Printers discovered that an especially fine-grained limestone that was quarried in Germany could be used to print finely detailed pictures. The limestone had the handy characteristic of shearing off in large, flat sheets of rock, rather than in chunks, making it ideal for the process.
In 1861, at a lithographic limestone quarry in Solenhofen, southern Germany, an exciting fossil discovery was made. While shearing the limestone into sheets, the workers at the quarry discovered a fossil of what appeared to be a small reptile. On closer examination, strange impressions in the limestone around the body of the animal were observed. The fine grained limestone left no doubt that these distinctive traces had been left by feathers, and the Solenhofen fossil was that of an early, pigeon-sized bird. The fossil was given the name Archaeopteryx, which means "ancient wing."
Archaeopteryx has often been referred to as the "missing link" between dinosaurs and the first birds. Archaeopteryx arose in the late Jurassic Period, a time when dinosaur diversity was high. Its bones resemble those of the small dinosaur Compsognathus, and this is part of the evidence that birds arose from the Theropod dinosaurs (see my article "Dinosaur Primer" for more information about the Theropod dinosaurs and bird evolution).
Its wings were more like dinosaur arms than bird wings, and had hooked claws. It also did not have a sternum or keel; in modern birds, the sternum is the attachment site for the wing muscles, and, without a sternum, Archaeopteryx was probably not a strong flyer. (Some recently discovered specimens are suspected to have a sternum.) Paleontologists believe that Archaeopteryx may have used the claws on its wings to climb up trees, and would then glide down to catch prey, or to escape predators.
Archaeopteryx also had teeth, while modern birds do not. It also had a long, wide tail, while modern birds have a short tail bone, called the pygostyle, and long tail feathers. Archaeopteryx also had bones with thick walls, and had only a few air ducts in its bones like modern birds and Pterosaurs. Bones with thin walls and air ducts are lighter, and light bones make it easier for birds to fly. Bones with thick walls and few air ducts are further evidence that Archaeopteryx was more of a glider than a strong flyer.
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