Letter

Nature 456, 497-501 (27 November 2008) | doi:10.1038/nature07533; Received 25 July 2008; Accepted 3 October 2008

An ancestral turtle from the Late Triassic of southwestern China

Chun Li1, Xiao-Chun Wu2, Olivier Rieppel3, Li-Ting Wang4 & Li-Jun Zhao5

  1. Laboratory of Evolutionary Systematics of Vertebrates, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of SciencesPO Box 643, Beijing 100044, China
  2. Canadian Museum of Nature, PO Box 3443, Station D, Ottawa, Ontario K1P 6P4, Canada
  3. Department of Geology, The Field Museum, 1400 South Lake Shore Drive, Chicago, Illinois 60605-2496, USA
  4. Geological Survey of Guizhou Province, Guiyang 550005, China
  5. Zhejiang Museum of Nature History, Hangzhou 310012, China

Correspondence to: Chun Li1Xiao-Chun Wu2 Correspondence and requests for materials should be addressed to C.L. (Email: lichun@ivpp.ac.cn) or X.-C.W. (Email: xcwu@mus-nature.ca).

The origin of the turtle body plan remains one of the great mysteries of reptile evolution. The anatomy of turtles is highly derived, which renders it difficult to establish the relationships of turtles with other groups of reptiles. The oldest known turtle, Proganochelys from the Late Triassic period of Germany1, has a fully formed shell and offers no clue as to its origin. Here we describe a new 220-million-year-old turtle from China, somewhat older than Proganochelys, that documents an intermediate step in the evolution of the shell and associated structures. A ventral plastron is fully developed, but the dorsal carapace consists of neural plates only. The dorsal ribs are expanded, and osteoderms are absent. The new species shows that the plastron evolved before the carapace and that the first step of carapace formation is the ossification of the neural plates coupled with a broadening of the ribs. This corresponds to early embryonic stages of carapace formation in extant turtles, and shows that the turtle shell is not derived from a fusion of osteoderms. Phylogenetic analysis places the new species basal to all known turtles, fossil and extant. The marine deposits that yielded the fossils indicate that this primitive turtle inhabited marginal areas of the sea or river deltas.

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