STL Science Center

STL Science Center

11 March 2016

Difficulty in Ancestry

The skulls of some animals are strangely similar to animals that they are exceedingly distantly related to. We can understand the similarities in the context of convergent evolution; animals that require extreme biting forces develop similarly strong muscles and similarly shaped skulls to house the attachments of those muscles. Generally we only discuss the morphologies as how they occur and are similar and not the time at which they occur, geologically speaking. Therefore, we can discuss how an animal like Prestosuchus chiniquensis living in the Triassic of Brazil has a skull that looks considerably like that of a Cretaceous tyrannosaurid. Prestosuchus is only related to tyrannosaurs in that they are both archosaurs as the dinosaurs, and therefore tyrannosaurids, diverged from the early suchians, ancestors of modern crocodilians. The skulls of tyrannosaurids and Prestosuchus are deep and filled with large serrated teeth and have been mistaken for one another many times because of their similarities. The skull of Prestosuchus is not as air filled and lightweight (relative to size) as a tyrannosaurid skull, however. Skulls of Prestosuchus are clearly strong and beginning to show some of the solidifying characteristics of its descendants. Prestosuchus as a genus belongs nestled with Rauisuchia (by some accounts a wastebin group), a group of early Triassic archosaurs within Pseudosuchia that contains some fierce looking reptiles that, unlike their descendants, stood with a specialized erect posture and were definitely much more terrestrial than their descendants would eventually become.
AMNH, photo by Vince Smith

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