DIET OF ORNITHOCHEIROID PTEROSAURS INFERRED FROM STABLE CARBON ISOTOPE ANALYSIS OF TOOTH ENAMEL

The stable carbon isotope composition of structural carbonate within ornithocheiroid pterosaur tooth enamel is analyzed to determine dietary preferences. These data are compared with the δ¹³C values of enamel/enameloid of contemporary terrestrial and aquatic consumers in order to determine if toothed ornithocheiroids were exclusively marine piscivores or if some also exploited terrestrial food sources. Enamel and enameloid samples were acquired from the teeth of pterosaurs, theropod dinosaurs, pycnodont fish, and sharks collected from nearshore and marginal marine deposits in the Lower Cretaceous Twin Mountains and Paw Paw formations in north Texas. The δ¹³C values of pterosaur enamel from the Aptian Twin Mountains Formation range from -7.7 to -4.4‰ PDB, with an average of -5.9‰. In contrast, the δ¹³C values of pterosaur enamel from the Albian Paw Paw Formation are consistently more positive, ranging from -2.4 to -0.2‰ PDB, with an average value of -1.2‰. Within both the Aptian and Albian datasets, pterosaur tooth enamel is characterized by more negative δ¹³C values, on average, than the teeth of aquatic taxa (pycnodonts and sharks), but the δ¹³C values of the Aptian pterosaur teeth show substantial overlap with those of the theropod teeth. These results suggest that ornithocheiroid pterosaurs in the Twin Mountains Formation, like theropods, preyed primarily on terrestrial taxa, whereas pterosaurs in the Paw Paw Formation included some marine taxa in their diet. The elongate, conical tooth crowns found in many ornithocheiroid pterosaurs are often cited as evidence of piscivory, but isotopic evidence of terrestrial resource utilization indicates that tooth morphology is not always a reliable indicator of diet in pterosaurs.