Wednesday, April 11, 2012

Older fourlegs

China seems to have had the lion's share of the cool fossils unearthed in the last 10 years or so. A new   paper1 on a coelacanth fossil from south China is another example of their phenomenal treasure trove of fossils. It pushes back the origin of anatomically modern coelacanths by 17 million years to 409 million years ago. The previous oldest coelacanth was known from a jaw found in Australia. 

Coelacanths are interesting for many reasons, not least because they are more closely related to us than they are to other fish. The group was though to have gone extinct around the same time as the dinosaurs, 65 million years ago. But, in 1938 an extant representative was found in South Africa (although it had been known by the local fishermen for a while before that). A book about the discovery dubbed the fish 'old fourlegs'. There was more excitement in 1997, when a second extant species of coelacanth was found off Indonesia.

A preserved specimen of the extant coelacanth, Latimeria chalumnae, or old fourlegs.
The modern coelacanths look almost the same as their ancestors did a few hundred million years ago. So, much like the sharks, they represent 'living fossils'. To put their ancient history in a little perspective, about the same time as the anatomically modern coelacanth body plan emerged, our ancestors were probably taking their first steps on land2


References:
Zhu, M., Yu, X., Lu, J., Qiao, T., Zhao, W., and Jia, L. (2012) Earliest known coelacanth skull extends the range of anatomically modern coelacanths to the Early Devonian. Nature Communications 3, doi: 10.1038/ncomms1764


2 Niedz´wiedzki, G., Szrek, P., Narkiewicz, K., Narkiewicz, M., and Ahlberg, P. E. (2010) Tetrapod trackways from the early Middle Devonian period of Poland. Nature 463, 43 - 48.

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