Latimeria chalumnae, one of only two known living species of coelacanth.
Credit: Wikipedia
SYDNEY, 28 August 2006: The oldest known fossil coelacanth has been uncovered by Australian researchers, pushing back the geological record for the group by more than 30 million years.
"We're looking at our ultimate deep, deep time ancestry with these creatures," says John Talent of Macquarie University in Sydney, one of the authors of the paper published in the international journal Biology Letters.
Coelacanths ("see-la-kanths"), or lobe-finned fish, are closely related to the first fish to make the evolutionary journey from the oceans onto land. They predate the dinosaurs by millions of years, and were thought to have become extinct along with them ... until they were rediscovered by fishermen in the Indian Ocean in 1938.
Along with lungfish, coelacanths are classified in the group Sarcopterygii. Fossil records of other major sarcopterygian groups, including the lungfish, extend to the beginning of the Devonian, but until now coelacanth fossils were only known from the Middle Devonian (385 to 390 million years ago), indicating a 'gap' in the fossil record.
"Based on these relationships, we would have predicted that we'd find fossils this old, but we didn't know where," says Talent's colleague and co-author Zerina Johanson. "Now we've found them in Australia, and filled in that gap."
The new coelacanth fossil was collected in the 1970s from an Early Devonian freshwater lake deposit in the state of Victoria, in south-eastern Australia. But it was not closely studied until this year. "It's a very beautiful jaw that leaves no doubt as to what it is, and the age of the rocks it comes from is very tightly constrained," says Talent. "But I didn't appreciate what it was at the time."
He made that discovery years later as he and Johanson sorted through the huge collection of fossils drawn from the site.
The new species, Eoactinistia foreyi, is described from a single lower jaw bone that preserves a mix of primitive and more derived coelacanth jaw characters. For example, a pore opening is present that is otherwise only found among substantially younger coelacanths.
"This little fellow takes us back in time about 35 million years before the oldest coelacanth that we've got in the geological record," says Talent. "We've been very excited since we recognised the significance of this creature."
