How Paleontologists Know Birds Descended from Dinosaurs
Feathered Deinonychus antirrhopus model at the Royal Ontario Museum.
Credit: Aaron Gustafson
Copyright: Wikimedia Commons
Birds are descendants of dinosaurs. Although this is not a new theory in the dinosaur world, there is now evidence that proves some dinosaurs evolved into birds.
In September of 2009, five different species of dinosaur fossils with feathers or feather-like structures were found in north-eastern China, according to The Telegraph. Before this find, the only possible link between dinosaurs and birds was archaeopteryx, which is the oldest known bird and it is also older than other feathered dinosaurs that had been found.
However, these archaeopteryx lived 145-150 million years ago, and these fossils are much older. The fossils were found in two different rock formations. One was in the tiaojishan, which means those fossils are 151-168 million years old, and the other set of fossils was found in the daohugou, which makes the fossils 158-164 million years old.
According to Dr. Xing, one of the lead scientists who discovered the fossils, said that one of the dinosaurs, anchiornis huxlevi, has plumage and feathered feet. He also said, “This fossil provides confirmation that the bird-dinosaur hypothesis is correct and supports the idea that birds descended from theropod dinosaurs, the group of predatory dinosaurs that include allosaurus and velociraptor.”
Before this discovery, scientists had found that Dilong paradoxus, an earlier cousin ofTyrannosaurus rex, had “at least a partial coat of hairlike feathers,” according to National Geographic. In 2004, Dilong comes from the Mandarin words for “emperoro” and “dragon,” andparadoxus refers to its feathers. Dilong was found in the Liaoning Province in northern China. Dilongis a five-foot long tyrannosaurid, (typically a large carnivorous dinosaur with short arms such as T-rex), that lived 130 million years ago.
Although paleontologists suspected tyrannosaurids had featherlike structures, Dilong was the first fossil to provide evidence of this. Mark Norell, who co-wrote the paper about Dilong, said that the discovery of Dilong fossils “supports theories that dinosaurs were birdlike, warm-blooded creatures that evolved feathers to stay warm-not to fly,” according to National Geographic.
The reason paleontologists predicted tyrannosaurids were related to birds was because they have a more recent common ancestor than Sinosauropteryx, which is the most primitive known feathered dinosaur. This made paleontologists infer that “the feathers of birds and other feathered dinosaurs are all expressions of the same evolutionary change,” according to National Geographic.
Paleontologists classify tyrannosaurids into the broader group coelurosaurs, which they believe evolved into birds. The tyrannosaurid Dilong’s head has many of the same characteristics as later tyrannosaurids, but it has a more primitive body and longer arms. The Dilong fossils had evidence of protofeathers, which are “precursors to the feathers found on modern birds.”
Norell said that adult tyrannosaurs, such as Tyrannosaurus rex, probably did not have primitive feathers, which indicates that the protofeathers were meant to keep warm-blooded dinosaurs warm, and not to help them fly. Because bigger animals do not need insulation to keep warm-think of the elephant-then the adult T-rex would not have needed feathers, and probably did not have feathers. However, it may have had feathers as a juvenile.
Other dinosaurs that have evidence of having feathers include Caudipteryx, Microraptor, andPedopenna, among others.
References:
http://news.nationalgeographic.com/news/2004/10/1006_041006_feathery_dino_2.html
