The mass extinction of the Cretaceous, 66 million years ago, killed half of all animal species. D. Rex (Dinosaur rex), such as Triceratops and Ankylosaurus, disappeared from the face of the Earth, marking the end of the Mesozoic Era, a geological period of more than 186 million years known as the “Age of the Dinosaurs,” and paved the way for the arrival of dinosaurs. of mammals. However, contrary to what scientists thought for a long time, not all dinosaurs became extinct, far from it. As the work of identifying and classifying current and past species progressed, paleontologists had a completely different overall view of the animal kingdom and its evolution.
What does science say?
It is generally accepted by the scientific community today that the division of archosaurs, an enormous group of prehistoric reptiles, gave rise to two main lineages of animals: the pseudosuchians, or crocodilians and relatives, on the one hand, and the ornithodorians on the other. . Among the Ornithodirians, we find the Pterosaurs, the extinct flying reptiles, and the superorder. Dinosauria, real dinosaurs. The phylogenetic tree of dinosaurs has two main branches that are classified according to their pelvis shape. saurischiens, or “dinosaurs with a reptilian basin”, and ornithischiens, “a bird basin”.
Discoveries of feathered dinosaur fossils have revolutionized our understanding of animal evolution; Birds were indeed found to be descendants of dinosaurs, but surprisingly they were not descended from ornithischians, which included stegosaurs, ankylosaurs and triceratops. They are Velociraptor or D. Descendants of reptilian-hip dinosaurs such as rex, their bird-like hips evolved independently much later. We now speak of “avian dinosaurs” to refer to birds, and “non-avian dinosaurs” to refer to all the others that actually disappeared.
From crocodiles to birds
So not all dinosaurs are thought to have died: the small saurischians of the group Maniraptora Birds that appeared in the Jurassic continued to evolve into the birds we know today. As for alligators and crocodiles, they are descended from pseudosuchians, distant relatives of dinosaurs. So they are not strictly speaking dinosaurs, but actually living fossils. Originating 95 million years ago, before the extinction of the non-avian dinosaurs, crocodiles are the closest surviving relatives of birds today.
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