The Rioarribasaurus Controversy; or, How We Almost Lost Coelophysis


Juvenile Coelophysis at the New Mexico Museum of Natural History and Science

Thanks in large part to me attending SVP in Albuquerque, I have become very fascinated with the genus Coelophysis. The quintessential early theropod, it is also one of the most completely known dinosaurs, thanks to the spectacular bonebed at Ghost Ranch preserving hundreds of skeletons. However, this bonebed also placed Coelophysis at the center of a heated naming controversy that, had history taken another path, would have led to us using a different name for this iconic Triassic dinosaur.

The story begins in 1887, when famed paleontologist Edward Drinker Cope named a new species, Coelurus bauri, based on some fragmentary material from New Mexico. Two years later, Cope transferred this species to a new genus, Coelophysis, meaning “hollow form”. Nearly sixty years later, in 1947, a paleontological field crew led by Edwin Colbert of the American Museum of Natural History discovered new Triassic theropod material at Ghost Ranch, which Colbert identified as Coelophysis. Further excavation revealed a startling number of skeletons, many of them complete. This incredible discovery made Coelophysis a household name in paleontology, and was almost invariably associated with the Ghost Ranch specimens.

But there was a problem. As mentioned above, Cope’s original Coelophysis material was fragmentary. So fragmentary, in fact, that they preserved no distinctive characteristics that would allow other fossils to be definitively identified as this genus. Because of this, Colbert’s assumption that the fossils found at Ghost Ranch belonged to Coelophysis was problematic. In 1991, paleontologists Adrian Hunt and Spencer Lucas sought to address this problem. Their solution was to give the Ghost Ranch specimens a new name, Rioarribasaurus colberti. Coelophysis bauri, the name coined by Cope a century earlier, was considered by Hunt and Lucas to be a nomen dubium, or “doubtful name”.

Needless to say, this move was highly controversial. Coelophysis had become a very well established name, almost entirely due to the discoveries at Ghost Ranch. By renaming these fossils as Rioarribasaurus, almost every reference to Coelophysis in both the technical and popular literature would actually apply to this new genus. Many felt the confusion caused by this would outweigh the technical justification. In an effort to preserve stability, Colbert and several colleagues submitted a petition to the International Commission on Zoological Nomenclature (ICZN), the organization that governs the naming of animals. They requested that the type specimen of Rioarribasaurus be designated the neotype of Coelophysis, thus preserving the latter name and rendering the former invalid.

Predictably, Hunt and Lucas opposed this petition, arguing that assigning a neotype for Coelophysis under these conditions went against the code put out by the ICZN. They also argued that Cope’s type material was from a different stratigraphic layer than the Ghost Ranch quarry, making it unlikely that they were the same species. Other comments in favor of Rioarribasaurus came from Robert Sullivan, Sam Welles, George Olshevsky, and Philip Huber.

However, support for Colbert et al.’s petition came from Hans Sues, Hilde Schwartz, Ralph Molnar, Zdenek Spinar, Thomas Holtz, Farish Jenkins, Benjamin Creisler, Nicholas Hotton, Dale Russell, Elizabeth Nicholls, Louis Jacobs, Donald Glut, and Armand de Ricqles. The predominant opinion of these supporters mirrored the petition’s original argument, that the name Coelophysis was so entrenched in the paleontological literature that erecting a new name would only cause confusion. Arguments were also made that, contrary to Hunt and Lucas, the type specimen of Coelophysis was from the same formation as Rioarribasaurus”, and may very well be the same species.

In 1996, five years after Hunt and Lucas published their paper that started this debate, the ICZN voted in favor of the petition and established a neotype for Coelophysis. Rioarribasaurus was chucked into the dustbin of rejected names, never to be available for scientific use again. Whatever one thinks about this decision, Coelophysis is here to stay, and the small Triassic dinosaur that bears its name remains one of the most famous and well-studied animals from this fascinating time period.


2 thoughts on “The Rioarribasaurus Controversy; or, How We Almost Lost Coelophysis

  1. Team Rioarribasaurus created a “Eucoelophysis” (literally, “true Coelophysis“) from bones they thought was a coelophysoid-type theropod. But this turned out to be a non-dinosaurian silesaurid.

    Liked by 2 people

    • Very true! Thanks for bringing that up. Another detail I considered including in this post but didn’t was Greg Paul’s alternate combination of Syntarsus colberti for Rioarribasaurus. Obviously this was before that whole Megapnosaurus fiasco (it seems like coelophysoids are cursed with nomenclatural controversies).


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