The fossils of Tiktaalik roseae show the evolution from fins to feet

Fossil of Tiktaalik in the Field Museum, Chicago
Fossil of Tiktaalik in the Field Museum, Chicago

A team of paleontologists led by Professor Neil Shubin from the University of Chicago published in the journal “Proceedings of the National Academy of Sciences” the results of a research on Tiktaalik roseae (Photo ©Eduard Solà). It’s a species that lived during the Devonian period, about 375 million years ago, which is a transitional form between fish and legged animals. This research highlights the adaptation of the hind fins of this animal, showing that it had already started in fish.

Three fossil skeletons of Tiktaalik roseae were discovered in 2004 on Ellesmere Island, Nunavut, in northern Canada. The appearance of this animal was of a cross between a fish and a crocodile and was a predator with sharp teeth that could reach a length of nearly 3 meters (9 feet).

For a long time, only fossils containing the front part of this fish were described. When the paleontologists examined further blocks recovered from their expeditions to the dig site, they also found the rear part. This allowed them to carry out more detailed studies with really interesting results.

Tiktaalik roseae has become the best known transitional form between fish and land animals and its study has provided new insights that have changed the scientists’ minds about the way legs evolved. Paleontologists thought that fins had evolved only after the first animals had started living at least partially out of water, initially using a locomotion of the type used by seals. Instead, the study of Tiktaalik roseae’s fins shows that they were already evolving in this fish.

The fossils of Tiktaalik roseae include a complete pelvis and a partial pelvic fin that made ​​it possible to reconstruct the anatomical structure of this fish. The results of the research show an animal with gills but also primitive lungs. It was clearly a fish but it was already showing various features of later tetrapods.

Professor Neil Shubin argues that it’s reasonable to assume that Tiktaalik roseae used its hind fins as a paddle for swimming due to their strong rays but it’s possible that it used them to walk as well. In any case, what’s clear is that the strengthening of the hind appendages and the pelvic-propelled locomotion based is a trend that started in fishes and later developed in tetrapods.

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