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Dinosaurs first appeared between 247 and 240 million years ago. They ruled the Earth for about 175 million years until an extinction event 65.5 million years ago wiped out all of them, except for the avian dinosaurs. Scientists don’t agree entirely on what happened, but the extinction likely was a double or triple whammy involving an asteroid impact, choking chemicals from erupting volcanoes, climate change and possibly other factors.Flying onOnly the big, classic dinosaurs are extinct. Birds are living dinosaurs, most experts believe. Think of that next time a pigeon strafes you.Fossils show that some of the more advanced dinosaurs had feathers or feather-like body covering, but many of them didn’t fly and probably didn’t even glide. Archaeopteryx, which was for a long time considered to be the first bird (although this status is not certain), could likely launch itself from the ground, but probably couldn’t fly far, according to unpublished research presented at the 2016 Society of Vertebrate Paleontology meeting in Salt Lake City, Utah. Instead, feathers, likely helped these bird-like dinosaurs stay warm as juveniles or send signals to other individuals.
Most of the well-known dinosaurs — including Tyrannosaurus rex, Deinonychus and Velociraptor — fall into the order known as Saurischian dinosaurs (pronounced sor-ISK-ee-en). These “reptile-hipped” dinosaurs have a pelvis that points forward, similar to more primitive animals. They are often long-necked, have large and sharp teeth, long second fingers, and a first finger that points strongly away from the rest of the fingers.Saurischians are divided into two groups – four legged herbivores called sauropods and two-legged carnivores called theropods (living birds are in the theropod lineage).Theropods walked on two legs and were carnivorous. “Theropod” means “beast-footed” and they are some of the fearsome and most recognizable dinosaurs — including Allosaurus and T. rex.Scientists have wondered whether large theropods — such as Giganotosaurus and Spinosaurus — actively hunted their prey, or simply scavenged carcasses. The evidence points to the animals working together as opportunistic hunters: they would bring down prey, but also eat animals that were lying around. When fossil-hunters found bones with bite marks on them, they wondered if theropods engaged in cannibalism. It appears now that the animals may have scavenged their own kind, but they didn’t hunt down their own.