and place ralde-Vinent and MacPhee, 1999) have ar- it as the sister group of Aotus at the base of gued on theoretical grounds that most line- the Ceboidea. When hypothetical characters ages of Antillean land mammals (including exclusively present in Aotus and Xenothrix the joint initiator of the Antillean monkey were added to the analysis, four of them were clade) were likely present on Caribbean land- needed before results began to change. With masses by ϳ33 Ma. If this inference is cor- this option, some of the trees showed Aotus rect, then the Antillean monkeys have a long and Xenothrix together, whereas others still and almost completely unknown history as showed the same topology for the Antillean an independent lineage. This point applies clade as the sister group of Callicebus.A equally well to Pitheciidae in general, which ®fth character would be needed to make Xen- seem to have undergone a prodigious radia- othrix and Aotus sister taxa in all shortest tion on the continent early in platyrrhine his- trees. In all cases in which Xenothrix ap- toryÐa radiation that is only spottily record- peared dissociated from the other Antillean ed in the existing fossil record (see Kay et taxa, it joined Aotus in the Ceboidea, and al., 1998a). We are aware that a claim that Aotus never appeared among the pitheciids. pitheciids were in existence and had already differentiated into several subclades by the CONCLUSION Early Oligocene is not in accord with the view that places the basal split in Platyrrhini The craniodental evidence we have treated (often incorrectly resolved as Callitrichinae in this and earlier papers supports three prin- vs. other platyrrhines) as late as 34±24 Ma cipal conclusions concerning the systematic (e.g., Purvis, 1995). Because molecular position of Xenothrix (Horovitz and Mac- clocks are ultimately calibrated against the Phee, 1999; MacPhee and Horovitz, 2002): received fossil record, it is scarcely surpris- (1) Xenothrix is most closely related to extant ing that the origin of Platyrrhini is still rel- pitheciids among living platyrrhines (and egated by many authors to the latest part of within that group, to Callicebus); (2) among the Paleogene, which is when the empirical extinct platyrrhines, Xenothrix groups with record begins in South America in the form other Antillean primates; and (3) Aotus and of Branisella boliviana, a platyrrhine of un- Xenothrix display no uniquely derived char- certain relationships found in beds currently acters in common. Candidate synapomor- dated to Chron 8 (25.8±27.0 Ma) (Kay et al., phies suggested by Rosenberger (2002), in- 1998b; Fleagle and Tejedor, 2002). However, cluding enlarged orbits and spatulate upper if the implications of the diversi®cation mod- incisors, either do not occur in Xenothrix or el of TavareÂ et al. (2002) are accepted, the apply to a greater or lesser extent to a host last common ancestor of Primates could have of other platyrrhines. In short, there is no de- lived no later than the latest Mesozoic (ca. cisive evidence that would warrant placing 80 Ma), with the basal split between strep- Xenothrix next to Aotus to the exclusion of, sirhines and haplorhines following shortly or even in combination with, the members of thereafter. Anthropoids were certainly in ex- family Pitheciidae. Exclusion of Aotus from istence by the Early Eocene because their close association with pitheciids is also sup- fossils have already been found (Beard and ported by postcranial (Ford, 1986a), molec- MacPhee, 1994; Beard, 2002). Yet if no more ular (Schneider et al., 1993), and combined than 7% of all primates species that have molecular and morphological evidence (Ho- ever lived have been recovered as fossils, as rovitz et al., 1998; Horovitz, 1999). Indeed, TavareÂ et al. (2002) also claim, it is extreme- the molecular and combined molecular and ly unlikely that even the earliest anthropoids morphological evidence suggests instead that so far recognized are perched on or near the

