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A new symmetrodont mammal from China and its implications for mammalian evolution

Nature volume 390, pages 137142 (13 November 1997) | Download Citation

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Abstract

A new symmetrodont mammal has been discovered in the Mesozoic era (Late Jurassic or Early Cretaceous period) of Liaoning Province, China. Archaic therian mammals, including symmetrodonts, are extinct relatives of the living marsupial and placental therians. However, these archaic therians have been mostly documented by fragmentary fossils. This new fossil taxon, represented by a nearly complete postcranial skeleton and a partial skull with dentition, is the best-preserved symmetrodont mammal yet discovered. It provides a new insight into the relationships of the major lineages of mammals and the evolution of the mammalian skeleton. Our analysis suggests that this new taxon represents a part of the early therian radiation before the divergence of living marsupials and placentals; that therians and multituberculates are more closely related to each other than either group is to other mammalian lineages; that archaic therians lacked the more parasagittal posture of the forelimb of most living therian mammals; and that archaic therians, such as symmetrodonts, retained the primitive feature of a finger-like promontorium (possibly with a straight cochlea) of the non-therian mammals. The fully coiled cochlea evolved later in more derived therian mammals, and is therefore convergent to the partially coiled cochlea of monotremes.

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Acknowledgements

We thank K. C. Beard, M. Dawson, R. Fox, Z. Kielan-Jaworowska, B. Krebs, T.Martin, J. Meng, R. Presley, G. Rougier, P. Sereno, A. Sun and J. Wible for suggestions on the manuscript; L.-H. Hou for field assistance; G.-H. Cui for photography; and H. Zhang for preparation. Research was supported by National Natural Science Foundation of China (to C.L.), the Rea Postdoctoral Fellowship of Carnegie Museum (to Y. W.), National Science Foundation of USA, National Geographic Society, and the M.Graham Netting Fund of Carnegie Museum (to Z.L.).

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  1. *Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, PO Box 643, Beijing 100044, China

    • Yaoming Hu
    • , Yuanqing Wang
    •  & Chuankui Li
  2. †Section of Vertebrate Paleontology, Carnegie Museum of Natural History, 4400 Forbes Avenue, Pittsburgh, Pennsylvania 15213, USA

    • Yuanqing Wang
    •  & Zhexi Luo

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https://doi.org/10.1038/36505

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