The most famous Jurassic dinosaur is Coelophysis. Hundreds of Coelophysis skeletons have been found in New Mexico, at the Ghost Ranch Quarry. Coelophysis was a small early theropod dinosaur. Let's take a look at a portion of the quarry. What you can see here, is the vertebral column, part of the hip, as well as the leg and a skull. About six individuals are represented here. Early sauropodomorph dinosaurs had also evolved by this time, including plateosaurus. Early dinosaur morphs, early theropods and early sauropodomorphs have been found in the late Triassic sediments all over the world. Although the current hypothesis is that dinosaurs originated near what is now Argentina. Can you think of a reason why similar species of early dinosaurs were found all of the world, and not just in the Southern or Northern regions? There's only one correct answer, so consider your selection carefully. Was it because there were similar climates in different areas? Or that land masses were connected to one another? Or was it that dinosaurs wouldn't migrate between regions? During the Triassic period, the continents were joined together into Pangea. This meant that land animals like dinosaurs, could move easily all over the earth. So B is the correct answer. Pangea did not begin to break apart until the end of the Triassic period. As such, there were no sea barriers preventing dinosaurs from moving to different areas. They were able to disperse across all the land. Only later as we learned in the paleo geography lesson, did the continent become separated, helping dinosaurs to significantly differentiate from each other. The transition from Triassic to the Jurassic periods is marked by yet another mass extinction. The End-Triassic extinction saw the end of many of the pseudo sukian archosaurs that were dominant during the Triassic. The iedosaurs, fightosaurs, row sukians and poposauroids did not make it into the Jurassic. This left only the crocodylomorphs as the sole representatives of the crocodile line lineage. Nearly all of the dicynodont synapsids went extinct. And only a few small proto-mammals survived. The cause of the End-Triassic extinction is even murkier than the End-Permian extinction. About 50% of all species on Earth went extinct at this time. We believe that the extinction may have been related to intense volcanism during the initial breakup of Pangea. Let's take a few minutes to put together the story of the origin of dinosaurs. Two extinction events set the stage for the rise of the dinosaurs. When were these extinction events? Check the two time period boundaries that you believe are correct. A, Permian-Triassic. B, Triassic-Jurassic. C, Jurassic-Cretaceous. Or D, Cretaceous-Paleogene. The main extinction events that had a role in the origin of the dinosaurs were the Permo-Triassic extinction, which gave dinosaurs their first break, and the Triassic-Jurassic extinction. After which, dinosaurs went from small players to the dominant terrestrial vertebrates. So A and B are correct. Based on what we've talked about so far, how would you characterize the rise of the dinosaurs? Did dinosaurs suddenly appear and assume immediate dominance over their environment? Not at all. The story of the dinosaurs' rise to power was a slow but steady one. After the Permo-Triassic extinction, pseudosuchians were the first group of archosaurs to diversify and become common. So, did dinosaurs eventually succeed at out-competing the pseudosuchians? Or did dinosaurs just get lucky when the End-Triassic extinction event wiped out all the pseudosuchians? Right now, there is insufficient evidence to prove that dinosaurs out-competed the Pseudo-Sukians on all evolutionary fronts. However, it is also probably inaccurate to claim that dinosaurs merely got lucky, and capitalized on the misfortune of others. Remember, that early in the Triassic, dinosaur morphs were uncommon. But by the end of the Triassic, some like coelophysis were the most abundant large vertebrates in their ecosystems. In particular, prosauropods show early hints of the dinosaur domination that was to begin in the Jurassic. Prosauropods were not only the largest herbivores in any late Triassic environment, but they were also the largest terrestrial herbivore that had ever evolved up to that point. Whatever the reason for their successes, dinosaurs and their close relatives began the Triassic as small and unassuming animals low down on the ancient food chain. But, by the end, dinosaurs were large and in charge. But as we'll see in the next lesson, the odds caught up with the dinosaurs in the end. That's when a third mass extinction event occurred and brought the age of the dinosaurs to a sudden and violent close.
