What Was Archaeopteryx? The Fossil That Settled Where Birds Came From
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Two years after Darwin published On the Origin of Species, a quarry in Bavaria gave up a slab of limestone with the impression of a feather in it, and a few months later a whole skeleton: a creature the size of a magpie with the wings and feathers of a bird and the teeth, claws and long bony tail of a small dinosaur. Nothing could have arrived at a better moment for a theory that had just predicted intermediate forms and been mocked for their absence. Archaeopteryx has been argued over ever since, and it remains the best-known fossil in the world after the dinosaurs themselves.
The quarry
The Solnhofen limestone of southern Germany is a fine-grained rock laid down about 150 million years ago at the bottom of a warm, still, oxygen-poor lagoon, where anything that sank was buried in lime mud too quiet to be disturbed and too airless for scavengers. The stone was quarried for lithographic printing, which is why it was split into flat sheets by the thousand, and the splitting revealed jellyfish, insects with their wings, pterosaurs with their membranes, and, in 1861, a single feather and then a skeleton. Twelve more skeletons have turned up since, one of them identified in a private collection only in the 1970s and one bought by the Bavarian state in 1999, and each has added something.
Bird and dinosaur at once
What made the animal famous is that it is unmistakably both. The bird features are the feathers, asymmetrical on the wings in the pattern that flight requires, the wishbone, and the reversed first toe; the reptile features are what no living bird has:
- •Teeth in both jaws, small and conical, where a bird has a beak
- •A long bony tail of more than twenty vertebrae, with feathers along both sides, where a bird's tail is a stump carrying a fan
- •Three clawed fingers free on each wing, which it could probably use to climb
- •A flat breastbone with no keel, so the great flight muscles of a modern bird had nowhere to anchor
- •Gastralia, belly ribs, which birds lost and crocodiles and dinosaurs kept
Could it fly
The asymmetry of the flight feathers is the strongest evidence that it flew at least somewhat, since symmetrical feathers do not generate lift efficiently and are found on flightless birds. Against that, the shoulder joint did not allow the full upstroke of a modern bird, the breastbone had no keel, and the bones of the wing were built more like a pheasant's than an albatross's. The current picture, supported by a 2018 study that put a specimen through a particle accelerator to image the bone structure, is that it flew in short bursts, taking off from the ground or a low branch and flapping hard over a short distance, in the way a pheasant escapes a dog; it was not a soarer and not a glider, and it was probably a poor flier by the standards of anything alive.
The argument it settled and the one it started
Thomas Huxley, Darwin's most vigorous defender, used the fossil in the 1860s to argue that birds had descended from dinosaurs, a proposal that was accepted, abandoned for most of the twentieth century in favour of an older reptile ancestor, and revived from the 1970s by John Ostrom, who noticed that the bones of Archaeopteryx matched those of the small predatory dinosaur Deinonychus in detail after detail. The feathered dinosaurs that came out of north-eastern China from 1996 finished the case: dozens of species with feathers of every grade, from filaments to full flight feathers, on animals that never flew, showed that feathers evolved before flight and for something else, insulation or display. Archaeopteryx is no longer the only intermediate; it is one of many, and the argument now is about exactly where it sits among them, with some analyses putting it just outside the birds proper.
Why it still matters
The fossil's importance is partly historical, as the specimen that arrived when the theory needed it and that creationists have attacked, unsuccessfully, ever since; the charge that the London specimen was a forgery, made in 1985 by the astronomer Fred Hoyle, collapsed when the feather impressions were shown to run into the rock's own crystal structure. Its scientific importance now is as a benchmark. Every new feathered dinosaur from China, every argument about how flight began, from the ground up or the trees down, and every reconstruction of the origin of birds is measured against a magpie-sized animal with teeth and a bony tail that was lying in a printing-stone quarry in 1861.
The takeaway
Archaeopteryx is a 150-million-year-old animal from the Solnhofen limestone of Bavaria with the feathers, wishbone and wings of a bird and the teeth, clawed fingers, bony tail and belly ribs of a small dinosaur, found two years after Darwin's Origin and used by Huxley to argue that birds descend from dinosaurs. It probably flew in short bursts rather than soaring, and the feathered dinosaurs found in China since 1996 have confirmed its lesson and taken away its uniqueness.