actual point of the clade's origin. This argu- and John Fleagle and Chris Heesy (State ment applies a fortiori to the origin of Antil- University of New York, Stony Brook) re- lean monkeys (let alone platyrrhines), as it viewed our submitted text and caught several does, not so incidentally, to the origin and grievous errors and omissions. Permission to early radiation of caviomorph rodents (cf. work in Jamaica was granted by the Natural Wyss et al., 1993). We continue to stand by Resource Conservation Department, Minis- our view that New World monkeys and ro- try of Mining, Government of Jamaica. Field dents ®rst entered the tectonically evolving investigations were partly supported by insular Neotropics during the Oligocene from grants from the Adler Fund (to RDEM) and South America (Iturralde-Vinent and Mac- the National Geographic Society (to Don Phee, 1999), where their diversi®cation must McFarlane). have already been well advanced (despite the absence of an empirical record to date). REFERENCES No name has been assigned previously to the grouping of Xenothrix, Paralouatta, and Beard, K.C. 2002. Basal anthropoids. In W.C. Antillothrix. In view of the current taxonomic Hartwig (editor), The primate fossil record: hierarchies in use for higher-level groups of 133±149. New York: Cambridge University platyrrhines, it is appropriate to assign the Press. Antillean platyrrhine clade to Xenotrichini Beard, K.C., and R.D.E. MacPhee. 1994. Cranial Hershkovitz (1970), new tribe. This tribe is anatomy of Shoshonius and the antiquity of An- the sister group of the monogeneric tribe Cal- thropoidea. In J.G. Fleagle and R.F. Kay (editors), Anthropoid origins: 55±97. New York: licebini; these two tribes are in turn the con- Plenum Press. stituents of Callicebinae, one of the two sub- Bremer, K. 1988. The limits of amino-acid se- families of Pitheciidae. The ranking of this quence data in angiosperm phylogenetic recon- last clade was elevated from subfamily to struction. Evolution 42: 795±803. family by Horovitz (1999: ®g. 2B) to accom- Bugge, J. 1974. The cephalic arterial system in modate an increasing number of hierarchical insectivores, primates, rodents, and lago- levels due to new fossil discoveries. We hope morphs, with special reference to the systematic that the new material explored in this paper classi®cation. Acta Anatomica 87(suppl. 62): reduces some of the mystery surrounding 1±160. Xenothrix, the ``most enigmatic of all the Canavez, F.C., M.A.M. Moreira, J.J. Ladasky, A. South American extinct monkeys'' (Simons, Pissinatti, P. Parham, and H.N. SeuaÂnez. 1999a. Molecular phylogeny of New World Primates 1972). (Platyrrhini) based on ␤2-microglobulin DNA sequences. Molecular Phylogenetics and Evo- ACKNOWLEDGMENTS lution 12: 74±82. Canavez, F.C., M.A.M. Moreira, F. Simon, P. Par- It is a great pleasure to thank the col- ham, and H.N. SeuaÂnez. 1999b. Phylogenetic leagues and volunteers who have participated relationships of the Callitrichinae (Platyrrhini, in our projects in Jamaica over the past de- Primates) based on ␤2-microglobulin DNA se- cade. These include Lisa DeNault, Stephen quences. American Journal of Primatology 48: Donovan, Adam Fincham, Alan Fincham, 225±236. Clare Flemming, Ray Kielor, Greg Mayer, Cartmill, M. 1980. Morphology, function, and Don McFarlane, and Simon Mitchell. We evolution of the anthropoid postorbital septum. also thank the Jackson's Bay Gun Club for In R.L. Ciochon and A.B. Chiarelli (editors), permission to stay on its property and to Gun Evolutionary biology of the New World mon- Club personnel Izzy and Makka. For illustra- keys and continental drift: 243±274. New York: tions we thank Lorraine Meeker and Patricia Plenum Press. Fincham, A. 1997. Jamaica underground, 2nd ed. Wynne, assisted in various ways by Chester Kingston: University of the West Indies. Tarka and Ruth O'Leary (all current AMNH Fleagle, J.G. 1999. Primate adaptation and evo- personnel). Clare Flemming (The Explorers lution, 2nd ed. San Diego: Academic Press. Club) read and improved an earlier version Fleagle, J.G., and A.L. Rosenberger. 1983. Cra- of this paper. Gary Morgan (New Mexico nial morphology of the earliest anthropoids. In Museum of Natural History and Science), M. Sakka (editor), Morphologie evolutive, mor-

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TavareÂ, S., C.R. Marshall, O. Will, C. Soligo, and Indian fossil monkeys. American Museum R.D. Martin. 2002. Using the fossil record to Novitates 1546: 1±16. estimate the age of the last common ancestor Wyss, A.R., J.J. Flynn, M.A. Norell, C.C Swisher, of extant primates. Nature 416: 726±729. R. Charrier, M.J. Novacek, and M.C. McKenna. Warwick, R., and P.L. Williams. 1978. Gray's 1993. South America's earliest rodent and rec- anatomy, 35th British ed. Philadelphia: Saunders. ognition of a new interval of mammalian evo- Williams, E.E., and K.F. Koopman. 1952. West lution. Nature 365: 434±437.

