Anatomy of the temporal bone in early anthropoids with remarks on the problem of anthropoid origins.код для вставкиСкачать
AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 56:3-21 (1981) Anatomy of the Temporal Bone in Early Anthropoids, With Remarks on the Problem of Anthropoid Origins M. CARTMILL, R.D.E. MAcPHEE, AND E.L. SIMONS Department of Anatomy (M.C.,R.D.E.M.,E.L.S.),Department of Anthmpology (M.C.,E.L.S.), and Center for the Study of Primate Biology and History (E.L.S.),Duke University, Durham, North Carolina 27710 KEY WORDS Parapithecidae Ear region, Primates, Fayum, Oligocene, Pongidae, ABSTRACT New and previously undescribed specimens of the petrous, squamous, and tympanic parts of the temporal bones of anthropoid primates from the Oligocene of Egypt display a general morphological resemblance to the equivalent parts of Recent ceboid skulls. Like that of ceboids, the ectotympanic bone of Fayum anthropoids is a simple anulus, fused to the squamosal at both its extremities. The petrosal's bullar contribution appears to bear transverse septa running laterally from promontory to ectotympanic; similar septa are seen in callitrichids and some prosimians. The definitive stylomastoid foramen is in a position characteristic for ceboids but not found among adult catarrhines. As far as can currently be determined, pneumatization of the petrous and squamous temporal is specifically anthropoid-like in pattern and extent, but exhibits no special resemblances to that found in any particular anthropoid taxon. On the other hand, Fayum anthropoids appear to resemble other catarrhines and to differ from most extant ceboids in lacking a vascular canal leading from the subarcuate fossa to the sigmoid venous sinus. Vascular impressions on a squamosal fragment tentatively assigned to Aegyptopithecus zeuxis show that the petrosquamous and cranio-orbital venous sinuses were persistently large, as in prosimians. A squamosal fragment previously attributed to Apidium phiomense, and adduced as evidence for a lemuriform ancestry of Anthropoidea, is probably that of a hyaenodontid creodont. I t is certainly not that of a primate. The ceboid-like morphology of the early catarrhine ear region is probably primitive for anthropoids, and in any case it does not argue for an Old World origin of ceboids -but it emphatically suggests that Anthropoidea is a strictly monophyletic taxon. With the possible exceptions of Branisella boliuiana and the enigmatic Burmese Eocene primates Pondaungia and Amphipithecus (Hoffstetter, 1969; Szalay, 1970;Simons, 1971; Ba et al., 1979; Ciochon and Savage, 1979; Szalay and Delson, 1979),the earliest anthropoids known are those recovered from Oligocene sediments of the Fayum Province, Egypt. Since 1907, when the first Fayum primates were recovered by Richard Markgraf, those sediments have yielded over 500 specimens of early anthropoids belonging to the families Pongidae (sensu lato) and Parapithecidae. Most of the identifiably anthropoid remains consist of 0002-9483/81/5601-0003$05.50 0 1981 ALAN R. LISS, INC. teeth and mandibular fragments, predominantly those of parapithecids. However, postcranial bones attributable to anthropoids of both families are also numerous in collections from the Fayum, and provide us with our sole source of information about the locomotor adaptations of early anthropoids (Fleagle et d., 1975; Conroy, 1976; Fleagle and Simons, 1978, 1979). The Fayum primates have also furnished the only direct evidence we have concerning the cranial morphology of early anthropoids. AlReceived November 11, 1980 accepted April 16,1981 4 M. CARTMILL. R.D.E. MacPHEE. AND E.L. SIMONS most all of the diagnostic peculiarities that distinguish extant anthropoids from extant prosimians are features of the cranial skeleton. These peculiarities include an enlarged neurocranium, an almost complete postorbital septum, a fused mandibular symphysis, absence of the stapedial artery and its bony canal, and an internal carotid artery which enters an anteriorly positioned carotid foramen and traverses a canal in a bony septum between 1)the tympanic cavity proper and 2) the anterior accessory cavity, a trabeculated chamber pneumatizing the apex and adjacent parts of the petrous temporal (Gingerich, 1973; Szalay, 1975a; Gingerich and Schoeninger, 1977;Cartmill and Kay, 1978; Cartmill, 1980; MacPhee and Cartmill, 1981). Apart from numerous maxillae and mandibles, and the nearly complete skull of the primitive pongid Aegyptopithecus zeuxis found by G.E. Meyer in the 1966-67 field season (Simons, 1967, 1969,1972), only a handful of cranial fragments of Fayum anthropoids have been recovered, and few of these have been described. Various facial elements and teeth attributable to the parapithecid Apidium phiomense were assembled by Simons (1972)into a composite reconstruction of a rather marmoset-like facial region. Fragmentary frontals and parietals referred to A . zeuxis were used by Radinsky (1973)in reconstructing the endocast of the braincase from the 1966 skull. Gingerich (1973) described two bony fragments found in association with A. phiomense teeth, interpreting those fragments as remains of a right temporal bone of that species. From these few, mostly provisional studies of the scanty remains available, much has been learned. Like modern anthropoids, the pongids and parapithecids from the Fayum exhibit complete fusion of the mandibular symphysis. The postorbital septum of Aegyptopithecus was at least as well developed as that of some extant ceboids; and maxillary and frontal fragments of Apidium suggest that the septum of parapithecids was ceboid-like (Simons, 1959; R.F. Kay, pers. comm.). However, the brain of Aegyptopithecus did not exceed that of extant Malagasy lemurs in relative size (Gingerich, 1977; Kay and Simons, 1980), which implies that the marked brain enlargement characteristic of modern anthropoids was acquired independently in more than one anthropoid lineage. The only published study of the ear region of the Fayum catarrhines is that of Gingerich (1973).This controversial study represents the first investigation of the possible phyletic implications of the anular ectotympanic of these primates. Immediately prior to Gingerichs study, Simons (1972)had briefly described the narrow ectotympanic of Aegyptopithecus and likened it to that of ceboids. Gingerich, however, argued that in a fossil he identified as Apidium the ectotympanic was not only anular but “free and intrabullar,” like that of adapids and Malagasy lemurs. From this and other resemblances between adapids and early anthropoids, Gingerich drew the conclusion that anthropoids and lemurs alike were derived from Eocene adapids, whereas Tarsius and its Eocene relatives were derived from Paleocene plesiadapiforms. These conclusions have been assailed by other investigators who, for various reasons, prefer to think that anthropoids originated from Eocene tarsioids, and dismiss Gingerichs analysis of the supposed Apidium squamosal on the grounds that (inter alia) the fragments in question either differ significantly from the temporals of lemurs and adapids, or do not differ significantly from those of tarsioids and ceboids in the respects alleged, or both (Hoffstetter, 