Hadrocodium

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Hadrocodium
Temporal range: Sinemurian
~195 Ma
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Clade: Therapsida
Clade: Cynodontia
Clade: Mammaliaformes
Genus: Hadrocodium
Luo, Crompton, & Sun, 2001
Species

Hadrocodium wui (hadro from Greek ἁδρός/hadros, "large, heavy, fullness";[1] Latin: codium, from Greek κώδεια/kodeia, "head [of a plant]" [2] (alluding to its enlarged cranial cavity);[3] and wui, the Latinized version of discoverer Xiao-Chun Wu's name[4]) is an extinct mammaliaform that lived during the Sinemurian stage of the Early Jurassic approximately 195 million years ago[5] in the Lufeng Formation of the Lufeng Basin in what is now the Yunnan province in south-western China[4] (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).[6]

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[7] 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.[8] 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.

Features[edit]

Hadrocodium might 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,[9] including the middle-ear structure characteristic of modern mammals and a relatively large brain cavity.[7] These features had been considered limited to the crown group mammals, which emerged in the Middle Jurassic; the discovery of Hadrocodium suggests that these attributes appeared 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 former group.

Hadrocodium are capable of laying eggs like today's platypus and echidna.

Family Tree[edit]

Cynodontia

Dvinia

Procynosuchidae

Epicynodontia

Thrinaxodon

Eucynodontia

Cynognathus

Tritylodontidae

Traversodontidae

Probainognathia

Tritheledontidae

Chiniquodontidae

Prozostrodon

Mammaliaformes

Morganucodontidae

Docodonta

Hadrocodium

Kuehneotheriidae

crown group Mammals

Phylogeny [10]
Mammaliaformes 

 Adelobasileus

 Sinoconodon

 Morganucodon

 Megazostrodon

 Haramiyida

 Haldanodon

 Castorocauda

 Hadrocodium

 Mammalia

See also[edit]

References[edit]

  1. ^ a b Luo, Crompton & Sun 2001, Note 1
  2. ^ Liddell & Scott 1940
  3. ^ Luo, Z.-X. (2001). "A New Mammaliaform from the Early Jurassic and Evolution of Mammalian Characteristics". Science. 292 (5521): 1535–40. Bibcode:2001Sci...292.1535L. doi:10.1126/science.1058476. PMID 11375489.
  4. ^ a b Parsell 2001
  5. ^ Luo, Crompton & Sun 2001, Abstract
  6. ^ Hei Koa Peng, Lufeng (CUP, IVPP) (Jurassic of China) in the Paleobiology Database. Retrieved April 2013.
  7. ^ a b CNN 2001
  8. ^ CMNH 2001
  9. ^ Symmetrodonta - Palaeos
  10. ^ Close, Roger A.; Friedman, Matt; Lloyd, Graeme T.; Benson, Roger BJ (2015). "Evidence for a mid-Jurassic adaptive radiation in mammals". Current Biology. 25 (16): 2137–2142. doi:10.1016/j.cub.2015.06.047. PMID 26190074.

Bibliography[edit]

External links[edit]