Wikipedia
The Tritheledontidae or tritheledontids, also known as ictidosaurs, were small to medium-sized (about 10 or 20 cm long) cynodonts. They were extremely mammal-like, highly specialized cynodonts, although they still retained a very few reptilian anatomical traits. Tritheledontids were mainly carnivorous or insectivorous, though some species may have developed omnivorous traits. Their skeletons show that they had a close relationship to mammals. Tritheledontids or their closest relatives may have given rise to primitive mammals. The tritheledontids were one of the longest lived non-mammalian therapsid lineages, living from late Triassic to the Jurassic period. Tritheledontids became extinct in the Jurassic period, possibly due to competition with prehistoric mammals such as the triconodonts. They are known from finds in South America and South Africa, indicating that they may have lived only on the supercontinent of Gondwana. The family Tritheledontidae was named by South African paleontologist Robert Broom in 1912. The family is often misspelled "Trithelodontidae".
It is possible that Tritheledontidae had vibrissae, according to the PBS documentary, Your Inner Fish. A common ancestor of all therian mammals did so. It is possible that the development of the whisker sensory system played an important role in mammalian development, more generally.