Lycosuchus vanderrieti (Broom 1903, BMNH 1647; Lat Permian, 260-255) mya; 23cm skull length, 1.2-2m long). Note the very narrow cranium (there's actually a brain in there!) which provides more room for powerful jaw muscles to drive those long fangs deep into prey. The long rostrum is inherited from a sister to Eotitanosuchus.Lycosuchus was basal to cynodonts like Procynosuchus and ultimately mammals like Megazostrodon.
Broom R 1903. On an almost perfect skull of a new primtiive theriodont (Lycosuchus vanderrieti). - Transactions of the South African Philosophical Society col14, issue 1