Evolution: Feathered Dinosaurs?

Birds are unmistakable creatures. They all have feathers, beaks, and wings, and most can fly. No other modern animals possess feathers. But what is a bird? Where did they come from? Who are their closest relatives?


To answer these questions, we have to look back in time approximately 400 million years, when the first vertebrates (animals possessing backbones) came onto land. These animals became known as tetrapods (tetrapod means “four-footed”, vertebrate animals with four limbs). Tetrapods evolved into amphibians, represented today by frogs, toads and salamanders. Around 350 million years ago, some of the amphibians had evolved into primitive reptiles. The primitive reptiles evolved into two groups, the Synapsids and Eureptilia. The Synapsids eventually gave rise to primitive mammals around 220 million years ago; however the mammals would not start evolving into the diverse group we see today until the end of the reign of dinosaurs around 65 million years ago.


The Eureptilia also diverged into two groups, the Anapsida and Diapsida. The Anapsida survive today in the form of turtles, tortoises and terrapins. The Diapsida became ichthyosaurs, pliosaurs, plesiosaurs, lepidosauromorpha and archosauria. The first three groups are all long extinct (unless you believe in the Loch Ness monster which scientists have proposed would most likely be a plesiosaur!). Lepidosauromorpha are represented today by lizards, snakes and the tuatara (a lizard-like New Zealand reptile which shares the common ancestor of lizards and snakes). The archosaurs diverged into the crocodilians (crocodiles, alligators and their relatives), the pterosaurs (flying reptiles such as pterodactyls), and the dinosaurs. The dinosaurs in turn evolved into different types, first the ornithiscians which did not evolve further, and the saurischians who became the sauropods and theropods. The theropods in turn became the species Allosaurus, and another branch known as maniraptors. Finally, maniraptors evolved into other types of dinosaur (including Tyrannosaurus rex) and birds. The earliest type of bird known to palaeontologists is the Archaeopteryx genus. Archaeopteryx was around the size of a chicken, and possessed both bird-like and reptile-like features. Scientists have found evidence that it could fly due to the presence of a large bony breastbone found in one species, but have concluded that it was not the first of its lineage to do so. Therefore there may be other fossilised early birds yet to be discovered.


Birds had evolved into nine ‘subclasses’ at this stage (one of which was Archaeopteryx), but only one lineage has survived to present day, the Neornithes. The Neornithes split into Palaeognaths and Neognaths. Palaeognaths include the Kiwis, Ostriches, Cassowaries and Emus alive today, as well as a few extinct cousins. Most birds alive today are Neognaths, and of these, the most abundant group is the Passeriformes which are the perching birds. Passeriformes include about 60 per cent of all living birds such as flycatchers, treecreepers, bowerbirds, lyrebirds, honeyeaters, fairy wrens, robins, shrikes, drongos, crows, currawongs and whipbirds, to name but a few.


Therefore the closest living relatives of birds are the crocodilians, as birds are in fact the ancestors of dinosaurs from the group known as maniraptors. 

 

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