Bipedal browsing adaptations of the unusual Late Eocene-earliest Oligocene tylopod Anoplotherium (Artiodactyla, Mammalia)

Abstract

The first well-preserved, partial associated skeleton of Anoplotherium latipes, with critical details of tibia, femur, ulna and cervical vertebrae, is described from the UK earliest Oligocene. Anoplotherium and related genera are interpreted as facultatively bipedal, extended-limb, high browsers, based especially on the following: pelvis with flared ilia and long pubic symphysis; medially bowed tibiae shorter than femora; trunk vertebrae enlarging caudally; extensive attachment for supraspinous and deltoid muscles for raising the forelimbs; long muscular tail for balance; and large hind foot processes for attachment of suspensory ligaments. Although overall most like extinct ground sloths among bipedal browsers, Anoplotherium is unique in combining long muscular tail, hooves instead of claws and relatively short forelimbs. Primitive retention of the long tail facilitated an erect stance without need for the long, clawed forelimb support evolved by chalicotheres. Emphasis was instead on strengthening support by the hind-quarters. With only toe-number differences, A. latipes and A. commune may have been sexual dimorphs. The large Anoplotherium species would have been able to browse 2-3 m above the ground with no competition from other contemporaneous European terrestrial mammals. Bipedal browsing is an adaptation previously unrecognized in European Eocene communities. © 2007 Natural History Museum.