Repenomamus

Taxobox
name = "Repenomamus"
fossil_range = Early Cretaceous

---

image_width = 240px
regnum = Animalia
phylum = Chordata
classis = Mammalia
ordo = Triconodonta
familia = Repenomamidae
familia_authority = Li, Wang, Wang, Li, 2000
genus = "Repenomamus"
genus_authority = Li, Wang, Wang, Li, 2000
subdivision_ranks = Species
subdivision = "Repenomamus robustus"
Li, Wang, Wang, Li, 2000
"Repenomamus giganticus"
Hu, Meng, Wang, Li, 2005

"Repenomamus" is the largest mammal known from the Cretaceous period of the Mesozoic, and it is the mammal for which there is the best evidence that it fed on dinosaurs. It is not possible to determine if "Repenomamus" actively hunted live dinosaurs or scavenged dead dinosaurs.

"Repenomamus" was probably not a fast runner. The humerus and femur left their joints at a somewhat splayed angle, and the legs were relatively short compared to the body. The feet were plantigrade. "Repenomamus"'s behavior and overall body shape may have resembled those of modern day Tasmanian devils.

Repenomamus was carnivorous. A specimen of "R. robustus" has been discovered with the fragmentary skeleton of a juvenile "Psittacosaurus" preserved in its stomach. This the strongest evidence that Mesozoic mammals fed on dinosaurs, and this created interest in the popular press. There were, however, earlier indications that Mesozoic mammals fed on dinosaurs (see "Archaeornithoides").Elzanowski, Andrzej, Wellnhofer, Peter. (1993) "Skull of "Archaeornithoides" from the Upper Cretaceous of Mongolia" "American Journal of Science" Vol. 293-A-A, pp.235-252]

Size of a small dog

The larger species, "R. giganticus", holds the distinction of being the largest mammal known from the Cretaceous. A few other described mammals, such as an early giant platypus, "Kollikodon", may have been larger, but they are only known from small fragments so their actual size is in question. "R. giganticus" was more than 1 meter (39 inches) long and weighed about 12–14 kg (26–31 lb). Its skull measures 16 centimetres long, its body 52 cm, and the preserved part of its tail 36 cm. The other species, "R. robustus", was less than 0.5 m (20 in) long and weighed 4–6 kg (9–13 lb). These finds are considered important, because they expand the ecological niches known to be inhabited by mammals during the 150 million year reign of the dinosaurs. Previously, the only known mammals of this time period were small nocturnal insectivores, not unlike modern-day shrews. It had been assumed that the niches of animals larger than 1 meter (39 inches) in length were filled entirely by dinosaurs and reptiles like crocodilians, and were off limits to mammals until after the Cretaceous-Tertiary extinction event wiped out the dinosaurs and allowed the diversification of mammals during the Cenozoic. "Repenomamus" was an exception to this rule.

"R. giganticus" is larger than a number of species of feathered dinosaurs also from the same rock formation in China, including "Microraptor", "Sinornithosaurus", "Caudipteryx" and "Mei".

Classification and discovery

The fossils were recovered from the lagerstätte of the Yixian Formation in the Liaoning province of China, which is renowned for its extraordinarily well-preserved fossils of feathered dinosaurs. They have been specifically dated to 130 million years ago, during the Early Cretaceous period.

"Repenomamus" is a genus of triconodonts, a group of early mammals with no modern relatives. "R. robustus" was described by Li, Wang, Wang and Li in 2000, and "R. giganticus" was described by Hu, Meng, Wang, Li 2005. The two known species are the sole members of the family Repenomamidae, which was also described in the same paper in 2000.

References

*cite journal |author=J. Li, Y. Wang, Y. Wang, & C. Li |year=2001 |month= |title=A new family of primitive mammal from the Mesozoic of western Liaoning, China |journal=Chinese Science Bulletin |volume=46 |issue=9 |pages=782–785 |id= |url=http://dml.cmnh.org/2001May/msg00969.html |accessdate= |quote= |doi=10.1007/BF02900425
*cite journal |author=Yaoming Hu, Jin Meng, Yuanqing Wang, Chuankui Li |year=2005 |month= |title=Large Mesozoic mammals fed on young dinosaurs |journal=Nature |volume=433 |issue= |pages=149–152 |doi=10.1038/nature03102 |url= |accessdate= |quote=

ee also

* Mammaliformes
* Cynodonts
* "Cynognathus"
* Evolution of mammals

External links

* " [http://www.nature.com/news/2005/050110/full/050110-11.html Prehistoric badger had dinosaurs for breakfast] ". Michael Hopkin. "Nature.com". January 12, 2005.
* " [http://news.bbc.co.uk/2/hi/science/nature/4165973.stm Fierce mammal ate dinos for lunch] ". "BBC News". January 12, 2005.