Repenomamus

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Repenomamus
Life picture of Repenomamus giganticus

Life picture of Repenomamus giganticus

Temporal occurrence
Lower chalk
139 to 128 million years
Locations
Systematics
Amniotes (Amniota)
Synapsids (Synapsida)
Mammals (mammalia)
Eutriconodonta
Gobiconodontidae
Repenomamus
Scientific name
Repenomamus
Li , Wang , Wang & Li , 2000
species
  • R. robustus Li, Wang, Wang, Li, 2000
  • R. giganticus Hu, Meng, Wang, Li 2005

Repenomamus is an extinct genus of mammals from the Lower Cretaceous Period . These animals were carnivores and the largest known mammals of the Mesozoic Era . Two species have been described, R. robustus and R. giganticus , which differ in terms of size and details in the skull structure.

features

R. giganticus reached a head trunk length of over 60 centimeters (the skull was 16 centimeters long). Its length including the tail is likely to have been over 1 meter, its weight is estimated at 12 to 14 kilograms. R. robustus was about half its size and weighed 4 to 6 kilograms. This made them the largest known mammals of the Mesozoic Era. Only Kollicodon , an early representative of the monotremes , could have reached similar proportions; but only jaw parts of this genus are known that make an exact estimate of the size impossible.

Repenomamus had an elongated trunk, the short, strong limbs were attached to the side of the body compared to modern mammals. The animals walked on soles , the structure of the limbs suggests a soil-dwelling way of life.

Repenomamus giganticus skull

The large head is likely to have housed strong masticatory muscles. The structure of the teeth speaks for a carnal diet. The cutting , corner and Vorbackenzähne were large and pointed, and suitable for holding and ripping prey. The molars, on the other hand, were rather small and blunt, they were not suitable for chewing, so that the animals were more likely to have devoured their food whole. The tooth formula was I 3/2 C 1/1 P 2/2 M 4/5. Well-preserved finds of R. robustus even showed the stomach contents: in addition to mammal bones, the remains of a young Psittacosaurus were found - this is an astonishing indication that Mesozoic mammals also ate dinosaurs . It was discussed whether Repenomamus could have been a scavenger, but the attachments of the masticatory muscles and the formation of the teeth suggest a predatory lifestyle.

discovery

Remains of repenomamus were in the Yixian Formation of the Chinese province of Liaoning - also for their feathered dinosaur known - found and in the lower Cretaceous dated (year around 139-128 Million). R. robustus was described by Jinling Li, Yuan Wang, Yuanqing Wang, and Chuankui Li in 2000; R. giganticus by Yaoming Hu, Jin Meng, Yuanqing Wang and Chuankui Li in 2005.

Systematics

The closest relatives of Repenomamus are members of the Gobiconodontidae , a group of carnivorous mammals known from the Lower Cretaceous Asia and North America. In some classifications Repenomamus is classified in this family, in others as a separate family, Repenomamidae. The position as a separate family is justified by differences in the structure and number of teeth; but it is considered certain that Repenomamus and the Gobiconodontidae are closely related.

Together with some other Mesozoic mammals, which are characterized by a similar three-humped structure of the molars, they are classified in the group of the eutriconodonta . However, whether these are really closely related animals or just convergent developments is a matter of dispute. Their position in the mammalian system is also unclear, but it is likely to have been a relatively early, specialized branch. They are not closely related to today's mammals.

Importance of the find

Until recently, almost all mammals of the Mesozoic Era were thought to be small, relatively unspecialized animals that were mostly nocturnal insectivores. The findings of Repenomamus show that the mammals of that era were significantly larger than previously thought and possibly competed with smaller dinosaurs for food and hunting grounds. The finds fit into a number of recent discoveries (such as the genus Castorocauda , which is adapted to aquatic life , the anteater-like genus Fruitafossor or the Volaticotherium with sliding membranes ), which prove that the Mesozoic mammals were more specialized and also occupy more diverse ecological niches than previously accepted.

Individual evidence

  1. ↑ Pharyngula: Repenomamus giganteus ( Memento of February 9, 2008 in the Internet Archive ) (English)

literature

  • Thomas S. Kemp: The Origin & Evolution of Mammals . Oxford University Press, Oxford 2005, 331 pages, ISBN 0-19-850761-5 .

Web links