A comprehensive report on the morphology of the scales adorning the iconic horned theropod dinosaur, Carnoturus sastrei

The scaly skin of the abelisaurid Carnotaurus sastrei (Theropoda: Ceratosauria) from the Upper Cretaceous of Argentina.

By: Christophe Hendrickx and Phil R. Bell

Summarized by: Israel J. Rivera-Molina, a senior Geology major at the University of South Florida. He plans to attend graduate school in paleontology in order to start a career within the field of dinosaur morphology and evolution. 

What data were used? The holotype (i.e., the fossil specimen that ‘defines’ a species) of Carnotaurus, which was recovered from La Colonia Formation in Argentina; scientists also looked  at skin casts and 3D models of various other dinosaur taxa.

Methods: In this study, fossilized skin impressions of Carnotaurus were studied and a 3D model was generated using a camera and various imaging softwares. The skin was examined and then compared to various other taxa of dinosaurs from repositories, museums and other places where researchers keep fossils, from around the world.

Results: The scales covering the Carnotaurus (Figure 1) were found to be different in shape, size, orientation, and distribution. It was previously thought that the scales of the Carnotaurus were the same throughout the animal’s body, but it turns out that that is not the case. On the contrary, the scales were diverse: coming in six different shapes from elliptical to diamond-shaped scales. The scales also differed in textures ,ranging from smooth to granular, and were oriented in more than one way depending on which part of the body being observed. The tail especially displayed scales of a wide array of shapes that were arranged in various directions, while also ranging in size. 

A slab of preserved Carnotaurus skin containing grooved skin and circular scales; important scaled features circled to show which parts were measured by the researchers. There are 17 marked features, but none are discussed in depth in this summary here.
Figure 1: Portion of the skin located on the tail of Carnotaurus; outlined are the areas containing scale structures whose areas were measured by Hendrickx and Belll this was done to categorize the size and shape of the scales, compared to scales on other regions of the body.

Why is the study important? This study is important because it calls to attention the lack of emphasis placed on the research done on the skin of the Carnotaurus. Carnotaurus has some of most well-preserved scales amongst the theropods (the bipedal, carnivorous dinosaurs), yet past articles made little to no mention of the skin of the dinosaur. The authors also suggested that regarding the function of scales, scientists should think outside the box when comparing dinosaurs to extant lifeforms. They encourage researchers to not be afraid to venture away from reptilian analogues to attempt to discern what use(s) the scales served.

Big picture: This research provided a more in-depth look into the architecture of the scales covering the Carnotaurus. This body of work encourages scientists to look at and think more critically about the scales of dinosaurs, not only to reconstruct their appearance, but also to possibly discern some of their behaviors. Whether the scales served as a means of thermoregulation or as sexual display structures, further studies done on scales can lead to a greater understanding of how extinct dinosaurs lived.

Citation: Hendrickx, C., Bell, P. B., 2021, The scaly skin of the abelisaurid Carnotaurus sastrei (Theropoda: Ceratosauria) from the Upper Cretaceous of Patagonia. Cretaceous Research, p. 1-18. https://doi.org/10.1016/j.cretres.2021.104994

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