1974a; Hershkovitz, 1974; Cartmill, 1975; Szalay, 1975a; Cartmill and Kay, 1978). In addition to the specimens described by Gingerich and the still imperfectly described ear region of the Aegyptopithecus skull, the temporal bone of Fayum anthropoids is known from three petrosals collected by Yale University expeditions in 1964 and 1966, and by a squamosal fragment collected by the 1977 Duke University expedition to the Fayum. We here offer descriptions of these fossils and a reexamination of the assemblage (Yale Peabody Mus. No. 23968)from which Gingerich extracted the material he described. We hope thereby to arrive at a more precise understanding of the morphology of the ear region in the skull of early catarrhines. PETROSAL Four isolated petrosals (Figs. 1,3,4) from Yale Quarry I in the Upper Fossil Wood Zone (Jebel el Qatrani Formation, Fayum Province) are attributable to anthropoids. One of these (YPM 25972) is larger than the other three (YPM 25973,25974, and 23968). Although differential breakage of these specimens makes it impossible to quantify this difference precisely, the few homologous measurements that can be taken or estimated suggest that YPM 25972 is about 25% larger than the smaller ones (which are essentially identical in size). 5 EARLY ANTHROPOID TEMPORAL BONES a .I , fossa for tensor tympani hiatus can. n. pet ma/::, faciaJ cma/ fen. vestibuli carotid conal stylomastoid foramen groove for tympanic n. medaJ wall of bu/Ja fenestra cochleae transbullor septum Fig. 1 Ventrolateral view (a,b)of isolated left petrosal of Fayum catarrhine (YPM 25972).Large arrow points anteriorly, small arrow laterally. Scale = 1 rnm. This specimen nreserves r-- - - a small Dortion of the posteromedial segment of the medial buliar wall, inciuding a part of the ectotympanic’sposterior crus. One transbullar septum, connecting the promontory with the ectotympanic fragment, is also preserved. Arrow indicates pyramidal eminence (for m. stapedius). Hachure shows probable extent of remaining portion of ectotympanic. 6 M. CARTMILL, R.D.E. MacPHEE, AND E.L. SIMONS The large petrosal is comparable in size to that of a squirrel monkey (Saimizf).Since the parapithecid Apidium phiomense is the only Quarry I anthropoid that resembles Saimin in body size (Kay and Simons, 1980), it is possible that all four specimens represent remains of that species. If so, the three smaller petrosals may represent female or juvenile specimens of Apidium. Apidium phiomense occurs in the Quarry I fauna with greater frequency than other anthropoids, and juvenile specimens are common (R.F. Kay, pers. comm.). Contravening this interpretation is the fact that pneumatization is more extensive in the three smaller specimens than in the larger -just the reverse of what would be expected if the size difference were due to degree of maturity or to sexual dimorphism. A few other minor features, noted below, also suggest that the petrosal sample may include at least two species. We cannot rule out the possibility that the large petrosal represents one of the other Quarry I anthro- poids: Parapithecus grangeri, Propliopithecus chirobates, or even Aegyptopithecus zeuxis. The smaller anthropoid petrosals, on the basis of size alone, can most parsimoniously be assigned to Apidium phiomense. The preserved parts of the petrosal in all four specimens comprise most of the extremely dense bone surrounding the otic capsule’s labyrinth, together with various remnants of the more fragile cortical bone delimiting the pneumatic cavities of the middle ear. Although almost nothing remains of the auditory bulla and tegmen tympani in any single specimen, enough of the accessory pneumatic cavities and carotid canal has been preserved in one or another fragment to stamp them all unmistakably as anthropoid petrosals. Tympanic cavity Small sections of the medial wall of the tympanic cavity proper are preserved on YPM Fig.2. Left ear region of Cullithriz sp. seen from ventral posterolateralaspect, with portions of bulla and ectotympanic removed to display transbullar septa (asterisks).Scale = 1 mm. EARLY ANTHROPOID TEMPORAL BONES 23968 and 25972; the latter is especially interesting, because the rearmost parts of the petrosal plate and ectotympanic are still in place. In this specimen, the remaining portion of the plate is that which rims the sinus tympani (diverticulum D, of Saban 119631 and other authors). As may be seen in Figure 1,this sinus is deeply excavated and is bounded by small crests (transbullar septa), which run downward and backward to converge on a thick ridge descending from the external aspect of the facial canal. If, as we suspect, this ridge is a small remnant of the ectotympanic’s posterior crus (see below), then the intratympanic surface of the petrosal plate bore subtympanic transbullar septa running from the promontory and fossular area to the ectotympanic. Among living small anthropoids, such septa are best developed in callitrichids (Fig. 2), although they occur widely among prosimians (Allocebus, Necrolemur, Rooneyia, Plesiadupis; cf. Cartmill and Kay, 1978). Because of extensive damage, the pattern of middle-ear pneumatization exhibited by the Fayum anthropoids cannot be ascertained precisely. However, there are sufficient clues to demonstrate that pneumatization was substantial and not at all lemur-like. Small cellules, delimited by worn crests representing the bases of broken septa and trabeculae, surround the auditory capsule on its medial, superior, anterior, and posterior aspects. By analogy with extant anthropoids, these can be divided into two major complexes; a posterior, mastoid group and an anterior, apical group. Mastoid group. The network of crests and depressions on the posterior surfaces of the Fayum petrosal (cf. Fig. 4)represents what remains of the mastoid antrum and its ramifying diverticula. The mastoid group of cellules was unquestionably a large one. As we reconstruct it, this group extended from the antrum (and epitympanic recess) around the gyri of the semicircular canals and into the floor of the subarcuate (parafloccular) fossa. The fossa’s floor did not, therefore, contribute to the side wall of the skull in the mastoid region (as it does in Tarsius and Malagasy lemurs), but was instead separated from it by air-filled spaces (as it is in extant anthropoids and lorisiforms). Although mastoid pneumatization penetrated the petrosal crest to a slight extent, it did not extend past the level of the hiatus canalis nervi facialis. Apical group. Little can be said about the degree of pneumatization of the anterior end of the otic capsule, although persistent traces of 7 cellules and septa suggest that it must have been extensive (cf. Fig. 3). Medially, the apical group’ penetrated the bone of the petrosal plate a t least as far as the posterior carotid foramen. Anterodorsally, it excavated the petrosal apex in front of the anterior wall of the internal acoustic meatus. The anterior portion of the petrosal crest was also slightly inflated by the apical group of air cells. I t is certain that in life the mastoid and apical groups communicated via the tympanic cavity proper, into which they opened. In extant anthropoids, mastoid and apical air-cell complexes sometimes develop secondary