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Proc. Natl. Acad. Sci. USA Vol. 91, pp. 9946-9950, October 1994 Anthropology A remarkable cranium of Plesiopithecus teras (, Prosimii) from the of Egypt (LorIformes/ evolutlon/cranial morphology) ELWYN L. SIMONS* AND D. TAB RASMUSSENt *Department of and , Duke University, Durham, NC 27705; and tDepartment of Anthropology, Washington University, St. Louis, MO 63130 Contributed by Elwyn L. Simons, May 18, 1994

ABSTRACT Between 1991 and 1993 seimens ofa highly dinary abundance of hyracoids at this site (8). These distinctive primate, named Pksiopithecus teras [Simons, E. L. represent a diverse radiation with extremes of (1992) Proc. Natl. Acad. Sci. USA 89, 10743-10747], were size and adaptation never seen elsewhere in this order. found at site L-41 in late Eocene deposits of the Fayum Other unusual faunal elements are abundant small cre- Depression, Egypt. The most important of these specimens odonts and , elephant shrews of several different consists of a nearly complete skull, which facilitates the eval- sorts, and a wide variety of water birds. Lithologically this uation ofaffinities ofthis primate. Characteristics ofthe known site is also unusual in that it is a greenish clay deposit in a material now demonstrate that Plesiopithecus is a , stratigraphic setting where sands of various degrees of although mandibular molar morphology, in particular, bears coarseness are the normal regimen. The fime clay accounts similarity to that in molars of archaic members of Anthro- for preservation in great detail of many specimens, and poidea. Plsiopithecus has a postorbital bar but lacks postor- there is a much higher incidence of complete skulls and bital closure, it has upper molars without hypocones, and it partial skeletal associations than is typical of most early may retain four lower . Its familial rank was con- Tertiary fossil sites. Because of such occurrences, this very sidered incertae sedis by Simons [Simons, E. L. (192) Proc. large locality holds great potential for further finds of skulls Nall. Acad. Sci. USA 89,10743-10747]; it can now be demon- and skeletal remains that will illuminate the evolutionary strated that Plsiwpithecus justifies establishment of a new history of primates. family and superfamily. The new superfamily apparently lies Kappelman et al. (9) presented paleomagnetic reversal closer to the toothcomb (streprhines) than to any analyses of sediments in the Jebel Qatrani Formation that other known primate group. Under this interpretation the suggest the L-41 beds were deposited during chron C15r, enlarged, procumbent tooth in the jaw of Plesiopithecus is which has been dated to 35.6-35.9 million years (My). These homologous to either the lateral incisor or the canine of the results are based on preliminary sampling of Fayum sedi- prosimian toothcomb. ments and may be subject to further refinement with future work. This date ranks the fauna ofL-41 in the late Eocene as In papers published in thisjournal in 1989 and 1992, one ofus indicated by recent geological research (10, 11). Faunal (E.L.S.) described several new primates from an African correlations also support an Eocene age for the locality (12) Eocene locality (site L-41) in Fayum Province, Egypt (1, 2). and faunal comparisons suggest to us that this site is older This Fayum site is remarkable for the diversity of primates than Algerian sites reported to be of middle Eocene age (13, that it contains. The majority of species (Arsinoea kallimos, 14). Site L-41 is older than Omani sites that have also yielded Serapia eocaena, Catopithecus browni, Proteopithecus early anthropoid primates (15). The site of Chambi, Tunisia, sylviae) belong to the higher primate suborder Anthropoidea may be of similar or greater antiquity than site L-41 (16). (1-4). It is possible that these four primates may belong in is not an separate families. The fifth species, now identified and here Although Plesiopithecus early anthropoidean, it is described in detail, demonstrates the early occurrence of contemporary with Catopithecus and other earliest demon- another major group of prosimians. Another undescribed strable simians at L-41. Eosimias recently described by prosimian recently recovered from L41 may be ranked as a Beard et al. (7) from 45-My-old deposits near Shanghuang, cercamoniine adapid (5), a group otherwise known from China, is not a simian (=anthropoidean) and may not even be Europe, North America, and