Repenomamus
Encyclopedia
Repenomamus is the largest mammal
known from the Cretaceous
period of Manchuria
, and it is the mammal for which there is the best evidence that it fed on dinosaur
s. It is not possible to determine if Repenomamus actively hunted live dinosaurs or scavenged dead dinosaurs.
and femur
left their joints at a somewhat splayed angle, and the legs were relatively short compared to the body. The feet were plantigrade
. Repenomamuss behavior and overall body shape may have resembled those of modern day Tasmanian devil
s.
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 niche
s 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 insectivore
s, not unlike modern-day shrew
s. 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-Tertiary extinction event
wiped out the dinosaurs and allowed the diversification of mammals during the Cenozoic
. Repenomamus disproves this.
R. giganticus is larger than a number of species of feathered dinosaurs
also from the same rock formation in China, including Sinornithosaurus
, Caudipteryx
and Mei
.
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 mammal
s 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.
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
known from the Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
period of Manchuria
Manchuria
Manchuria is a historical name given to a large geographic region in northeast Asia. Depending on the definition of its extent, Manchuria usually falls entirely within the People's Republic of China, or is sometimes divided between China and Russia. The region is commonly referred to as Northeast...
, and it is the mammal for which there is the best evidence that it fed on dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
s. It is not possible to determine if Repenomamus actively hunted live dinosaurs or scavenged dead dinosaurs.
Paleobiology
Repenomamus was probably not a fast runner. The humerusHumerus
The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....
and femur
Femur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
left their joints at a somewhat splayed angle, and the legs were relatively short compared to the body. The feet were plantigrade
Plantigrade
right|151px|thumb|Human skeleton, showing plantigrade habitIn terrestrial animals, plantigrade locomotion means walking with the podials and metatarsals flat on the ground. It is one of three forms of locomotion adopted by mammals...
. Repenomamuss behavior and overall body shape may have resembled those of modern day Tasmanian devil
Tasmanian Devil
The Tasmanian devil is a carnivorous marsupial of the family Dasyuridae, now found in the wild only on the Australian island state of Tasmania. The size of a small dog, it became the largest carnivorous marsupial in the world following the extinction of the thylacine in 1936...
s.
Repenomamus was carnivorous
Carnivore
A carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of animal tissue, whether through predation or scavenging...
. A specimen of R. robustus has been discovered with the fragmentary skeleton of a juvenile Psittacosaurus
Psittacosaurus
Psittacosaurus is a genus of psittacosaurid ceratopsian dinosaur from the Early Cretaceous Period of what is now Asia, about 130 to 100 million years ago. It is notable for being the most species-rich dinosaur genus...
preserved in its stomach
Stomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
. This is the strongest evidence that Mesozoic
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
mammals fed on dinosaurs, creating interest in the popular press. There were, however, earlier indications that Mesozoic mammals fed on dinosaurs (see Archaeornithoides
Archaeornithoides
Archaeornithoides is a genus of maniraptoriform theropod dinosaur. It was found in Late Cretaceous river sandstones of the Djadokhta Formation beds located in Bayn Dzak, Mongolia...
).
Size
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
, 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
Platypus
The platypus is a semi-aquatic mammal endemic to eastern Australia, including Tasmania. Together with the four species of echidna, it is one of the five extant species of monotremes, the only mammals that lay eggs instead of giving birth to live young...
, Kollikodon
Kollikodon
Kollikodon ritchiei is a fossil monotreme species. It is known only from an opalised dentary fragment, with one premolar and two molars in situ...
, 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
Pound (mass)
The pound or pound-mass is a unit of mass used in the Imperial, United States customary and other systems of measurement...
). 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 niche
Ecological niche
In ecology, a niche is a term describing the relational position of a species or population in its ecosystem to each other; e.g. a dolphin could potentially be in another ecological niche from one that travels in a different pod if the members of these pods utilize significantly different food...
s 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 insectivore
Insectivore
An insectivore is a type of carnivore with a diet that consists chiefly of insects and similar small creatures. An alternate term is entomophage, which also refers to the human practice of eating insects....
s, not unlike modern-day shrew
Shrew
A shrew or shrew mouse is a small molelike mammal classified in the order Soricomorpha. True shrews are also not to be confused with West Indies shrews, treeshrews, otter shrews, or elephant shrews, which belong to different families or orders.Although its external appearance is generally that of...
s. 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-Tertiary extinction event
Cretaceous-Tertiary extinction event
The Cretaceous–Paleogene extinction event, formerly named and still commonly referred to as the Cretaceous-Tertiary extinction event, occurred approximately 65.5 million years ago at the end of the Maastrichtian age of the Cretaceous period. It was a large-scale mass extinction of animal and plant...
wiped out the dinosaurs and allowed the diversification of mammals during the Cenozoic
Cenozoic
The Cenozoic era is the current and most recent of the three Phanerozoic geological eras and covers the period from 65.5 mya to the present. The era began in the wake of the Cretaceous–Tertiary extinction event at the end of the Cretaceous that saw the demise of the last non-avian dinosaurs and...
. Repenomamus disproves this.
R. giganticus is larger than a number of species of feathered dinosaurs
Feathered dinosaurs
The realization that dinosaurs are closely related to birds raised the obvious possibility of feathered dinosaurs. Fossils of Archaeopteryx include well-preserved feathers, but it was not until the early 1990s that clearly non-avialan dinosaur fossils were discovered with preserved feathers...
also from the same rock formation in China, including Sinornithosaurus
Sinornithosaurus
Sinornithosaurus is a genus of feathered dromaeosaurid dinosaur from the early Cretaceous Period of the Yixian Formation in what is now China. It was the fifth non–avian feathered dinosaur genus discovered by 1999...
, Caudipteryx
Caudipteryx
Caudipteryx is a genus of peacock-sized theropod dinosaurs that lived in the Aptian age of the early Cretaceous Period . They were feathered and remarkably birdlike in their overall appearance....
and Mei
Mei (dinosaur)
Mei is a genus of duck-sized troodontid dinosaur first unearthed by paleontologists in Liaoning, China in 2004. Mei lived during the Early Cretaceous Period. Its binomial name, Mei long means sleeping dragon...
.
Classification and discovery
The fossils were recovered from the lagerstätte of the Yixian FormationYixian Formation
The Yixian Formation is a geological formation in Jinzhou, Liaoning, People's Republic of China, that spans 11 million years during the early Cretaceous period...
in the Liaoning province of China, which is renowned for its extraordinarily well-preserved fossils of feathered dinosaurs
Feathered dinosaurs
The realization that dinosaurs are closely related to birds raised the obvious possibility of feathered dinosaurs. Fossils of Archaeopteryx include well-preserved feathers, but it was not until the early 1990s that clearly non-avialan dinosaur fossils were discovered with preserved feathers...
. They have been specifically dated to 130 million years ago, during the Early Cretaceous
Early Cretaceous
The Early Cretaceous or the Lower Cretaceous , is the earlier or lower of the two major divisions of the Cretaceous...
period.
Repenomamus is a genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of triconodonts, a group of early mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s 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
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
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
Gobiconodontidae
The Gobiconodontidae are a group of extinct mammals from the Early Creataceous, belonging to the triconodonts.- Phylogeny :Cladogram after Marisol Montellano, James A. Hopson, James M. Clark and Gao et al. .-References:...
; although this assignment is controversial, a close relationship to this family is well-founded.
External links
- "Prehistoric badger had dinosaurs for breakfast". Michael Hopkin. Nature.com. January 12, 2005.
- "Fierce mammal ate dinos for lunch". BBC News. January 12, 2005.