Fossil may be missing evolutionary link


By Reuters Published: April 5, 2006, 10:25 PM PDT

Fossils of a 375-million-year-old species of ancient fish found north of the Arctic Circle fill an evolutionary gap in the transition between water and land animals, scientists said Wednesday.

Remains of the new species named Tiktaalik roseae were found encased in frozen rock. It has the fins and scales of a fish but its crocodile-like skull, neck and ribs resemble those of a land animal.

"It is a fish that shows a surprising combination of characteristics of land-living animals," said Neil Shubin, leader of the University of Chicago team that found the fossils.

"This animal represents the transition from water to land--the part that includes ourselves," he said.

The nearly complete and very well-preserved specimens show the creature had sharp teeth, a jaw ranging from 10-20 inches across and a flattened body that could reach 3 yards in length.

"It shows us the stages by which land-living animals were constructed," said Shubin who reported the discovery in the journal Nature.

The scientists battled freezing temperatures and blustery storms to get to the site on the remote Ellesmere Island more than 600 miles north of the Arctic Circle in Canada.

Shubin was accompanied by Ted Daeschler, of the Academy of Natural Sciences in Philadelphia, and Farish Jenkins of Harvard University.

They also faced the threat of polar bears during their search for so-called elpistostegid fish, which are thought to be most closely related to tetrapods--land animals with limbs such as amphibians, reptiles, birds and humans.

They uncovered the specimens during the first few days of a month-long expedition in 2004. It was the culmination of a five-year project that began in 1999.

They plan to return for more specimens in July.

"Previous fossils representing this evolutionary event have really been fish with a few land characteristics, or land vertebrates with a few residual fish characteristics," said Andrew Milner, of the Natural History Museum in London.

"These fossils show an animal that sits bang in the middle between the fish and land animals."

The fossils also indicate that the transition from water to land occurred gradually in fish living in shallow water. They gradually developed features to live on land over time.

"This find is a dream come true," Daeschler said.

He added in a statement: "We knew that the rocks of Ellesmere Island offered a glimpse into the right time period and were formed in the right kinds of environments to provide the potential for finding fossils documenting this important evolutionary transition."