The Independent - 20 October 2006
http://news.independent.co.uk/world/australasia/article1904967.ece

Ancient fish fossil provides missing link in evolution of land animals

By Kathy Marks in Sydney

The discovery of a 380 million-year-old fossil in a remote region of
Western Australia has given scientists new insight into the process by
which fish evolved into land animals.

The perfect skeleton of the Gogonasus fish was found preserved in
limestone during an expedition organised by Melbourne's Museum
Victoria.

"It looks like it died yesterday," said the expedition leader, John
Long. "You can still open and close the mouth."

Dr Long said the fossil demonstrated that fish developed the
anatomical features of four-legged land creatures, or tetrapods, much
earlier than once thought. Other specimens from that era had been
incomplete, or squashed flat. This one was complete and
three-dimensional, enabling palaentologists to analyse it in greater
detail.

Gogonasus, which swam in an ancient reef system before there was life
on land, had a large hole in its skull and a fin strong enough to
support its body weight. "It's definitely a fish," Dr Long told the
Australian Broadcasting Corporation. "It's got gills, it swims in
water, it's got fins. But it's a fish that is showing the beginnings
of the tetrapod's advanced body plan that would eventually carry on to
all living land animals."

The skeleton, which he called "the most perfect, complete,
three-dimensional fish of its kind ever discovered in the whole
world", was found in the rugged Kimberley region, in a fossil area
known as the Gogo site. In 1985 Dr Long discovered a snout and skull
fragment of the same species there. He named it Gogonasus, which means
"snout from Gogo".

The latest specimen was found by Tim Senden, a member of the team that
went on the expedition in July last year. Dr Senden, who was on his
first field trip, told the Melbourne Herald-Sun that he did not
initially appreciate its significance. "I was the lucky one that
picked up the right rock," he said. "It was the thrill of a lifetime."

It took Dr Long four months to extract the fossil from the limestone.
It was then analysed, using new software technology developed by Dr
Senden, at the Australian National University in Canberra.

Dr Long, who reported the team's findings online yesterday in the
journal Nature, said that analysis of the limited specimens previously
available had suggested that Gogonasus had quite primitive features.
But the new fossil - which has gone on display at Museum Victoria -
demonstrated that it was "hiding a lot of deceptively advanced
features that were not recognised before, until we had such a perfect
specimen". Dr Long added: "This particular fish is a bit like a wolf
in sheep's clothing."

The hole in the skull is believed to be an early version of the middle
ear in land animals. Gogonasus's pectoral fin had the same bone
pattern as tetrapod forelimbs. It also had a single pair of nostrils,
like those of humans.

The transition from fish living and breathing in water to animals with
arms and legs, living on land and breathing air, is a key stage in the
history of evolution.

Dr Long believes that Gogonasus is more closely related to tetrapods
than another fish, Eusthenopteron, which was considered the common
ancestor of all land animals. "It's replaced Eusthenopteron as the
best fish to use when studying the ancestry of the first tetrapods,"
he said.

Another ancient species, Tiktaalik, which was discovered this year, is
the most amphibian-like fish identified so far. Dr Long said many
questions remained , such as the manner in which fin rays evolved into
digits.