Crocodylian Snouts in Space and Time: Phylogenetic Approaches Toward Adaptive Radiation

Abstract

Recent phylogenetic analyses of fossil and living crocodylians allow us to compare the taxonomic, geographic, and temporal distributions of morphological features, such as snout shapes. A few basic snout morphotypes—generalized, blunt, slender, deep, and excessively broad (“duck-faced”)—occur multiple times in distantly-related lineages. Some clades—especially those found in the Northern Hemisphere or with minimum origination dates in the Cretaceous or lower Tertiary—are morphologically uniform, but geographically widespread; crocodylian faunas of the early Tertiary tend to be composite, with sympatric taxa being distantly related, and similar-looking taxa on different continents being close relatives. In contrast, crocodylian faunas of the later Tertiary tend to be more endemic, with local adaptive radiations occurring in Africa and Australia containing members of most basic snout shapes. Endemic radiations in Africa and Australia have largely been replaced by Crocodylus, which can be divided into subclades that may individually represent endemic adaptive radiations.