<i>Pyrotherium macfaddeni</i>, sp. nov. (late Oligocene, Bolivia) and the pedal morphology of pyrotheres

ABSTRACT The common pyrothere of Salla, Bolivia (Deseadan, late Oligocene) is described as a new species, Pyrotherium macfaddeni. It is distinguished by its small size (linear dimensions but two-thirds those of Pyrotherium romeroi) and pi-shaped upper premolare. Recovery at Salla of the first known calcaneum of Pyrotherium permits the description and analysis of the proximal tarsus. It is distinctive by the pronounced dorsoventral compression of the calcaneal tuber and similar flattening of the astragalar trochlea, concavity of the ectal facet of the calcaneum, and extreme reduction of contact between the calcaneum and the cuboid. These derived characters were not seen in any other mammal examined except the embrifhopod Arsinoitherium from the Tertiary of Africa. Whether this is due to common ancestry or the unusual mode of locomotion used by these animals (graviportal and plantigrade) remains to be seen. This more complete study of the tarsus of Pyrotherium fails to support the proposed relationship of pyrotheres with the Xenungulata.