Hadrocodium

Hadrocodium
Temporal range: Early Jurassic, 195 Ma
↓
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, "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 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

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, 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

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

References

  1. 1 2 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. doi:10.1126/science.1058476. PMID 11375489.
  4. 1 2 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. 1 2 CNN 2001
  8. ↑ CMNH 2001
  9. ↑ Symmetrodonta - Palaeos

Bibliography

External links

Wikispecies has information related to: Hadrocodium


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