Variation in parrot jaw musculature.

Psittaciformes, the order encompassing parrots and their relatives, are highly diverse and generally known for having a strong beaks used for multiple behaviors. The muscles related to the masticatory apparatus should reflect this functional complexity; however, few studies have described the cranial myology across the order. Through original dissections, we describe and compare the masticatory musculoskeleton of 27 species-the most taxonomically diverse sample of psittaciformes to date. As in previous studies, we found osteological differences in the configuration of the suborbital arch, zygomatic process, and temporal fossa, and while most muscles are relatively similar across the order, there are notable exceptions found in the morphology of the m. pseudomasseter, m. adductor mandibulae externus, pars rostralis, and a venter externus portion of the m. pterygoideus ventralis, pars lateralis. Our findings reinforce the amazing anatomical diversity found within this group-data that can be incorporated into future studies of the biomechanics and diversification of this order. Further analysis should focus on (a) filling in more of the remarkable number of species across the order, especially uncommon and functionally interesting taxa unavailable in the present study, (b) examining dietary specialization to understand whether dietary adaptive signals are encoded within this anatomy, and (c) advancing to anatomical studies with other techniques such as DiceCT to visualize the relationship and biomechanics of these muscles in 3D space and be able to evaluate specimens relatively non-destructively, a priority for hard-to-dissect (e.g., small) taxa and (e.g., rare) specimens that collections wish to more fully preserve.