The tympanic part of the temporal bone was particularly developed, even more than its relative Pachyrukhos, and it is probable that its auricle was quite large, similar to the ears of a hare.

The pelvis was elongated, slender and lightly build, while the femur was equipped of a small head separated from the main bone.

The femur was even longer than in Pachyrukhos, and had a small trochanter curiously pushed back in the posterior part.

[1] Its body was slender, with a very short tail and strong forelegs, although much shorter than the hind legs, equipped with long metatarsals.

[citation needed] The genus Prosotherium was first described in 1897 by Florentino Ameghino, over fossilized remains discovered in Patagonia in Late Oligocene terrains.

Despite this, until 2019, phylogenetic analyses regularly scored Propachyrucos for cranial and post-cranial characters, which are known only from the synonymized P. ameghinorum and P.

[2] The Late Oligocene terrains of Patagonia present at least three genera of hegetotheres with hypsodont teeth : Prosotherium, Propachyrucos and Medistylus, the latter of which is sometimes considered an interatheriid.

This implies a strict repartition of ecological niches among the Oligocene hegetotheres, but also reflects the remarkable evolutionary radiation of rodent-like ungulates during the Cenozoic of South America, and suggest environmental differences between the fauna of Patagonia and the fauna of Uruguay and Bolivia, where those animals were absent.