Hold on to your seats, but the entire human race just might just be descendants of our watery friends. Scientists have discovered a 375-million-year-old fossil of a fish found in northern Canada's Ellesmere Island, and this particular fish may have had rear legs.
The fossils are of a fish known as Tiktaalik roseae. It had the gills, scales, and fins of a fish. It also had a mobile neck and robust ribcage, anatomical characteristics it has in common with some amphibians, reptiles, birds, and mammals. It had large forefins, shoulders, elbows, and partial wrists with which it supported itself on the ground. These qualities made scientists believe that they may have found the evolutionary link between vertebrates that lived on water and vertebrates that lived on land.
Researchers already had existing specimens of the Tiktaalik, but they comprised only the front portions of the fish. They found the latest fossils in blocks of rock recovered from the dig site where the earlier fossils of the Tiktaalik were discovered, and spent years removing the rock surrounding the fossils, so the remains could be studied. It was then that they discovered that the fish had big, strong pelvic bones. The results of their findings have been published in the journal Proceedings of the National Academy of Sciences.
The pelvic girdle of the Tiktaalik was large enough to help support strong rear appendages, and had a ball-and-socket hip join connected to a highly mobile femur. There were crests found on the hipbone, and scientists believe these served as points for muscles to attach to, suggesting advanced fin function.
"I was expecting to find a diminutive hind fin and pelvis,"study lead author and paleontologist at the University of Chicago, Neil Shubin, said. "Seeing the whopping pelvis set me back a bit - I looked at it again and again, because I was quite surprised. We had long thought that expanded hind limbs and hips were features of limbed animals. Tiktaalik shows that our closest fish relatives had expanded hips and hind fins; hence, this feature may well have arisen in fish."
"That wrist you use to write with, the neck you use to move your head around with, the lungs you're using to breathe . . . all derive from parts in the bodies of fish. Your hands and arms derive from parts of the fins," Shubin continued."What the fossil record tells us is how deeply we are connected to life on the rest of the planet. In this case, this tells us how closely we are related to fish."
However, Shubin clarified that the Tiktaalik is not the ancestor of all limbed, vertebrates but its closest known relative. Yet, however groundbreaking this discovery might be, scientists still remain uncertain on hope these hind appendages were used by the Tiktaalik.
It also remains unclear how the Tiktaalik actually moved from water to land, but the environment of the Late Devonion Period, about 395 million to 362 million years ago, in which the Tiktaalik lived, provides some clues. It was prior to the growth of plants, and land was barren sand and mud. Being able to move to shallow waters by pushing off the ground became an evolutionary advantage because it allowed the vertebrates to escape predators and catch food.
"You can't separate the evolutionary history of life from the conditions of the world at the time," said co-author of the study and paleontologist Ted Daeschler of the Academy of Natural Sciences in Philadelphia.
"It's what we've all been waiting for," said Jennifer Clack, curator of vertebrate paleontology at the University of Cambridge's Museum of Zoology in the United Kingdom. "Until this discovery, we weren't able to see the changes by which the pelvic fins of the fish became much larger and more robust, and gradually turned into the tetrapod hind limb."
