Megazostrodon

Megazostrodon is an early proto-mammal,  discovered in Lesotho, southern Africa.Crompton and Jenkins, "Molar occlusion in late Triassic mammals", Biological Review, 43 1968:427-458.

It is one of the first mammals, and appeared in the fossil record about 200/205  million years ago (mya).Fur and Fangs: Mammal Origins . Palaeobiology and Biodiversity Research Group, University of Bristol. It did have some non-mammalian characteristics,the evolution of the ear ossicles had not reached its modern state but overall this animal, and Morganucodon, probably show the final stage of the transition between the cynodonts and true mammals.

 Characteristics 
It is thought that the animal was nocturnal as it had a relatively much larger brain than its cynodont relatives, and the enlarged areas of its brain  were found to be those which process sounds and smells.

Nocturnal activity in an animal of this size virtually requires an increased internal production of heat.Kemp T.S. 2005. The origin and evolution of mammals. Oxford University Press. p124
From their size and teeth, Megastrozodon were probably insectivores, as were all its relatives at the time.Benton, Michael J. 2005. Vertebrate paleontology. 3rd ed, Oxford: Blackwell. p300 Their small size suggests some kind of temperature regulation, which in turn suggests insulation in the form of fur.

The night-time behaviour and insectivorous habits gave these early mammals a niche which did not compete with the reptiles.Smithsonian Science Abstract

These early mammals developed many traits which made them well-suited for an active lifestyle. They developed four types of teeth.First Mammals Appear There is evidence that the inward-closing movement of the mandible suggests a shearing action to chew food. Their skeletons changed so that their limbs were more flexible (they became less laterally splayed,Mammalian Characteristics. Sam Houston State University. allowing for faster forward motion) and they developed a shorter ribcage and larger lungs to allow for faster respiration. The structure of their jaw bones changed, the lower jaw becoming a single bone — the dentary. The other bones which once made up the jaw moved to the middle ear to create a hearing system.

 References 

Category:Theriodonts