Morganucodon watsoni (Kühne 1949; Late Triassic, 235–200mya; 2–3cm skull length) is known from fissue fills (abundant, 3D and completely disarticulated) fossils from Wales and China. This insectivore was like a shrew. The anterior teeth had a single replacement. Traditionally considered a mammaliaform, here Morganucodon nests with Ukhaatherium at the base of the Theria, close to the base of the Mammalia (= Prototheria). The jaw retains some tiny rear jaw elements, so the hearing was not perfected yet.

Volaticotherium antiquus (Meng et al. 2006; Middle to Late Jurassic, 164 mya; 5 cm skull length; IVPP V14739) was described a few years back as a gliding mammal of uncertain affiintiy. It is based on a preserved patagium, or gliding membrane, complete with short hair and skin. Here, derived from a sister to Ukhaatherium and Morganucodon, this is the last of its kind, at present.

The molars resemble rotary saw blades, the external naris is divided by an ascending process of the premaxilla (rare among higher cynodonts and mammals), proximally the femur has no 'neck' and not much of a 'head', and the tail is extraordinarily long. We also see a deeper mandible medial to sabertooth fangs in Thylacosmilus, and this may be the reason for the oddly deeper chin here.

Kuehne WG 1949. On a triconodont tooth of a new pattern from a fissure-filling in South Glamorgan. Proceedings of the Zoological Society of London 119:345-350.

Meng J, Hu YM, Wang YQ, Wang XL and Li CK 2006. A Mesozoic gliding mammal from northeastern China. Nature 444:889-893.

wiki/Volaticotherium
wiki/Morganucodon