Fish With First Neck Evolved Into Land Animal -- Slowly

October 15, 2008

The skull of a 375-million-year-old walking fish reveals new clues to how our fish ancestors evolved into land dwellers.

The fossil fish—called Tiktaalik roseae—was discovered in the Canadian Arctic in 2004 and provides the 'missing link' between fish and land vertebrates, according to scientists. It's also the proud owner of the world's first known neck.

The new study confirms that the prehistoric fish, which had limblike fins, heralded a momentous departure from water for vertebrates (animals with backbones) but that this evolutionary transition wasn't as sudden as previously thought.

Careful analysis of the fossil skull indicates that Tiktaalik was an intermediate step between fish and land animals, with physical features from both—allowing the fish to live in shallow water.

"We see that cranial features once associated with land-living animals were first adaptations for life in shallow water," said study co-author Jason Downs of the Academy of Natural Sciences in Philadelphia, Pennsylvania.

From Fins to Limbs

Researchers already knew that Tiktaalik was a nine-foot (three-meter) crocodile-style predator with a neck, primitive lungs, and leglike fins adapted for life in the shallows.

The team's latest findings, to be published tomorrow in the journal Nature, reveal the switch from an aquatic to a terrestrial life in vertebrates also involved incremental, complex changes to the skull.

The study indicates Tiktaalik shared many internal skull features with more primitive fishes, but that its head was also amphibianlike, suggesting the animal was possibly capable of breathing air and feeding on land.

"The new study reminds us that the gradual evolutionary transition from fish to tetrapod [four-limbed land animals] and the transition from aquatic to terrestrial lifestyles required much more than the evolution of limbs," said Ted Daeschler, a paleontologist at the Academy of Natural Sciences who co-led the 2004 team.

Air Breather?

"It may have been more capable of air breathing and land walking than more primitive finned animals, but it's still an aquatic animal," said Downs.

Continued on Next Page >>


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