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Science 9 October 2009:
Vol. 326. no. 5950, pp. 278 - 281
DOI: 10.1126/science.1178501
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Reports

Evolutionary Development of the Middle Ear in Mesozoic Therian Mammals

Qiang Ji,1 Zhe-Xi Luo,2,* Xingliao Zhang,3 Chong-Xi Yuan,1 Li Xu3

The definitive mammalian middle ear (DMME) is defined by the loss of embryonic Meckel’s cartilage and disconnection of the middle ear from the mandible in adults. It is a major feature distinguishing living mammals from nonmammalian vertebrates. We report a Cretaceous trechnotherian mammal with an ossified Meckel’s cartilage in the adult, showing that homoplastic evolution of the DMME occurred in derived therian mammals, besides the known cases of eutriconodonts. The mandible with ossified Meckel’s cartilage appears to be paedomorphic. Reabsorption of embryonic Meckel’s cartilage to disconnect the ear ossicles from the mandible is patterned by a network of genes and signaling pathways. This fossil suggests that developmental heterochrony and gene patterning are major mechanisms in homplastic evolution of the DMME.

1 Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China.
2 Carnegie Museum of Natural History, Pittsburgh, PA 15213, USA.
3 Henan Geological Museum, Zhengzhou 450003, China.

* To whom correspondence should be addressed. E-mail: LuoZ@CarnegieMNH.Org

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
On the Mammalian Ear.
T. Martin and I. Ruf (2009)
Science 326, 243-244
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