Sinoconodon
| Sinoconodon | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Temporal occurrence | ||||||||||||
| Lower Jurassic | ||||||||||||
| around 200 million years | ||||||||||||
| Locations | ||||||||||||
| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Sinoconodon | ||||||||||||
| Patterson & Olson , 1961 | ||||||||||||
Sinoconodon is one of the earliest known mammalian animals ( Mammaliaformes ). Fossils of this animal, including a fully preserved skull , were found in southern China and dated to around 200 million years ago.
features
Sinoconodon shows in its skull structure transitional features between the synapsid ancestors of the mammals and the actual mammals. The lower jaw and the structure of the ear and the temporomandibular joint are already developed in a mammal-like manner, but in contrast to these there was repeated tooth change and lifelong growth of the skull, which are reptilian characteristics. Sinoconodon also had only one type of molar teeth and the occlusion (the interlocking of the teeth of the upper and lower jaw) was not yet fully developed.
These animals were larger than comparable early mammals from the same era, the maximum skull length was 6 centimeters and the weight of these animals is estimated to be up to 500 grams. Due to the lifelong growth, the lengths of the skulls found vary from 2 to 6 centimeters. Nothing is known about the rest of the body of these animals.
Systematics
Apart from the sparse finds of Adelobasileus cromptoni and the early Haramiyida , Sinoconodon is one of the earliest known representatives of the mammals. Because of the differences to today's representatives of this group, Sinoconodon and other early forms are sometimes referred to as Mammaliaformes ("mammalian") or summarized as Mammalia sensu lato (in a broader sense). It is largely undisputed that Sinoconodon and today's mammals form a monophyletic group, this genus being a sister taxon to the other representatives of this group. Whether they are already referred to as mammals or still as mammalian ancestors is largely a question of definition.
Several species of Sinoconodon have been described, including S. rigneyi , S. changchiawaensis , S. parringtoni, and S. youngi , which may just represent different growth stages of the same species. The genus Lufengoconodon is probably only a synonym for Sinoconodon .
literature
- TS Kemp: The Origin & Evolution of Mammals. Oxford University Press, Oxford et al. 2005, ISBN 0-19-850761-5 .