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Using Museum’s CT Scanner, Researcher Makes Defensive Discovery

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This image of a Pseudocordylus subviridis highlights its tail armor. Image: © AMNH/E. Stanley


Edward Stanley, a doctoral candidate in comparative biology at the Museum’s Richard Gilder Graduate School, made a surprising discovery using the Museum’s new state-of-the-art CT scanner: the presence of tiny osteoderms, or bony plates, along the legs of the craglizard Pseudocordylus subviridis. This particular lizard was thought to have such plates, which are believed to serve as protective armor, only on its head and tail.

A graduate of the University of St. Andrews in Scotland with a master’s degree from Villanova, Stanley is aiming to tease apart the evolutionary history of a family of African “girdled lizards” (Cordylidae). Osteoderms are embedded in the skin and not attached to the skeleton, exactly the kind of evidence that can be disturbed in dissection. Seeing these features in place using the CT scanner gives him a set of clearly defined characteristics for sorting out the relationships among species. This technique, says Stanley, “allows you to see traits and patterns that were simply not observable before.”

Girdled lizards are vulnerable to predators from the air and on the ground. It appears that the slower-moving the species, the more heavily they are armored, presumably protecting them from attacks by mongooses, snakes, and other land predators. The less-armored species seem to have evolved a quickness needed to evade dive-bombing birds. While it is too early to say for certain, Stanley’s research, which focuses on the correlation between amount of armor and speed, suggests that Pseudocordylus subviridis fits the latter category. Several members of this lizard family live high up in the mountains where avian predators are common, and this lightly armored form has evolved multiple times independently in these environments.

A version of this story originally appeared in the Winter issue of Rotunda, the magazine for Museum Members.

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