We’ve had several posts recently about the fossil fish discovered by Neil Shubin’s team and dubbed Tiktaalik; it’s one of the best examples yet of a “transitional” species of marine vertebrate evolving into a land animal. After extensive cleaning of the fossil, new research has revealed interesting details of the skull and neck that have great significance for evolutionary science: Fish Fossil Yields Anatomical Clues on How Animals of the Sea Made It to Land.

Several skeletons of the fish were excavated four years ago on Ellesmere Island, in the Nunavut Territory of Canada, 700 miles above the Arctic Circle, by a team led by Neil H. Shubin, an evolutionary biologist at the University of Chicago and the Field Museum, and Ted Daeschler of the Academy of Natural Sciences. The Devonian Age rocks containing the fossils indicated that the fishapod lived in shallow waters of a warm climate. It may have made brief forays on land.

Since the discovery was reported in 2006, Dr. Downs and two specimen preparators, C. Frederick Mullison of the academy and Bob Masek at Chicago, spent more than a year prying deeply into the skulls of several fishapod skeletons. The results were also analyzed by Dr. Shubin and two other co-authors of the report, Dr. Daeschler and Farish Jenkins Jr., an evolutionary biologist at Harvard.

“Our work demonstrates that 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,” Dr. Daeschler said.

Dr. Shubin said Tiktaalik was “still on the fish end of things, but it neatly fills a morphological gap and helps to resolve the relative timing of this complex transition.”

For example, fish have no neck but “we see a mobile neck developing for the first time in Tiktaalik,” Dr. Shubin said.

“When feeding, fish orient themselves by swimming, which is fine in deep water, but not for an animal whose body is relatively fixed, as on the bottom of shallow water or on land,” he added. “Then a flexible neck is important.”

One of the most intriguing findings, scientists said, was the reduction in size of a bony element that, in fish, links the braincase, palate and gills and is associated with underwater feeding and respiration. In more primitive fish, the bony part of what is called the hyomandibula is large and shaped like a boomerang. In this fossil species, the bone was greatly reduced, no bigger than a human thumb.

“This could indicate that these animals, in shallow-water settings, were already beginning to rely less on gill respiration,” Dr. Downs said, noting the specimen’s loss of rigid gill-covering bones, which apparently allowed for increased neck mobility.

More details on the new findings: Living the Scientific Life (Scientist, Interrupted): ‘Fishapod’ Fossil Provides More Clues for the Evolution of Terrestriality.