January 8, 2009
Even though museums all over the world are filled with dinosaur skeletons, it is very rare for paleontologists to find a complete, articulated specimen. Scraps and fragments of dinosaur bone are far more common, and often only the hardest parts of the skeleton become fosslized. In the case of the armored dinosaurs, the ankylosaurus, the plates, spikes, and bony knobs called tubercles are much more common than complete skeletons. A new study published in the Journal of Vertebrate Paleontology confirms that it is possible to use some of these tell-tale fossils to identify these dinosaurs.
While fossil hunting in the San Juan Basin of New Mexico in 1919, the paleontologist Charles Gilmore discovered a few bony scutes, fossils similar to the armor of other ankylosaurs. When the specimens were re-examined over 80 years later, they were thought to represent a new genus and species, Glyptodontopelta mimus, but could a new kind of dinosaur be established on the basis of just a few bits of armor? In the new study, paleontologist Michael Burns compared the Glyptodontopelta material to new armor fossils found from the same area to determine if they could be used to tell the difference between different ankylosaurs.
Burns’ analysis showed that both Gilmore’s fossils and the new ones did, in fact, belong to Glyptodontopelta, and that this dinosaur was a nodosaurid. (Nodosaurids were a kind of armored dinosaur that, unlike many ankylosaurids, lacked a bony tail club.) More importantly, however, by looking at the details of the texture of the armor (the pits, pores, and furrows that mark each specimen), Burns was able to reliably differentiate between genera and, in some cases, species. Since the armor of ankylosaurs is common in many Cretaceous deposits, the comparison of the armor fossils has the potential to detect the presence of new genera or even species of armored dinosaurs that are otherwise unknown.
Still, as Burns points out in the paper, paleontologists do not yet have a good idea how the armor grew on any one individual over time, and it may be possible to mistake the armor of a young individual (or variations in the armor of among individuals) for a new kind of dinosaur. This was not the case with Glyptodontopelta, however, as various remains matched each other to the exclusion of other types of ankylosaur known from more complete skeletons. Great care must be taken in such comparisons, but at least in this case, the existence of a new genus of nodosaurid was confirmed.
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