APPENDIX 1

CHARACTER LIST 19. Ectotympanic, shape (nonadditive): 0 ϭ tube I, 1 ϭ ring, 2 ϭ tube II. See Horovitz and MacPhee (1999) for refer- 20. Temporal emissary foramen: 0 ϭ present ences and discussion concerning chs. 1 through and large, 1 ϭ small or absent. 77 and 84 (originally numbered 1±29, 31, 33±79, 21. Eyeball physically enclosed: 0 ϭ absent, 1 and 80), and Horovitz (1999) for chs. 78±83 (orig- ϭ present. inally numbered 80±85). Characters that are mul- 22. Cranial capacity: 0 ϭ less than 15 cm3,1 tistate and nonadditive are noted; all others are ϭ more than 15 cm3. additive. 23. Zygomatic arch, ventral extent: 0 ϭ below plane of alveolar border of posterior cheek- 1. Offspring per birth, number: 0 ϭ one, 1 ϭ teeth, 1 ϭ above plane of border. two. 24. Pterion region, contacts: 0 ϭ zygomatic- 2. Lumbar vertebrae, number: 0 ϭ more than parietal, 1 ϭ frontal-alisphenoid. ®ve, 1 ϭ ®ve or fewer. 25. Nasal fossa width: 0 ϭ narrower than pal- 3. External thumb: 0 ϭ absent or reduced, 1 ate at level of M1, 1 ϭ wider. ϭ present. 26. Infraorbital foramen, vertical position rel- 4. External tail: 0 ϭ absent (not projecting), ative to maxillary cheekteeth in Frankfurt 1 ϭ present. plane: 0 ϭ above interval between (or cau- 5. Tail, ventral glabrous surface: 0 ϭ absent, dal to) M1 and PM4, 1 ϭ above interval 1 ϭ present. between PM4 and PM3, 2 ϭ above (or ros- 6. Claws on all manual and pedal digits ex- tral to) anteriormost premolar. cept hallux: 0 ϭ absent, 1 ϭ present. 27. Zygomaticofacial foramen, size relative to 7. Carpometacarpal joint of thumb: 0 ϭ non- maxillary M1 breadth: 0 ϭ smaller, 1 ϭ saddle, 1 ϭ saddle. larger. 8. Rib cage, shape: 0 ϭ larger dorsoventrally, 28. Deciduous i2, shape (nonadditive): 0 ϭ 1 ϭ larger laterally. bladelike, lingual heel absent, 1 ϭ blade- 9. Ulnar participation in wrist articulations: 0 like, lingual heel present, 2 ϭ styliform, ϭ present, 1 ϭ absent. lingual heel absent. 10. Sternebral proportions: 0 ϭ manubrium 29. Relative height of i1 to i2: 0 ϭ i1 absent, shorter than 36% of corpus length, 1 ϭ ma- 1 ϭ i1 lower than i2, 2 ϭ i1 and i2 sube- nubrium longer than 46% of corpus length. qual. 11. Orbit size: 0 ϭ smaller than 1.9, 1 ϭ larger 30. Permanent i1±i2, shape: 0 ϭ spatulate, 1 ϭ than 2.1. styliform. 12. Postglenoid foramen: 0 ϭ absent, 1 ϭ re- 31. Diastema between c1 and i2: 0 ϭ absent, duced, 2 ϭ large. 1 ϭ present. 13. Tentorium cerebelli, ossi®cation: 0 ϭ ab- 32. Root of c1, shape: 0 ϭ rounded/suboval, 1 sent, 1 ϭ present. ϭ highly compressed. 14. Middle ear, pneumatization of anteroven- 33. Lingual cingulum on c1, completeness: 0 tral region: 0 ϭ absent, 1 ϭ present. ϭ complete, 1 ϭ incomplete or absent. 15. Middle ear, paired prominences on cochle- 34. Lingual crest on c1, sharpness: 0 ϭ round- ar housing: 0 ϭ absent, 1ϭ present. ed, 1 ϭ sharp. 16. Pterygoid fossa, depth: 0 ϭ deep, 1 ϭ shal- 35. Lingual cingulum on c1, mesial elevation low. of: 0 ϭ not elevated, 1 ϭ elevated. 17. Canal connecting sigmoid sinus and subar- 36. Lingual cingulum on c1, forming spike on cuate fossa: 0 ϭ absent, 1 ϭ present. mesial edge of tooth: 0 ϭ absent, 1 ϭ pre- 18. Vomer, exposure in orbit: 0 ϭ absent, 1 ϭ sent. present. 37. Buccolingual breadth of alveolus of c1,

