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Fossil ID'd As 1st Walking Creature


July 3, 2002
Filed at 8:23 p.m. ET

A fossil found in 1971 has been newly identified as the
earliest known animal built to walk on land, a
salamanderlike creature that marked a previously unknown
stage in the evolution of fish into the ancestors of all
vertebrates alive today.

The toothy animal, Pederpes finneyae, lived between 348
million and 344 million years ago in what is now Scotland.
It was perhaps a yard long, and probably split its time
between the water and land where it walked on four feet,
said Jenny Clack, of the Cambridge University Museum of

``It trudged through the swamp catching anything that moved
-- not terribly exciting, I suppose,'' Clack said.

Clack formally describes Pederpes in this week's journal
Nature. The creature's nearly complete fossil skeleton had
lain, mislabeled as a fish, in a Scottish museum since its
discovery 31 years ago. Further work on the fossil in the
1990s revealed it had legs.

The identification helps close a hole in the early fossil
record of a group of creatures called tetrapods.

The gap, or Romer's Gap -- named for the late Harvard
paleontologist Alfred Sherwood Romer -- had stumped
scientists seeking to chart the evolution of the first
four-limbed creatures with backbones. Tetrapods were the
first animals known to walk the Earth and are the ancestors
of today's mammals, reptiles, amphibians and birds.

``Discovery of a nearly complete skeleton in the middle of
Romer's Gap should help in establishing the pattern of
evolutionary change among early tetrapods,'' wrote Robert
Carroll, of Montreal's Redpath Museum, in an accompanying

The earliest tetrapods appeared roughly 365 million years
ago when scientists believed they used their paddlelike
feet to scoot around underwater. Only later did they emerge
to use those rudimentary feet to walk on land.

Scientists knew of no other fossils, until Pederpes, that
represented any sort of intermediate stage between the
aquatic and terrestrial tetrapods. The fossil record picks
up again 20 million to 30 million years later with a
variety of more modern-looking animals with feet and legs
that were clearly for walking on land.

Clack said by the time Pederpes appeared, its feet did not
stick out straight from the body, as was the case in
earlier tetrapods that used their limbs as paddles.
Instead, they pointed forward, suggesting they were built
for use on land. Later tetrapods elaborate on that form of
foot construction, she said.

``We are now, finally, with the discovery of animals such
as this, beginning to get some actual data as opposed to
speculation,'' said John Bolt, curator of fossil amphibians
and reptiles at the Field Museum in Chicago.