A new study funded by the National Geographic Society has established that the land-walking fish Tiktaalik roseae possessed remarkably robust hips, facilitating its movement across terrain.
With the discovery of well-preserved fossils in the Canadian Arctic, in 2004, Tiktaalik roseae has become a source of great scientific study. The lobe-finned, bony fish roamed the Earth during the Devonian Period, some 375 million years ago. Tiktaalik – meaning “large, freshwater fish” in the tongue of the Nunavut people – inhabited marshy river environments that resemble today’s Amazon. The lobed fish is believed to have hunted for prey in rivers and inlets, boasting a flexible neck and primitive lungs.
The fossils demonstrated that the fish had leg-like fins, and was heralded as the “missing link” between fish and land animals. Upon its initial discovery, researchers claimed that the fins of Tiktaalik roseae presented evidence to show the beginnings of an evolutionary transformation in freshwater species. It is thought that this enormous evolutionary leap may have paved the way for the emergence of vertebrates from the waters.
The fossilized remains measured up to three meters in length and bore a crocodile-like head and remarkably strong, bony fins. A new study, spearheaded by University of Chicago Paleontologist Neil Shubin, explored the creature’s morphology in further detail and suggested how the migrated from water to land.
Shubin has dubbed Tiktaalik the “fishapod,” creatively playing off the scientific term tetrapod – the very first four-limbed vertebrates and their descendents. The researchers found that a change to the pelvic girdle of Tiktaalik roseae may have sparked their migration from water to land. Shubin recently talked about his team’s efforts in attempting to manufacture a life-sized reconstruction of the formidable beast:
“Our original discovery of Tiktaalik was so big that we had to split it into two parts, because we didn’t have enough plaster… This was the back end, and we were surprised to find a pelvis inside.”
Tiktaalik‘s hips point outwards, in similar fashion to that of a land animal’s hips. In addition, the Tiktaalik‘s hips were much larger than the rear, fin-supporting pelvis bones of a typical fish. The finding that “fishapod” possessed strong hind fins challenges the notion that such appendages failed to arise, until much later. An evolutionary paradigm, called the “front-wheel drive” hypothesis, suggested that front limbs evolved first and foremost, while the hind limbs remained relatively small and weak; the remains of fossilized Tiktaalik specimens seem to contradict this model.
The strong hind-limbs and large pelvis indicated that the unusual fish, perhaps, used these limbs as a means of propulsion, evolving simultaneously with their front fins. The upper section of the pelvis – the ilium – is large enough to make contact with the vertebral column; this would have been a pre-requisite for using hind-limbs for walking.
Paleontologist Per Ahlberg, from Sweden’s Uppsala University, recently informed the National Geographic that – until recently – researchers had very little knowledge of the anatomical connection between ancient fish and larger land creatures.
Catherine Boisvert, of Australia’s Monash University, recently suggested that the latest research findings were merely the tip of the iceberg. Although the exact reason for the migration of fish onto land remains shrouded in mystery, Boisvert theorizes that their migration could have been born out of necessity.
Some 395 million years ago, movement of Gondwana – the southernmost, ancient supercontinent – towards the early American continent was believed to have created a series of tropical, water habitats. It has been suggested that the Tiktaalik may have been driven onto land to escape predation, or to locate a secure region to lay their eggs.
Meanwhile, Edward Daeschler, who works as associate curator at the Academy of Natural Sciences at Drexel University, and lead researcher on the project, explained that plants had started to flourish on the dry lands, just a few million years before Tiktaalik departed the waters. Daeschler believes that the diversification in the ecosystems on land may have incentivized vertebrates to grace the terrain.
The latest findings were published in the Proceedings for the Natural Academy of Sciences (PNAS).
By James Fenner