Researchers who scanned its skull and ran digital simulations found that the creature most likely had a primitive eardrum in its jaw. While Thrinaxodon didn’t yet have the sophisticated hearing equipment of modern mammals, it shows that eardrums began evolving much earlier than assumed. A series of simulations showed that the curve of Thrinaxodon’s jaw was built to hold the prototype version of an eardrum. The simulations also revealed that Thrinaxodon was sensitive to the dual functions (hearing and chewing) of which its mandible was capable. If it relaxed the temporalis muscle, which the mandibular nerve runs through, it would have been better able to hear lower sounds.