http://www.nytimes.com/2006/04/05/science/05cnd-fossil.html?pagewanted=2&ei=5070&en=d343adaa4f78126e&ex=1145937600

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Scientists Call Fish Fossil the 'Missing Link'
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By JOHN NOBLE WILFORD
Published: April 5, 2006
Scientists have discovered fossils of a 375 million-year-old fish, a large
scaly creature not seen before, that they say is a long-sought "missing
link" in the evolution of some fishes from water to a life walking on four
limbs on land.

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University of Chicago
A model of the 375 million-year-old fish, which exhibits changes that
anticipate the emergence of land animals. In addition to confirming
elements of a major transition in evolution, the fossils are widely seen
by scientists as a powerful rebuttal to religious creationists, who hold a
literal biblical view on the origins and development of life.

Several well-preserved skeletons of the fossil fish were uncovered in
sediments of former stream beds in the Canadian Arctic, 600 miles from the
North Pole, it is being reported on Thursday in the journal Nature. The
skeletons have the fins and scales and other attributes of a giant fish,
four to nine feet long.

But on closer examination, scientists found telling anatomical traits of a
transitional creature, a fish that is still a fish but exhibiting changes
that anticipate the emergence of land animals — a predecessor thus of
amphibians, reptiles and dinosaurs, mammals and eventually humans.

The scientists described evidence in the forward fins of limbs in the
making. There are the beginnings of digits, proto-wrists, elbows and
shoulders. The fish also had a flat skull resembling a crocodile's, a
neck, ribs and other parts that were similar to four-legged land animals
known as tetrapods.

The discovering scientists called the fossils the most compelling examples
yet of an animal that was at the cusp of the fish-tetrapod transition. The
fish has been named Tiktaalik roseae, at the suggestion of elders of
Canada's Nunavut Territory. Tiktaalik (pronounced tic-TAH-lick) means
"large shallow water fish."

In two reports in Thursday's issue of the journal Nature, the science team
led by Neil H. Shubin of the University of Chicago wrote, "The origin of
limbs probably involved the elaboration and proliferation of features
already present in the fins of fish such as Tiktaalik."

Dr. Shubin, an evolutionary biologist, let himself go in an interview.
"It's a really amazing remarkable intermediate fossil — it's like, holy
cow," he enthused.

Two other paleontologists, commenting on the find in a separate article in
the journal, said that a few other transitional fish had been previously
discovered from approximately the same Late Devonian time period, 385
million to 359 million years ago. But Tiktaalik is so clearly an
intermediate "link between fishes and land vertebrates," they said, that
it "might in time become as much an evolutionary icon as the proto-bird
Archaeopteryx," which bridged the gap between reptiles, probably
dinosaurs, and today's birds.

The writers, Erik Ahlberg of Uppsala University in Sweden and Jennifer A.
Clack of the University of Cambridge in England, are often viewed as
rivals to Dr. Shubin's team in the search for intermediate species in the
evolution from fish to the first animals to colonize land.

In a statement by the Science Museum of London, where casts of the fossils
will be on view, Dr. Clack said the fish "confirms everything we thought
and also tells us about the order in which certain changes were made."

H. Richard Lane, director of paleobiology at the National Science
Foundation, said in a statement, "These exciting discoveries are providing
fossil 'Rosetta Stones' for a deeper understanding of this evolutionary
milestone — fish to land-roaming tetrapods."

The science foundation and the National Geographic Society were among the
financial supporters of the research. Besides Dr. Shubin, the principal
discoverers were Edward B. Daeschler of the Academy of Natural Sciences in
Philadelphia and Farish A. Jenkins Jr., a Harvard evolutionary biologist.

Michael J. Novacek, a paleontologist at the American Museum of Natural
History in Manhattan, who was not involved in the research, said: "Based
on what we already know, we have a very strong reason to think tetrapods
evolved from lineages of fishes. This may be a critical phase in that
transition that we haven't had before. A good fossil cuts through a lot of
scientific argument."

While Dr. Shubin's team played down the fossil's significance in the
raging debate over Darwinian theory, which is opposed mainly by some
conservative Christians in the United States, other scientists were not so
reticent. They said this should undercut the creationists' argument that
there is no evidence in the fossil record of one kind of creature becoming
another kind.

One creationist Web site (emporium.turnpike.net/C/cs/evid1.htm) declares
that "there are no transitional forms," adding: "For example, not a single
fossil with part fins part feet has been found. And this is true between
every major plant and animal kind."




Scientists Call Fish Fossil the 'Missing Link'
E-MailPrint Single Page Reprints Save

Published: April 5, 2006
(Page 2 of 2)



Dr. Novacek responded in an interview: "We've got Archaeopteryx, an early
whale that lived on land and now this animal showing the transition from
fish to tetrapod. What more do we need from the fossil record to show that
the creationists are flatly wrong?"

Dr. Shubin and Dr. Daeschler began their search on Ellsmere Island in
1999. They were attracted by a map in a geology textbook showing the
region had an abundance of Devonian rocks exposed and relatively easy to
explore. At that time, the land was part of a supercontinent straddling
the equator and had a warm climate.

It was not until July 2004, Dr. Shubin said, that "we hit the jackpot."
They found several of the fishes in a quarry, their skeletons largely
intact and in three dimensions. The large skull had the sharp teeth of a
predator. It was attached to a neck, which allowed the fish the unfishlike
ability to swivel its head.

"Fish feeding in water readily orient the mouth toward food by maneuvering
the entire body," said Dr. Jenkins, who assisted in the interpretation of
the fossils. "The head is rigidly attacked to the trunk by bones linking
the skull and shoulder girdle, and thus fish have no neck."

If the animal spent any time out of water, he said, it needed a true neck
that allowed the head to move independently on the body.

Embedded in the pectoral fins were bones that compare to the upper arm,
forearm and primitive parts of the hand of land-living animals. The
scientists said the joints of the fins appeared to be capable of
functioning for movement on land, a case of a fish improvising with its
evolved anatomy. In all likelihood, they said, Tiktaalik flexed its
proto-limbs primarily on the floor of streams and may have pulled itself
up on the shore for brief stretches.

In their journal report, the scientists concluded that Tiktaalik is an
intermediate between the fish Panderichthys, which lived 385 million years
ago, and early tetrapods. The known early tetrapods are Acanthostega and
Ichthyostega, about 365 million years ago.

Tiktaalik, Dr. Shubin said, is "both fish and tetrapod, which we sometimes
call a fishapod."


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