Insights into the Ecology and Evolutionary Success of Crocodilians Revealed through Bite-Force and Tooth-Pressure Experimentation

Abstract

BackgroundCrocodilians have dominated predatory niches at the water-land interface for over 85 million years. Like their ancestors, living species show substantial variation in their jaw proportions, dental form and body size. These differences are often assumed to reflect anatomical specialization related to feeding and niche occupation, but quantified data are scant. How these factors relate to biomechanical performance during feeding and their relevance to crocodilian evolutionary success are not known.Methodology/Principal FindingsWe measured adult bite forces and tooth pressures in all 23 extant crocodilian species and analyzed the results in ecological and phylogenetic contexts. We demonstrate that these reptiles generate the highest bite forces and tooth pressures known for any living animals. Bite forces strongly correlate with body size, and size changes are a major mechanism of feeding evolution in this group. Jaw shape demonstrates surprisingly little correlation to bite force and pressures. Bite forces can now be predicted in fossil crocodilians using the regression equations generated in this research.Conclusions/SignificanceCritical to crocodilian long-term success was the evolution of a high bite-force generating musculo-skeletal architecture. Once achieved, the relative force capacities of this system went essentially unmodified throughout subsequent diversification. Rampant changes in body size and concurrent changes in bite force served as a mechanism to allow access to differing prey types and sizes. Further access to the diversity of near-shore prey was gained primarily through changes in tooth pressure via the evolution of dental form and distributions of the teeth within the jaws. Rostral proportions changed substantially throughout crocodilian evolution, but not in correspondence with bite forces. The biomechanical and ecological ramifications of such changes need further examination.

Ontogeny of bite force in a validated biomechanical model of the American alligator

“…Erickson and colleagues conducted a series of studies that measured bite force in a growth series of American alligator (Erickson et al, 2003;Gignac and Erickson, 2015) and extant crocodylian species (Erickson et al, 2012(Erickson et al, , 2014. Across a size range of 31.5 to 405.5 cm total length, these studies found a positive allometric relationship (b) between maximum bite force and a variety of body size proxies, such as total length (b=2.62; isometry=2), snout-vent length (b=2.59; isometry=2), mass (b=0.79; isometry=0.667) and head length (b=2.75; isometry=2).…”

Human-crocodile conflict and conservation implications of Saltwater Crocodiles Crocodylus porosus (Reptilia: Crocodylia: Crocodylidae) in Sri Lanka

“…The Saltwater Crocodile is the largest living reptile on Earth; it can grow up to 6-7 m (Webb et al 1978;Whitaker & Whitaker 2008;Erickson et al 2012). Like other crocodilians it is an opportunistic feeder, using active hunting or 'sit and wait' strategies (Cooper & Jenkins 1993), and the frequency of different prey items varies significantly with habitat and body size (Taylor 1979;Webb & Manolis 1989).…”

Structure, innervation and response properties of integumentary sensory organs in crocodilians

“…For example, the ISOs of crocodylids are found across their entire body and are thus poorly situated for receiving surface waves. In alligators, the highest densities of ISOs are found around the teeth, inside the mouth,and at the rostral margins of the mandibles and maxilla, suggesting a role in discriminating food items or determining appropriate bite force (Erickson et al, 2012). Reflecting this uncertainty regarding their functions, these receptors have also been identified as 'integumentary osmoreceptors' in respect to the body receptors found in crocodylids (Jackson and Brooks, 2007).…”