Ancient Fish Fossil May Rewrite Story of Animal Evolution

October 18, 2006

A fish that swam on an ancient barrier reef in Australia 380 million years ago had fins and nostrils remarkably similar to the limbs and ears of the first four-limbed creatures to walk on land, according to a new study.

Four-limbed land animals, also known as tetrapods, such as modern amphibians, reptiles, birds, and mammals, evolved from lobed-finned fish.

That transition from water to land has long fascinated scientists, but the fossil record of how it occurred is still incomplete.

The new finding suggests that certain aspects of tetrapod ears and limbs can be traced much further back in "fishy looking" fish than had been previously known, says John Long, head of sciences at Museum Victoria in Melbourne, Australia.

"They were just cunningly disguised in the fossil record by their more fishlike overall features," he said in an email interview.

"They tell us that evolution progresses steadily but often hides the evidence until a really well preserved fossil like this turns up."

Long and colleagues report their findings in tomorrow's issue of the science journal Nature.

Fishy Fish

The team analyzed a remarkably well preserved fossil specimen of a fish called Gogonasus.

Previously the lobed-finned fish—which was about 12 inches (30 centimeters) long and covered in diamond-shaped scales—was known only from crushed or fragmented fossil remains.

But the new specimen, discovered last year in Western Australia, is nearly complete, with an almost intact skull, body, and fin bones (map of Australia).

Among the most remarkable features are slits on the roof of the skull called spiracles that scientists had previously seen only in creatures more closely related to tetrapods, such as the "missing link" fish Tiktaalik. (Related story: "Fossil Fish With 'Limbs' Is Missing Link" [April 5, 2006].)

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