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Repenomamus
 
 
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Repenomamus is the largest mammal
Mammal

Mammals are a class of vertebrate animals whose name is derived from their distinctive feature, mammary glands, with which they feed their young....
 known from the Cretaceous
Cretaceous

The Cretaceous , usually abbreviated K for its German translation Kreide, is a geologic period from circa to million years ago . In the geologic timescale, the Cretaceous follows on the Jurassic period and is followed by the Paleogene period....
 period of the Mesozoic
Mesozoic

The Mesozoic Era is one of three Geologic time scale of the Phanerozoic eon . The division of time into eras dates back to Giovanni Arduino, in the 18th century, although his original name for the era now called the 'Mesozoic' was 'Secondary' ....
, and it is the mammal for which there is the best evidence that it fed on dinosaur
Dinosaur

Dinosaurs were the dominant vertebrate animals of Landform ecosystems for over 160 million years, from the late Triassic Period until the end of the Cretaceous Period , when most of them became extinct in the Cretaceous?Tertiary extinction event....
s. It is not possible to determine if Repenomamus actively hunted live dinosaur
Dinosaur

Dinosaurs were the dominant vertebrate animals of Landform ecosystems for over 160 million years, from the late Triassic Period until the end of the Cretaceous Period , when most of them became extinct in the Cretaceous?Tertiary extinction event....
s or scavenged dead dinosaurs.

Repenomamus was probably not a fast runner. The humerus
Humerus

The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow.Anatomically, it connects the scapula and the ulna, and consists of the following three sections:...
 and femur
Femur

The femur, or thigh bone, is the most proximal bone of the leg in vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs....
 left their joints at a somewhat splayed angle, and the legs were relatively short compared to the body.






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Repenomamus is the largest mammal
Mammal

Mammals are a class of vertebrate animals whose name is derived from their distinctive feature, mammary glands, with which they feed their young....
 known from the Cretaceous
Cretaceous

The Cretaceous , usually abbreviated K for its German translation Kreide, is a geologic period from circa to million years ago . In the geologic timescale, the Cretaceous follows on the Jurassic period and is followed by the Paleogene period....
 period of the Mesozoic
Mesozoic

The Mesozoic Era is one of three Geologic time scale of the Phanerozoic eon . The division of time into eras dates back to Giovanni Arduino, in the 18th century, although his original name for the era now called the 'Mesozoic' was 'Secondary' ....
, and it is the mammal for which there is the best evidence that it fed on dinosaur
Dinosaur

Dinosaurs were the dominant vertebrate animals of Landform ecosystems for over 160 million years, from the late Triassic Period until the end of the Cretaceous Period , when most of them became extinct in the Cretaceous?Tertiary extinction event....
s. It is not possible to determine if Repenomamus actively hunted live dinosaur
Dinosaur

Dinosaurs were the dominant vertebrate animals of Landform ecosystems for over 160 million years, from the late Triassic Period until the end of the Cretaceous Period , when most of them became extinct in the Cretaceous?Tertiary extinction event....
s or scavenged dead dinosaurs.

Repenomamus was probably not a fast runner. The humerus
Humerus

The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow.Anatomically, it connects the scapula and the ulna, and consists of the following three sections:...
 and femur
Femur

The femur, or thigh bone, is the most proximal bone of the leg in vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs....
 left their joints at a somewhat splayed angle, and the legs were relatively short compared to the body. The feet were plantigrade
Plantigrade

In mammals, plantigrade locomotion means walking with the podials and metatarsals flat on the ground.Primates are examples of plantigrade species; in humans, the podials and metatarsals constitute the sole of the foot....
. Repenomamuss behavior and overall body shape may have resembled those of modern day Tasmanian devil
Tasmanian Devil

The Tasmanian Devil is a carnivore marsupial now found in the wild only in the Australian island states and territories of Australia of Tasmania....
s.

