Incorporating Trace Fossils when Exploring the Interplay of Form and Function in the Crocodyliform Feeding Apparatus

Abstract

Many crocodylians, both living and extinct, fill the semi‐aquatic ambush predator niche, and their prey preferences roughly can be predicted based on a combination of snout shape, tooth morphology, and body size. Among extant crocodylians, slender‐snouted taxa such as Gavialis gangeticus and Tomistoma schlegelii generally prefer smaller‐bodied prey, whereas the broader‐snouted taxa divide into generalists like Crocodylus niloticus and macro‐generalists like Alligator mississippiensis, who will eat a diversity of prey items including animals that are as big or even bigger than themselves. Large‐bodied members of these generalist ecomorphotypes generate the highest bite forces observed in modern taxa and are often apex predators in their ecosystems. The availability of a robust phylogenetic hypothesis for crocodylians makes them an excellent clade with which to explore these types of ecomorphological hypotheses, which link form and function in the feeding apparatus within an evolutionary framework. The resulting synthesis of extant and extinct datasets has provided both exciting new insights, but also some complications. The addition of extinct taxa into studies of morphological disparity, both within the crown group and deeper in the crocodyliform evolutionary tree, introduce a diverse array of snout shapes and associated niches that are not represented in the surviving members of the clade (e.g. fully marine, fully terrestrial, durophagous, omnivorous, and even possibly herbivorous forms). Though hypotheses regarding diet in these diverse groups are based on craniodental morphology, indirect evidence, in the form of trace fossils, provides an independent means of testing those predictions. Gut contents are extremely rare in this clade because of the highly destructive digestion of crocodyliforms, and coprolites, though comparatively common, contain remains that are so degraded as to be largely unidentifiable and uninformative. Isotopic and dental microwear studies can provide broad patterns of diet. However, for detailed, direct evidence of crocodyliform feeding, bite marks are a particularly useful source of direct evidence with which to explore patterns of diet in this clade. A recent, concentrated effort to characterize modern crocodylian bite marks has resulted in the identification of novel patterns and diagnostic traces associated with feeding behavior in that clade. These trace fossils provide critical insights into diet, feeding strategy, and even intraspecific competition in crocodyliforms and their extinct relatives. By integrating these ichnological data with traditional dietary hypotheses based on morphology and phylogeny of extinct groups, a more complete, and oftentimes more complex and realistic, concept of past ecosystems and trophic structures can be explored.Support or Funding InformationFunding provided by the National Science Foundation, the Leakey Foundation, and National Geographic.