Suppressor genes solve Heilmann’s paradox, the problem of evolving birds with big collarbones from dinosaurs with atrophied collarbones.(realistic dinosaur) Evolution at some point must have been able to remove the genes that suppressed collarbones from the dinosaur that was ancestor of the birds. This is not farfetched, nor even mildly implausible.(Dinosaur costume) The scenario might have run like this: A long-armed dinosaur, such as Deinonychus, might evolve extra-long arms with extra-long scales (feathers are modified scales) and begin to jump from branch to branch, using its arm scales to gain a few extra feet of glide, much like a flying squirrel. This proto-bird has no collar-bone, but its ancestors long before did. The genetic code for a collarbone remains in the dinosaur, stored in its inactive genefile. Once the proto-bird uses its forelimbs for gliding, a bony strut in front of the shoulder blade becomes an advantage. Any mutation that removes genes suppressing the clavicle now becomes favored by natural selection. In a few hundred generations, the proto-bird could therefore re-evolve a collarbone, rearranging it a bit to produce the distinctive V-shaped wishbone characteristic of birds.
Why would dinosaurs begin to fly and thus cross the thresh-old into the avian class? What was Archaeopteryx’s niche? Most paleontologists have leaned toward an analogy with flying squirrels. (animatronic dinosaur rides)Proto-birds are supposed to have been tree climbers who evolved wings first for gliding, then for powered flight. But there’s an alternative possibility the speedy jogger. Birds might have evolved flight first by running at high speeds over the Mesozoic landscape, employing their arms, outfitted with protofeathers, as airfoils for increasing ground speed. According to this theory, hypothetical proto-birds finally evolved a speed fast enough to become air-borne. John Ostrom champions this speedy-jogger theory. He was unhappy with the traditional restoration of Arcbaeopteryx as a tree-climbing glider and flier. (dinosaur factory)Among other details, he had observed that Arcbaeopteryx’s foot couldn’t get the same grip on a branch as can modern birds. Climbing birds have an inner toe that faces backward and flexes forward to grasp a branch against the other three toes. For the most efficient performance, all four of these toes must be long and their base joint must be at the same level, located at the very bottom of the long ankle bones (metatarsals). Arcbaeopteryx’s foot was not so built. The toe facing rearward was too short and too high up on the ankle, so that its grip on a branch wouldn’t be anywhere near as effective as a modern bird’s.