connections through their conjoint inflation of 1) the entire petrosal crest and 2), more frequently, the medial wall of the bulla. The first sort of connection is demonstrably absent in YPM 25972; the second sort appears to be present in the smaller petrosals, although breakage renders this uncertain. I t is clear at any rate that pneumatic spaces separate the posteroinferior end of the carotid canal from the auditory capsule in the smaller petrosals, but not in the large one. Vascular channels Arteries. The carotid channel is preserved to some extent in all four specimens, and is more complete in YPM 23968 than in the other three (Fig. 4).The internal carotid entered the bulla at a point anterior to the coronal plane of the fenestra vestibuli and considerably medial to the fenestra cochleae, curved upward and forward along the anteromedial side of the promontory, and apparently left the middle ear cavity after passing through some portion of the apical complex of air cells. Like that of Tarsius, but unlike that of all other known extinct and extant nonanthropoid primates (Szalay, 1975a),the internal carotid canal of the Fayum IThe apical complex of anthropoids is sometimes referred to as the hypotympanic sinus or cavity (e.g.. by Hershkovitz,1977).This term appears to have been introduced into the English literature by Gregory (1920).who in turn adopted it from van Kampen 11905).It was originally intended to refer b a quite-improbableventrad expansion of the primitive mammalian middle ear cavity whereby a supposedlydistinct space (the hypotympanicsinus) was gradually incorporatedinto the true tympanic cavity. In addition to its application to any volume subjacent to the tympanic cavity proper (which surrounds the auditory ossicles and windows),in primatology the term “hypotympanic sinus”has also been used to refer to the medial chamber of the lorisiform bulla (Saban,1963;Cartmill. 1975)and to the anteriorchamber of the tarsiiform bulla (Saban, 1963; Szalay, 1975% Szalay and Delson, 19’79).This scattershot application of one name to several different cavities that can be shown to be nonhomologous on developmental grounds (MacPhee,1981) is inappropriate. The term “hypotympanic sinus”has lost what little intelligiblemeaning it had in the first place, and it should be withdrawn from scientific usage. M. CARTMILL, R.D.E. MacPHEE, AND E.L. SIMONS 8 Fig. 3. Isolated right petrosal of Fayum catarrhine (YPM 25973), ventral view; direction arrows as in Figure 1. Scale = 1 mm. This specimen preserves some of the petrosal‘s highly pneumatized apex, although almost all of the mastoid air cells are lost. The pointer identifies the entrance to the fenestra cochleae, which is hidden in this view by the basal turn of the cochlea. Key: a, apex of the petrosal; ac. air cell (member of the mastoid group, penetrating the petrosal’s dorsal surface);ag, air cells of the apical group; cc, carotid canal; fca, facial canal; ftt, fossa for tensor tympank fv, fenestra vestibuli; lsc, lateral semicircular canal; ms, mastoid region; pr, promontory. sulcus for internal carotid n. tegmen tympani (br.) hiatus can. n. pet. maj. transverse septum fossa for tensor tym. medial wall of bulla “denticulate”septum fenestra cochleae facial canal (bd lat semicircular can. groove for tympanic n. \ U Fig. 4. Isolated right petrosal of Fayum catarrhine (YPM 239681, ventral view; anterior is toward top of page, lateral toward left. Scale = 1mm. This petrosal, referred to Apidium by Gingerich (1973). is the only specimen with a moderately complete carotid canal. The ridge of bone forming the posterior border of the sinus tympani may be a transbullar septum (cf. Fig. l a , b); so may the “denticulate” septum (cf. Gingerich, 1973). although its original orienta- floor of subarcuate fossa (br.1 tion seems to have been horizontal rather than vertical. The mastoid and apical groups apparently met medially in the region of the carotid canal, within the substance of the petrosal component of the bulla. The arrow identifies a shallow sulcus, which may have held part of the tympanic plexus or caroticotympanic artery. Broken surfaces indicated by “(br.)”. EARLY ANTHROPOID TEMPORAL BONES anthropoid petrosals traverses only a small portion of the promontorium and does not shield the fenestra cochleae from ventral view. The size and relations of the carotid canal constitute the principal reason why these specimens can be unequivocally identified as anthropoid. As Gingerich (1973) noted, the YPM 23968 specimen resembles anthropoids and differs from early tarsioids and most other prosimians in lacking a stapedial artery, although certain grooves running from the carotid canal across the promontory’s ventral surface may have contained caroticotympanic arteries (see below),one of which may represent a vestige of the stapedial stem. Veins. A deep jugular fossa is well preserved on the ventral surface of YPM 25972 and 25973. The slitlike aperture of the cochlear canaliculus opens into the top of this fossa. A shallow but well-defined sulcus running medially backward behind this fossa toward the region of the rather large fossula for the saccus endolymphaticus probably represents the terminal end of the indentation for the sigmoid sinus. No other major venous impressions are well enough preserved to warrant description. Examination of a representative sample of 45 anthropoids1indicates that in nonateline ceboids, a patent canal leads from the depths of the subarcuate fossa caudally and medially to an opening in the channel of the sigmoid sinus, behind and below the aperture (fossula sacci endolymphatici) of the vestibular aqueduct. The only other mammal known to possess such a canal is the colugo (Cynocephulus uoluns),in which the canal is occupied by a vein (Cartmill and MacPhee, 1980); we have found a dried vessel in this position in one Suguinus skull. Small pits occur in a similar position on the wall of the sigmoid sinus in some juvenile pongids and cercopithecids, but we have found none that is demonstrably connected by a canal to the subarcuate fossa. No such canal occurs in prosimians, in human fetuses (Padget, 1957), in adults of extant catarrhines, or in any of the Fayum petrosals. Neural channels The canal of the facial nerve is broken to varying extents in all specimens, but it was definitely a complete bony tube in the living animals. The entire intrapetrosal course of the nerve is discernible on YPM 25972 (Fig. 1)as a result of breakage. A small foramen situated behind the (damaged) stylomastoid foramen opens into the facial canal; it presumably 9 transmitted the auricular ramus of the vagus. (Theexternal aperture of this vagal canaliculus is hidden in Figure 1 by the projecting frag ment of the ectotympanic.) Owing to breakage of the mastoid air cells, the stylomastoid foramen is not preserved intact on any of the specimens, but it is clear that it lay high up on the posterior side of the bulla’s meatal rim, a position not seen in modern catarrhines but typical of New World monkeys generally. This difference between extant New and Old World anthropoids is probably largely or wholly interpretable as a secondary effect of their differences in length of the bony meatal tube and degree of mastoid