OK... it's not a dinosaur...

[Guy Leahy <xrciseguy@sbcglobal.net>]

But it's still really cool... :-)

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Fossil fish sheds light on transition to living on
land

By MALCOLM RITTER
AP Science Writer
Published April 5, 2006, 12:00 PM CDT

NEW YORK -- Scientists have caught a fossil fish in
the act of adapting toward a life on land, a discovery
that sheds new light one of the greatest
transformations in the history of animals.

Scientists have long known that fish evolved into the
first creatures on land with four legs and backbones
more than 365 million years ago, but they've had
precious little fossil evidence to document how it
happened.

The new find of several specimens looks more like a
land-dweller than the few other fossil fish known from
the transitional period, and researchers speculate
that it may have taken brief excursions out of the
water.

"It sort of blurs the distinction between fish and
land-living animals," said one of its discoverers,
paleontologist Neil Shubin of the University of
Chicago.

Experts said the discovery, with its unusually
well-preserved and complete skeletons, reveals
significant new information about how the
water-to-land evolution took place.

"It's an important new contribution to (understanding)
a very, very important transition in the history of
life," said Robert Carroll of McGill University in
Montreal.

The new find includes specimens, 4 to 9 feet long,
found on Ellesmere Island, which lies north of the
Arctic Circle in Canada. It is reported in Thursday's
issue of the journal Nature by Shubin, Ted Daeschler
of the Academy of Natural Sciences in Philadelphia and
Farish A. Jenkins Jr. of Harvard.

Some 375 million years ago, the creature looked like a
cross between a fish and a crocodile. It swam in
shallow, gently meandering streams in what was then a
subtropical climate, researchers say. A meat-eater, it
lived mostly in water.

Yet, its front fins had bones that correspond to a
shoulder, upper arm, elbow, forearm and a primitive
version of a wrist, Shubin said. From the shoulder to
the wrist area, "it basically looks like a
scale-covered arm," he said.

"Here's a creature that has a fin that can do
push-ups," he said. "This is clearly an animal that is
able to support itself on the ground," probably both
in very shallow water and for brief excursions on dry
land. On land, it apparently moved like a seal, he
said.

It might have pulled itself onto stream banks, perhaps
moving from one wet area to another, and even crawled
across logs in swamps, said Daeschler.

The researchers have not yet dug up any remains from
the hind end of the creature's body, so they don't
know exactly what the hind fins and tail might have
looked like.

The creature was dubbed Tiktaalik (pronounced
"tic-TAH-lick") roseae, and also had the
crocodile-shaped head of early amphibians, with eyes
on the top rather than the side. Unlike other fish, it
could move its head independently of its shoulders
like a land animal. The back of its head also had
features like those of land-dwellers. It probably had
lungs as well as gills, and it had overlapping ribs
that could be used to support the body against
gravity, Shubin said.

Yet, the creature's jaws and snout were still very
fishlike, showing that "evolution proceeds slowly; it
proceeds in a mosaic pattern with some elements
changing while others stay the same," Daeschler said.

If one considers adaptation as a process of collecting
tools to live in a new environment, the new finding
offers "a snapshot of the toolkit at this particular
point in this evolutionary transition," Daeschler
said.

In fact, much of its value comes from this insight
into the order in which those tools appeared in fish,
said Jennifer Clack of Cambridge University, an expert
unconnected with the study.

Knowing that detail about the transition from fish to
land-dweller, she said, "might help us to unravel why
it happened at all. Why did creatures come out of the
water and get legs and walk away?"

It's impossible to tell if Tiktaalik was a direct
ancestor of land vertebrates, she said, but if a
scientist set out to design a plausible candidate,
"you'd probably come up with something like this."

Shubin said the researchers plan to return to the
small rocky outcropping that yielded the fossils and
recover more material. "We've really only begun to
sort of crack that spot," he said.

The site is in Nunavut Territory, and "Tiktaalik" in
the creature's name comes from the traditional
language used in the area. It refers to a large
freshwater fish seen in the shallows.

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On the Net:

www.nature.com/nature 
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Guy Leahy