Missing link found: This fish had arms
April 6, 2006
Say hello to our most bizarre ancestor — a part crocodile, part seal-like fish that was able to take the first baby steps on to land roughly 380 million years ago.
The discovery, 1,400 kilometres above the Arctic Circle, of fossilized skeletons of a creature dubbed Tiktaalik roseae is seen as filling a missing evolutionary link between fish and the first land animals.
The findings were announced yesterday by a U.S.-Canada team that included a University of Toronto graduate researcher.
Steve Cumbaa, a research paleontologist at the Canadian Museum of Nature in Ottawa not connected with the work, hailed the discovery.
"These are the first little baby steps on getting animals `out of ooze and born to cruise,'" Cumbaa said, quoting a catchphrase by American cartoonist Ray Troll.
Experts say that within a few million years Tiktaalik was followed by creatures completely adapted to terrestrial life, collectively called tetrapods. These then evolved into all the land animals on Earth today, including humans.
The discovery is important because it helps researchers reconstruct the detailed path of anatomical adaptation at a critical state of evolution.
University of Chicago paleontologist Neil Shubin, senior member of the research team, called Tiktaalik an "evolutionary mosaic" because the creature combines key elements of fish and land animals in a single body.
The crocodile-shaped head was able to shift from side to side without also moving the shoulders. As well, overlapping ribs provided support against gravity once the creature was out of the water.
"It could have breathed on land and done a sort of push-up with its fins but it couldn't have walked. It probably flopped like a seal," Shubin said in an interview.
Yet Tiktaalik, the Inuit word for "large freshwater fish," also sported scales and fins. But the front fins had bones similar to a shoulder, upper arm, elbow, forearm and a rudimentary wrist.
The largest of the three specimens stretches a little less than three metres, but is missing its tail.
In the period between 380 and 360 million years ago when animals made the move from oceans to land, the Canadian Arctic resembled the Amazon basin. Tiktaalik would have swum in gently meandering streams but could have made brief forays onto land, the researchers speculated.
The researchers plan to return to the fossil trove this summer, seeking younger rocks that might hold fossils revealing how and when fingers developed in the Tiktaalik fin.
In Edmonton, Arctic researcher David Hik said the fossil fish is merely one example of scientific riches waiting to be discovered when International Polar Year (IPY) kicks off next March.
An estimated 50,000 researchers are expected to spend as much as $3 billion probing every aspect of the Arctic and Antarctic during the campaign.
"We know that much of the terrain in the Canadian high Arctic simply hasn't been visited by anybody," said Hik, who heads the IPY secretariat at the University of Alberta.
That was true in the case of the remote southwestern corner of Ellsemere Island in Nunavut, where the U.S.-Canadian research team made its find. But the team headed there because it had what amounted to a fossil treasure map produced by a federal science agency.
Extensive studies of the Arctic by the Geological Survey of Canada identified the area as rich in rocks from the right time period. The first three expeditions, in the summers of 1999, 2000 and 2002, turned up fossil bits and pieces but no substantial discoveries.
But in 2004, a six-person research party hit a paleontology bonanza within days of arriving, recalled expedition member Corwin Sullivan, a former Toronto resident.
"We weren't expecting anything near the richness of the finds we uncovered that summer," said Sullivan.
The 29-year-old remembered one day when team members spotted the snout of a Tiktaalik skull sticking out of a rock bluff where they were digging.
"It turned out to be the tip of a fairly complete specimen. It's such an exciting place to look for fossils because it has hardly been explored," he said.
The fossil bones, still being studied in the U.S., will eventually return to Canada, first to the Museum of Nature in Ottawa and eventually to Nunavut when a suitable institution is available. The nature museum will soon put on display an artist's model of Tiktaalik, which arrived this week from the U.S.