Dietary differences in archosaur and lepidosaur reptiles revealed by dental microwear textural analysis

Abstract

Reptiles are key components of modern ecosystems, yet for many species detailed characterisations of their diets are lacking. Data currently used in dietary reconstructions are limited either to the last few meals or to proxy records of average diet over temporal scales of months to years, providing only coarse indications of trophic level(s). Proxies that record information over weeks to months would allow more accurate reconstructions of reptile diets and better predictions of how ecosystems might respond to global change drivers. Here, we apply dental microwear textural analysis (DMTA) to dietary guilds encompassing both archosaurian and lepidosaurian reptiles, demonstrating its value as a tool for characterising diets over temporal scales of weeks to months. DMTA, involving analysis of the three-dimensional, sub-micrometre scale textures created on tooth surfaces by interactions with food, reveals that the teeth of reptiles with diets dominated by invertebrates, particularly invertebrates with hard exoskeletons (e.g. beetles and snails), exhibit rougher microwear textures than reptiles with vertebrate-dominated diets. Teeth of fish-feeding reptiles exhibit the smoothest textures of all guilds. These results demonstrate the efficacy of DMTA as a dietary proxy in taxa from across the phylogenetic range of extant reptiles. This method is applicable to extant taxa (living or museum specimens) and extinct reptiles, providing new insights into past, present and future ecosystems.

Dietary diversity and evolution of the earliest flying vertebrates revealed by dental microwear texture analysis

“…1a-f for examples of digital elevation models of extant reptile and pterosaur tooth surfaces from which texture data were acquired. As previously reported 18 , four texture parameters differ significantly between reptile guilds (ANOVA; Supplementary Data 3 and 4) and principal components analysis separates them in a texture-dietary space defined by PC axes 1 and 2 ( Fig. 2 and Supplementary Fig.…”

“…beetles, crustaceans and shelled gastropods); 'softer' invertebrate consumers (e.g. grasshoppers); omnivores; and piscivores (fish consumers) 18 ( Supplementary Fig. 1 and Supplementary Data 1 and 2).…”

“…Specimen availability enabled Crocodylus porosus to be sampled as two separate life-history groups for analysis. Specimens with lower jaw lengths of less than 50 cm were classified as juveniles; specimens with jaw lengths exceeding 50 cm were classified as adults 18,61 .…”

“…Analyses use standardised texture parameters 14,19 to quantify microwear, and thus dietary, differences between species and/or populations and therefore do not assume direct relationships between the morphology and inferred functions of teeth 14,15,17 . Recent work has demonstrated that DMTA of non-occlusal (non-chewing) tooth surfaces of extant reptiles, including archosaurs (the clade to which pterosaurs belong), differs between dietary guilds 18,20 . This relationship between microwear texture and diet in taxa that do not chew food items provides a robust multivariate framework for this study, allowing us to quantitatively test and constrain pterosaur dietary hypotheses, and to explore dietary shifts within this clade across evolutionary time.…”

“…We use DMTA to test three hypotheses: that pterosaur teeth preserve evidence of dietary differences between taxa, between sympatric species and between ontogenetic stages of the same species. Our hypothesis testing uses the multivariate framework provided by DMTA of extant reptiles 18 as well as additional, independent tests using a DMTA framework derived from the non-occlusal tooth surfaces of bats, the only extant group of dentulous flying vertebrates (given the differences between bats, extant reptiles and pterosaurs, consilience in the results of these independent analyses represents a very stringent test of our approach). Our results allow us to propose a number of specific dietary interpretations, including carnivores, piscivores and invertebrates consumers, and to distinguish between dietary specialists and pterosaurs that consumed a range of different prey types.…”