compared to pm4: 0 ϭ c1 larger than pm4, 59. I2 orientation: 0 ϭ vertical, 1 ϭ procli- 1 ϭ c1 smaller than pm4. vious. 38. Deciduous pm2, angle subtended by distal 60. C1 alveolus size relative to PM4 equiva- portion of mesiodistal axis and postproto- lent: 0 ϭ C1 larger than PM4, 1 ϭ C1 cristid: 0 ϭ smaller than 45Њ,1ϭ larger smaller or equal to PM4. than 45Њ. 61. Deciduous PM2, trigon: 0 ϭ absent, 1 ϭ 39. Deciduous pm2, cross-sectional shape: 0 ϭ present. rounded, 1 ϭ mesiodistally elongated. 62. Deciduous PM3, hypocone: 0 ϭ absent, 1 40. Size of pm2, relative to pm3 and pm4: 0 ϭ present. ϭ pm2 smallest in premolar series, 1 ϭ 63. PM3 preparacrista: 0 ϭ absent or vestigial, pm2 not the smallest. 1 ϭ present. 41. Deciduous pm3, metaconid: 0 ϭ absent, 1 64. PM4 protocone position: 0 ϭ mesial to ϭ present. widest point of trigon, 1 ϭ on widest point. 42. Protoconid of pm3, size relative to pm4 65. PM4 lingual cingulum: 0 ϭ absent, 1 ϭ protoconid: 0 ϭ pm3 and pm4 protoconids present. subequal, 1 ϭ pm3 protoconid largest. 66. PM4 lingual cingulum mesial projection: 0 43. Talonid of pm3: 0 ϭ larger than pm2 tal- ϭ absent, 1 ϭ present. onid, 1 ϭ subequal to pm2 talonid. 67. PM4 hypocone: 0 ϭ absent, 1 ϭ present. 44. Metaconid height of pm3, relative to pro- 68. PM4 and M1, relative buccolingual toconid height: 0 ϭ metaconid absent, 1 ϭ breadth: 0 ϭ PM4 narrower than M1, 1 ϭ metaconid lower than protoconid, 2 ϭ PM4 subequal to or wider than M1. metaconid and protoconid subequal, 3 ϭ 69. M1 mesostyle/mesoloph (nonadditive): 0 ϭ metaconid taller than protoconid. absent, 1 ϭ mesostyle present, 2 ϭ meso- 45. Metaconid of pm4, height relative to pro- loph present. toconid height: 0 ϭ metaconid lower than 70. M1 hypocone/prehypocrista presence: 0 ϭ protoconid, 1 ϭ metaconid and protoconid hypocone and prehypocrista present, 1 ϭ subequal, 2 ϭ metaconid taller than pro- hypocone present and prehypocrista absent, toconid. 2 ϭ hypocone and prehypocrista absent. 46. Hypoconid of pm4: 0 ϭ absent, 1 ϭ pre- 71. M1 postmetacrista slope: 0 ϭ distobuccal sent. slope, 1 ϭ distal or distolingual slope. 47. Entoconid of pm4: 0 ϭ absent, 1 ϭ present. 72. M1 mesiodistal alignment of protocone and 48. Number of premolars: 0 ϭ two, 1 ϭ three. hypocone: 0 ϭ parallel, 1 ϭ hypocone lin- 49. m1 projection of distobuccal quadrant (DB gual. complex): 0 ϭ not projecting, 1 ϭ project- 73. M1 pericone/lingual cingulum: 0 ϭ absent, ing (crown sidewall hidden in occlusal 1 ϭ lingual cingulum only, 2 ϭ distinct view). pericone on lingual cingulum. 50. m1 intersection of oblique cristid and pro- 74. M2 hypocone: 0 ϭ absent, 1 ϭ present. tolophid: 0 ϭ intersects protolophid buc- 75. M2 cristae on distal margin of trigon (non- cally, directly distal to apex of protoconid, additive): 0 ϭ cristae form distinct, contin- 1 ϭ intersects protolophid more lingually, uous wall between protocone and meta- distolingual to apex of protoconid. cone, 1 ϭ cristae interrupted by small fossa 51. m1 buccal bulging of protoconid: 0 ϭ ab- or do not form distinct wall, 2 ϭ cristae sent, 1 ϭ present. absent or differently organized. 