"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.
"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."
|Contact: Cheryl Dybas|
National Science Foundation