Temporal range: Early Cretaceous, 125Ma
|Fossil skull of R. giganticus|
Li et al., 2000
Li et al., 2000
†Repenomamus robustus Li et al., 2000
Repenomamus is a gobiconodontid mammal genus containing two species, Repenomamus robustus and Repenomamus giganticus, both known from fossils found in China and dating to the early Cretaceous period, about 125 million years ago. R. robustus is the only Mesozoic mammal for which there is the good 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 is the strongest evidence that Mesozoic mammals fed on dinosaurs, creating interest in the popular press. There were, however, earlier indications that Mesozoic mammals fed on dinosaurs (see Archaeornithoides).
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 m (39 in) long and weighed about 12–14 kg (26–31 lb). Its skull measures 16 cm (6.25 in) long, its body 52 cm (20.5 in), and the preserved part of its tail 36 cm (14 in). The other species, R. robustus, was less than 50 cm (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 the niches of animals more than 1 m (39 in) long were filled entirely by dinosaurs and reptiles like crocodilians, and were off limits to mammals until after the Cretaceous–Paleogene extinction event wiped out the nonavian** dinosaurs and allowed the diversification of mammals during the Cenozoic. Repenomamus disproves this.
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. It is sometimes alternatively listed as a member of the family Gobiconodontidae; although this assignment is controversial, a close relationship to this family is well-founded.
- J. Li, Y. Wang, Y. Wang, & C. Li (2001). "A new family of primitive mammal from the Mesozoic of western Liaoning, China". Chinese Science Bulletin 46 (9): 782–785. doi:10.1007/BF03187223. ISSN 1001-6538.
- Yaoming Hu, Jin Meng, Yuanqing Wang, Chuankui Li (2005). "Large Mesozoic mammals fed on young dinosaurs". Nature 433 (7022): 149–152. doi:10.1038/nature03102. PMID 15650737.
- Marisol Montellano, James A. Hopson, James M. Clark (2008). "Late Early Jurassic Mammaliaforms from Huizachal Canyon, Tamaulipas, México". Journal of Vertebrate Paleontology 28 (4): 1130–1143. doi:10.1671/0272-4634-28.4.1130.
- 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