A new study of a the fossilized remains of the Tiktaalik, the “walking fish” that illuminates how swimming fish evolved into land-dwelling amphibians, shows that there was more to the transition than the switch from fins to limbs. The study shows that the head and braincase were changing, a mobile neck was emerging and a bone associated with underwater feeding and gill respiration was diminishing in size, a beginning of the bone’s adaptation for an eventual role in hearing for land animals [The New York Times].
The creature, dubbed Tiktaalik roseae — or, to be less formal, Fishapod — lived 375 million years ago 600 miles north of the Arctic Circle in a subtropical floodplain that eventually became Ellesmere Island, where it was discovered in 2004 [Wired News]. The fishapod has already earned its reputation as a “missing link” in evolutionary history due to its sturdy, jointed fins and its dual breathing system, with both gills and lungs. But the new study suggests that changes to the animal’s head and the development of the first neck also played a critical role in its evolution.
In the study, published in Nature [subscription required], researchers showed that the Tiktaalik‘s head bones weren’t fused to its shoulder bones, giving it a flexible neck. This could have allowed the fishapod to easily poke its head out of the shallow water to gulp down air or to go after prey. Meanwhile, the diminishing of the head bone that helps fish control their gills may indicate that the Tiktaalik was already less dependent on gill respiration.
Study coauthor Jason Downs says the new findings show that many of the traits that would come in handy on land evolved much earlier. “So what it’s really demonstrating is that many of these changes that are occurring and things that we once associated with terrestrial life are turning out, in fact, to be adaptations for life in shallow water settings that Tiktaalik might had found himself in,” Downs added. It likely inhabited the mudflats of freshwater flood plains of a subtropical environment. It was a large aquatic predator, measuring up to 9 feet long, with sharp teeth and a flattened head like a crocodile and unlike primitive fish [Reuters].
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Image: Ted Daeschler