Birds are one of the most successful animals on the planet and, when it comes to wildlife watching, one of the easiest to see. Thanks to modern technology and some very dedicated researchers our understanding their behaviour, including migration routes, has greatly increased over the last few years. However, how they evolved has always been a bit of an enigma.
The first hint of their possible evolutionary origin came in the 1860s from a quarry in south Germany where the first specimen of Archaeopteryx was discovered. As the first known bird, its arms and tail were covered with modern appearing feathers, but unlike modern birds it also had teeth, a long bony tail, and its hands, shoulder girdles, pelvis and feet bones are distinctive and not fused. This led to Darwin’s friend, Thomas Huxley, to first suggest the link between dinosaurs and birds in 1868. The idea fell out of favour, however, in the early 20th Century when palaeontologist Gerhard Heilmann published ‘The Origin of Birds’ stating that birds evolved directly from thecodonts, a reptilian group which also gave rise to dinosaurs, crocodiles, and pterosaurs.
Then in the 1970s palaeontologists noticed that Archaeopteryx shared a number of features with small carnivorous dinosaurs called theropods, and the resulting evolutionary tree implies that birds are just a ‘twig’ off the dinosaur branch. Fossils discovered over the last 15 years, predominantly in China and South America, have backed up this theory with the theropods seen to be closest to birds on the evolutionary tree showing several different types of feathers. Changes to the hand digits of dinosaurs in the theropod group also show evidence of this connection between the two groups as the fifth and then fourth digit is completely lost as you move towards the bird twig. The wrist bones under the first and second digits is also shown to fuse together and become more semi-circular, allowing the hand to rotate sideways against the forearm. More recent research, published in Science, has found that theropods were the only dinosaurs to get continuously smaller, shrinking 12 times before becoming the size of modern birds.
As with all theories, there are some anomalies that need to be looked into further. Developmental studies on bird hands now indicate that they actually comprise of digits 2, 3, and 4 rather than the 1, 2, and 3 you would expect if they evolved from theropods. There is also evidence that the feathers seen of earlier theropod fossils may actual just be collagen fibres found in skin that has been preserved in an unusual way.
Despite this, the evidence behind birds descending from dinosaurs is a compelling one. So instead of them being extinct, we could in fact be feeding small dinosaurs in our back gardens.
Georgina Bowie, Visitor Centre Assistant