Diet of bird-like troodontid dinosaurs: synthesis of a contentious clade

Troodontidae is a clade of small-to medium-sized maniraptoran theropods that mainly lived in Laurasia (modern Asia, North America and Europe) during the Jurassic and Cretaceous periods and are believed to have had a variety of diets. The uniqueness of troodontid teeth suggests that they diverged from the typical flesh-based diet of non-avian theropods. Some Asian troodontids even lack tooth serrations completely, which has been linked to herbivory or omnivory. However, troodontids still possessed multiple traits suited for predation. These include a large curved second pedal digit; laterally compressed, curved, and serrated teeth; and 'puncture-and-pull' microwear on their teeth. Extrinsic evidence, such as stomach contents and gastric pellets, supports a diverse dietary intake among troodontids with evidence that they ingested both plant and animal material. Environmental, morphological, and biogeochemical analyses suggest that the iconic North American troodontid, Troodon, was likely to have been omnivorous, potentially preying on both plants and small animals, such as mammals and baby dinosaurs (hatched or unhatched). Our understanding of different diets among troodontids remains limited due to the sparsity of both relevant fossil material and palaeodiet research. Nevertheless, what information we have on troodontid diet informs ancestral deinonychosaurian and paravian diets, which we suggest were omnivorous. We encourage research into troodontids outside the Late Cretaceous of North America and further study of troodontid biogeochemistry and postcranial anatomy to improve our understanding of troodontid diet and the larger story of theropod ecological diversity.