What is "estemmenosuchidae"

Estemmenosuchidae is a family of large, very early herbivorous therapsids that flourished during the Middle Permian period. They are distinguished by horn-like structures, probably for display or agonistic behavior. Apart from the best known genus, Estemmenosuchus, the group is poorly known. To date, their fossils are known only from the Perm region of Russia (a region referred to by Russian paleontologists as the Cis-Urals).