Fossil remains have been found in the Late Paleocene Nomogen and Khashat Formations in Nao-mugen and Bayn Ulan of China and Mongolia, dated to 59-55 million years ago from the Thanetian age.

Indirect evidence suggest that hair first appeared on non-mammalian therapsids (Therapsida), back in the Triassic or even earlier.

This is inferred from small hollows on the bone of the snout similar to holes in the skulls of cats which provide space for concentrations of nerves and blood vessels that innervate prominent whiskers (specialized hairs).

[citation needed] In the same Upper Paleocene strata, exceptionally preserved coprolites, originally excreted by unknown carnivorous animals, were discovered to contain undigested remains, including hair from Lambdopsalis and three other different mammal taxa.

[8] Fully grown L.bulla individuals were estimated to have had a body mass of 0.78 kilograms (1.7 lb) and skull length of about 60.8 millimetres (2.39 in).