In two related articles highlighted on the April 6 cover of the journal Nature, Dr. Ted Daeschler of The Academy of Natural Sciences in Philadelphia, co-leader of the expedition to Ellesmere Island, and his colleagues announced the discovery of 375-million-year-old fossils with numerous features that place them squarely at the evolutionary transition from fish to limbed animals. The new species has a skull, neck, ribs and part of a fin like the earliest limbed animals, but also has fins and scales like a fish.
The new species, named Tiktaalik roseae, shows that the evolution from life in water to life on land happened gradually in fish living in shallow water.
For about a century, scientists have been able to trace the broad outline of the millions-of-years-long transition of lobe-finned fish to limbed animals (tetrapods). The new find, however, is the most compelling evidence yet of an animal that was on the verge of the transition from water to land. "The find is a dream come true," said Daeschler, the Academy's curator of vertebrate biology. "We knew that the rocks on Ellesmere Island offered a glimpse into the right time period and were formed in the right kinds of environments to provide the potential for finding fossils documenting this important evolutionary transition."
Tiktaalik was a predator with sharp teeth, a crocodile-like head, and a flattened body that lived in what was then a subtropical climate. The quality of the fossils allowed the team to examine the joint surfaces on many of the fin bones and figure out that shoulder, elbow and wrist joints were capable of supporting the body like limbed animals. "Tiktaalik blurs the boundary between fish and land animals," said Dr. Neil Shubin of the University of Chi
Contact: Carolyn Bealrdo
The Academy of Natural Sciences