I have a fantastic story to tell – one of good science and a determined hunt for a fossil which no one knew about but which was predicted to exist. Plenty of Lobe Finned Fish had been discovered in the fossil record, but none older than 380 million years. After that the fossil record is silent. But around 363 million years ago the first primitive tetrapod (four legged) creatures show up on the fossil record. So what happened in between? And the more relevant question is, where are the transitional fossils that link Lobe Finned Fish to Tetrapods? Well, clearly if you want to find those kind of fossils you have to look in rocks that are between 380 and 363 million years old, and which are of sedimentary origin representing the type of ancient environment in which a transitional animal would have lived. In plain English, this means sediments deposited by freshwater streams and swampy areas.
With these criteria set out, a team from the Harvard University, The Academy for Natural Sciences and The University of Chicago consulted geological maps to determine where sediments of that age and type were located. And the result were rocks in the Canadian Arctic – an unexplored remote accumulation of Devonian deposits. Digging began in 1999 but they didn’t find much. It turned out that they were too far west and were digging in marine sediments. Bear in mind that digging in the Arctic is a tough job – it is bitterly cold even in summer, the distances are large and access is by plane and helicopter. When winter comes there is no choice but to head south. But they came back the following year, moving east until they found the right sediments at a place called Bird Fiord Quarry, which began to yield up a heap of fish fossils. And each year they came back until they struck palaeontological gold in 2004 when they found Tiktaalik. Not one but several! Confirmation indeed that their science and predictions were correct.
Tiktaalik had half-fish, half-tetrapod limb bones and joints, including a functional wrist joint and radiating, fish-like fins instead of toes, and a half-fish, half-tetrapod ear region. Wikipedia
“Tiktaalik looks like a cross between the primitive fish it lived amongst and the first four-legged animals (a group called “tetrapods” from tetra-, meaning four, and -pod, meaning foot. Actually, all animals that descended from these pioneer amphibians, including us, can be called tetrapods). Tiktaalik lived about 12 million years before the first tetrapods (which are approximately 363 million years old). So, the existence of tetrapod features in a fish like Tiktaalik is significant because it marks the earliest appearance of these novel features in the fossil record.”
Tiktaalik‘s head and body are flat with eyes on the top of its skull, more like a crocodile than most fish. Its shoulders are not connected to its skull, giving it a functional neck, a feature which fish lack. And it has ribs like some of the earliest tetrapods which were used to support the body and aid in living and breathing on land. These features in Tiktaalik show that many of the body features we associate with the earliest tetrapods actually evolved in fish first.
All images by Kalliopi Monoyios