SPINOSAURS AS PHYTOSAUR MIMICS: A CASE OF CONVERGENT EVOLUTION BETWEEN TWO EXTINCT ARCHOSAURIFORM CLADES

Abstract

Spinosaurids are a highly morphologically specialized clade of large tetanuran theropod dinosaurs, characterized by their proportionally long, narrow snouts and conical teeth with fluted surfaces. The unusual morphology of spinosaurids has been usually compared with modern crocodilians, but distinct differences between them have been reported as well. Here, numerous craniodental characters that are shared by spinosaurids and large, robust phytosaurs often termed as “brachyrostral” forms are reviewed. Phytosaurs are a clade of carnivorous archosauriforms that resemble crocodilians in overall morphology, and as such a similar lifestyle has been inferred for them as well. Although based on preliminary observations, the shared craniodental characters of spinosaurids and “brachyrostral” phytosaurs, including those not shared with crocodilians, raise the possibility that at least some aspects of the lifestyle of these extinct archosauriform clades were more similar to each other rather than to that of crocodilians.