inflation. The sympathetic and glossopharyngeal roots of the tympanic plexus are traceable in the fossils, and were described in part by Gingerich (1973). The tympanic canaliculus through which the tympanic branch of nerve IX enters the bulla is preserved only in the large petrosal (YPM 25972), where its inferior orifice lies posterior and lateral to the jugular fossa. The nerve emerges into the tympanic cavity within the sinus tympani in YPM 25972, under cover of a transbullar septum. In that specimen (Fig. 1) and in YPM 25974 and 23968, a sulcus leads anteriorly upward from the tympanic canaliculus past the posterior upper corner of the fenestra cochleae to a point below the vestibular window; in YPM 23968, it continues through a short bony tunnel into the fossa for the tensor tympani, whence it cannot be further traced. In YPM 23968, a minute foramen can be discerned within the carotid canal, on its posterior aspect, a t about the point where that canal comes into contact with the promontory. Farther up, on the medial wall of the semicanal for the auditory tube, another small foramen opens into a deep sulcus that runs upward and forward in parallel with the posterior edge of the carotid canal (Fig. 4). We infer that the two foramina are connected, and that they and the sulcus represent the course of a caroticotympanic branch of the sympathetic carotid nerve or plexus within the carotid canal. The foramina and sulcus may have contained a caroti’Anthropoids examined for presence of subarcuate canal (sample sizes in parentheses):Cebuellapygmaea (2). Callithrix jacchus (2),Saguinus oedipus (3), Leontopithecus msalia il), Callimico goeldii (1). Aotus trivirgatus (21, Cacajao melnnocephalus (11. Pithecia monacha (1). Callicebus moloch (3),Cebus albifmns (11, Cebus capucinus (1). Alouatta sp. (2). Ateles geoffmyi (1).Ateles fusciceps ( l ) ,Lagothrix lagotricha 111. CercoDithecur talaooin 12). CercoDithecusDetaurista(l1. Cep cocebus torquatus 12). Macaca sp. (11,Papw anubis (2),Colobus guereza (21. Presbytzs cristatus (2),Hylobutes lar ( 2 ) ,Hylobates moloch (21. Pongo pygmaeus (2),Pan tmglodytes (4). Total = 45. 10 M. CARTMILL, R.D.E. MacPHEE, AND E.L. SIMONS cess, a ventrally facing concavity in the squamosal represents the upper half of the external acoustic meatus. The postglenoid foramen lies just posterior to the medial end of the postglenoid process; it retains the primitive large diameter seen in lemurs and some ceboids (Conroy, 1980b).On the endocranial surface of the specimen, a sulcus representing the squamosal surface of the petrosquamous venous siIntratympanic muscles nus runs forward and downward to terminate On the smaller petrosals, the lower edge of in the postglenoid foramen. The foramen has the fossa for m. tensor tympani is delimited by the form of a short bony canal, about as long as a crest that runs forward and slightly upward it is wide, which in life surrounded the terminal from the anterior border of the fossula fenes- end of the venous sinus (See note, p. 21). In typical prosimians, as in primitive euthertrae vestibuli (Fig. 4).The corresponding fossa on the large petrosal (Fig. 1)has no definite ians generally, venous blood entering the lower edge. This is another slight morphologi- transverse sinus drains laterally and leaves the cal difference suggesting that the three braincase through two parallel outflow chansmaller petrosals represent one anthropoid nels: 1)the sigmoid sinus, which empties into species and the large petrosal another. the internal jugular vein, and 2) the petrosquaIn YPM 25972 only, enough of the rear of the mous sinus, which runs forward in a channel tympanic cavity is preserved to permit identi- wholly enclosed by the petrosal and squamosal fication of the pyramidal eminence or osseous (hence its name) and becomes the external jugchamber that held the origin and belly of the ular vein after traversing the postglenoid forastapedius. A tiny perforation in the pyramids men. The distal part of the petrosquamous siapex represents the aperture through which nus also receives a major venous channel runthis muscle's tendon entered the tympanic cav- ning backward from the orbit through the cranio-orbital foramen in company with the ramus ity (Fig. 1). superior of the stapedial artery. This cranio-orSQUAMOSAL AND ECTOTYMPANIC bital venous sinus drains the meningeal veins The isolated right squamosal, Duke Univer- of the side wall of the braincase. I t is representsity No. 1065, which was recovered from Quar- ed on dried skulls by a broad straight sulcus, ry I in 1977, is similar in known parts to the usually referred to as the sinus canal. In ansquamosal of Aegyptopithecus zeuxis (Fig. 5). thropoids, the sigmoid drainage is emphasized and may have come from a female or other at the expense of the petrosquamous system; small individual of that species. The specimen the postglenoid foramen is reduced or absent, preserves the glenoid fossa, the postglenoid the bony petrosquamous canal becomes a shalforamen, the posterior root of the zygomatic low sulcus (persistently roofed over in some cearch, and the inferior part of the temporal boids), and the cranio-orbital sinus is greatly squama, together with the lateral half of the reduced in conjunction with the loss of the stamastoid process of the petrosal, with which the pedial ramus superior and the capture of its squamosal is completely fused. The mastoid branches by branches of the maxillary and lacprocess exhibits pneumatization of a sort typi- rimal arteries. In Homo and many other catarcal for anthropoids, with cellules extending in- rhines, all these elements of the petrosquato the temporal squama. The anterior surface of the postglenoid process has spalled off, but the process is otherwise intact and appears to have been feebly developed. Except for having Fig. 5. Ventral views of glenoid region in Fayum antbroa relatively gracile postglenoid process, the en- poids: a) isolated right squamosal DU 1065; b) correspondregion of basicranium of Aegyptopithecus zeuxis (Cairo tire fragment resembles the corresponding ing Geol. Mus. 40237; photograph courtesy of Dr. R.F. Kay). Inparts of a small Alouatta skull. The formation set on u, postglenoid region with oblique lighting to emphaof the medial wall of the glenoid fossa by a size contours of anterior CNS of ectotympanic. Key: b, bulla; stout downward expansion of the squamosal e, ectotympanic (apex of anterior crus);ep. entoglenoidproof squamosal;gf,glenoid fossa: mg, mastoid group; ms, (an entoglenoid process) is a particularly strik- cess mastoid region; pcf, posterior carotid foramen; pgf, posting resemblance to Alouatta glenoid foramen: pgp, postglenoid process; zp, zygomatic Immediately behind the postglenoid pro- process of squamosal. cotympanic branch of the internal carotid artery as well; if present, the caroticotympanic artery would have occupied the faint groove indicated by an arrow in Figure 4. Since the facial canal is perforated for most of its length in this specimen, the place where the chorda tympani escaped into the tympanic cavity can no longer be identified. EARLY ANTHROPOID TEMPORAL BONES 11 12 M. CARTMILL, R.D.E. MacPHEE, AND E.L. SIMONS Fig. 6. Dorsal view of isolated anthropoid right squamosal