Megazostrodon
| Megazostrodon | ||||||||||||
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Model of Megazostrodon in the Natural History Museum in London. |
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| Temporal occurrence | ||||||||||||
| Lower Jurassic | ||||||||||||
| approx. 195 million years | ||||||||||||
| Locations | ||||||||||||
| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Megazostrodon | ||||||||||||
| Crompton & Jenkins , 1968 | ||||||||||||
Megazostrodon is one of the oldest representatives of mammals or mammalian-like animals ( Mammaliaformes ). The animal lived in the Lower Jurassic and its fossils were found in the South African country of Lesotho .
description
Outwardly , megazostrodon was probably a shrew-like animal, it reached a length of around 10 centimeters, its weight is estimated at 20 to 30 grams. In its physique it showed some transitional features between the synapsid mammalian ancestors and the actual mammals. The structure of the temporomandibular joint still shows traces of the "reptilian" primary temporomandibular joint between the articular and quadratum bones . On the other hand, these animals already had the four different types of teeth typical of mammals ( incisors , canines , premolars and molars ). Compared with the similarly built Morganucodon , the sharp cusps of the molars were significantly larger and formed a obtuse triangle. There is also evidence of a one-time change of teeth, another characteristic of mammals. Because of this change of teeth, it is conceivable that Megazostrodon was already suckling his young.
The brain is comparatively larger than that of older synapsid mammalian ancestors, and the sense of smell and hearing of these animals were probably well developed. Maybe they led a nocturnal lifestyle, the diet probably consisted of insects and other small animals.
Systematics
Megazostrodon forms the family Megazostrodontidae with some closely related genera. While many classifications assign this family to the Morganucodonta group , others consider a relationship to the Docodonta to be more likely. Today, however, membership of the Triconodonta , a group of mammals that was characterized by three-humped molars , but which has not turned out to be a natural group, is largely rejected today .
These animals showed advanced mammalian-like characteristics, but differed in details from today's mammals. Whether it is already classified in mammals in the broader sense ( sensu lato ) or in mammal-like animals ( Mammaliaformes ) is controversial and largely a question of definition.
literature
- Thomas S. Kemp: The Origin & Evolution of Mammals . Oxford University Press, Oxford 2005, 331 pages, ISBN 0-19-850761-5 .