Details of evolutionary transition from fish to land animals revealed

"The braincase, palate and gill arches of Tiktaalik help reveal the pattern of evolutionary change in this part of the skeleton," said Downs. "We see that cranial features once associated with land-living animals were in fact the first adaptations for life in shallow water."

"The gradual evolutionary transition from fish to tetrapod, and the transition from aquatic to terrestrial lifestyles required much more than the evolution of limbs," said Daeschler. "The head of these animals was becoming more solidly constructed and, at the same time, more mobile with respect to the body across this transition."

Trends in head shape include a flattening of the skull and a lengthening of the snout.

Using several well-preserved specimens of Tiktaalik roseae, the research helps document the relative timing of the particular skeletal changes associated with changes in head shape.

Scientists look for fossil evidence of Tiktaalik on Ellesmere Island, Nunavut Territory, Canada. Click here for more information.

"We used to think of this transition of the neck and skull as a rapid event, largely because we lacked information about the intermediate animals," said Neil Shubin of the University of Chicago, who co-led the team that discovered Tiktaalik roseae. "Tiktaalik neatly fills this morphological gap, and helps to resolve the timing of this complex transition."

During this transition, interactions among the different parts of the head skeleton also were changing.

"Fish in deep water move and feed in three-dimensional space, and can easily orient their bodies in the direction of their prey," said Farish Jenkins, Jr., an evolutionary biologist at Harvard University and co-author of the paper. "A mobile neck is advantageous in settings where the body is relatively fixed, as is the case in shallow water and on land."

It took more than a year for fossil preparators C. Frederick Mullison, of The Academy in Philadelphia, and Bob Masek, of the University of Chicago, to expose and preserve the delicate details in the fossil head skeleton.

The public can see a cast and a reconstruction of Tiktaalik roseae on permanent display in The Academy's museum.

The fossil research in Nunavut is carried out with authorization from the Department of Culture, Language, Elders and Youth, Government of Nunavut. All fossils are the property of the people of Nunavut and will be returned to Canada after they are studied.

In addition to NSF, the research was supported by private donors, the Academy of Natural Sciences, the Putnam Expeditionary Fund (Harvard University), the University of Chicago and the National Geographic Society.

http://www.nsf.gov/news/news_summ.jsp?org=NSF&cntn_id=112416&preview=false