Scientists have discovered fossils of a 375 million-year-old fish, a large scaly creature not seen before, that they say is a long-sought "missing link" in the evolution of some fishes from water to a life walking on four limbs on land.
In addition to confirming elements of a major transition in evolution, the fossils are widely seen by scientists as a powerful rebuttal to religious creationists, who hold a literal biblical view on the origins and development of life.
Several well-preserved skeletons of the fossil fish were uncovered in sediments of former stream beds in the Canadian Arctic, 600 miles from the North Pole, it is being reported on Thursday in the journal Nature. The skeletons have the fins and scales and other attributes of a giant fish, four to nine feet long.
But on closer examination, scientists found telling anatomical traits of a transitional creature, a fish that is still a fish but exhibiting changes that anticipate the emergence of land animals — a predecessor thus of amphibians, reptiles and dinosaurs, mammals and eventually humans.
The scientists described evidence in the forward fins of limbs in the making. There are the beginnings of digits, proto-wrists, elbows and shoulders. The fish also had a flat skull resembling a crocodile's, a neck, ribs and other parts that were similar to four-legged land animals known as tetrapods.
The discovering scientists called the fossils the most compelling examples yet of an animal that was at the cusp of the fish-tetrapod transition. The fish has been named Tiktaalik roseae, at the suggestion of elders of Canada's Nunavut Territory. Tiktaalik (pronounced tic-TAH-lick) means "large shallow water fish."
In two reports in Thursday's issue of the journal Nature, the science team led by Neil H. Shubin of the University of Chicago wrote, "The origin of limbs probably involved the elaboration and proliferation of features already present in the fins of fish such as Tiktaalik."
Dr. Shubin, an evolutionary biologist, let himself go in an interview. "It's a really amazing remarkable intermediate fossil — it's like, holy cow," he enthused.
Two other paleontologists, commenting on the find in a separate article in the journal, said that a few other transitional fish had been previously discovered from approximately the same Late Devonian time period, 385 million to 359 million years ago. But Tiktaalik is so clearly an intermediate "link between fishes and land vertebrates," they said, that it "might in time become as much an evolutionary icon as the proto-bird Archaeopteryx," which bridged the gap between reptiles, probably dinosaurs, and today's birds.
