Morganucodon is an early mammaliaform genus.p79 It lived during the latest Upper Triassic or earliest Jurassic.p299

Unlike many other early mammals, Morganucodon is known from abundant and well preserved material. Most of this comes from Glamorgan in Wales (Morganucodon watsoni).

According to Kemp, it is impossible to say whether the rock fissures (cracks), where the remains were found, are latest Triassic or earliest Jurassic.p142

Morganucodon first appeared about 205 million years ago. "It was a small animal with a skull 2-3 cm in length and a body length of about 10 cm [4 inches]. In general appearance it would have looked like a shrew or mouse".p143