Comparative Sulcal Morphology of the Late Miocene Fossil Ape, Rudapithecus hungaricus

Endocasts of fossil hominoids are exceedingly rare. The only fossil ape endocast analyzed in detail is that of Ekembo nyanzae (KNM-RU 7290), from the early Miocene of Kenya. Two partial crania of Rudapithecus hungaricus, from the late Miocene of Hungary, preserve sufficient details to reconstruct large amounts of endocranial morphology of this fossil hominine. No other non-hominin fossil hominid endocast preserves external morphology with the same completeness and detail. Here, we provide the first complete description of the Rudapithecus sulcal pattern.

Sulcal patterns from a comparative sample of extant non-hominin hominoid endocasts were identified according to classical descriptions of hominoid sulcal patterns. Sulcal patterns of both Rudapithecus endocasts were identified using both classical descriptions of hominoid sulcal patterns and comparisons with morphology identified in the extant sample.

We identify a hominid-like sulcal pattern in Rudapithecus that is more complex than hylobatids but simpler than Pan, most closely resembling Gorilla and Pongo while exhibiting several Gorilla affinities.

The study of the Rudapithecus crania reveals a de-coupling in hominid brain evolution. Cranial shape overall is African ape-like, the shape of the endocast is more primitive, and the sulcal pattern is generally hominid-like. The Rudapithecus endocasts provide evidence of the primitive condition of the brain in hominine evolution.