Eomaia

Eomaía
Fossil range: Early Cretaceous
Enlarge picture
Eomaia

Eomaia
Scientific classification
Kingdom:Animalia
Phylum:Chordata
Class:Mammalia
Subclass:Theria
Infraclass:Eutheria
Genus:Eomaia
Species:E. scansoria
Binomial name
Eomaia scansoria
Ji et al., 2002


Eomaia scansoria ('climbing dawn mother') is a recently discovered extinct mammal that may be one of the earliest ancestors of the eutheria yet to have been found.

The fossil was discovered in Yixian Formation, Liaoning Province, China. It dates from the Barremian Age, in the Lower Cretaceous.

The fossil is 10 cm in length and virtually complete. An estimate of the body weight is between 20-25g. It is exceptionally well-preserved for a 125-million-year-old. Although the fossil's skull is squashed flat, its teeth, tiny foot bones, cartilages and even its fur are visible.


Enlarge picture
Fossil cast of Eomaia, showing preserved fur.


According to palaeontologist Anne Weil, Eomaía was not a placental mammal. It was an early, primitive representative of the lineage of all placental mammals[1], including species of pig, horse, cat, dog, bat, mouse, rabbit, gorilla, chimpanzee, and human. The narrowness of the hips suggests an animal which gave birth to live young, but the babies were not well developed. This strongly indicates there was no well developed placenta.

According to an article published in Nature, the epipubis is present. This is highly unusual for eutherids, though not completely unknown from early representatives. Otherwise, this is a feature of marsupials, monotremes and non-mammalian therapsids.

It seems certain that Eomaía was a eutherid. It had a typical ancestral eutherian dental formula, 5.1.5.3/4.1.5.3 (incisors, canines, premolars, molars) The animal had five upper incisors, four lower incisors, and five premolars. These are not the typical numbers for modern eutherians. Modern eutherians have three incisors on top and bottom and four premolars.

The authors claim that on the basis of 268 characters sampled from all major Mesozoic mammal clades and principal eutherian families of the Cretaceous, Eomaía is placed at the root of the eutherian tree with Murtoilestes and Prokennalestes. Clearly, these three taxa are closer to living placentals than to living marsupials. Eomaia is placed in Eutheria by numerous apomorphies in the dentition, the wrist and the ankle.

There are even traces of hair. The previous record for such a feature was about 60 million years ago - this fossil is around 65 million years older. This is not to suggest that previous mammals had been hairless. Skeletal evidence suggests hair possibly appeared in non-mammalian ancestors back in the deep Triassic or Upper Permian. Fur hardly ever fossilizes and the amazing quality of the Liaoning fossils is highly unusual.

References

  • Ji et al (2002), The earliest known eutherian mammal. Nature (416), p.816-822.

See also

External links

The Cretaceous Period is one of the major divisions of the geologic timescale, reaching from the end of the Jurassic Period (i.e. from 145.5 ± 4.0 million years ago (Ma)) to the beginning of the Paleocene epoch of the Tertiary Period (about 65.5 ± 0.3 Ma).
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Scientific classification or biological classification is a method by which biologists group and categorize species of organisms. Scientific classification also can be called scientific taxonomy, but should be distinguished from folk taxonomy, which lacks scientific basis.
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Chordata
Bateson, 1885

Typical Classes

See below

Chordates (phylum Chordata) are a group of animals that includes the vertebrates, together with several closely related invertebrates.
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Mammalia
Linnaeus, 1758

Subclasses & Infraclasses
  • Subclass †Allotheria*
  • Subclass Prototheria
  • Subclass Theria

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Eutheria

Orders[1]
  • Bobolestes
  • Eomaia
  • Maelestes
  • Montanalestes
  • Murtoilestes
  • Prokennalestes
  • Placentalia
  • Superorder

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binomial nomenclature is the formal system of naming species. The system is also called binominal nomenclature (particularly in zoological circles), binary nomenclature (particularly in botanical circles), or the binomial classification system.
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Mammalia
Linnaeus, 1758

Subclasses & Infraclasses
  • Subclass †Allotheria*
  • Subclass Prototheria
  • Subclass Theria

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Eutheria

Orders[1]
  • Bobolestes
  • Eomaia
  • Maelestes
  • Montanalestes
  • Murtoilestes
  • Prokennalestes
  • Placentalia
  • Superorder

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The Yixian Formation is a geological formation in Liaoning, People's Republic of China, that stems from the early Cretaceous period. It is known for its fossils. It was initially recognized during the time the Japanese Empire controlled a large chunk of Manchuria (Northern China)
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辽宁省
Liáoníng Shěng

Abbreviations: ?  (Pinyin: Liáo)

Origin of name 辽 liáo - Liaoyang
宁 níng - Ningyuan (now Xingcheng)

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This page contains Chinese text.
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China (Traditional Chinese:
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The Barremian faunal stage was a period of geological time between 130.0 ± 1.5 Ma and 125.0 ± 1.0 Ma (million years ago). It is considered to be of the early Cretaceous period.
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The Early Cretaceous (timestratigraphic name) or the Lower Cretaceous (logstratigraphic name), is the earlier of the two major divisions of the Cretaceous Period. It began about 146 million years ago.
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Palaeontology redirects here. For the scientific journal, see Palaeontology (journal).


Paleontology, palaeontology or palæontology (from Greek: paleo, "ancient"; ontos
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Eutheria

Orders[1]
  • Bobolestes
  • Eomaia
  • Maelestes
  • Montanalestes
  • Murtoilestes
  • Prokennalestes
  • Placentalia
  • Superorder

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The placenta is an ephemeral (temporary) organ present in placental vertebrates, such as some mammals and sharks during gestation (pregnancy).

The placenta develops from the same sperm and egg cells that form the fetus, and functions as a fetomaternal organ with two
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Eutheria

Orders[1]
  • Bobolestes
  • Eomaia
  • Maelestes
  • Montanalestes
  • Murtoilestes
  • Prokennalestes
  • Placentalia
  • Superorder

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Marsupialia
Illiger, 1811

Orders
  • Didelphimorphia
  • Paucituberculata
  • Microbiotheria
  • Dasyuromorphia
  • Peramelemorphia
  • Notoryctemorphia
  • Diprotodontia
  • Sparassodonta (extinct)
  • Yalkaparidontia (extinct)
Marsupials
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Monotremata
C.L. Bonaparte, 1837

Families

†Kollikodontidae
Ornithorhynchidae
Tachyglossidae
†Steropodontidae
Monotremes (from the Greek monos 'single' + trema
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Therapsida *
Broom, 1905

Clades
  • Suborder Biarmosuchia *
  • Suborder Dinocephalia
  • Suborder Anomodontia *
  • Infraorder Dicynodontia
  • (unranked) Theriodontia *

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The Mesozoic Era is one of three geologic eras 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' (making the modern era the 'Tertiary').
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This article has been tagged since July 2007.
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The Triassic is a geologic period that extends from about 251 to 199 Ma (million years ago). As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events.
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Permian is a geologic period that extends from about 299.0 ± 0.8 Ma to 251.0 ± 0.4 Ma (million years before the present; ICS 2004). It is the last period of the Paleozoic Era.
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Sinodelphys

Sinodelphys or "Chinese opossum" is to date the oldest marsupial fossil known, estimated to be 125 million years old. It was discovered around 2003 in Liaoning Province, China, by a team of scientists including John Wible and Zhe-Xi Luo.
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