Cranial and dental anatomy of Antilohyrax pectidens: a Late Eocene hyracoid (Mammalia) from the Fayum, Egypt

Abstract

ABSTRACT The hyracoid Antilohyrax pectidens Rasmussen and Simons, 2000 from quarry L-41 in the Fayum, Egypt displays many interesting features, including a comb-like, pectinate lower first incisor similar to that of the dermopteran Cynocephalus. Antilohyrax was originally described as lacking upper incisors, and having retracted nasal bones and selenodont cheek teeth, functionally resembling characters found in bovid artiodactyls. Analysis of cranial and postcranial material led to the hypothesis that Antilohyrax was a cursorial browser. Recent expeditions have recovered additional material that contributes greater detail about cranial and dental morphology and allows for the reassessment of characters previously unknown or misinterpreted. Among these is the presence of at least two pairs of upper incisors, the central pair of which form tusks as in all other hyracoids, and a slender nasal bone which projects anteriorly to the level of the premaxilla. There is evidence of a pad on the premaxilla that occludes with the pectinate lower incisors. In the mandible, a second pair of incisors has been recovered that are sickle shaped, lack pectinations, and occlude with the upper tusks. Other notable characters preserved in the new specimen include the presence of a complete postorbital bar, a large, round, and blunt postorbital boss, a lateral flange on the zygomatic arch, a deep antorbital groove of the frontal bone, a lambdoid crest, a long paroccipital process, and a unique nuchal region. Comparisons with newly recovered and as yet undescribed cranial material of Titanohyrax reveal more characters shared by these genera, strengthening the case for their inclusion as sister taxa within the Titanohyracinae. Examination of characters relevant to paenungulate phylogenetics confirm earlier observations that extant hyracoids have changes in cranial proportions that result in some character states not representative of early hyracoids. Functional inferences lend further support to the suggestion that Antilohyrax was a folivorous browser.