Sinoconodon

• China, Lufeng Formation

Sinoconodon is one of the earliest known mammal -like animals ( Mammaliaformes ). Fossils of this animal, including a completely preserved skull, were found in southern China and dated to an age of about 200 million years.

Features

Sinoconodon shows in his skull structure transition features between the synapsids ancestors of mammals and the actual mammals. The mandible and the construction of the ear and the jaw joint is already developed mammal -like, in contrast to these, there was still a repeated change of teeth and a lifelong growth of the skull, which are reptilian characteristics. Also Sinoconodon had only one type of jaw teeth and occlusion ( the engagement of the teeth of the upper and lower jaw ) was not yet fully developed.

These animals were larger than those in early mammals from the same period, the maximum skull length was 6 inches and the weight of these animals is estimated at up to 500 grams. Due to the lifelong growth vary the lengths of the skull found 2-6 centimeters. From the rest of the body of these animals so far, nothing is known.

System

Apart from the sparse finds of Adelobasileus cromptoni and the early Haramiyida Sinoconodon is one of the earliest known representatives of mammals. Because of the differences to the present representatives of this group Sinoconodon and other early forms sometimes as Mammaliaformes be ( "mammal -like " ) referred to or summarized as Mammalia sensu lato ( in the broad sense ). It is largely undisputed that Sinoconodon and today's mammals form a monophyletic group, this genus is a sister taxon of the remaining members of this group. Whether they are already referred to as mammal or even as a mammal ancestors, is largely matter of definition.

Several types of Sinoconodon have been described, including S. rigneyi, p changchiawaensis, S. and S. parringtoni youngi which may represent only different growth stages of the same species. The genus Lufengoconodon likely to be only a synonym of Sinoconodon.