Early therapsids like Karenites lack the well - developed auditory system of mammals and probably had a poor sense of hearing .
Mammals had evolved from a restructuring of bones in the back of the skull and the lower jaw .
Early therapsids like Karenites lack the well - developed auditory system of mammals , which had evolved from a restructuring of bones in the back of the skull and the lower jaw , and probably had a poor sense of hearing .