WASHINGTON – An international team of scientists has discovered a long-sought missing link between fish and the first animals to walk on land.
They found nearly complete fossils of a flat-bodied, sharp-toothed creature with a crocodile-like head and the scales and fins of a fish, but a neck, ribs and limbs more like a land creature.
It would have been able to haul itself out of shallow water and push itself along the shore, like an awkward seal, in what’s now Arctic Canada, about 375 million years ago, the scientists report in this week’s Nature magazine.
“This really is what our ancestors looked like when they began to leave the water,” said Per Ahlberg, an evolutionary biologist at Uppsala University in Uppsala, Sweden.
The shift of animals from water to land was “one of the major transformations in the history of life,” said Edward Daeschler, a paleontologist at the Academy of Natural Sciences in Philadelphia.
The scientists named the new species Tiktaalik (tick-TAH-lick), a native Inuit word for “large freshwater fish.” They think it could survive on land for short periods but had to return to the water to stay alive.
Tiktaalik used its snout to breathe air and its gills to get oxygen in the water, like modern lungfish, Ahlberg said in an e-mail message.
He said the animal’s powerful pectoral fins, the equivalent of a forelimb, could raise its head and forequarters slightly off the ground.
The fossils of at least 10 specimens, ranging from 4 to 9 feet long, were found at the Ellesmere site after about five years of searching. Although the site lies in the Arctic zone today, it had a subtropical climate at the time Tiktaalik was alive, rather like the Mississippi Delta.
The expeditions were supported by the National Science Foundation, National Geographic, the Philadelphia Academy of Natural Sciences, Harvard University and the University of Chicago.
“This suggests a walking mode similar to that in the (modern) mudskipper or the catfish,” Ahlberg said. “It’s not elegant, but it works reasonably well. I think it had enough walking ability to allow it both to come out of the water and to return to the water at will, without getting stranded on land.”
Tiktaalik’s behavior was a “major departure from more primitive fishes,” said Daeschler, who’s a leader of the team that discovered the snout of one specimen sticking out of a cliffside on Canada’s frigid Ellesmere Island in 2004.
The discovery supports the view that animals’ transition from water to firm land began on an ancient continent called Euramerica, which included parts of what are now Canada and Northern Europe, rather than in Africa or Asia.
University of Chicago paleontologist Neil Shubin, a member of the discovery team, said Tiktaalik’s fins contained bones comparable to the arms and hands of land animals.
“Most of the major joints of the fin are functional in this fish,” Shubin said. “The shoulder, elbow and even parts of the wrist are already there. This animal represents the transition from water to land – the part of history that includes ourselves.
“Tiktaalik goes a long way to bridging a very big transition in the history of life on Earth.”