Pterosaur dietary hypotheses: a review of ideas and approaches

Abstract

Pterosaurs are an extinct group of Mesozoic flying reptiles, whose fossil record extends from approximately 210 to 66 million years ago. They were integral components of continental and marginal marine ecosystems, yet their diets remain poorly constrained. Numerous dietary hypotheses have been proposed for different pterosaur groups, including insectivory, piscivory, carnivory, durophagy, herbivory/frugivory, filter-feeding and generalism. These hypotheses, and subsequent interpretations of pterosaur diet, are supported by qualitative (content fossils, associations, ichnology, comparative anatomy) and/or quantitative (functional morphology, stable isotope analysis) evidence. Pterosaur dietary interpretations are scattered throughout the literature with little attention paid to the supporting evidence. Reaching a robustly supported consensus on pterosaur diets is important for understanding their dietary evolution, and their roles in Mesozoic ecosystems. A comprehensive examination of the pterosaur literature identified 314 dietary interpretations (dietary statement plus supporting evidence) from 126 published studies. Multiple alternative diets have been hypothesised for most principal taxonomic pterosaur groups. Some groups exhibit a high degree of consensus, supported by multiple lines of evidence, while others exhibit less consensus. Qualitative evidence supports 87.3% of dietary interpretations, with comparative anatomy most common (62.1% of total). More speciose groups of pterosaur tend to have a greater range of hypothesised diets. Consideration of dietary interpretations within alternative phylogenetic contexts reveals high levels of consensus between equivalent monofenestratan groups, and lower levels of consensus between equivalent non-monofenestratan groups. Evaluating the possible non-biological controls on apparent patterns of dietary diversity reveals that numbers of dietary interpretations through time exhibit no correlation with patterns of publication (number of peer-reviewed publications through time). 73.8% of dietary interpretations were published in the 21st century. Overall, consensus interpretations of pterosaur diets are better accounted for by non-biological signals, such as the impact of the respective quality of the fossil record of different pterosaur groups on research levels. That many interpretations are based on qualitative, often untestable lines of evidence adds significant noise to the data. More experiment-led pterosaur dietary research, with greater consideration of pterosaurs as organisms with independent evolutionary histories, will lead to more robust conclusions drawn from repeatable results. This will allow greater understanding of pterosaur dietary diversity, disparity and evolution and facilitate reconstructions of Mesozoic ecosystems.

Pterosaurs ate soft-bodied cephalopods (Coleoidea)

“…A large number of taxa from the Solnhofen Archipelago, including 'fishes' and marine reptiles, supposedly fed on aquatic organisms such as cephalopods 4,9,[49][50][51][52] . The conical, slender and recurved shape of the tooth excludes several groups of fish and reptiles as possible culprits.…”

“…Interpreting ecological relationships between extinct taxa based on the spatial association of specimens can be flawed if taphonomic biases, such as post-mortem specimen transport, are not taken into consideration 4,64 . However, abiotic explanations for the association of Plesioteuthis and Rhamphorhynchus can be ruled out for several reasons: 1) As reflected in the perfectly horizontally bedded sediments, the lagoons of the Solnhofen Archipelago are generally regarded as a low energy depositional environment barring storm events 52 .…”

“…Direct evidence of pterosaurs as predators is currently restricted to fossil gut and throat contents. Fish, crustaceans and tetrapods have been identified from stomach contents from several pterosaur taxa 4,65 (and references therein). Such stomach contents are most often preserved with Rhamphorhynchus and confidently identified remains are currently limited to fish 65 .…”

“…Such stomach contents are most often preserved with Rhamphorhynchus and confidently identified remains are currently limited to fish 65 . A coprolite assigned to Rhamphorhynchus was interpreted to have contained coleoid arm hooklets 14 , although this interpretation has since been challenged 4 . Speculative cases of attempted pterosaur feeding involve odonatan insects from the Solnhofen Archipelago with damaged wings 65 (and references therein).…”

“…There is a general lack of agreement concerning pterosaur feeding behaviour 4 . In the case of our specimen, some conclusions on behaviours can be drawn with some reservation.…”