Today marks the 200th anniversary of the birth of Charles Darwin, whose book
Darwin worked for over twenty years before he revealed the fruits of his labor in On the Origin of Species in 1859. He had collected a wide array of evidence, from the breeding of farm animals to biogeography, but one area of science important to his theory was a little problematic. Paleontology was still a relatively new science, and since scientists had only begun to scratch the surface of the fossil record, they had not yet found the minutely-graded transitional forms that would support evolution by natural selection. Darwin was sure that transitional forms must have existed, but why they had not yet been found was puzzling.
Dinosaurs stuck out like a sore thumb. We closely associate them with evolution today, particularly the evolution of birds, but in Darwin's time they were gigantic creatures that seemed to have little connection to earlier or later types of animals. If anything Darwin used the largest of the dinosaurs to state how the strong did not always survive, "as if mere bodily strength gave victory in the battle of life." For all their strength and ferocity, they ultimately perished.
Even the famous Archaeopteryx, the feathered dinosaur that still represents the earliest known bird, was given little attention by Darwin. The first correctly identified Archaeopteryx skeleton was discovered in 1861, just two years after On the Origin of Species was published. (At least one Archaeopteryx skeleton was found prior to this date, but it was confused for the remains of a pterodactyl.) Even though paleontologists were excited by the discovery of this creature that showed both reptile-like and bird-like characteristics, no one quite knew what to make of it. At the time the older three-toed tracks of the Connecticut Valley were still thought to have been made by gigantic birds (it would soon be found that they were made by non-avian theropod dinosaurs), which meant that Archaeopteryx was too late to be a bird ancestor. It was instead perched on a side branch of bird evolution, a late vestige that hinted at a much earlier transition.
Yet Archaeopteryx was important in another way. In the 4th edition of On the Origin of Species published in 1866 Darwin wrote:
Had it not been for the rare accident of the preservation of footsteps in the new red sandstone of the United States, who would have ventured to suppose that, besides reptiles, no less than at least thirty kinds of birds, some of gigantic size, existed during that period? Not a fragment of bone has been discovered in these beds. Notwithstanding that the number of joints shown in the fossil impressions corresponds with the number in the several toes of living birds' feet, some authors doubt whether the animals which left these impressions were really birds. Until quite recently these authors might have maintained, and some have maintained, that the whole class of birds came suddenly into existence during the eocene period; but now we know, on the authority of Professor Owen, that a bird certainly lived during the deposition of the upper greensand; and still more recently, that strange bird, the Archeopteryx , with a long lizard-like tail, bearing a pair of feathers on each joint, and with its wings furnished with two free claws, has been discovered in the oolitic slates of Solenhofen. Hardly any recent discovery shows more forcibly than this how little we as yet know of the former inhabitants of the world.Even though he was reluctant to herald Archaeopteryx as a grand confirmation of his theory, Darwin still highlighted it as an amazing fossil that hinted at the riches yet to be uncovered. The fossil record was not as well-sampled as some geologists thought, and even though it would never present a 100 percent history of life on earth (only a very small number of all the organisms that have ever lived have become fossils), there was still much work to do.
Thankfully, paleontologists continued their work and have exhumed absolutely stunning evidence that Darwin was right. Among the fossil riches some of the most precious are those of feathered dinosaurs, and I can only imagine what Darwin might say if he could see the proof that the swallows in the air and pigeons in the street are living dinosaurs.