Beak morphology and limb proportions as adaptations of hadrosaurid foraging ecology

Abstract

Hadrosauridae, consisting of two subfamilies (Hadrosaurinae and Lambeosaurinae), is a successful herbivorous dinosaur group that established a high taxonomic diversity and a cosmopolitan biogeographic distribution during the Late Cretaceous. While its success is often attributed to a highly specialized oral processing system, the foraging strategy of this group remains unclear. This study focuses on two critical factors in foraging strategy, food selectivity and locomotor ecology, in these hadrosaurid subfamilies. Three-dimensional beak shapes and limb segment proportions are used as the proxies for food selectivity and locomotor ecology, respectively. The beak shape analysis demonstrates trends of anteriorly acute beaks in hadrosaurines and anteriorly wide beaks in lambeosaurines. The limb segment proportion analysis shows short proximal limb segments in hadrosaurines and long proximal limb segments in lambeosaurines. These results suggest that hadrosaurines preferred selective consumption of high-quality food with energy-inefficient locomotor ecology, while lambeosaurines preferred mass consumption of low-quality food with energy-efficient locomotion and that differences in foraging strategy might have enhanced dietary niche partitioning in the subfamily level of hadrosaurids. In addition, this study tests a relationship between limb proportions and habitat environments in hadrosaurids. We demonstrate that hadrosaurids from the coastal environments have shorter forelimbs than those from the terrestrial environment. Since short forelimbs are better suited for temporal bipedalism than long forelimbs, the limb proportion difference may indicate adaptations to different feeding heights, possibly due to different regional vegetations.