The long-lost wishbone of Oviraptor

The study of the evolution of avian dinosaurs is one of the most active and exciting areas of paleontology (if not science in general) today, and I've been fortunate enough to see a revolution in this field during my own lifetime. When I was first learning about dinosaurs as a child, a few documentaries and books mentioned that dinosaurs and birds were probably related to each other, the overall tone being very cautious, but now there is little doubt that ornithology is really "extant dinosaur biology." Still, some old hypotheses die hard, and even though I greatly appreciate the beauty and brilliance of Gerhard Heilmann's The Origin of Birds, it cast a long shadow on the question of from what stock birds sprung.

To briefly review, Heilmann thought that the ancestors of birds would be found among a motley group of archosaurs called "pseudosuchians," and while he recognized the extremely close similarities between birds and dinosaurs the fact that no dinosaur had been then discovered with clavicles made his choice clear. Because Heilmann agreed with a concept called Dollo's Law (essentially that no feature of an organism can evolve again and appear the same after it has been lost), he felt that the lack of a wishbone in dinosaurs ruled them out of bird ancestry entirely. The little "pseudosuchians" like Ornithosuchus did have clavicles, though, and they might have represented the group from which dinosaurs evolved, thus killing two birds with one stone. The similarities between dinosaurs and birds could then be chalked up to convergence from a common ancestor, and it seemed like a neat, solid hypothesis.

Heilmann's book had a major impact on the discussion about the evolution of birds and is certainly a classic in the field, but oddly enough a dinosaur with a wishbone was discovered before his book received its English translation in 1927. The problem was that no one knew that this feature was discovered! During the 1920's the American Museum of Natural History sent a wave of expeditions to Mongolia in search of early mammals, but what the team found were the white bones of dinosaurs embedded in the reddish sands. In 1923 the team hit the fossil jackpot, finding dinosaur eggs and several new kinds of dinosaurs. The fossils were collected and shipped back to New York City to be examined by Henry Fairfield Osborn, and in 1924 he published a paper about three new theropods from Mongolia; Velociraptor, Saurornithoides, and Oviraptor.

All three of the dinosaurs Osborn described are significant to the study of the evolution of birds, but the remains of Oviraptor is the most important to the discussion here. In addition to a fragmented skull, a slab was discovered nearby with portions of the ribs and forelimbs. What Osborn missed, though, was that the slab contained the wishbone of Oviraptor, the very feature that kept Heilmann from accepting dinosaurs as the ancestors of birds.

Even if Osborn recognized the wishbone, though, would it have made a difference in terms of Heilmann's conclusions? Perhaps not. Heilmann's book was actually a longer adaptation of materials already published in the Danish in The Journal of the Ornithological Society of Denmark in 1913. The Origin of Birds makes no mention of Osborn's Mongolian theropods, and there was no later revision to include them. Whether Heilmann was aware of the discovery or not, I have no idea, and it's possible that even if the wishbone of Oviraptor was recognized Heilmann's book might have still been presented as we know it today (although it might not have been so influential). Playing "what if" isn't especially constructive though, and I don't want to speculate on who would have said what under different circumstances. In recent years a number of theropods have been found with wishbones, though, so Heilmann's principal objection has certainly been refuted..

In a strange coincidence, the team that found the remains of the theropod dinosaurs in 1923 made another discovery that was not fully appreciated until very recently. The team brought back the weathered hind limbs of an animal labeled as a "bird-like dinosaur" but could not otherwise be identified. Many decades later, the fossil was "re-discovered" and found to be the remains of an alvarezsaurid, a feathered bird-like dinosaur grouped within the maniraptoriformes. I would imagine that there are other "hidden treasures" in museum vaults all over the world as well, and I hope the old material continues to be examined as you never know what you might find in a dusty drawer or in an old plaster jacket.

References;

Chiappe, L.M. (2007) Glorified Dinosaurs. John Wiley & Sons, NJ.

Osborn, H.F.; Kaisen, P.C.; Olsen, G.D. (1924) "Three new Theropoda, Protoceratops zone, central Mongolia." American Museum novitates, No. 144, pp. 1-12