New data on the cranial anatomy of Lycaenops (Synapsida, Gorgonopsidae), and reflections on the possible presence of streptostyly in gorgonopsians

Study of a skull attributed to Lycaenops angusticeps reveals the presence o f a ventral flange of the jugal that supports the transverse flange of the pterygoid. The quadrate was apparently not streptostylic, contrary to previ ous reports because its articulation with the epipterygoid and the pterygoi d would only allow slight bending and because extensive movement of the qua drate would have been accompanied by similar movements of the stapes. Sever al characters previously used to argue for streptostyly of the gorgonopsian quadrate are primitive characters that were present in Permo-Carboniferous synapsids. The reduction of the contact between quadrate and pterygoid may have been selected for improved hearing of air-borne sounds. The reflected lamina was possibly involved in the reception of air-borne sounds (if gorg onopsians could detect them), along with the tympanum.