Hadrocodium

Hadrocodium
Temporal range: Sinemurian
~195 Ma
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Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Synapsida
Clade: Therapsida
Clade: Cynodontia
Clade: Mammaliaformes
Genus: †Hadrocodium
Luo, Crompton, & Sun, 2001
Species

Hadrocodium wui is an extinct mammaliaform that lived during the Sinemurian stage of the Early Jurassic approximately 195 million years ago[1] in the Lufeng Formation in what is now the Yunnan province in south-western China[2] (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).[3] It is considered as the closest relative of the class Mammalia.

Life restoration

The fossil of this mouse-like, paper-clip sized animal was discovered in 1985 but was then interpreted as a juvenile morganucodontid.[4] Hadrocodium remained undescribed until 2001; since then its large brain and advanced ear structure[5] 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.[6] Hadrocodium is known only from a skull 1.2 cm (0.47 in) long, and its body would have measured 3.2 cm (1.3 in) long in total and weighed up to 2 g (0.071 oz), making it one of the smallest Mesozoic mammaliaforms.[1][7][8] The specimen is thought to have been that of a mature adult.[9]

The name Hadrocodium alludes to its large cranial cavity,[10] deriving from the Greek word hadrós (ἁδρός 'large, heavy, fullness')[4] and the Latin word codium, from Greek kṓdeia (κώδεια 'head [of a plant]').[11] The species name, wui, is the Latinized version of discoverer Xiao-Chun Wu's name.[2]

While initially suggested to have possessed a fully mammalian ear akin to those of modern mammals, a 2022 restudy suggested that it actually had a primitive mandibular middle ear similar to those of other primitive mammaliaforms.[9]

  1. ^ a b Luo, Crompton & Sun 2001, Abstract
  2. ^ a b Parsell 2001
  3. ^ Hei Koa Peng, Lufeng (CUP, IVPP) (Jurassic of China) in the Paleobiology Database. Retrieved April 2013.
  4. ^ a b Luo, Crompton & Sun 2001, Note 1
  5. ^ CNN 2001
  6. ^ CMNH 2001
  7. ^ T. S. Kemp (2005). The Origin and Evolution of Mammals. Oxford University Press, USA. p. 183. ISBN 9780198507611. Retrieved 22 September 2022.
  8. ^ Donald R. Prothero (November 15, 2016). The Princeton Field Guide to Prehistoric Mammals. Princeton University Press. p. 27. ISBN 9780691156828.
  9. ^ a b Luo, Zhexi; Bhullar, Bhart-Anjan; Crompton, Alfred; Neander, April; Rowe, Timothy (2022). "Reexamination of the Mandibular and Dental Morphology of the Early Jurassic Mammaliaform Hadrocodium wui". Acta Palaeontologica Polonica. 67. doi:10.4202/app.00949.2021. ISSN 0567-7920.
  10. ^ 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. S2CID 8738213.
  11. ^ Liddell & Scott 1940