Contents Updated: Thursday, August 05, 1999
Birds today are thought to be closely related to dinosaurs. Indeed some say that birds are dinosaurs. The link between them since 1861 has been the fossil of a creature called archaeopteryx, six specimens of which were found and which looks like a dinosaur with flight feathers. Recently a spate of fossils of early birds has been reported, especially in China, which have added considerably to our understanding.
Palaeontologists have looked carefully at the archaeopteryx specimens for many years and increasingly they have convinced themselves that it is a dinosaur with feathers and wings. It looks exactly like a group of small fast carnivorous dinosaurs belonging to the theropods. The main differences between archaeopteryx and the theropods were the long arms of the archaeopteryx, adapted as wings, the feathers and the presence in archaeopteryx of a wishbone that the theropods did not have. Now experts believe some theropods had wishbones and they also believe they had primitive feathers.
Archaeopteryx does not have the deep breast bone that birds have to anchor their huge flight muscles but nor do bats yet they fly perfectly well. It seems that archaeopteryx could fly modestly well by flapping its wings, though, like bats, it might have had to launch itself from a tree, a cliff or a rock to get going. It was probably not powerful enough to take off from level ground. Its immediate ancestor might have started to take to the air by gliding from rock to rock using its feathers as a sort of parachute to limit its terminal velocity through the air—a sort of living shuttlecock. The ancestor perhaps guided itself by the movement or flapping of its feathered arms and thus started to learn powered flight. Archaeopteryx could certainly flap quite well.
Some experts think archaeopteryx could take off from flat ground, reasoning that even if the animal were cold blooded, lizards can produce twice the power of mammals in short bursts. Archaeopteryx therefore could fly just like a bird but will have had no stamina. Much of the bulk of modern birds' flight muscles is to allow them to fly long distances.
The problem of the chain of linkages between dinosaurs and birds is that birds quickly evolved to be light in weight. Their bones were therefore hollow and could not resist decay long enough to fossilise. Another reason was that like apes, which are also not often found fossilised, they tended to live in woods where their flight allowed them the advantage of access to the trees. But the soils of woodlands are inevitably acid and decompose bones, especially the spongey bones of a bird, particularly easily. Yet, a bird fossil found in Mongolia and dated to 125 million years ago, called Ambiortus, is a modern bird in all its essentials. So in only the 25 million years from Archaeopteryx, modern birds evolved.
Then in 1988, birds 132 million years old were found in Las Hoyas, Spain. Then Sinornis, a bird 138 million years old was found in China. These are tiny birds about the size of a sparrow and yet show common features between birds and dinosaurs. Sinornis had fully developed bird wings which it could flap and fold up against itself just as modern birds do, but each wing was clawed. It also had a bird-like breastbone, even though perhaps not quite fully developed. It must nevertheless have been capable of long flights and must have been warm blooded to do so. It also had an opposed toe to allow it to perch on branches like modern birds. They had short tails but longer and more flexible than modern birds and tipped with a fan of feathers emerging from the pygidium bone in the parsons nose, just like modern birds but quite different from the long bony tail of the Archaeopteryx. Their tales were therefore perfect links between Archaeopteryx and modern birds. Otherwise, these strange little birds are like dinosaurs. Their bodies are flexible whereas birds today have rigid bodies for lightness and strength. Their backbones are flexible and their anklebones separate whereas in modern birds they are fused together. Their long pronged hip-bones are like dinosaurs'.
The fossils confirm that dinosaurs developed the power of flight and then their bodies adapted to optimise their new skill. Creationists will ignore these discoveries but they look like a neat vindication of Darwin, even though the little birds are not in the direct line of Archaeopteryx and modern birds.