The most dominant reptile on Earth
Introduction
Where do dinosaurs come from? Dinosaurs are one of the most successful groups of animals that have wandered the planet. For more than 170 million years they dominated the earth, from small creatures a few feet long to some of the largest animals that have ever walked on Earth. But despite its long evolutionary history, the origin of dinosaurs remains wrapped in a mystery. When did dinosaurs evolve and how were the first?
Developing
The oldest definitive dinosaur is not an animal but a complete ecosystem that contains some different species. There is no kind of universally accepted dinosaur that has lived before in time. The Ischigualasto formation in Argentina, which dates from about 230 million years ago, in the late Triassic period, contains a variety of animal remains. It shows that the environment was dominated by the first reptiles known as Rhynchesours, as well as by animals closely related to the origins of mammals called Cinodontes.
However, crucially, it reveals that there were also several species of different early dinosaurs in the mixture. These include small bipeda creatures, such as Eodromaeus and Eoraptor, and larger animals such as blacksaurus. Professor Paul Barrett is a museum’s dinososaur researcher who has been investigating the early evolution of dinosaurs during the late Triassic and Early Jurassic. Herrerasaurus is one of the oldest dinosaurs. Herrerasaurus, who dates from about 230 million years ago, is one of the oldest definitive dinosaurs.
"There are a lot of places in Argentina and Brazil that are competing for the crown of the birthplace of the first defined dinosaurs," says Paul. But when they first appeared, they were already recognizable dinosaurs. ‘This suggests that dinosaurs had to have a longer evolutionary story that we still do not know, and there is some debate about what part of that evolutionary story is currently missing’. What is a dinosaur? Dinosaurs belong to a group of animals known as arcosaurs.
Today this group is represented by birds and crocodiles (some scientists also include turtles in this group). In the past it was much more diverse, since it also included all extinct dinosaurs, pterosaurs and many ancestors of strange -looking crocodiles. ‘There are a number of different characteristics that define a dinosaur, but perhaps the clearest things have to do with modifications to the hips and legs,’ Paul explains. ‘In particular, they make a much stronger connection between the hips and their spine.
They do it by converting some of their vertebrae into a special modified structure called sacred that creates these additional connections in their hips ’. Reptiles have up to two vertebrae merged into a sacred, but to be a dinosaur, an animal needs at least three. Some modern birds have up to 12 sacrals. Birds, crocodiles (and possibly turtles) are the only arcosaurs that have survived until today. This feature is so distinctive that Sir Richard Owen, the museum’s founder.
He used it when he first defined Dinosauria in 1842 after noticing that extinct animals Iguanodon and Megalosaurus had a sacrum composed of five fused vertebrae. These changes probably occurred as a result of the first dinosaurs walking on their hind legs or were biped. ‘Bipedestation is really important to define the first dinosaurs,’ says Paul. ‘To do that, they also had to modify their hind legs’. While crocodiles and lizards have the legs that stand out from the body at right angles.
To become bipeds, dinosaurs had to put them directly under the body. This means that they had to modify the connections of the hip and the spine, the upper part of the bones of the thigh where the bones bind to the hip, in addition to the joints of the knees and ankles. Together, all these characteristics help define a dinosaur. The search for the first dinosaur. If the dinosaurs found in the Ischigualasto formation are already recognizable dinosaurs, it suggests that their origins are even older.
The relatives closest to dinosaurs have only been identified in the last two decades. They are known as the Silesáurids: medium -sized quadruped animals that looked high and long legs that sit on the outskirts of dinosauria. Fossil remains of the first dinosaur. There is not much of Nyasasaurus, but what it indicates that it could have been one of the first dinosaurs. ‘But there is this 10 to 15 million years gap that separates the common ancestor from the Silesáurids and Dinosaurs of the first true dinosaurs,’ says Paul.
It is not yet known what fills this emptiness, but it can include the partial fossil of 240 million years of an animal called Nyasasourus parringtoni, discovered in Tanzania near Lake Nyasa in the 1930s. Largely ignored due to its rudimentary nature, the fossil is composed by the bone of an arm plus some vertebrae. However, crucially, some of these vertebrae are close to the hip and show that three of them were sacred vertebrae, and this three vertebrae is one of the defining characteristics of dinosaurs.
Due to the fragmentary nature of fossil, it is difficult to say with certainty if it was a true dinosaur. Anyway, it is believed that it is very close to its origins. ‘Nyasasaurus is the only animal that has been tentatively placed in that space, since it is of the same age as the first silesaurs,’ explains Paul. ‘So that could mean that it is the oldest dinosaur, or it could be the closest relative of the dinosaurs found so far’. As a small bipedid predator, Nyasasaurus would have been typical of the first dinosaurs.
Regardless of the state of Nyasasaurus, you can discern a fairly good image of how the first dinosaur looked based on the evidence provided by the first true dinosaurs. They were probably small and active predators. Probably starting with a body length of only a couple of meters, they would have been bipeds with small hands and grabs. ‘It is likely that they were carnivores or omnivorous, but they were definitely not herbivores,’ says Paul. They were relatively unusual, since even when the first definitive dinosaurs are obtained about 230 million years ago
conclusion
They are still rare members of fauna. It would not be until the extinction event of the end of the Triassic that occurred 201 million years ago that dinosaurs would finally have their opportunity. Mass extinction ended almost all other competitors, which means that the environment was completely open to fill the dinosaurs. During the Jurassic and Cretaceous, dinosaurs took full advantage of this, evolving in an incredible variety of creatures.
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