Jaw muscle reconstruction and vector analysis in ornithischian dinosaurs (17.4)

Abstract

Jaw muscle reconstruction has long been utilized for inferences in the paleobiology of ornithischian dinosaur feeding mechanisms. Previous studies in dinosaur jaw musculature have used extant phylogenetic bracketing methods to qualitatively compare muscle origins and insertions in a select few ornithischian genera. The current study uses criteria from previous jaw muscle studies, as well as more in‐depth case‐by‐case analyses, to reconstruct musculature and measure vector angles of the m. adductor mandibulae externus (MAME) complex as well as m. adductor mandibulae posterior (MAMP) in a large diversity of ornithischian taxa spanning all subclades. Results of both MAME and MAMP vectors show general trends from a mid‐range caudodorsal orientation in basal ornithischians and most armored thyreophorans to a decrease in vector angles indicating more caudally oriented jaw movements convergently in other taxa (e.g., derived thyreophorans, basal ornithopods, lambeosaurines, pachycephalosaurs, and derived ceratopsids). The extensive amount of variation in muscle vectors, both between and among subclades, however, suggests highly variable feeding mechanisms among genera and shows that feeding mechanisms of an entire subclade should not be based only on a single taxon, as has been previously done.