52. m1 entoconid position: 0 ϭ on talonid cor- 76. M3/PM4 relative mesiodistal length: 0 ϭ ner, 1 ϭ distally separated from talonid M3 absent, 1 ϭ M3 shorter than PM4, 2 ϭ corner by sulcus. M3 and PM4 subequal, 3 ϭ M3 longer 53. m1/m2 buccal cingulum: 0 ϭ absent, 1 ϭ than PM4. present. 77. Maxillary molar parastyles: 0 ϭ absent, 1 54. m2 trigonid/talonid relative height: 0 ϭ tri- ϭ present. gonid taller than talonid, 1 ϭ subequal. 78. Buccolingual width of maxillary M3 com- 55. m2 mesoconid: 0 ϭ absent, 1 ϭ present. pared to M1: 0 ϭ M3 at least 0.67 of M1, 56. m3/pm4 relative length: 0 ϭ m3 absent, 1 1 ϭ M3 almost 0.5 of M1. ϭ m3 shorter, 2 ϭ subequal, 3 ϭ m3 lon- 79. Buccolingual width of m1 talonid plus buc- ger. cal cingulum compared to talonid alone: 0 57. Molar enamel surface: 0 ϭ smooth, 1 ϭ ϭ cingulum narrow, 1 ϭ cingulum wide. crenulated. 80. Mandibular molar m1 buccolingual talonid 58. I1 lingual heel: 0 ϭ absent, 1 ϭ present. width relative to the trigonid: 0 ϭ trigonid

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is 0.8±1 times talonid, 1 ϭ trigonid is 0.6± slightly larger than the latter. Alveolar 0.7 times talonid. ``size'' is de®ned as the product of the me- 81. Vertical prominence on c1: 0 ϭabsent, 1 ϭ siodistal and labiolingual dimensions of the present. alveolar aperture, and is therefore an esti- 82. Relationship of zygomatic arch with infe- mator of alveolar aperture area. Two char- rior orbital ®ssure: 0 ϭ independent, 1 ϭ acter states were implemented: ``0'' was zygomatic arch represents anterior limit of scored for all individuals having an alveo- inferior orbital ®ssure. lar area index (I2/I1) of 0.66 or smaller 83. Prominence on pm2 crown buccal wall: 0 (which includes Aotus and Xenothrix), ϭ absent, 1 ϭ present. while ``1'' was scored for individuals hav- 84. Ventral ¯exion of the skull (airorhynchy): ing an index larger than 0.66. Pithecia, 0 ϭ absent, 1 ϭ present. Ateles, Chiropotes, and Leontopithecus dis- 85. Parietal lower edge in pterion region: 0 ϭ played polymorphism (both categories rep- high, 1 ϭ low. This character is based on resented in samples). All individuals of the dihedral angle between the modi®ed Aotus, Callicebus, Cacajao, and the single Frankfurt plane (inferiormost point on or- representative of Xenothrix were found to bital sill to the inner surface of the dorsal exhibit state ``0'', while all other genera rim of the external auditory meatus) and an exhibit ``1''. intersecting line drawn between the afore- 87. Inferior orbital ®ssure, anterior width: 0 ϭ mentioned rim and the parietal's anteroin- small, 1 ϭ intermediate, 2 ϭ large. This feriormost point (which normally occurs at character is scored by employing the index the triple junction of parietal, zygomatic, of the minimum distance across the AIOF and greater wing of sphenoid, although (1 mm posterior to its rostralmost point) other con®gurations are also found). The divided by palatal breath (at M1). The ob- angle to be measured is taken at the point jective here is to capture the ``size'' of the of intersection (demonstrated for Callice- AIOF by controlling for body size via the bus in ®g. 14B). This can be easily accom- palatal breadth measurement. Because in plished with a microscope having a camera most platyrrhines the rostralmost part of lucida attachment: the three required points the AIOF