So feathers might be a defining feature of birds yet not be exclusive to birds. Some reptiles, we have seen, became anatomically mammal-like, some turtles and ichthyosaurs became mammal-like in their metabolism, some fish developed limbs. But what is a bird? Until recently, it seemed sufficient to say that a bird was an animal that had feathers, just as all reptiles have scales and mammals hair the purpose of feathers being to enable flight. There are around 10,000 species of bird today, and there must have been manifold more in the past which the fossil record never captured. Why should we permit reductionism to overrule these other perceptions of reality? If we lived in a world without birds, the very idea of a bird would be unimaginable. How could the frenetic humming-bird, the flamboyant peacock, the woodpecker all have descended from cousins of Tyrannosaurus rex? Having had such thoughts myself, I sympathise. You recall how swallows every autumn fly south over the English Channel, down western France, across the Pyrenees, through eastern Spain and Morocco, across the Sahara and, if they have not died from starvation or exhaustion, relentlessly on until they arrive in South Africa. You draw on your knowledge of living birds and think: are they not miraculous, these gravity-defying wonders of engineering, these masterpieces of colouration, these unwitting musicians from paradise? You marvel at how a sparrow flies into a hedge and processes spatial information faster than lightning as it selects a perch. Or perhaps your reaction is more intuitive. On the one hand, there is an obligation to respect the fossil evidence on the other, the ancient Hebrew record speaks about an ark on which there were ravens and doves, and since these preceded everything in the fossil record, the conclusion must be that birds as a group could not have evolved from anything – not those birds, at any rate. For those who believe that animals were created, the question is more difficult. To the extent that some might look similar to antediluvian birds, that would be through their having converged on those original forms after a vast amount of Cenozoic speciation.ĭid birds evolve from dinosaurs? Palaeontologists say that they had to have evolved from non-birds, and dinosaurs are the obvious ancestors. Modern birds are distinct and of unknown origin, though they must have had forbears in the Mesozoic. Mesozoic birds evolved, in a non-incremental way, from theropod dinosaurs.
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