Feathered Dinosaurs

Australia: The Land Where Time Began

Feathered Dinosaurs

Many fossils have now been found in China that indicates that at least the theropod dinosaurs had feathers, and there is other evidence that the similarities between dinosaurs and birds go much deeper than the feathers. When the arm bones of Velociraptor were restudied in 2007 it was noted that they had quill knobs, a clear indication of feathers as these knobs are the attachment sites in modern birds for feathers. It became apparent that the these dinosaurs were covered with feathers. Other characters now known to be shared by dinosaurs and birds are the possession of a wish bone, hollow bones, and they nested in a similar manner to birds.

In the 1970s a 70 cm bipedal beaked dinosaur was found in Mongolia by the Russian palaeontologist Sergei Kurzanov. He named it Avimimus portentosus (the amazing bird mimic) because he believed it was so bird-like, having similarities such as quill knobs on the bones. The significance of these quill knobs were overlooked until they were also found on other dinosaurs such as Velociraptor.

In the 1970s it was also claimed by the by some that the theropods were both warm-blooded and bird-like. The 1996 discovery of Sinosauropteryx prima in Liaoning, China, proved to be further evidence of how bird-like the theropods were, it was covered with downy feathers. The fossil was so well-preserved that small mammals were found in its gut and eggs in its oviduct. Other theropods found in the same deposit included Caudipteryx and Microraptor. More than 24 species of dinosaur are now known to have been covered with feathers, though palaeontologists usually refer to these types of feather as dinofuzz. The range of species now known to be feathered is so wide that it indicates it was a common feature in dinosaurs.

There is an accumulating body of evidence for the similarity between some dinosaurs and birds includes, growth rates, physiology, bone structure and feathers. A small dinosaur was found at the Liaoning site, Mei long (sleeping dragon), that had apparently died in the same position adopted by sleeping birds to reduce heat loss, the legs tucked under its body and its head tucked under its arm. It was covered by a a rain of volcanic ash.

About 228 million years ago in the Middle Triassic of Argentina lived one of the oldest known theropods, Herrerasaurus, in the bones of which are the first indications of bird-like characteristics such as feathers. The coelurosaurians (hollow lizards), referring to their hollow vertebrae, were an early theropod groups that displayed these bird-like characteristics that continued through into the birds of today.

The coelurosaurians include a wide range of carnivorous dinosaurs, varying in size from about 2 m (Coelurus) to about 14 m (Tyrannosaurus). The position of Coelurus in the evolution of Tyrannosaurids has been widely debated, mostly because it is known only from a partial skull and only some of the post cranial bones. It is widely believed to fit somewhere in the early stages of the evolution of feathered dinosaurs. Being of a generalised form, it had evolved some of the features that were to continue on into the birds, such as light, hollow bones and, together with the rest of the feathered dinosaurs, had a brain that was relatively larger than occurred in other predatory lines such as Allosaurus and a group that arose in Gondwana, the Abelisaurids.

The earliest known forms that may be part of the Tyrannosaurus lineage are Eotyrannus and the Chinese feathered form, Dilong. Among the most primitive of the group was Coelosurus fragilis. It lived about 150 million years ago in the Late Jurassic, making it a contemporary of Archaeopteryx, the first known bird. A suggested contender for the first form in the line leading to Tyrannosaurus was Tanycolagreus, a 3-4 m long predator that was lightly built, with long arms and fingers. There are features of its pelvic bones and femurs that are similar to those of the Tyrannosaurids.

A paper published in Nature, September 2009, describes a troodontid, a theropod dinosaur, Anchiornis huxleyi that lived between 161 and 151 million years ago, in the earliest part of the Late Jurassic in Tiaojishan Formation of western Liaoning, China. It had an extensive covering of feathers, with long pennaceous feathers attached to the pes. This specimen adds to other evidence, such as Microraptor gui, from the Early Cretaceous, that the earliest birds probably had 4 wings, as do both of these species.

Asilisaurus kongwe, that was possibly omnivorous, was an archosaur that lived in the Triassic, about 240 Ma, in the 10 million years before the dinosaurs arose and was an early member of the ornithodira clade that led to theropods and eventually birds.

Sources &Further reading