Repenomamus was carnivorous
Carnivore

A carnivore , meaning 'meat eater' , is any animal with a diet consisting mainly of meat, whether it comes from animals living or dead .In a more general sense, an animal may be considered a carnivore if it prefers feeding on animal matter over plant matter....
. 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....
 preserved in its stomach
Stomach

In most mammals, the stomach is a hollow muscular organ of the gastrointestinal tract involved in the second phase of digestion, following mastication....
. This the strongest evidence that Mesozoic
Mesozoic

The Mesozoic Era is one of three Geologic time scale of the Phanerozoic eon . The division of time into eras dates back to Giovanni Arduino, in the 18th century, although his original name for the era now called the 'Mesozoic' was 'Secondary' ....
 mammals fed on dinosaur
Dinosaur

Dinosaurs were the dominant vertebrate animals of Landform ecosystems for over 160 million years, from the late Triassic Period until the end of the Cretaceous Period , when most of them became extinct in the Cretaceous?Tertiary extinction event....
s, and this created 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 of a small dog

The larger 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....
, 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 states of 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 Egg 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 Molar s 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 meter (39 inches) long and weighed about 12–14 kg (26–31 lb
Pound (mass)

The pound or pound-mass is a Units of measurement of massused in the Imperial unit, United States customary units and other systems of measurement....
). 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 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 will be in another ecological niche to one that travels in a different school.....
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.Although individually small, insects exist in enormous numbers and make up a very large part of the animal biomass in almost all non-marine environments....
s, not unlike modern-day shrew
Shrew

Shrews are small, superficially mouse-like mammals of the Family Soricidae. Although their external appearance is generally that of a long-nosed mouse, the shrews are not rodents and not closely related: the shrew family is part of the order Soricomorpha....
s. 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
Cretaceous-Tertiary extinction event

The Cretaceous?Tertiary extinction event, which occurred approximately , was a large-scale Extinction event of animal and plant species in a geologically short period of time....
 wiped out the dinosaurs and allowed the diversification of mammals during the Cenozoic
Cenozoic

The Cenozoic Era...
. Repenomamus was an exception to this rule.

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 nonavian dinosaur fossils were discovered with preserved feathers....
 also from the same rock formation in China, including Microraptor
Microraptor

Microraptor is a genus of small, dromaeosaurid dinosaur. About two dozen well-preserved fossil specimens have been recovered from Liaoning, China....
, Sinornithosaurus
Sinornithosaurus

Sinornithosaurus is a genus of Feathered dinosaurs dromaeosaurid dinosaur from the Lower Cretaceous Period of the Yixian Formation in what is now China....
, Caudipteryx
Caudipteryx

Caudipteryx is a genus of peacock-sized theropod dinosaurs that lived in the Barremian age of the early Cretaceous Period . They were feathered and remarkably birdlike in their overall appearance....
 and Mei
Mei

Mei or MEI may refer to:Mei*Mei , Chinese family name*Mei , a genus of bird-like Chinese dinosaur*Mei , a Japanese given name.*Persian wine, a Persian wine used in traditional Persian culture...
.

Classification and discovery

The fossils were recovered from the lagerstätte of the Yixian Formation
Yixian Formation

The Yixian Formation is a geological formation in Jinzhou, Liaoning, People's Republic of China, that stems from the early Cretaceous period. It is known for its fossils....
 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 nonavian 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 of the two major divisions of the Cretaceous Period . It began about 146 million years ago....
 period.

Repenomamus is a genus
Genus

A genus is a low-level taxonomic rank used in the classification of living and fossil organisms. The taxonomic ranks are domain , kingdom , phylum, class , order , family , genus, and species....
 of triconodonts, a group of early mammal
Mammal

Mammals are a class of vertebrate animals whose name is derived from their distinctive feature, mammary glands, with which they feed their 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....
 are the sole members of the family Repenomamidae, which was also described in the same paper in 2000.

See also

  • Mammaliformes
  • Cynodont
    Cynodont

    Cynodonts, or 'dog teeth', are a taxon of Therapsids which includes modern mammals and their extinct close relatives. They were one of the most diverse groups of therapsids....
    s
  • Cynognathus
    Cynognathus

    Cynognathus was a metre-long predator of the Lower Triassic. It was one of the more mammal-like of the "mammal-like reptiles", a member of a grouping called Eucynodontia....
  • Evolution of mammals
    Evolution of mammals

    __FORCETOC__The evolution of mammals from synapsids was a gradual process which took approximately 70 million years, beginning in the mid-Permian....


External links


  • "". Michael Hopkin. Nature.com. January 12, 2005.
  • "". BBC News. January 12, 2005.