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Published online: 3 December 2008 | doi:10.1038/nchina.2008.283
Palaeontology: Shell shocked
Felix Cheung
Abstract
A fossil unearthed in China exhibits an incomplete shell that might explain how turtles evolved their protective armour
Original article citation
, , , & An ancestral turtle from the Late Triassic of southwestern China. Nature 456, 497–501 (2008).Introduction
© (2008) Nature
The question of how turtles evolved their protective shells has always been a mystery. Chun Li at the Chinese Academy of Sciences in Beijing, Xiaochun Wu at the Canadian Museum of Nature and co-workers1 have solved this mystery by unearthing a fossil of the turtle's ancestor in Guizhou Province, China.
Proganochelys, the oldest-known turtle fossil before this discovery, offered few clues to the origin of turtle shell because its protective body armour was already fully developed. The limbs of Proganochelys, however, did have bony plates in the skin. The finding led some scientists to suggest that the turtle shell evolved from these bony plates, which eventually fused together to form a full piece.
Li, Wu and co-workers have now discovered a 220 million-year-old turtle fossil, Odontochelys, which is slightly older than Proganochelys.
Odontochelys has a half-shell: a fully developed ventral (abdominal) side reminiscent of turtles today and a dorsal (back) side consisting of neural plates (patches of hardened ectodermal cells) extending from its backbone. There are also signs of a widening of the ribs.
The findings indicate that the turtle shell evolved not from the fusion of bony plates in the skin, rather from the hardening of tissues. Because reptiles living on land have their ventral side close to the ground with little exposure to danger, the half-shell feature also indicates that Odontochelys was a water dweller.
The authors of this work are from:
Laboratory of Evolutionary Systematics of Vertebrates, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing, China; Canadian Museum of Nature, Ottawa, Ontario, Canada; Department of Geology, Field Museum, Chicago, Illinois, USA; Geological Survey of Guizhou Province, Guiyang, China; Zhejiang Museum of Nature History, Hangzhou, China.
Reference
- Li, C., Wu, X. C., Rieppel, O., Wang, L. T. & Zhao, L. J. An ancestral turtle from the Late Triassic of southwestern China. Nature 456, 497–501 (2008). | Article |
