Nearly complete skeleton ofTetraclaenodon(Mammalia, Phenacodontidae) from the early Paleocene of New Mexico: morpho-functional analysis

Abstract

We describe the relatively complete skeleton ofTetraclaenodonundoubtedly associated with its dentition, from the Torrejonian interval of the Nacimiento Formation in the San Juan Basin, New Mexico.Tetraclaenodonis the most primitive and oldest genus of the family Phenacodontidae and is very important for assessing the phylogenetic relationships of the family. The newly described skeleton belonged to a lightly built terrestrial mammal that could use trees for shelter. The structure of the ulna, manus, femur, crus, and pes corresponds to that of a typical terrestrial mammal, while morphological features such as the low greater tubercle of the humerus, long deltopectoral crest, pronounced lateral supracondylar crest, and hemispherical capitulum indicate some scansorial adaptations ofTetraclaenodon. The postcranial skeleton ofTetraclaenodondoes not exhibit the cursorial adaptations seen in later phenacodontids and early perissodactyls. Phylogenetic analysis did not recover monophyletic “Phenacodontidae”; instead, phenacodontids formed a series of sister taxa to the Altungulata clade.Tetraclaenodonis the basal-most member of the “Phenacodontidae” + Altungulata clade.