The New York Times reports today that a recently released study, to be published tomorrow in the journal Nature, reveals some of the intermediate steps in the evolution of marine vertebrates to land-based animals.
Researchers from the Academy of Natural Sciences in Philadelphia, studying fossilized skeletons of fish that had been excavated several years ago on Ellesmere Island in Canada, have been able to note changes in the cranial cavity, the development of a mobile neck, and the transformation of a bone that was used in underwater feeding and breathing. This latter bone eventually made up part of the hearing mechanism for subsequent land-based animals.
The object of this study, a fish that has been named Tiktaalik roseae, lived 375 million years ago. The significance of the development of the flexible neck and the reduction of the gills demonstrates, the study's scientists assert, that a fish previously suited for deep-water environments was adapting to shallow water. As Dr. Ted Daeschler, one of the study's participants said, "The new study reminds us that the gradual transition from aquatic to terrestrial lifestyles required much more than the evolution of limbs."
For the full-text of John Noble Wilford's article, see http://www.nytimes.com/2008/10/16/science/16fossil.html?hp