AIG on Sea Turtle Evolution: Yes, we find turtles in the fossil record, and we find them today—thus they are called “living fossils.” But the reality is that turtles appear suddenly in the fossil record with no hint of a nonturtle ancestor. The statement about “200 million years ago” is made as if that period of time is an observed historical fact. It is not. WRONG: It is believed that the first sea turtles roamed Earth more than 245 million years ago. It is believed they were part of the late Triassic Period based on fossil records. It is believed that these sea creatures where once land animals that evolved to spend most of their time in the water in order to survive. They were very similar to land turtles but much larger. (Figure 2) They would have lived of prey that was on land. When that wasn’t available they had to evolve in order to live on what was found in the waters around them. The one part that didn’t change was the deposit of their eggs on land. There is sufficient evidence to indicate the sea turtles did go back and forth between land and sea during the Mesozoic Period. However, by the Cretaceous Period they had evolved and were in the water mainly as they now had flippers to help them. Soon after they developed their hard shells as a form of protection. It isn’t known exactly when this took place. It is believed that this significant change in their lifestyle occurred approximately 120 million years ago. It is believed that the evolution process for sea turtles took place very rapidly instead of slowly over a long period of time. This suggests to researchers that there were some significant changes that took place on Earth. Perhaps the same one that caused so many other animals in the world to either evolve or to become extinct. We do have at least one transitional fossil species for the origin of turtles, which evolved in water, not on land. It is a ~220-million year old species with half a turtle shell. It had the plastron (underside portion) but not the carapace (the upper portion). Lately, the bulk of the evidence points to an ancestral role for Eunotosaurus, a late Permian reptile whose wide, elongated ribs curved over its back (a striking adumbration of the hard shells of later turtles). Eunotosaurus itself seems to have been a pareiasaur, an obscure family of ancient reptiles the most notable member of which was the (completely unshelled) Scutosaurus. Until recently, fossil evidence linking the land-dwelling Eunotosaurus and the giant, marine turtles of the late Cretaceous period was sorely lacking. That all changed in 2008 with two major discoveries: first up was the late Jurassic, western European Eileanchelys, touted by researchers as the earliest marine turtle yet identified. Unfortunately, only a few weeks later, Chinese paleontologists announced the discovery of Odontochelys, which lived a whopping 50 million years earlier. Crucially, this soft-shelled marine turtle possessed a full set of teeth, which subsequent turtles gradually shed over tens of millions of years of evolution. Odontochelys prowled the shallow waters of eastern Asia about 220 million years ago; another important prehistoric turtle, Proganochelys, pops up in the western European fossil record about 10 million years later. This much bigger turtle had fewer teeth than Odontochelys, and the prominent spikes on its neck meant that it couldnt fully retract its head under its shell (it also had an ankylosaur-like clubbed tail). Most important, the carapace of Proganochelys was fully baked: hard, snug and pretty much impervious to hungry predators. The Permian ‘parareptile’ Eunotosaurus shares uniquely derived features with turtles that help fill important gaps in the evolutionary origin of the turtle shell. Uncovered in south west China last year, Odontochelys semistestacea seems to be the oldest known turtle fossil – believed to date 220 million years back. More important it was used to put back the pieces regarding the evolution of the turtle shell. (Figure 1) Since long, paleontologists have been debating over the course of how the turtle developed its shell as some claimed that it evolved from underneath the body, while the other talked about it having been an extension of the scaly skin on top. And now we have the answer. The uncovered fossil definitively supported the theory that the shell would have formed from below as extensions of the backbone and ribs, rather than as bony plates from the skin as others have theorized. The fossil with its half formed lower shell and an absent upper shell proved the fact that it was the lower shell that first came into existence as a defensive mechanism of marine animals to protect themselves from attacks coming from the depths of the sea. As they started evolving as land creatures, the upper shell became an equally important form of defense and continued the evolution into its next step. This also suggested to the team of scientists from Canada, China and the US who undertook this extensive research that the earliest turtles were indeed marine creatures and later moved onto land. earthhistory.org.uk/transitional-fossils/origin-of-turtlesrsbl.royalsocietypublishing.org/content/early/2010/06/03/rsbl.2010.0371.full https://answersingenesis.org/reptiles/sea-turtles/ dinosaurs.about/od/otherprehistoriclife/a/Prehistoric-Turtles-The-Story-Of-Turtle seaturtle-world/sea-turtle-evolution/-Evolution.htm greenpacks.org/2008/12/03/evolution-of-turtle-shell/
Posted on: Wed, 01 Oct 2014 18:59:33 +0000
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