Eurasia. At another early a primate. Fayum site (locality E) an omomyid prosimian occurs, and in Abbreviations used in the text: CGM, Cairo Geological the upper sequence ofthe Fayum there are also a and Museum; DPC, Duke University Primate Center; YPM, Yale a loris (6). This great diversity of primates still provides the Peabody Museum. best evidence that Anthropoidea, and perhaps even Primates as an order, arose in Africa, in spite ofrecent assertions to the SYSTEMATICS contrary by Beard etal. (7). The "simian" described from the latter fauna is not an early anthropoidean. Order Primates Lineus, 1758; Suborder Prosimi , hIger, Quarry L-41 is also of interest because the primates that 1811; Infraorder cf. Lrisiformes; Superfamily occur in it are quite distinct from most of those occurring Pleskolteaodea, new; Family Plpithecdae, new; genus higher in the stratigraphic section (in what appear to be Plesiopithecus Simons, 1992. early deposits). This suggests that there was not only a temporal difference of considerable magnitude but Type species. Plesiopithecus teras Simons, 1992. also possible environmental differences as well that af- Revised diagnosis. Can be distinguished from Anthro- fected the faunal composition. Most striking is the extraor- poidea by the absence of postorbital closure and from all other primates in showing the following combination: large The publication costs of this article were defrayed in part by page charge orbits with the lacrimal foramen at the margin of the orbit; payment. This article must therefore be hereby marked "advertisement" an upper dental formula of (?0-2)-1-3-3 and lower dental in accordance with 18 U.S.C. §1734 solely to indicate this fact. formula of 0-1-4-3 or 1-1-3-3; enlarged procumbent lower 9946 Downloaded by guest on October 2, 2021 Anthropolgy: Simons and Rasmussen Proc. Natl. Acad. Sci. USA 91 (1994) 9947

FIG. 1. Lateral view of right and left sides of the cranium of P. teras (DPC 12393). canine or lateral incisor and enlarged, vertical upper canine; Type locality. Quarry L-41, Jebel Qatrani Formation, molar trigonids short mesiodistally with paraconid reduced Fayum Province, Egypt. to shelf-like crest; slight metastylids present; hypocones Referred material. DPC 12393, a crushed but nearly com- absent. plete cranium with maxillary (Figs. 1 and 2); DPC 11636, left with C, P1-4, M1-3 (Fig. 3); DPC 13607, P. teras Simons, 1992 left mandible with C, P2, P4, M1-3. Diagnosis. As for genus. Holotype. CGM 42291, right mandible with C, P2-4, M1-3. Measurements. Table 1.

FIG. 2. Crown view of the palate and upper teeth of P. teras (DPC 12393). Downloaded by guest on October 2, 2021 9948 Anthropolgy: Simons and Rasmussen Proc. Natl. Acad Sci. USA 91 (1994)

FIG. 3. Medial view of the mandible of P. teras (DPC 11636).

DESCRIFION from quarry I (6), the basal cingulum is not distinct on the The anterior border, nor is it clear on the buccal side ofthe tooth. known cranium (DPC 12393) is nearly complete, but The M2 of the new L-41 much ofit is badly crushed in the Parts primate further resembles YPM sagittal plane (Fig. 1). 23987 in having relatively small paracone and metacone of all the maxillary teeth are present; the preillae and placed close together (the latter smaller than the former) and incisors, ifany, are features ofthe missing. Some face, orbits, a much larger protocone placed relatively far lingually. The zygoma, cranial vault, and basicranium can be determined, resemblances between the Plesiopithecus M2 and YPM and these are described in sections below. The postcanine 23987 suggest the latter may be an M2, rather than an M3, as dentition and snout are about the size ofthose in Nycticebus originally reported (6). M3 is small and simple in structure, coucang, but brain volume was smaller the clearly and exhibiting only the three main cusps. rostrum was unusually deep. Facial Sleton. The orbits are clearly quite large and Maxillary Dentition. The canines are and large vertically almost certainly imply a nocturnal adaptation The with roots (Fig. 4). implanted, big extending upward into the face (Fig. right orbit appears to have been increased in size by distor- 1). In shape, the canines are buccolingually compressed ton, whereas that ofthe left side is decreased (Fig. 1). Skull (Table 1), forming distinct mesial and distal edges. There is length (about 52-54 mm) is similar to that ofN. coucang, and a small occlusal wear facet at the tip of the unbroken left it appears