August 16, 2012
Ankylosaurs can be frustrating dinosaurs. In life, armor covered the bodies of these dinosaurs from snout to tail, but those bony adornments often fell out of place between the death and ultimate burial of the ankylosaurs. Reconstructing an ankylosaur, therefore, requires that paleontologists not only figure out the articulations of the bones but also the arrangement of the armor. Every now and then, though, researchers discover one of these dinosaurs with some armor still in place. According to an in-press Acta Palaeontologica Polonica paper, ankylosaur expert Victoria Arbour and colleagues have just identified one such specimen from the Late Cretaceous of Mongolia.
The dinosaur in question is most likely a specimen of Tarchia–an ankylosaur that could grow to about 26 feet long and, like many of its close relatives, carried a tail club. Rather than being a brand new find, though, this Tarchia was originally discovered in 1971 during the Polish-Mongolian Palaeontological Expedition and was sent to the Geological Museum in Oslo, Norway in 1998. Now, after over three decades, the dinosaur gets its time in the scientific spotlight.
What makes this Tarchia so significant isn’t the completeness of the skeleton. Only the left side of the back half of the body, including most of the tail, is preserved. What’s special is that parts of the dinosaur’s armor are still in place, including triangle-shaped bits of armor along the dinosaur’s slender tail and impressions of the tough sheaths that covered some of the armor in life. Indeed, the bony armor of dinosaurs was not exposed to the outside but was covered in a hard keratinous coating–horns, claws, plates and spikes were all covered in this, often making weapons sharper and ornaments more expansive.
While such soft tissue fossils are relatively rare, Arbour and her co-authors follow what paleontologist Phil Bell recently suggested on the basis of hadrosaur skin impressions–that preserved soft tissue impressions such as these might eventually be useful in distinguishing between different genera or species of dinosaur. In fact, this may be particularly important in cases like this exceptional ankylosaur. While the specimen is most similar to other specimens of Tarchia, it also differs in some minute tail characteristics. Are the differences the result of growth or individual variation, or could they be signs of a previously-unrecognized species? Detailed comparisons of skin impressions, in addition to skeletal differences, may help paleontologists winnow down the possibilities. We just need a better collection of ankylosaur soft tissue traces first.
Arbour, V.M., Lech-Hernes, N.L., Guldberg, T.E., Hurum, J.H., and Currie P.J. (2012). An ankylosaurid dinosaur from Mongolia with in situ armour and keratinous scale impressions Acta Palaeontologica Polonica DOI: 10.4202/app.2011.0081
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