DU 1065, showing impressions of petrosquamous sinus (pss) and cranio-orbital sinus (cos). Direction arrows as in mous system are normally absent in the adult. The Fayum squamosal retains a prosimian-like petrosquamous system, in which the petrosquamous sinus and postglenoid foramen are relatively as large as those of the most primitive of living anthropoids, and the cranio-orbital sinus is represented by a broad, straight sulcus resembling that of Lemur or Tarsius (Fig. 6 ) .Whether the petrosquamous sinus lay in a complete bony canal or an open sulcus cannot be determined from the available fossils. The tip of the anterior crus of the ectotympanic anulus remains attached to the Fayum squamosal; it is discernible as a flat, expanded lamina immediately behind the postglenoid foramen, of which it forms the posterior edge (Fig. 5a). A broken surface posteromedial to the foramen represents the plane along which the anulus fractured when the squamosal was separated from the lost bulla. The occurrence and position of this break demonstrate what is also inferrable from the appearance of the edges of the terminal lamina: the anterior crus of the ectotympanic was solidly fused to the squamosal in the living animal. Had a joint Figure 1. Asterisk indicates “bristle”drawn as if traversing postglenoid foramen. Key: ac, air eellules;z, zygomatic process of squamosal. persisted between the two bones, the tip of the anterior crus would have been lost with the rest of the ectotympanic. A portion of the ectotympanic’s posterior crus is seemingly preserved on the YPM 25972 specimen, but it is battered and broken beyond easy recognition. Our identification is hesitant, and is largely influenced by what we have found in our survey of extant primates. There are two morphological justifications for thinking that the area shaded in Figure 1 is ectotympanic in origin: 1)In all ceboids, but especially in medium- and small-sizedones, the definitive stylomastoid foramen is situated immediately behind the margin of the posterior crus, close to its apical end; 2) In those ceboids that exhibit small ridges or transbullar septa on the floor of the sinus tympani (i.e,, callitrichids other than Saguinus, and some cebids), the system of ridges extends as far as the petroectotympanic suture, but no further; they end flush with the ectotympanic’s posterior crus. Since the foramen and at least one transbullar septum are partly preserved in YPM 25972, the rear of the tympanic cavity in Fayum anthropoids may be directly compared with the EARLY ANTHROPOID TEMPORAL BONES 13 corresponding region in modern ceboids. We feel that the morphological correspondences are sufficientlydetailed to warrant the identification of the thick ridge (see above)as the ectotympanic. This ridge, or ectotympanic fragment, is not demarcated from adjacent bone by a suture; complete synostosis of the anulus and petrosal plate evidently occurred here in Fayum anthropoids as it does in other fossil and modern primates. Neither end of the ectotympanic, as we identify it on the Fayum fossils, differs significantly from the equivalent parts of the ectotympanic in platyrrhines. THE YPM 23968 ASSEMBLAGE The material catalogued with the accession number 23968 in the Yale Peabody Museum is an assemblage of ten items which were found closely associated with each other at Quarry I. Two of these-the petrosal and the supposed Apidium squamosal- were described by Gingerich (1973). The remaining eight items comprise a fragment of a small anthropoid frontal, a second petrosal, and six teeth. One of the teeth is caniniform, with a short crown and a long, thick root; it may be a lower canine of Apidium phiomense, but it lacks diagnostic features that would enable us to identify it confidently. The other five teeth in the assemblage are cheek teeth of Apidium phiomense. With the kind assistance of our colleague R.F. Kay, we have identified them as follows: 1)a very badly 2) an unworn left P4(orposworn right P3or P4; sibly P3);3) an almost unworn left M', plus surrounding alveolar bone including part of the M3 socket; 4) a heavily worn right M'; 5) a very badly worn small cheek tooth, either a somewhat ill-formed M3or an upper premolar. It is obvious that more than one individual of Apidium is represented in the YPM 23968 assemblage. Of the two petrosals included in this assemblage, one is anthropoid and was described in some detail by Gingerich (1973).The other (Fig.7),which was not mentioned by Gingerich, differs considerably from the first. Although this particular specimen is poorly preserved, the most recent Duke Fayum expedition (November 1980) collected several more petrosals of the same type. There can be no question that these elements came from anonprimate mammal species. This is evinced by the broad, uninflated mastoid region, the anteroposteriorly short endocranial surface, the anteriorly positioned parafloccular fossa, and the absence of any arterial grooves or canals on the promontory. A pronounced vascular Fig. 7. Isolated left petrosal from YPM 23968 assemblage; ventral view. Direction arrows as in Figure 1.Scale = 1 mm. This specimen lacks any sign of a petrosal tympanic process and is clearly nonprimate. The internal carotid may have been accommodated in the vascular groove on the medial side of the petrosal, a position typical for carnivores. The basal turn of the cochlea (asterisk)is fully exposed, o w ing to loss of the bone forming the fenestra cochleae. Key: fca, facial canal; fv,fenestra vestibuli; lsc, lateral semicircular canal; pr. promontory; vg, vascular groove (probably for the internal carotid artery). groove running anteroposteriorly along the petrosal's medial and inferior edge may have held a medially positioned internal carotid artery like that of a carnivore or rodent. The medial and anterior edges of these specimens are smooth and unbroken, indicating that the petrosal was separated from the surrounding basicranial bones by unossified tissues and so became detached easily from the skull base after death. In no case is there a trace of a bony bulla; the bulla, if osseous, was apparently not formed by the petrosal. In all these respects, these petrosals differ from those of primates and resemble those of early carnivorous placentals, either creodonts or primitive carnivoranS. Because the YPM 23968 assemblage contains disparate elements secondarily brought together from more than one individual of Apidium (as shown by the dental-wear distribution) and from more than one order of mam- 14 M. CARTMILL, R.D.E. MacPHEE. AND E.L. SIMONS mals (as shown by the second petrosal), the association of the supposed Apidium squamosal with teeth of A. phiomense provides no warrant for attributing it to that species. The identification of this squamosal must be based exclusively on its morphology. We have made extensive comparisons of the supposed Apidium squamosal (Fig. 8)with reptilian, avian, and mammalian cranial and postcranial material in the osteological collections of the American and U.S. National Museums of Natural History. After successively trying and failing to persuade each other that the specimen represents a carnivore atlas, a turtle atlas, a primate zygomatic, and a lizard articular, we are convinced that Gingerichs identification of it as a mammalian squamosal is correct. However, we are also convinced that the squa- mosal is not that of a primate, for the following reasons: 1. The articular surface of the glenoid is hemicylindrical in form, suggesting a uniaxial pattern of rotation like that of a carnivoran. 