Fossil of a Fishapod

A recently-discovered fossil could explain how animals transitioned from water to land over 375 million years ago.

Photo courtesy of The Academy of Natural Sciences Credit: Ted Daeschler Tiktaalik roseae: The most complete fossils ever found of a transitional fish with limbs.

To some, the story sounds fishy. Evolutionists believe that about 400 million years ago, animals started to make the transition from living in water to living on land. In those early days, it is thought that animals dwelling in water slowly started to evolve certain features, like limbs and lungs, which allowed them to live on land. Fossils found in Greenland in the past 15 years have shown some evidence of these creatures, but in April 2006, the discovery of a fossil called Tiktaalik roseae is the most compelling evidence to date of the transition.

The fossil was found on Ellesmere Island in Canada's Nunavut Territory by a team of scientists led by Neil Shubin of the University of Chicago. At the suggestion of Inuit elders, they named the fossil Tiktaalik which means "large shallow water fish" in Inuktitut. This creature lived about 370 million years ago during the late Devonian Period, also called the "Age of Fishes." At this time, Ellesmere Island was part of a large landmass straddling the Equator. Competition among fish in the oceans was intense, but the land was largely unexploited. Additionally, the expansion of terrestrial plants transformed the land, setting the stage for its colonization by tetrapods, or four-legged animals.

Scales and fins still qualify Tiktaalik as a fish, but several other characteristics set it apart. The bones in Tiktaalik's fins formed jointed wrists, the primary characteristic that scientists believe makes Tiktaalik a transitional species. Also, its flat skull was disconnected from its shoulders, giving it the ability to turn its neck. Based on the shape of Tiktaalik's head and its eyes positioned on the top of its head, scientists believe it probably spent most of its time in shallow water. "Tiktaalik was probably an unwieldy swimmer," John Maisey, a paleontologist at the American Museum of Natural History in New York, told Nature Online News. "Tetrapods did not so much conquer the land, as escape from the water."

The discovery of this fossil is groundbreaking because it is so well-preserved and complete. Researchers are confident that Tiktaalik is an intermediary between fish and tetrapods and they believe it will become the same kind of evolutionary icon as Archaeopteryx, the species linking reptiles and birds. Archaeopteryx lived about 150 million years ago and had fully-formed feathers, although it may or may not have been able to fly. The first Archaeopteryx skeleton was discovered in Germany in 1861.