Maotherium

Maotherium Temporal range: Early Cretaceous
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Subclass:	Theriiformes
(unranked):	Trechnotheria
Superfamily:	Spalacotherioidea
Genus:	Maotherium
Species
M. sinensis M. asiaticus

Maotherium was discovered in Early Cretaceous rocks in Liaoning Province, China, in 2003. Its scientific name means "Mao's beast" after the Chinese politician Mao Zedong. Maotherium belongs to an extinct group of Mesozoic mammals called symmetrodonts. Though little is known about this group, the symmetrodonts have several similarities - specifically their teeth. They have tall pointed, but simple molars in a triangular arrangement. Originally symmetrodonts were known since the 1920s. Now a vast majority have been restored, such as Zhangheotherium and Akidolestes, during the early 21st century. One of the fossils of Maotherium preserved the imprints of fur, like the mammals Eomaia and Sinodelphys.

A species described in 2009, Maotherium asiaticus, sheds light on the evolution of the mammalian middle ear. In modern mammals, the Meckel's cartilage appears during development but disappears before adulthood. In Maotherium asiaticus, that cartilage not only remained, but turned into bone.^[1] This event in evolution may be an example of heterochrony, a change in the timing of development.^[2]

References

1. ^ Ji Qiang, Luo Zhe-Xi, Zhang Xingliao, Yuan Chong-Xi, Xu Li (2009). "Evolutionary development of the middle ear in Mesozoic therian mammals". Science 326 (5950): 278–281. doi:10.1126/science.1178501. PMID 19815774. http://www.sciencemag.org/cgi/content/abstract/326/5950/278. 
2. ^ Martin, Thomas, & Ruf, Irina (2009). "On the mammalian ear". Science 326 (5950): 243–244. doi:10.1126/science.1181131. PMID 19815765. http://www.sciencemag.org/cgi/content/summary/326/5950/243.