2. The postglenoid foramen is located far behind the postglenoid process, rather than at its posteromedial edge, where it lies in primates that retain this foramen (cf. Figs. 5 and Fig. 8. a)Isolated squamosal (YPM239681, probably of a small creodont; ventrolateral view. Large arrow points anteriorly: small arrow dorsally. Scale = 1mm. b) Same specimen and scale, dorsal anterolateral view. Pointers in a identify a projecting ridge of bone beneath the posttympanic process, identified as the ectotympanic’sposterior CNS by Gingerich (1973).Key: d, cancellous tissue exposed through breakage of zygomatic process; gf,glenoid fossa; pgf, postglenoid foramen: pgp, postglenoid process: ptp, posttympanic process: tf, floor of temporal fossa (betweentemporal squama and posterior end of zygomatic arch);zp, zygomatic process of the squamosal. Asterisk in b identifies cancellous tissue exposed on medial side of specimen as a result of loss of temporal squama. 9). 3. The postglenoid foramen is the lower terminus of a vertical canal, about nine times as long as the foramen’s diameter. 4. The posterior root of the zygomatic arch is deeply excavated on its superior aspect. This excavation, which represents the floor of the posterior temporal fossa, becomes shallower but wider posteriorly (Fig. 8b), indicating that Fig. 9. Three views (ventral,ventrolateral, and dorsal anterolateral) of temporal bone anatomy in the Eocene Bridgerian creodont Limnocyon verus (USNM No. 299722). Key: gf,glenoid fossa; pgf, postglenoid foramen;pgp, postglenoid process; pr, promontory; ptp, posttympanic process; s, sulcus for chorda tympani and associated vessels; tf. floor of temporal fossa. The photographs are reversed for comparison with Figure 8% b. Fig 9a approx. natural size. 16 M. CARTMILL, R.D.E. MacPHEE. AND E.L. SIMONS the posterior part of the braincase was small relative to the adjoining part of the temporal fossa. 5. The process identified by Gingerich as the posterior crus of the ectotympanic juts from the lateral edge of this posterior expansion at an angle of about 45”.Our mental reconstruction of the remainder of the “ectotympanic“places the greater part of the bone lateral to the side wall of the skull. Since such a positioning is never encountered in mammals, we conclude that the feature in question is simply a projecting part of the squamosal-probably the posttympanic process. In all these respects, the YPM 23968 squamosal differs from those of known primates. The large postglenoid process rules out attributing this specimen to Rodentia. However, there are resemblances to creodonts and miacids (Matthew, 1909) in the posterior expansion of the temporal fossa, the form of the glenoid, the positioning of the postglenoid foramen, and other features. A shallow groove running anteriorly around the medial end of the postglenoid process (and notching it in passing)precisely resembles the sulcus for the chorda tympani and associated vessels in primitive fissipede Carnivora (Petter, 1966). In this and other details, the YPM 23968 squamosal is similar to that of a small hyaenodontid creodont like Limnocyon uerus from the Bridger Eocene (Fig. 9),which differs principally in features associated with its larger size-e.g., the greater saliency of the postglenoid process. Fissipede carnivorans first appear in Africa in the Miocene (Savage, 1978).The YPM 23968 squamosal is therefore more likely to represent a small creodont than a miacid. The only creodont previously described from the Upper Fossil Wood Zone is Metasinopa fraasi (Osborn, 1909), which is too large an animal to be the source of the YPM 23968 squamosal. However, Duke University expeditions have in the last three field seasons uncovered several mandibles of a small creodont at Quarry I, in the very same zone that yielded the disputed squamosal. Preliminary studies suggest that these represent a species of the genus Masrasector. The sole named species of this genus, M. a e g y p t i c ~ s is ~ , based on type material from Quarry G in the middle of the Qatrani Formation, slightly earlier than the level from which the YPM 23968 assemblage was recovered. Masrasector aegypticus was a fox-sized animal; the creodont mandibles from Quarry I are somewhat smaller in size, but show no other obvious differences from the Quarry G Masrasector material. The question of their taxonom- ic distinctiveness is currently under study; it is sufficient for our purposes to note that they represent a likely source for the YPM 23968 squamosal. We tentatively attribute that squamosal to an undetermined species of Masrasector, or another proviverrine hyaenodontid of similar size, and accordingly conclude that the specimen has no relevance to the problem of anthropoid origins. DISCUSSION In every anatomical feature, the ear region of Fayum catarrhines more closely resembles those of Recent anthropoids than it does those of any prosimians. It follows that virtually all of the important events in the evolution of the anthropoid temporal bone must have preceded the early Oligocene. Though the Fayum catarrhine basicranium is more primitive in some respects than that of any extant catarrhine, its differences from modern catarrhines all represent resemblances to platyrrhines. Because of these facts, the temporal bones of Fayum anthropoids shed very little new light on the problem of identifying the prosimian ancestors of the Anthropoidea. I t is now abundantly clear that the Fayum anthropoids exhibit no apomorphous features of the ear region that are shared with adapids or other “lemuroids” (in the broad sense). Lemurs, ceboids, and Fayum anthropoids resemble adapids, but differ from all tarsioids, in lacking a bony meatal tube extending laterally past the recessus. However, absence of this tube is probably a retention from the ancestral primate stock, and within-family differences among modern mammals strongly suggest that meatal elongation is highly labile. No exclusive resemblances between adapids and anthropoids in ectotympanic-squamosal relations, the pattern of carotid circulation, middle-ear pneumatization, or any other fundamental aspect of the organization of the otic region appear to exist. The hypothesis that anthropoids evolved from adapids now rests entirely on the evidence provided by the teeth and jaws (Gingerich and Schoeninger, 1977). The more popular hypothesis that anthropoids were derived from omomyids sensu lato, most persuasively urged in recent years by Szalay (197513,1976; Szalay and Delson, 197% also finds little or no support in the anatomy of the ear region. Rooneyia and Necrolemur, the only early tarsioids whose ear regions are ade’The original species name, aegypticum (Simons and Gingerich, 1974). is here emended to aegypticus in accord with Article 30aW of the International Code of Zoological Nomenclature. EARLY ANTHROPOID TEMPORAL BONES quately known, exhibit no striking otic specializations (with the possible