Eomaia scansoria ('dawn mother') is a recently discovered extinct mammal that may be one of the earliest ancestors of the eutheria yet to have been found. Scientific classification - Wikipedia /**/ @import /skins/monobook/IE50Fixes. ... Phyla Subkingdom Parazoa Porifera (sponges) Subkingdom Agnotozoa Placozoa Orthonectida Rhombozoa Subkingdom Metazoa Radiata Cnidaria Ctenophora - Comb jellies Bilateria Protostomia Acoelomorpha Platyhelminthes - Flatworms Nemertina - Ribbon worms Gastrotricha Gnathostomulida - Jawed worms Micrognathozoa Rotifera - Rotifers Acanthocephala Priapulida Kinorhyncha Loricifera Entoprocta Nematoda - Roundworms Nematomorpha - Horsehair worms Cycliophora Mollusca - Mollusks Sipuncula - Peanut worms Annelida - Segmented... Typical Classes Subphylum Urochordata - Tunicates Ascidiacea Thaliacea Larvacea Subphylum Cephalochordata - Lancelets Subphylum Myxini - Hagfishes Subphylum Vertebrata - Vertebrates Petromyzontida - Lampreys Placodermi (extinct) Chondrichthyes - Cartilaginous fishes Acanthodii (extinct) Actinopterygii - Ray-finned fishes Actinistia - Coelacanths Dipnoi - Lungfishes Amphibia - Amphibians Reptilia - Reptiles Aves - Birds Mammalia - Mammals Chordates (phylum Chordata) include the vertebrates, together with... Orders Subclass Monotremata Monotremata Subclass Marsupialia Didelphimorphia Paucituberculata Microbiotheria Dasyuromorphia Peramelemorphia Notoryctemorphia Diprotodontia Subclass Placentalia Xenarthra Dermoptera Desmostylia Scandentia Primates Rodentia Lagomorpha Insectivora Chiroptera Pholidota Carnivora Perissodactyla Artiodactyla Cetacea Afrosoricida Macroscelidea Tubulidentata Hyracoidea Proboscidea Sirenia The mammals are the class of vertebrate animals primarily characterized by the presence of mammary... Infraclasses Eutheria Metatheria Theria is a subclass of advanced mammals that give birth to live young without using a shelled egg. ... Eutheria is a classification system nearly synonymous with Placentalia. ... Orders Subclass Monotremata Monotremata Subclass Marsupialia Didelphimorphia Paucituberculata Microbiotheria Dasyuromorphia Peramelemorphia Notoryctemorphia Diprotodontia Subclass Placentalia Xenarthra Dermoptera Desmostylia Scandentia Primates Rodentia Lagomorpha Insectivora Chiroptera Pholidota Carnivora Perissodactyla Artiodactyla Cetacea Afrosoricida Macroscelidea Tubulidentata Hyracoidea Proboscidea Sirenia The mammals are the class of vertebrate animals primarily characterized by the presence of mammary... Eutheria is a classification system nearly synonymous with Placentalia. ...

The fossil was discovered in Yixian Formation, Liaoning Province, China. It dates from the Barremian Age, in the Lower Cretaceous. Liaoning (Simplified Chinese: 辽宁; Traditional Chinese: 遼寧; pinyin: Liáoníng) is a northeastern province of the Peoples Republic of China. ... The Barremian faunal stage was a period of geological time between 117 and 113 million years ago. ... The Cretaceous period is one of the major divisions of the geologic timescale, reaching from the end of the Jurassic period (about 135 mya) to the beginning of the Paleocene epoch of the Tertiary period (65 mya). ...

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.

According to palaeontologist Anne Weil, Eomaía was not a placental mammal. It was an early, primitive representative of the lineage that eventually led to placental mammals[1] (http://news.nationalgeographic.com/news/2002/04/0423_020425_firstmammal.html). 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. A paleontologist carefully chips rock from a column of dinosaur vertebrae. ... Orders Afrosoricida Macroscelidea Tubulidentata Hyracoidea Proboscidea Sirenia Xenarthra Dermoptera: Scandentia Primates Rodentia Lagomorpha Insectivora Chiroptera Pholidota Carnivora Perissodactyla Artiodactyla Cetacea Placentalia and Eutheria are terms used to describe major groupings within the animal class of Mammalia. ... Human placenta shown a few minutes after birth. ...

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. Orders Superorder Ameridelphia Didelphimorphia Paucituberculata Superorder Australidelphia Microbiotheria Dasyuromorphia Peramelemorphia Notoryctemorphia Diprotodontia Family Thylacinidae (extinct) Marsupials are mammals in which the female typically has a pouch (called the marsupium, from which the name Marsupial derives) in which it rears its young through early infancy. ... Families Kollikodontidae (extinct) Ornithorhynchidae - Platypus Tachyglossidae - Echidnas Steropodontidae (extinct) Monotremes are mammals that are best known for laying eggs, instead of giving birth to live young like marsupials and placental mammals (Eutheria). ... Groups Biarmosuchia Dinocephalia Anomodontia Theriodontia    Cynodontia       (...mammals) Therapsids, previously known as the mammal-like reptiles, are a group of synapsids. ...

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. The Mesozoic is one of three geologic eras of Phanerozoic eon. ... Greek clados = branch) or phylogenetic systematics is a branch of biology that determines the evolutionary relationships of living things based on derived similarities. ...

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. The Triassic is a Geologic period that extends from about 248 to 202 million years (My or megayears) before the present. ... The Permian is a geologic period that extends from about 280 to 248 million years before the present (mya). ...

Reference

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

External link

• New Scientist article on original find. (http://www.newscientist.com/news/news.jsp?id=ns99992210)