New research involving Nunavut fossil raises question over the origin of necks

A new study involving a 380-million-year-old fossil from Nunavut is sparking new questions amongst researchers as to why tetrapods originally developed necks. 

Since its discovery on Ellesmere Island two decades ago, researchers have pointed to Tiktaalik roseae as the first known tetrapod, or four-limbed animal, to exhibit a natural separation between its skull and its shoulders. Scientists have long hypothesized that the animal developed a neck in order to have greater head mobility as it adapted to land.

Dana Korneisel, a postdoctoral researcher at Carleton University, is the lead author of the new study published this month in the scientific journal Nature. A team led by researchers from Carleton and the University of Ottawa conducted tests on lake sturgeon, the closest modern anatomical comparison to Tiktaalik roseae.

The study also included researchers from Penn State University and the University of Washington in the U.S.

Following the tests, researchers estimated Tiktaalik roseae could likely only bend its neck less than six degrees side-to-side.

“So the pre-existing idea was that the origin of the anatomical neck … that would come along with an ability to bend and twist your neck and move your head relative to your body,” Korneisel said. 

“What we found was very limited mobility in bending, both side to side and bending up and down, kind of in the same range as what you get in a modern fish.” 

Hillary Maddin, a paleontologist at Carleton University, and a co-author of the study, says the findings generate new questions and new hypotheses about how necks evolved.

“Perhaps it had more to do with providing a more independent, robust stabilization of the limbs and the shoulder girdle on the substrate as it was beginning to basically be able to move on land,” Maddin said.

A need to move their arms

Using the results from the tests conducted on modern lake sturgeon, researchers now believe the Tiktaalik roseae developed its neck in order to have more control over its front limbs. Korneisel says little research had previously been conducted on how much early tetrapods were able to bend or twist their necks.

She adds the study benefited early on from a previous three-dimensional recreation of Tiktaalik roseae’s neck region from co-author Tom Stewart at Penn State University.

Alongside Tiktaalik roseae, the team used fossils of other prehistoric tetrapods to determine neck measurements, which were then applied to the backbone of a modern sturgeon on a universal testing machine at the University of Ottawa.

A modern recreation of Tiktaalik roseae at the Canadian Museum of Nature in Ottawa. The prehistoric tetrapod is believed to be the first species to have developed a neck. (Liam Baker/CBC)

“There’s some evolutionary driver that is causing this separation of the shoulder girdle and the skull … if the benefit isn’t letting you move your head around more, what might the kind of reason evolutionarily be for this?” Korneisel said.

“What I think is most consistent with other data that are out there from other researchers, is that the pectoral girdle and the forelimb was being used for novel types of motion and novel types of locomotion.”

In the new study, the researchers conclude that early, low neck mobility was most likely best suited for more efficient swimming patterns, and to support the shoulders with the movement of an animals’ forelimbs.

A link to human evolution

While the study points to a possible alternative explanation for exactly why tetrapods first developed necks, Korneisel says she hopes she may soon be able to conduct tests on other, well-preserved early fish. She says this kind of testing could provide greater insight into how Tiktaalik roseae and other early tetrapods moved as a whole, throughout their whole bodies.

Maddin says the study also provides insight into human evolution.

“If you think about life on Earth at this time, it was very minimal in terms of vertebrates, like the group of animal which we belong to. So this is a very key important step in the evolution of our lineage and basically all vertebrates on land,” Maddin said.