Isabelle Terranova
Author: University of Chicago- Medical Center
Source: http://phys.org/news/2014-01-discovery-tiktaalik-roseae-fossils-reveals.html
Published: January 13, 2014
Summary:
A group of scientists have discovered that the evolution of hind legs actually started as enhanced fins. This contradicts the theory that large, hind limbs were developed after vertebrates made the transition onto land. The scientists discovered that the transitional species discovered a decade ago, Tiktaalik roseae, actually had large hind limbs when they put together the back end of a prehistoric fossil. The fossil had a large hind fin which was previously believed to be a small appendage. Researchers believe that this fin was capable of walking on underwater surfaces, as well as propelling the fish through the water. The fossil showed that the fish had a large pelvic bone the size of it's shoulder. The pelvic bone is used to support the hind limbs, the fact that it was so large shows that the hind limbs were also large. This is a characteristic of early tetrapods; this relationship allows scientist to believe that the development of hind limbs started much earlier than they previously believed. They conclude that the fish were possibly able to walk before they made the transition onto land, and then the hind limbs were simply exaggerated as it made the transition to a tetrapod.
Connection:
In chapters 14 and 15 we discussed evolution. The discovery made was a turning point and changed what scientists believe about evolutionary history. The discovery of a pelvic bone and hind limbs in the Tiktaalik roseae are homologous structures to those of early tetrapods. This is a term that we discussed in class. It means that they are similar structures found in differnet species that came from the same ancestor. The fins on the fish turned into the hind limbs of the tetrapods; this made the tetrapods better adapted to land. We also discussed the how scientists use the fossil records to determine when certain evolutionary changes and adaptations occurred. The scientists who discovered the fossil put it back together and analyzed it. When they found the fin and hind limb, they were able to adjust their theory; the fossils also helped them date the species back to 375 million years ago, right before when tetrapods would have been emerging. This also ties back to the scientific method in a way because they came up with an idea, found evidence and discovered something new. The article is very interesting and provides many ways in which our units tie back to real life discoveries.
How would the front limbs evolve compared to the hind limbs? (If too hard to find answer): Why was there a drive to go onto land at all?
ReplyDeleteBefore the discovery of these hind limbs in the article, scientists believed that the transition of vertebrates onto land actually would have depended on the front limbs. The theory was that the fish would have dragged themselves out of the water with their front limbs, the scientists related this to a "front wheel drive" sort of mechanism. But, this theory was disproved however, the theory that front limbs evolved first still holds. To answer your second question, vertebrates would have moved onto land because there was more competition in the water. There were more open niches to be filled on land and therefore, and vertebrate that could withstand the pressures of terrestrial life and had competition, would have moved onto land.
DeleteDo scientists know how or when vertebrates formed Limbs in general? At that point what caused vertebrate species to have an advantage over invertebrates?
ReplyDelete