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Any examination of the evolution of birds must start with the Archaeopteryx. In 1861, two years after Darwin published Origin of Species, Archaeopteryx lithographica was discovered in Solnhofen, Bavaria. Preserved in carbonate mud dated as from the mid-Jurassic, the fossil was discovered as two slabs were split, producing mirror image impressions of the creature on both the slab and the counter-slab. And what a creature it was! It looked like a small, predatory dinosaur with one big twist: both sides of slab clearly showed the imprint of long, fully developed feathers splaying out from the clawed wings and long lizard-like tail.

Was it a bird? Was it a lizard? Closer inspection of Archaeopteryx allowed scientists to take notice of the clawed wings, the primitive furcula, the three towed feet, and the pubis pointing straight down, rather than backwards like a modern bird. But how did complex, asymmetrically veined feathers indistinguishable from those of modern birds show up on a dinosaur? Why did this branch of dinosaurs look so much like birds to begin with? For answers to these questions we need to look back at the dinosaur family tree.

Dinosaurs are divided into two large groups, the Ornithischia and the Saurischia, meaning "bird-hipped" and "lizard-hipped" respectively. The name bird-hipped refers to the pubis in this group of dinosaurs being rotated back to lay against the illium; the group contains stegosaurs, triceratops, and most non-sauropod herbivores. Ironically, the ancestors of birds are the lizard-hipped dinosaurs, a clade which includes all sauropods (brachiosaurs, apatosaurs, diplodocids, and all other dinosaurs that would be colloquially recognized as "the long necked ones" or worse, mislabeled as brontosaurus) and also theropods (all carnivorous dinosaurs and also bipedal herbivores similar to Gallimimus). Before we leave the sauropods behind to talk about the rise of birds from the theropods, it may be useful to note the bird-like characteristics that appear universal in sauropods, suggesting that they may have been present as early as the common ancestors of the two groups. The lungs mammals and all living reptiles possess are called bellows style lungs, because they pull air in and push it out again, at a loss to the air trapped in the trachea. Birds have a much more efficient unidirectional breathing set-up, pulling all air through the lungs and a series of air sacs and only then releasing it back out the trachea. Interestingly enough, the

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