Hadrocodium

Hadrocodium

Taxobox
name = "Hadrocodium"
fossil_range = Early Jurassic
regnum = Animalia


image_width = 250px
image_caption = "Hadrocodium" skull
phylum = Chordata
subphylum = Vertebrata
unranked_classis = Amniota
classis = Synapsida
unranked_ordo = Mammaliaformes
genus = "Hadrocodium"

"Hadrocodium wui" is an extinct basal mammal species that lived during the Lower Jurassic (approx. 195 million years ago, during the Sinemurian stage) in what is now the Yunnan province of China. "Hadrocodium" was a mere 3.2 cm (1.35 in) in length (about 2 grams), and is one of the smallest mammals of either the Mesozoic or Cenozoic periods.

"Hadrocodium" is the earliest known example of several features distinctive to mammals [ [http://www.palaeos.com/Vertebrates/Units/Unit420/420.300.html Symmetrodonta - Palaeos] ] , including mammal-like mandible and middle-ear structures and a relatively large brain cavity [ [http://archives.cnn.com/2001/TECH/science/05/24/tiny.ancestor/index.html Tiny creature may be ancestor of all mammals - CNN] ] . The discovery of "Hardocodium" suggests that the origination of these distinctive mammaliaform features was much older (45 million years older) than previously thought.

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

References

Bibliography

* cite journal
author = Z.-X. Luo, A. W. Crompton and A.-L. Sun
year = 2001
title = A New Mammaliaform from the Early Jurassic and Evolution of Mammalian Characteristics
journal = Science
volume = 292
pages = 1535–1540
url = http://www.carnegiemnh.org/vp/media/Luo(Hadrocodium).pdf


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