exception of the bony meatal tube), but remain in most respects persistently primitive. The posteromedial position of the posterior carotid foramen, which Szalay and others (e.g., Cartmill and Kay, 1978)have identified as a synapomorphy of an omomyid-tarsier-anthropoid clade, may well be a primitive primate feature. The posterolateral position of this foramen has been regarded as primitive for primates because it characterizes Plesiadapis, adapids, and some Malagasy lemurs. However, the posteromedial position is found in lorisiforms and omomyids (sensulato),and is also characteristic of most of the possible outgroups of Primates, including tree shrews, elephant shrews, and lipotyphlous Insectivora. In fetal Malagasy lemurs, the internal carotid artery enters the bulla from the medial side, exactly as in fetal lorises, and shifts laterally later in development; the degree of lateral displacement (maximal in most lemurids and indriids, minimal in cheirogaleids) is correlated with, and is probably an effect of, differences in the extent and pattern of pneumatization in the rear part of the petrosal plate (MacPhee, 1981).If the posteromedial position precedes the more lateral position in primate 17 phylogeny as well as ontogeny, as the insectivore evidence suggests, then the posteromedial position cannot be a shared derived feature of omomyids and anthropoids. However, the more lateral position of the foramen (and the associated pattern of pneumatization) in Malagasy lemurs might represent evidence for phyletic affinities between lemurs and adapids. Unlike anthropoids and Tarsius, known omomyids lack a transverse partition separating the tympanic cavity proper from a large anterior (or apical) accessory cavity. The latter cavity, as a separate entity, appears to be wholly unrepresented in Necrolemur, Rooneyia, and Tetonius (although we are not certain of this, because we have not studied the fossil material of Rooneyia, and because the poor condition of the only skull of Tetonius precludes a definite conclusion).These early Tertiary tarsioids also exhibit a transpromontorial carotid routing that is in most respects primitive for primates, whereas anthropoids from the Oligoceneto the Recent display a perbullar carotid pathway that is not presaged in any ancient tarsioid. The distinctive features of these two types of pathway are summarized in Table 1.The single feature of the ear region of Fayum anthropoids TABLE 1. Internal carotid pathways Transuromontorial uathwav Perbullar uathwav -1. The IClPA traverses the entire ventral or 1. The IClPA travels over only a small part ventrolateral surface of the promontory. of the promontory and in any event does not cross the latter’s ventrolateral surface. 2. From its entry point in the bulla’s posterior wall, the IC travels on or near the ventral lip of the cochlear window, where it divides into the PA and SA. 2. The IC does not travel near the cochlear window, but always well anterior to it. 3. The PA is never enclosed by material from the petrosal plate and is always situated lateral to the bullar medial Wall. 3. The IClPA is enclosed in a complete canal that is derived from the petrosal plate, and therefore it is morphologically situated “within”the bullar wall. 4. The IClPA is situated entirely within the 4. The IC/PA bypasses the tympanic cavity tympanic cavity proper until it leaves the middle ear. 5. The SC travels only a short distance from its origin to the obturator foramen of the stapes; among Recent forms, the SA is present throughout life (except when the entire internal carotid system is reduced, as in lorises and dwarf lemurs). and passes out of the middle ear after traveling through the anterior accessory cavity. 5. The SC, when present, begins beneath the anterior pole of the promontory, and travels backward along the length of the promontory in order to reach the stapes; among Recent forms the SA normally involutes perinatally, usually in its entirety. The transpromontorial pathway is found in living strepsirhines and all fossil nonanthropoid primates (so far as this can be determinedfrom existing evidence).The perbullarpathway is distinctive of Oligocene-Recentanthropoids,and a very similar routing is found in contemporary Tar sius. Of the two, the transpromontorial pathway is clearly the more primitive;it is frequently encountered in Eutheria and may be primitive for that infraclass. Omomyids consistently group with adapids and plesiadapoids for traits 1-5. although they may differ in other respects (e.g..in having a larger promontory canal). Tarsius differs from anthropoidsin retaining a stapedial canal (trait 5). which, however, contains only a fibrous remnant of the stapedial artery in the adult stage. Key: IC, internal carotid stem; PA, promontory artery; ICIPA, internal carotid stem and promontory artery considered together; SC. stapedial canal. 18 M. CARTMILL, R.D.E. MacPHEE. AND E.L. SIMONS that suggests a possible derivation from omomyids is the apparent presence, as in Rooneyia, Necrolemur, and most callitrichids (Fig. 2), of small transbullar septa or “struts”running across the tympanic surface of the petrosal plate to the ectotympanic. The occurrence of similar septa in Plesiadapis and Allocebus (Gingerich, 1975a, 1976; Cartmill and Kay, 1978), and the dubious identification and uncertain distribution of these septa in the Fayum anthropoids, render the significance of this resemblance unclear. Arterial canals in the middle ear have been invoked in arguments both for and against the notion that anthropoids evolved from omomyids. Szalay (1975a)proposed that a canal for the promontory artery larger than that for the stapedial artery may represent a shared derived feature linking tarsiers, omomyids, and anthropoids. Gingerich (1973)suggested that a relatively large promontory artery may also be found in some specimens of Notharctus, and that an enlarged promontory artery is therefore not necessarily a sign of omomyid affinities. We are inclined to believe that the relative proportions of these two arteries typically found in these several taxa do tend to support Szalay’sposition: but the support they provide is feeble, because the canals for these two arteries are subequal in size in Necrolemur (Szalay, 1975a), some extant strepsirhines exhibit marked reduction of the stapedial artery (Saban, 1963),and the presence of an arterial canal does not in any case imply the presence of a corresponding artery (Conroy and Wible, 1978).Gingerich (1973),assuming that it does, asserted that the YPM 23968 petrosal resembles that of extant anthropoids and differs from those of omomyids and Tarsius in lacking a stapedial artery. In fact, a stapedial canal is present in adult tarsiers, but the proximal part of the stapedial artery of Tarsius degenerates and becomes a mere fibrous cord early in fetal life (Hill, 1953;Wunsch, 1975).Whether the artery was equally regressive in any omomyids is impossible to say. Cartmill and Kay (1978), following Simons (1974)in refusing to lump omomyids together with anthropoids and Tarsius as a suborder Haplorhini, nevertheless proposed that Tarsius is the phyletic sister group of the Anthropoidea, and that tarsiers are more closely related to anthropoids than any early