that the orbits (14.0-17.6 mm) were comparably canine and evidence of wear on the distal edges of both large. When these estimated sizes are ranked with compar- canines. ative primate data (17), Plesiopithecus falls within the noc- The upper teeth are illustrated in Figs. 1 and 2. P1 is turnal range, near Avahi and Nycticebus. bilaterally absent. P2 is the smallest maxillary tooth; it is On the right side of the skull, a small lacrimal foramen is simple in structure with one primary cusp and with small nubs clearly present at the margin ofthe orbit. This differs from the or cuspules on the mesial and distal borders. The tooth is facial position ofthis foramen in and from the intraor- bilaterally compressed. P3 is also single-cusped, but it has a bital position in anthropoids. The orbital rim passes directly small lobe extending lingually from the cusp. The lobe does across the foramen, as in Nycticebus. There also appears to not bear a separate cusp. P4 is much larger than the other be a suborbital fissure open on the anterior floor of the orbit. premolars and it is more complex in shape. In outline the Presumably, a postorbital bar encircled the side of the tooth is mesiodistally short but buccolingually broad. It has orbit. The frontal process of this bar is preserved on each two distinct cusps, one buccal and one lingual (see dimen- side. As in Nycticebus, the dorsal root of the postorbital bar sions in Table 1). has three surfaces (it is trianlar in section): an orbital face, The three molars are all fairly simple, three-cusped a temporal face, and a dorsal face. teeth-no hypocones are present. They decrease in size from The facial exposure of the maxilla is short and deep. It front to back. Ml has a pronounced lingual cingulum bearing appears that small, vertically oriented premaxillae possibly small beaded cuspules. The protocone is the largest cusp; containing incisors have detached from the front of the face. there are slight but distinct paraconule and larger meta- The upper canines, in spite ofsagittal crushing, are separated conule. M2 is slightly smaller than Ml and has a basal from each other. In life, there would have been a gap of6 mm cingulum running around the protocone and along the distal or more, unlike the lower canines, which are in contact. Face border ofthe tooth. As in a lorisoid upper molar (YPM 23987) shape has probably been somewhat distorted by crushing Table 1. Dental measurements (in mm) of P. teras showing mesiodistal length (1) and buccolingual width (w) of the four known specimens DPC C P2 P3 P4 Ml M2 M3 no. I w 1 w 1 w w 1 w I w I w Upper dentition 12393 4.5 2.5 2.4 1.7 2.6 2.4 2.7 3.9 4.2 4.8 3.0 4.3 1.9 3.1 Lower dentition Type 3.8 1.9 2.6 1.4 2.5 1.8 2.9 2.3 3.5 3.0 3.3 2.7 3.3 2.4 11636* 3.6 2.1 2.7 1.4 2.9 1.7 3.1 2.2 3.5 2.9 3.1 2.8 3.2 2.3 13607 4.0 2.1 3.5 2.9 3.4 2.9 *Lower P1 in DPC 11636, the only specimen preserving this tooth has a mesiodistal length of 2.7 and buccolingual width of 1.0 mm. Downloaded by guest on October 2, 2021 Anthropolgy: Simons and Rasmussen Proc. Natl. Acad. Sci. USA 91 (1994) 9949

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FIG. 4. Drawing of a reconstructed lateral view of the skull and mandible of P. teras, based on material described in this report. together from side to side, but it seems clear that the face was very deep above the premolars. The anterior edge ofthe orbit runs forward to align just above the P4. The infraorbital foramen sits fairly low on the face, away from the orbital margin, and a short distance above the P3. The zygomatic arch is lightly built but is badly damaged so few details can be discerned. Basicranium. The glenoid surface of the temporomandib- ular joint is visible on the left side. It is relatively flat and broad, unlike the guttered fossa of tarsioids (18, 19). The pterygoid plates are damaged and compressed together. On the left side the mastoid is crushed and distorted in shape. On the right side the mastoid has been broken open (Fig. 1). The broken rim suggests that the mastoid may have been large and inflated like those of lorisoids. The wall enclosing what appears to be the mastoid air space is relatively thick. The occipital condyles are both present and are about the same size as in typical N. coucang or crassicaudatus. Cranial Vault. Remains of a nuchal crest are evident. The vault carries distinct temporal lines that converge and, at FIG. 5. Comparison of the crown views of the right mandible in