Beheading Naosaurus

5 06 2007

The AMNH archives really are a rich resource of information about paleontology, and I’ve definitely taken advantage of their availability to learn more about giant crocodilians, “mummified” dinosaurs, curious museum mounts, and the taxonomic confusion created by some early studies of dinosaurs. Continuing in the theme of cranial-confusion surrounding “Brontosaurus”/Apatosaurus that kicked off the last post, today we’ll be looking at a similar case involving Naosaurus, a fin-backed creature that also had to lose its head.

In 1896, Charles Sternberg discovered the most of the vertebrae and ribs of what E.D. Cope called a “sail-backed reptile,” the name stemming from Cope’s suspicion that the long spines had a membrane stretched between them and could be used to catch the wind, just like a sail, the fearsome Dimetrodon being named by Cope some years earlier in 1878. The material Sternberg found in the Texas red beds, however, was different from that of Dimetrodon despite the superficial similarities and so it was given a new name, Naosaurus (or “ship lizard”).

Naosaurus

A Charles R. Knight reconstruction of Naosaurus. Note the horizontal notches along the spine that belie the fossil’s true affinities. [From: The Project Gutenberg EBook of The Human Side of Animals, by Royal Dixon]

In 1907, a reconstruction of Naosaurus was undertaken at the American Museum of Natural History under the supervision of Henry Fairfield Osborn, although most of the material seemed pieced together. The Permian red beds of Texas gave up a lot of material, but it was difficult to figure out what bones belonged to Dimetrodon of various sizes and what belonged to Naosaurus. Despite this, an reconstruction of Naosaurus was attempted, despite warnings from other scientists that the reconstruction may not be accurate. From the 1907 AMNH Bulletin;

Dr. E. C. Case, the chief authority on this group writes his belief that the skull of Dimetrodon cannot be used as a basis for the restoration of the skull of Naosaurus.

The reader will, therefore, thoroughly understand that the assemblage is largely composite. It serves, nevertheless, to give us for the first time an adequate conception of the unique and imposing characters of these great extinct forms.

Indeed, despite Case’s contrary take on the fossils, the skull of Dimetrodon was used as a model for Naosaurus (see illustration above), the two animals looking exceedingly similar in reconstruction.

Dimetrodon

Reconstruction of Dimetrodon from “DESCRIPTION OF A SKELETON OF DIMETRODON INCISIVUIS COPE. BY E. C. CASE.” (1910)

What is most curious is that Naosaurus was reconstructed as a fanged predator much like Dimetrodon when its spines would have given away a different relationship. Rather than being straight bones that superficially resemble fingers | , the spines of this pelycosaur had horizontal projections when you looked at them straight on + , the tell-tale mark of Edaphosaurus, described by Cope in 1882. Even today Edaphosaurus often gets confused with Dimetrodon (“They’re both sail-backed reptiles, what’s the difference?”), but there is perhaps more to the story here as well. While we could go into detail about the errors in body reconstruction involved in “restoring” the non-existent Naosaurus, the skull, as in so many other cases, is what is most out of place. The year before Osborn published the 1907 Bulletin on Naosaurus, E.C. Case published his own 1906 paper on the skull of Edaphosaurus. The material available to Case, however, was partial and crushed, and while his efforts to reconstruct the skull were admirable, he was a bit off the mark.

Edaphosaurus, Case reconstruction

Interestingly, Case notes in his paper that Edaphosaurus was probably not closely related to Naosaurus, despite Cope’s earlier assertion that the two were related, so even though Case did not believe Dimetrodon would be a good candidate to reconstruct the skull of Naosaurus, Edaphosaurus seemed to be out of the running as well. In fact, it was not until D.M.S. Watson re-evaluated the skull of Edaphosaurus in 1916 based upon a new, un-crushed skull that we got an idea of what the animal’s head really looked like.

Edaphosaurus Watson Reconstruction

Eventually the dubious status of Naosaurus became apparent and faded from memory, although I’m sure if Knight’s reconstruction popped up today those unfamiliar with the story would immediately suggest it was an obscure rendering of Dimetrodon. Doubts seem to be apparent in Case’s 1910 paper on Dimetrodon which provided the skeletal reconstruction above, and the removal of Naosaurus as a valid taxon was probably not long following Case’s work. In the end, however, just as with Phobosuchus, Naosaurus no longer haunts the 4th floor of the AMNH, relegated to little more than a dusty memory.


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