Tertiary prosimians are. In support of this hypothesis, they noted that in Tarsius and anthropoids, but in no other primates, the internal carotid artery’s pathway is what we have here called perbullar, as opposed to transpromontorial. A similar observation had been made a half-century earlier by F. Wood Jones, who remarked that in tarsiers, as in anthropoids, “the internal carotid artery enters through the bulla, not by perforation of its posterior wall” (Jones, 1929, p. 151). The partitioning-off of an anterior accessory cavity of the middle ear, remarked on above, was cited by Cartmill and Kay as a second otic similarity between Tarsius and anthropoids which is not shared by omomyids. A third such similarity may be the prenatal loss of a functional stapedial artery, although widespread parallel evolution of this trait makes it an unreliable indicator of phyletic affinities, and its distribution among extinct primates cannot be ascertained in any case. Whether or not the Cartmill-Kay hypothesis holds up in the long run, it is clear that the ear region of Oligocene anthropoids differs radically, not only from those of extant strepsirhines, but also from those of Paleogene prosimians. All early prosimians for which the ear region is known resemble each other, and differ from anthropoids, in possessing a subtympanic extension of the tympanic cavity and a partial or complete bony tube enclosing the “intrabullar” recessus meatus (Stehlin, 1912; Szalay, 1975a; Cartmill, 1975; Gingerich, 1976; Conroy, 1980a),as well as in having a transpromontorial carotid pathway and in lacking a transverse septum delimiting an anterior accessory cavity of the middle ear. The anthropoid states of the characters in question (Fig. 10, Table l), taken together, define an otic complex distinctive of higher primates. Stratophenetic considerations (sensuGingerich)as well as considerations of parsimony imply that in all these respects, the Fayum anthropoids are more derived than any other Paleogene primates so far known. Since no fossil prosimians appear, in these same respects, to be suitable anthropoid antecedents, and since the distinctive and highly specialized anthropoid otic complex was already fully evinced in catarrhines from the early Oligoceneof the Fayum, it seems likely that anthropoids were derived from a group of Eocene prosimians that is currently unknown (or a t least not known from basicranial remains). We find it impossible to believe that the anthropoid otic complex could have evolved independently in the Old and New Worlds, no matter whether we postulate a last common ancestor that resembled known adapids or known omomyids in the morphology of the ear region. The hypothesis that separate lineages of New and Old World prosimians, EARLY ANTHROPOID TEMPORAL BONES 19 I A Fig. 10. Idealized schemata of the cut-open hullae of Paleogene primates. In early prosimians of modem aspect (A), the part of the ectotympanic that frames the eardrum is aphaneric or intrabullar (1);there is a partial or complete bony anular bridge (“ossified anulus membrane”)(2); a canal for the stapedial artery is present (3);and the internal carotid artery enters the bullar posteriorly (4) and courses across the ventrolateral surface of the promontory (5).In Oligocene and later anthropoids (B),the ectotympanic is phaneric or “extrabullar” (6), and the petrosal apex is inflated by a tra- beculated anterior accessory cavity (7). The internal carotid artery of anthropoids (8)enters the bulla through an anteriorly placed carotid foramen (9) and traverses the septum (asterisk)between the tympanic cavity and anterior accessory cavity; as a result, the fenestra cochleae (10)is directly visible from the ventral aspect. The position of the auditory tube is indicated by white arrows; the shorter white arrow in (B)shows the aperture through which the anterior accessory cavity communicates with the rest of the middle ear. whether omomyids sensu lato (Gregory, 1951, vol.1, p. 473; Gazin, 1958; Romer, 1968,p. 185), adapids (Gingerich, 1975b),or unspecified but presumably different prosimian stocks (Cachel, 1976, 1979), gave rise independently to Platyrrhini and Catarrhini, seems wholly untenable. Platyrrhines and catarrhines evidently had a last common ancestor that could not have been ancestral to any other known primates. When and where did that common ancestor live? The ceboid-like features of the ear region of the Fayum anthropoids, together with the persistence of three premolars in the Parapithecidae, have been invoked by Hoffstetter (1971,1972,1974b, 1977a, b) as support for his hypothesis that the last common ancestor of the Old and New World anthropoids inhabited Africa in the Eocene, and that the primates of South America are descended from a parapithecid-like form that managed to cross the South Atlantic by rafting. Our reasons for rejecting this hypothesis are those presented by Simons (1976). Other hypothetical South Atlantic connections, involving a common anthropoid ancestry in Gondwanaland prior to the separation of Africa and South America (Hershkovitz, 1977)or an invasion of Africa by early platyrrhines, again by rafting (Szalay, 1975b),seem equally implausible. In any case, there is no reason for believing that the few features of the platyrrhine ear region (anularecto- 20 M. CARTMILL, R.D.E. MacPHEE, AND E.L. SIMONS tympanic, more medial carotid foramen, less ventral stylomastoid foramen, etc.) which distinguish platyrrhines from modern catarrhines represent anything but primitive anthropoid features lost in post-Oligocene catarrhines. Although the earliest undoubted anthropoids are those of the Fayum, there are sound if not conclusive reasons for thinking that anthropoids were present at about the same time in South America (Branisella)and slightly earlier in Burma (Pondaungia; perhaps Amphipithecus). The intermediate spatial position and antecedent temporal position of the Burmese fossils suggest that the ancestral anthropoid was a mid-Eocene or earlier inhabitant of either eastern Asia (Conroy and Bown, 1974; Conroy, 1978)or western North America (Szalay and Delson, 1979), and that dispersal of anthropoids from one hemisphere to the other may have occurred via Beringia. Discovery of the ear region of Chumashius or other omomyids from the west coast of North America might well shed new light on the problem of anthropoid origins. ACKNOWLEDGMENTS We thank Drs. S. Anderson, E. Delson, R. Emry, M.C. McKenna, and R.W. Thorington, Jr., and Mr. D.H. Russell and other members of the staffs of the National and American Museums of Natural History for their invaluable help. We are grateful to Drs. R.F. Kay and J.G. Fleagle for their comments on the manuscript, and to Dr. Kay for his aid in identifying the Apidium teeth in the YPM 23968 assemblage and for allowing us to reproduce his stereophotograph of the Aegyptopithecus skull (Fig. 5 ) . The Fayum material used in this study has been recovered by expeditions under the third author’s direction from 1960 to 1980, made possible by grants BNS-77-20104 and BNS-80-16206 from the National Science Foundation and Smithsonian Foreign Currency Awards 23 and 809479. 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It may represent a large parapithecid.