Hadrocodium

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Hadrocodium
Temporal range: Early Jurassic, 195Ma
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
(unranked): Amniota
Class: Synapsida
(unranked): Mammaliaformes
Genus: Hadrocodium
Luo, Crompton & Sun 2001
Species

Hadrocodium wui (hadro from Greek ἁδρός/hadros, "fullness";[1] Latin: codium, from Greek κώδεια/kodeia, "head [of a plant]";[2] and wui, the Latinized version of discoverer Xiao-Chun Wu's name[3]) is an extinct mammaliaform that lived during the Sinemurian stage of the Early Jurassic approximately 195 million years ago[4] in the Lufeng basin in what is now the Yunnan province in south-western China[3] (25°12′N 102°06′E / 25.2°N 102.1°E / 25.2; 102.1, paleocoordinates 34°18′N 104°54′E / 34.3°N 104.9°E / 34.3; 104.9).[5]

The fossil of this mouse-like, paper-clip sized animal was discovered in 1985 but was then interpreted as a juvenile morganucodontid.[1] Hadrocodium remained undescribed until 2001; since then its large brain and advanced ear structure[6] have greatly influenced the interpretation of the earliest stages of mammalian evolution, as these mammalian characters could previously be traced only to some 150 million years ago.[7] Hadrocodium is known only from a skull, but the body is estimated to have been a mere 3.2 cm (1.3 in) in length and about 2 g (0.071 oz) in mass, making it one of the smallest mammals ever.

Hadrocodium may have been the first animal to have a nearly fully mammalian middle ear. It is the earliest known example of several features possessed only by mammals,[8] including the middle-ear structure characteristic of modern mammals and a relatively large brain cavity.[6] These features had been considered limited to the crown group mammals, who emerged in the Middle Jurassic; the discovery of Hadrocodium suggests that these attributes appeared earlier (45 million years earlier) than previously thought.

Whether Hadrocodium was warm-blooded or cold-blooded has not been settled, although its apparent nocturnal features would seem to place it in the endotherm group.

Family Tree[edit]

Main article: Evolution of mammals
Cynodontia


Dvinia



Procynosuchidae



Epicynodontia

Thrinaxodon


Eucynodontia


Cynognathus




Tritylodontidae



Traversodontidae




Probainognathia


Tritheledontidae



Chiniquodontidae





Prozostrodon


Mammaliaformes

Morganucodontidae




Docodonta




Hadrocodium




Kuehneotheriidae



crown group Mammals











See also[edit]

References[edit]

Bibliography[edit]

External links[edit]

  • Rowe, Timothy; Macrini, Thomas E; Luo, Zhe-Xi (2006). "Hadrocodium wui (On-line)". Digital Morphology at the University of Texas. Retrieved April 2013.  — 3D models from CT scans of the original fossil