Epidermal scale growth, allometry and function in non‐avian dinosaurs and extant reptiles

Abstract

Epidermal scales in sauropsids perform a wide array of biological functions, whichcan relate to their shape and size. Accordingly, growth-relatedchanges in scalemorphology may reflect distinct functions between juvenile and adult individuals,such as use in mating interactions. Such patterns are poorly explored in bothextant reptiles and non-aviandinosaurs, limiting functional interpretations. Here,we investigate scale growth in the ornithischian ceratopsid Chasmosaurus belli andhadrosaurid Prosaurolophus maximus by comparing scale morphologies betweenjuveniles and adults of each taxon. Scale shape is generally consistent across growthstages in both taxa, and changes in C. belli feature scale length cannot reject isometry.However, there is a greater increase in C. belli feature scale width. In practical terms,the magnitude of these size differences rejects the hypothesis that feature scalemorphology played a role in mating interactions, suggesting instead that their sizewas largely non-adaptive.To contextualise the patterns in the sampled dinosaurs, weassessed scale growth and allometry using an ecologically diverse sample of eightextant reptile species belonging to Crocodylidae, Scincidae, Elapidae and Pythonidae.While isometry is the overall most frequent pattern of scale growth in our sampleof extant reptiles, most species demonstrate positive scale allometry in at least onearea of their bodies, which is likely a response to changing body proportions. Scaleshapes in the studied extant species, as in both dinosaurs, are largely retained throughgrowth. This study provides the first detailed assessment of skin growth in non-aviandinosaurs, supporting morphological stasis in the growth of most of their scales.