Limb skeleton and locomotor adaptations of apidium phiomense, an Oligocene anthropoid from Egypt

Abstract

Apidium phiomense is the most common primate from the early Oligocene deposits of Fayum, Egypt. It is known from hundreds of dental remains and dozens of skeletal remains, including numerous representatives of the long bones of the forelimb and hindlimb. Apidium phiomense was a small (1,600 g) arboreal quadruped. The forelimb bones of this species show features characteristic of arboreal quadrupeds and lack characteristic features found in the forelimb bones of vertial clingers, terrestrial quadrupeds, or suspensory species. The pelvis and hindlimb bones show numerous adaptations for leaping from a quadrupedal position. In general, Apidium lacks characteristic features of either cercopithecoid monkeys or hominoid apes. Overall, the skeleton shows greatest similarities to the same elements of small platyrrhines such as Saimiri and is also very similar to the hypothetical morphotype for ancestral platyrrhine. The skeleton of Apidium phiomense is the most primitive anthropoid postcranial skeleton known.

Evolution of locomotion in Anthropoidea: the semicircular canal evidence

“…In contrast, the results for Apidium are somewhat surprising and contradict expectations. Postcranial remains of Apidium display adaptations to leaping [29,[31][32][33][34][35][36], suggesting this taxon was an agile arborealist. The semicircular canal size data, however, suggest a slower animal more similar to other Fayum anthropoids such as Catopithecus, Parapithecus and Aegyptopithecus.…”

Anthropoid humeri from the late Eocene of Egypt

“…Among primates, this index is more similar to that of cheirogaleids (35) than that of the small cebines (humerofemoral indices of Ϸ80-85) that otherwise appear to be the most appropriate extant analogues for early anthropoid locomotion. This humerofemoral index is considerably higher than the index of approximately 62 estimated for Apidium phiomense [based on the mean measurements of humeral and femoral length reported in Fleagle and Simons (22)] as well as the indices of 64.6 and 59 that have been reported for the omomyiforms Shoshonius (36) and Microchoerus (37), respectively; these indices are, in turn, much higher than the humerofemoral indices of 45-50 seen in small extant vertical clingers and leapers such as Tarsius. As in cheirogaleids and many small platyrrhines, P. sylviae also has a relatively high crural index (27).…”

“…1C) is complete and almost perfectly preserved aside from minor damage to the humeral head, a break on the ventral aspect of the distal shaft lateral to the entepicondylar foramen, and damage to the medial aspect of the trochlea. In many morphological details these humeri are most similar to DPC 1311, a specimen from quarry M (early Oligocene) referred to the parapithecid Qatrania fleaglei (22), than they are to the humeri of other Fayum primates.…”

“…Tarsals attributed to the purported basal anthropoid Eosimias have been described recently (14), but no postcranial material is available for southeast Asian primates such as Amphipithecus, Pondaungia, Siamopithecus, and Bahinia, all of which have been claimed to be basal anthropoids on the basis of recently recovered dental remains (5,6,9,10). In contrast, the postcranial anatomy of early Oligocene Fayum anthropoids is now fairly well documented (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25), but with the exception of five isolated specimens described by Gebo et al (26) and associated hindlimb remains of Proteopithecus sylviae recently described by Simons and Seiffert (27), very little is known about the postcranial morphology of the diverse anthropoid taxa preserved at the African late Eocene quarry L-41. Here we report on humeral material reliably referred to two anthropoids from quarry L-41, Proteopithecus sylviae and Catopithecus browni.…”

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“…Existen ciertos caracteres en varios de los primates del Fayum, tanto dentarios como postcraneales, que se asemejan notablemente a la morfología hallada en los platirrinos (Fleagle y Bown, 1983;Fleagle y Kay, 1987;Fleagle y Simons, 1995). No obstante, podrían significar retenciones primitivas de los ancestros de todos estos grupos, debido a la presencia simultánea en primates notablemente divergentes.…”