is simply an ever-narrowing gap, (lowest point on orbit, inner rim of audi- any minimum distance measurement taken tory meatus, lowest point on parietal) are at the end of the ®ssure would be in®nitely indicated on tracing paper, lines are drawn small. We therefore set the calipers slightly through the origin (in this case the meatal posterior to the ®ssure's terminus so that rim), and a protractor is used to measure all entries would be real numbers (and all the arc. Note that because platyrrhines lack indices rational). In many platyrrhines the a tubular meatus, the Frankfurt plane as de- foramen innominatum (demonstrated in ®ned here is trivially different from the one ®gs. 15 and 16) is properly the rostralmost de®ned in human osteology (meatal point part of the AIOF; in these cases the dis- is located slightly more laterally and ven- tance given in table 8 is the width of the trally in humans). foramen. Taxa with indicies between 0.005 86. Relative size of alveoli for I1 and I2: 0 ϭ and 0.068 were scored as ``0''; those be- alveolus for I2 much larger than alveolus tween 0.101 and 0.126 as ``1''; and those for I1, 1 ϭ alveoli subequal or the former between 0.24 and 0.42 as ``2''.

APPENDIX 2 DATA MATRIX Notation used: ? ϭ missing data, Ϫϭinapplicable character, a ϭ (01), b ϭ (12).

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APPENDIX 3

SPECIES-LEVEL TAXA UTILIZED FOR COMPARATIVE Alouatta seniculus 48120, 140527,140529, INVESTIGATIONS 142944 Presbytis pileatus 4307 American Museum of Natural History, De- Hylobates lar 31593 partment of Mammalogy (AMNHM) Homo sapiens (senior author's collection) Tarsius spectrum 196487 Callithix argentata 94933, 95915, 95921 Los Angeles County Museum of Natural His- Saguinus bicolor 37462, 94096, 94199 tory, Department of Mammalogy (LACM) Leontopithecus rosalia 3844, 70181, 70316, Callithrix argentata 5489, 27299, 27298; Callith- 119470 rix sp. 89 Callimico goeldii 98281, 98367, 176602, 183289, Saguinus midas 27292, 27294; Saguinus oedipus 183290, 239601 27340; Saguinus sp. 31542 Cebus olivaceus 32058, 78494, 100153 Leontopithecus rosalia 70212, 90759 Saimiri sciureus 42323, 64096, 94098 Cebus albifrons 27326, 27327, 56109; Cebus Aotus azarae 209916, 211458, 211460, 211463 apella 27343, 55233 Saimiri sciureus 5488, 27320±27324, 90823, Callicebus cupreus 34636, 75988, 98102, 130361; Aotus azarae 60645; Aotus lemurinus 27257± Callicebus caligatus 73705, 130361, 211460 27259 Pithecia monachus 76413; Pithecia pithecia Callicebus sp. 90817 36321±36323, 76815, 79387, 94133, 94147; Pithecia monachus 90818; Pithecia pithecia Pithecia sp. 187984 90819, 90821, 90822 Chiropotes satanus 76889, 94126±94128, 94160, Chiropotes satanas 27276±27279 95867, 95872, 96340, 96343, 96344, 96339 Cacajao calvus 27341 Cacajao calvus 73720, 76391, 78565, 78568, Ateles belzebuth 27358±27360 78571, 98316, 98473 Lagothrix sp. 90758, 90830 Ateles belzebuth 76878, 76882, 76883, 76897, Alouatta seniculus 14382, 27352, 27354, 27358 95038, 95039, 95042 Brachyteles arachnoides 128, 260, 80405 Museo Nacional de Historia Natural, La Ha- Lagothrix lagotricha 76042, 93713, 98357, bana (MNHNCu) 188153, 188154 Paralouatta varonai V 194

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