least toward the back ofthe vault, form a sagittal crest. There P. teras (the holotype, CGM 2291) and N. coucang. is no evidence of a metopic suture. On the frontal bone, between the internal and dorsal margins of the orbit and the canine appears to come to a rounded point, with only the temporal lines, is a flattened, diamond-shaped area, some- slightest evidence ofapical wear. From the apex a wear facet what depressed, which is similar to this region of the skull in runs down the posterior side of the tooth, but less than half lorisoids. way. The lack ofany wear surface reaching down to the base Mandible. The holotype mandible and dentition were de- of the tooth implies that, unlike in the modern strepsirhines, scribed and illustrated elsewhere (1, 4). In this section, we there was no occluding anterior lower . The lower describe additional details oftooth andjaw structure evident molars are highly distinctive from those of extant strep- on the two additional . In DPC 11636 the angle of sirhines, notably in the highly rounded talonid basin, the the mandible is extended backward a considerable distance lingually shifted protoconid, and the extensive buccal slope but it is increasingly damaged posteriorly, so that its full of the tooth. length is uncertain (Fig. 3). The mandibular condyle is well preserved on this specimen and shows a broad, relatively flat head, unlike those of tarsioid primates. This specimen also DISCUSSION AND CONCLUSIONS possesses a first lower premolar (Fig. 3), a tooth absent from Originally, Simons (1) as the other two specimens (perhaps due to postmortem loss or reported Plesiopithecus having variability). This tooth might also be the lateral canine affinities with anthropoids, even though he pointed out that derived from a toothcomb. The P1 is only about half the size its ranking with any known family was very dubious and ofP2 and is single-rooted with a crown that is angled forward placement should await further finds. The molars of the type and flange-like, reaching over the distal base ofthe canine. In mandible showed a decrease in size posteriorly similar to that all three specimens of P. teras the lower canine is greatly seen in Catopithecus and Proteopithecus. Also, unlike elongated and strikingly compressed from side to side. There lorisoids, the molar talonids are broader and the molar outline is a wear facet on the mesial side indicating contact with the is rounded, unlike the waisted outline of most prosimian opposite canine. It is clear from all three specimens that the molars. Moreover, the loss of permanent lower incisors and symphysis is unfused and that no lower incisors could have appressed lower canines appeared to be a shared specializa- been present. However, the canine is generally reminiscent tion found otherwise only in Parapithecus. In addition, the of the tooth that forms the lateral tine of the toothcomb in holotype did not show the P1 and therefore the lower dental extant and Lorisiformes (Fig. 5). The upper formula appeared to be the same as in Parapithecus. For Downloaded by guest on October 2, 2021 9950 Anthropolgy: Simons and Rasmussen Proc. NatL Acad. Sci. USA 91 (1994) these reasons, the resemblances to lorisids did not appear to they could have most easily been derived from a species be compelling evidence for affinity. having a toothcomb, through hypertrophy of the canines The cranium and upper dentition make it clear that Ple- coupled with loss of the incisors. Therefore, this late Eocene siopithecus is not an anthropoid. The cranium unambigu- species provides evidence that the toothcomb adaptation ously lacks postorbital closure. A postorbital bar is present. might have already developed in pre-late Eocene times. The similarities between Plesiopithecus and Parapithecus in the anterior lower dentition are clearly convergent because We thank F. A. Ankel-Simons, I. M. Tattersall, T. M. Bown, and parapithecids are undoubted anthropoids with postorbital P. D. Gingerich for offering their expertise on the manuscript. The closure and a whole series of other cranial and postcranial specimens were prepared by P. S. Chatrath, F. A. Ankel-Simons, and E.L.S. Illustrations were prepared by E.L.S. and D.T.R. The anthropoid features (20, 21). Otherfeatures ofPlesiopithecus research was supported by grants from the National Science Foun- that stand in contrast to most other Fayum anthropoids dation (BNS 88-09776 and BNS 91-08445). Research in Egypt was include lack