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Transitional “fishapod”
Apr 13, 2006

This is one for the realm of ironic. During the same week that world-wide attention was drawn to an extraordinary fossil discovery in Canada’s Arctic, heralded as a transitional species on the evolutionary ladder, a McGill University researcher was turned down for a grant because his proposal assumed evolution was a fact.

According to a report in the National Post, Dr. Brian Alters had approached the Ottawa-based Social Sciences and Humanities Research Council for $40,000 “to examine how the rising popularity in the United States of ‘intelligent design (ID)’ — a controversial creationist theory of life — is eroding acceptance of evolutionary science in Canada.”

In rejecting his application, the research council sent a letter to the director of McGill’s Evolution Education Research Centre, saying that he had failed to “substantiate the premise” of his study and had not provided “adequate justification for the assumption in the proposal that the theory of evolution, and not intelligent-design theory, was correct.”

Meanwhile, a team of American paleontologists reported in the prestigious British science journal Nature, that they had uncovered three nearly-complete fossil specimens of what is a 375-million-year-old “missing evolutionary link” from frozen river sediments on Ellesmere Island. 

Tiktaalik roseae connects fish and the first animals to walk on land. Tiktaalik in the Inuit language of Canada means “large freshwater fish” — the specimens found are just over a metre to just under three metres in length — while roseae is derived from an anonymous donor to the expedition.

The fossils show evidence of fish scales and fins, but more importantly primitive  wrists, fingers, shoulders, ribs and a neck, characteristics that are shared with all four-limbed land animals. To put the discovery into perspective, scientists had long assumed that fish evolved into land-based tetrapods (four-limbed animals, which includes humans), but there were gaps in the fossil record. The gap covered a period of between 10 and 20 million years.

“It (Tiktaalik) represents the transition from water to land — the part of history that includes ourselves,” Neil Shubin, of the University of Chicago and co-leader of the Arctic expedition, told the Chicago Tribune. “When we talk about the fish’s wrist, we’re talking about the origin of parts of our wrist.”

The newly-found fish narrows the gap in the fossil record of the fish to tetrapod transition. The first tetrapods to be successful on land were amphibians, followed by reptiles, who were the first full-time land-dwelling tetrapods.

Tiktaalik lived in shallow muddy water fed by emptying streams, a coastal region comparable to today’s Mississippi Delta. The creature is believed to have used its strong pectoral fins, which had jointed bones like land-dwelling animals and unlike fish, to flop up briefly onto shore to elude larger swimming predators or to feed on anthropods — insects, crabs, spiders, centipedes and the like — that were then the only land residents at the time (these creepy-crawlers have segmented bodies, an exoskeleton and more than four limbs and therefore are not tetrapods).

Tiktaalik didn’t so much walk on land as walk in shallow water. Hiding among a tangle of fallen tree branches in the water with the help of limbs propelling them through the jumble would be a good way to escape big predatory fish. On land, the limbs could have propped its head up and its strong ribs — fish have a weak rib system — would have helped support its body weight. Researchers refer to it as a fish that could do push-ups.

Shubin said the scientists also jokingly called the animal with both fish and tetrapod characteristics a “fishapod.”

One researcher suggested that possessing limbs allowed the creature to bask in the sun like a crocodile. Its cold-blooded metabolism, when warmed by the sun, allowed it to have faster reflexes and thus better survival skills.

Although the fossils found are nearly complete, they do not include the hind section fins, therefore, the shape and function of the two appendages remain a mystery.

Tiktaalik was itself a predator with a flattened body and a large crocodile-shaped head filled with sharp teeth. Unlike fish, its head was connected to its body with a neck, which allowed it to swivel its head, an advantage when hunting. Because fish don’t have a neck, they have to turn their whole body to feed. 

The new species lived during the Devonian period, when Ellesmere Island was near the equator and boasted a semi-tropical climate. Continental drift over millions of years has moved the island to its present location in the High Arctic. 

According to the Chicago Tribune report, H. Richard Lane, program director of the National Science Foundation’s division of earth sciences, said “human comprehension of the history of life on earth is taking a major leap forward” because of the discovery.

“There are controversies over the mechanisms of evolution,” said Maxine Singer, a member of the National Academy of Science, “and we should teach those. But there is no controversy in science about whether evolution occurs or not.”

The discovery in Canada’s Arctic will undoubtedly become an icon of evolution in the same manner as the previous discovery of Archaeopteryx, which linked dinosaurs to birds. But, the Arctic discovery is more significant because it demonstrates the evolutionary transition from sea to land.