Pachynolophidae Pavlow, 1888 Palaeotheriidae is an extinct family of herbivorous perissodactyl mammals that inhabited Europe, with less abundant remains also known from Asia,[3] from the mid-Eocene to the early Oligocene.

[4] Palaeotheres ranged widely in size, from small species like Palaeotherium lautricense, which is estimated to have only weighed 36 kg (79 lb)[5] to large species like Palaeotherium magnum, which are comparable in size to living equines, with body masses over 200 kg (440 lb).

[7] Evidence suggests that palaeotheriids went extinct in Eurasia during the Early Oligocene, approximately 33 Ma, as part of a faunal turnover event known as the Grande Coupure.

The Eocene-Oligocene transition marked a significant global cooling event caused by the onset of Antarctic glaciation.

This resulted in drier and more open habitats dominating the early Oligocene, and the loss of the dense forests that characterised the Eocene epoch.