ofhypocones on upper molars, lacrimal foramen carried out with the assistance ofthe Egyptian Geological Survey and on rim of orbit, lack of symphyseal fusion, possession of P1, Mining Authority and the director and staff of the Cairo Geological and elongated and compressed lower front teeth (resembling Museum. The specimens were found by E.L.S. (skull) and E.L.S., enlarged toothcomb teeth). K. C. McKinney, and P. S. Chatrath (jaws). This is Duke Primate There are no characters specifically resembling either Center publication no. 589. lemurs or in the new material. P. teras differs from all tarsiiform primates in its molar structure and in the 1. Simons, E. L. (1992) Proc. Natl. Acad. Sci. USA 89, 10743- nonguttered temporomandibular joint (18, 19). Nannopithex 10747. 2. Simons, E. L. (1989) Proc. Nati. Acad. Sci. USA 86, 9956- has an enlarged anterior lower tooth but it is not laterally 9960. compressed like the canine of Plesiopithecus, nor are there 3. Simons, E. L. (1990) Science 247, 1521-1612. any derived dental resemblances to it or other microchoer- 4. Simons, E. L., Rasmussen, D. T., Bown, T. M. & Chatrath, ines. Although there are several intriguing similarities be- P. S., in Anthropoid Origins, eds. Fleagle, J. G. & Kay, R. F. tween P. teras and extant lorisoids (Table 2, Fig. 5), it is clear (Plenum, New York), in press. that P. teras is not closely affined to this latter group either. 5. Simons, E. L., Rasmussen, D. T. & Gingerich, P. D., J. Hum. It lacks several shared features ofmodern lorisoids and bears Evol., in press. its own peculiar specializations. For example, in all extant 6. Simons, E. L., Bown, T. M. & Rasmussen, D. T. (1987) J. lorisoids, upper and lower fourth premolars are fully molar- Hum. Evol. 15, 431-437. are reduced to three in number, and 7. Beard, K. C., Qi, T., Dawson, M. R., Wang, B. & Li, C. (1994) ized, the lowerpremolars Nature (London) 368, 604-609. all share the toothcomb adaptation. Plesiopithecus therefore 8. Rasmussen, D. T. & Simons, E. L. (1990) Neues Jahrb. Geol. falls outside the superfamily Lorisoidea, clearly warranting Palaeontol. Abh. 182, 187-209. its own new superfamily. Plesiopithecus could prove to be a 9. Kappelman, J., Simons, E. L. & Swisher, C. C., III (1992) J. member of Lorisiformes, or it may eventually be seen as a Geol. 100, 647-667. sister to both the Lorisiformes and Lemuriformes. The 10. Odin, G. S. & Montanari, A. (1989) C. R. Acad. Sci. Paris 309, braincase ofP. teras appears to be distinctly smaller than that 1939-1945. of extant lorisoids relative to size (of the face, orbits, and 11. Prothero, D. R. & Berggren, W. A., eds. (1992) Eocene-Oli- teeth), as would be expected for early Tertiary forms (22). gocene Climatic and Biotic Evolution (Princeton Univ. Press, the lower canines and loss of lower Princeton). The specialization of 12. Rasmussen, D. T., Bown, T. M. & Simons, E. L. (1992) in incisors set the group represented by P. teras apart from all Eocene-Oligocene Climatic and Biotic Evolution, eds. Pro- other prosimians. Nevertheless, the compressed, forward- thero, D. R. & Berggren, W. A. (Princeton Univ. Press, Prince- tilted and elongated anterior teeth of this species look as if ton), pp. 548-566. 13. Gevin, P., Feist, M. & Mongereau, N. (1974) Bull. Soc. Hist. Table 2. Possibly derived morphological features shared by P. Nat. Afir. Nord. 65, 371-375. teras and extant lorisoid primates 14. Godinot, M. & Mahboubi, M. (1992) Nature (London) 357, 1. Buccolingually compressed, vertically implanted, large 324-326. 15. Thomas, H., Roger, J., Sen, S., Bourdillon-de-Grissac, C. & upper canines Al-Sulaimani, Z. (1989) Geobios 22, 101-120. 2. Lower canines laterally compressed, resembling much 16. Court, N. & Hartenberger, J. L. (1992) Palaeontology 35, enlarged toothcomb canines 309-317. 3. Lacrimal foramen at margin of orbit 17. Rasmussen, D. T. & Simons, E. L. (1992) Int. J. Primatol. 13, 4. Apparent pneumatization of the mastoid 477-508. 5. Obliquely oriented trigonids of lower molars, with 18. Simons, E. L. (1961) Bull. Br. Mus. (Nat. Hist.) Geol. 5, 45-69. paraconids reduced to a shelf 19. Rosenberger, A. L. (1985) Folia Primatol. 45, 179-194. 6. Reduced upper and lower third molars 20. Fleagle, J. G. & Kay, R. F. (1987) J. Human Evol. 16,483-532. 7. M1-2 morphologically similar to those of lorisoids 21. Simons, E. L., Am. Mus. Novit., in press. Upper 22. Le Gros Clark, W. E. (1956) Fossil Mamm. Afr. 9, 1-6. Downloaded by guest on October 2, 2021