New scale type from a small-bodied hadrosaur in the Frenchman Formation of southern Saskatchewan: Potential implications for integumentary diversity in Edmontosaurus annectens

Abstract

Among non-avian dinosaurs, fossilized skin is most comprehensively represented in the hadrosaurids. Here we provide the first full descriptions of hadrosaurid skin from the Upper Cretaceous (Maastrichtian) Frenchman Formation in southern Saskatchewan. Based on the geological age and associated skeletal material, the specimen is tentatively identified as Edmontosaurus annectens. The fossil record of skin from E. annectens is one of the best represented of any non-avian dinosaur, and the scale structure and patterning have been previously described across nearly the entire body. However, the current specimen, which likely derives from the pelvic region, possesses unique corrugated scales that have not been observed in this species before. Additionally, although its body length is estimated to be approximately 75% of larger, presumably fully-grown individuals, histological evidence suggests that this specimen was somatically mature. This unique specimen expands the morphological diversity of scales observed in E. annectens, demonstrating a higher level of intraspecific variation in hadrosaurid skin than previously recognized. Additionally, this specimen also suggests that there is variability in the maximum body length reached by some adult E. annectens. Although the exact cause of the variation in adult size and scale morphology is yet to be understood, it highlights the potential intraspecific diversity not observable based on skeletal morphology alone. The unique scale morphology seen in this specimen also has potentially important implications for the taxonomic utility of hadrosaurid skin.