This splinter of bone may not look like much, but it is, in fact, one of the oldest wishbones ever unearthed. It was buried some 210 million years ago, in the Late Triassic sediments from the famed Coelophysis (Whitaker) Quarry at Ghost Ranch, New Mexico.
At the close of the 19th century, anatomists and paleontologists had noted several similarities between theropod dinosaurs and birds, including their hollow bones, upright bipedal posture, long legs and three-toed feet. Scientists such as Thomas Huxley and Franz Nopcsa had gone so far as to suggest that small theropods like Compsognathus might have been close to the ancestry of the first birds.
By the 1920s, however, the relationship between dinosaurs and birds was discounted, and in many minds, definitively disproven. What caused such a shift in thinking? In a word, wishbones.
The wishbone (or furcula) was long believed to be a structure unique to birds, formed by the fusion of the two collarbones (clavicles) into a single V-shaped structure that helps brace the skeleton against the stresses incurred while flapping. The reptiles ancestral to birds, therefore, should, at the very least, show well-developed clavicles. But by 1926, when Danish artist and naturalist Gerhard Heilmann published his monumentally influential The Origin of Birds, no clavicles had been reported in any theropod dinosaur. Noting this fact, Heilmann suggested that birds evolved from a more generalized archosaurian ancestor, such as the aptly-named Ornithosuchus (literally, “bird-crocodile”), which is now believed to be closer to the crocodile end of the archosaur lineage. At the time, however, Ornithosuchus seemed a likely ancestor of more birdlike progeny. It, at least, had clavicles up to the challenge.
In the 1980’s, paleontologists began to realize that theropods not only possessed clavicles, they possessed clavicles that were fused into a wishbone! In 1983, Rinchen Barsbold reported the first dinosaurian furcula from a specimen of the Cretaceous theropod Oviraptor. Amazingly, a furcula-bearing Oviraptor specimen had been known since the 1920s, but because everyone knew that theropods didn’t have clavicles, it was misidentified for sixty years.
Following this discovery, paleontologists began to find furculae in other theropod dinosaurs. Wishbones are now known from dromaeosaurs like Velociraptor and the allosauroid Allosaurus, and even big bruisers like Tyrannosaurus rex are known to have furculae between their stubby little two-fingered(?) arms.
Bronze cast of a T. rex wishbone (furcula), as displayed at the Field Museum (photo credit: Wikipedia).
As Zach points out in the comments, this might not be a furcula at all,
but a pair of gastral ribs. Other tyrannosaurid furcula are known, however.
In 2000, Alex Downs reported an isolated furcula found within a block of Coelophysis bauri skeletons from the Late Triassic Rock Point Formation at Ghost Ranch, New Mexico. While it seemed likely that it originally belonged to Coelophysis, the block contained fossils from other Triassic animals as well, and Alex declined to make a positive identification.
Two years later, Tykoski et al. described several furculae from two species of the coelophysoid genus Syntarsus, S. rhodesiensis and S. kayentakatae, from the Early Jurassic of Zimbabwe and Arizona, respectively. Syntarsus was long considered to be the genus most closely related to Coelophysis, differing only in a few anatomical details and slightly younger age, so the identification of furculae in Syntarsus made it very likely that the furcula Alex Downs noted in 2000 came from Coelophysis after all.
Shortly after that, a trio of entomologists noted that there was a beetle named Syntarsus whose description predated the dinosaur. They decided to rename the dinosaur Megapnosaurus, or “big, dead lizard,” which might be how a dinosaur would appear to a beetle. Subsequent to this, most dinosaur workers began to take seriously the idea that the two species of Syntarsus/Megapnosaurus could really just be two species of Coelophysis. Better, I suppose, to lose a genus than be forced to use an entomologist’s punchline.
So, by 2006, wishbones were definitively known from the Early Jurassic Coelophysis rhodesiensis and Coelophysis kayentakatae, and a single isolated furcula was known that might have come from the “original” Coelophysis, the Late Triassic Coelophysis bauri. (Actually, there’s a good chance that the Ghost Ranch Coelophysis might not be the “original” Coelophysis, but that’s a tortured tale of nomenclature for another time.)
Earlier this year, Larry Rinehart, Spencer Lucas, and Adrian Hunt published a paper describing five new furculae from a Ghost Ranch Coelophysis block at the New Mexico Museum of Natural History and Science. These include the isolated furcula shown at the top of the post, and four others found articulated with Coelophysis skeletons, proving definitively that the Late Triassic Coelophysis bauri possessed the oldest wishbones yet discovered.
The photo above shows one of these articulated furcula preserved beautifully within the shoulder girdle of a young Coelophysis. The view is of the “collar” of the animal from below, with two long vertebrae from the base of the neck at the right side of the photo. The furcula is broken in the middle and skewed beneath the left side of the body (technically it is on top of the body, since the NMMNHS Coelophysis block was flipped over and prepared from the bottom up), but the right side of the furcula is preserved in perfect articulation with the scapula and coracoid.
Larry asked if I could draw a reconstruction of the furcula of Coelophysis bauri, which I based on several photos I took of the block, including the ones shown above. The reconstruction, showing the cranial (front) and lateral (side) view, is shown below, with a millimeter bar for scale:
Traditionally, the person who snaps off the largest piece of any wishbone is granted a wish. Now I’m certainly not about to break off a chunk of 210,000,000-year-old furcula to get something I want, and besides, most of them are already broken. But if there is any residual wishery preserved between the cracks of these boomerang-shaped bones, I’ve got my wish in mind. It’s probably a little premature to share it at this point, but suffice it to say, should it come true, there will be a whole lot more Coelophysis stories to be shared in the coming months…
Further reading:
Rinehart, L. F., Lucas, S. G., Hunt, A. P. 2007. Furculae in the Late Triassic theropod dinosaur Coelophysis bauri. Paläontologische Zeitschrift, vol 81, no. 2, pp. 174–180.
Downs, A. 2000. Coelophysis bauri and Syntarsus rhodesiensis compared, with comments on the preparation and preservation of fossils from the Ghost Ranch Coelophysis Quarry. New Mexico Museum of Natural History and Science Bulletin, vol. 17, pp. 33–37.
Tykoski, R. S., Forster, C. A., Rowe, T., Sampson, S. D., and Munyikwa, D. 2002. A furcula in the coelophysid theropod Syntarsus. Journal of Vertebrate Paleontology, vol. 22, no. 3, pp. 728–733.
—Matt Celeskey.
File under: Dinosaurs, Triassic.
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