Fossil reveals diverse elbows in early tetrapods

Researchers at Pennsylvania State University studied a 350-million-year-old fishapod fossil discovered on Ellesmere Island in Canada, revealing a unique forearm structure.

This ancient fish, one of several creatures with features between fins and limbs, possessed a pointed forearm bone and a simple hinge-like elbow joint. The team CT-scanned the single fin fossil and compared it to 16 other known fishapods, determining it represented a previously unknown species.

The fishapod’s radius, the bone extending from the elbow to the wrist, was triangular and sharply pointed, unlike the rounded shapes seen in other species. Its elbow also lacked the ability to twist and rotate, limiting its range of motion compared to other early tetrapodomorphs. Scientists also noted a longer intermedium, a small bone believed to be a precursor to the wrist.

Scientists believe the unusual fin structure may reflect experimentation with different modes of movement, allowing the fishapod to navigate its environment, likely shallow water or vegetation, and avoid predators. They emphasize that these variations were adaptations to current environments, not necessarily steps toward life on land. The discovery adds to evidence that the evolution of limbs wasn’t a linear process, but rather involved a wide range of forms as animals explored new ways of moving.