An article published in the journal “Nature” reports the identification of a precursor of the tetrapods that lived on today’s Ellesmere Island, in Canada, in the Devonian period, about 375 million years ago. A team of researchers named it Qikiqtania wakei and illustrated similarities and differences with Tiktaalik roseae, the possible ancestor of today’s tetrapods. The anatomical characteristics of Qikiqtania wakei indicate that it descended from the precursors of the tetrapods that ventured to the mainland but unlike Tiktaalik roseae it went back to the water, where it developed fins suitable for aquatic life.
The fossils now identified as Qikiqtania wakei were discovered in 2004 on present-day Ellesmere Island in the Nunavut Territory of northern Canada. The top image (Courtesy T. A. Stewart, J. B. Lemberg, A. Daly, E. B. Daeschler, & N. H. Shubin) shows some parts of the discovered specimen, cataloged as NUFV 137.
In 2004 those fossils were quickly forgotten due to the discovery, in the same area and almost at the same moment, of other fossils that were identified as Tiktaalik roseae. Discovering a transitional form between fish and tetrapods that could be the species from which tetrapods descended monopolized the attention of paleontologists, other scientists, and anyone interested in the evolution of life on the mainland.
Years later, the fossils that got set aside have been remembered and finally examined. The work was complex because the first attempt to subject the fossils to a CT-scan yielded limited results because they were too deep within the rocks where they were found and extracted. The pandemic lengthened the time for clearing out pieces of rock but a quality CT-scan was eventually possible.
The researchers noted the many similarities of the fossils just examined with Tiktaalik roseae but also the anatomical differences. The animal now called Qikiqtania wakei was much smaller than its famous cousin with a length of about 75 centimeters versus over 2.5 meters. The most interesting differences are those of the legs, which show how these two species had a divergent evolution.
Qikiqtania wakei had a pectoral fin with a humerus bone without the parts where the muscles that allow the tetrapods to walk on the mainland are inserted. The upper fins have a conformation that makes them more suitable for swimming in the water even though they are different from fish fins. In essence, it’s a species whose ancestors developed early adaptations to life on the mainland but returned to aquatic life. The ancestors of Tiktaalik roseae kept on living on the mainland, so this species had legs with shoulders, elbows, and wrists, which are all the parts that developed in the tetrapods.
This study offers new insights into an important period in vertebrate history showing once again how evolution is not linear. Qikiqtania wakei had limited success, as it probably went extinct leaving no descendants while Tiktaalik roseae may be the ancestor of tetrapods. Many millions of years later, some mammals returned to the water more successfully and became cetaceans.
It’s not easy to understand from a few fossils and limited information about the ecosystem in which they lived why certain adaptations were more successful than others. Studying species at the center of important transitions such as Tiktaalik roseae and Qikiqtania wakei can improve our understanding of the history of tetrapods, so the search for fossils and information on their environment will continue.