Jaw mechanics and evolutionary paleoecology of the megaherbivorous dinosaurs from the Dinosaur Park Formation (upper Campanian) of Alberta, Canada

ABSTRACTThe question of what role differential jaw mechanics may have played in facilitating dietary niche partitioning among Late Cretaceous megaherbivorous dinosaurs from Laramidia is examined, using the fossil assemblage of the Dinosaur Park Formation as a test case. We use phylogenetic inference to reconstruct the mandibular adductor musculature of these animals, which we then apply to the construction of biomechanical lever models of the mandible to estimate relative bite forces. Our findings reveal predictably weak bite forces in ankylosaurs, and comparatively high bite forces in ceratopsids and hadrosaurids, both of which possessed a mechanical advantage that produced bite forces 2–3 times higher than those forces exerted by the adductor musculature. The impressive jaw mechanism shared by the last two taxa evolved in a stepwise fashion, independently in each lineage. There is tentative evidence to suggest that nodosaurids had more powerful bites than ankylosaurids, but the overall mechanical diversity among megaherbivores from the Dinosaur Park Formation is low, suggesting that differential jaw mechanics could have played only a subsidiary role in niche partitioning. Such mechanical conservatism may have may have been selected for, or it may simply reflect the limits imposed by evolutionary constraints. Regardless, mechanical disparity patterns remained stable throughout the ∼1.5 Ma evolution of the Dinosaur Park Formation megaherbivore chronofauna.SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP摘要 本研究以古地理区域拉腊米迪亚（Laramidia）晚白垩世的巨型植食恐龙类群为研究对象，以恐龙公园组（Dinosaur Park Formation）的化石组合作为测试案例，探讨颌骨力学差异在促进该类群食性生态位分化中所发挥的作用。我们通过系统发育推断重建了此类动物的下颌收肌（mandibular adductor musculature）形态，并以此为基础构建下颌生物力学杠杆模型，以估算相对咬合力。研究结果显示，甲龙类（ankylosaurs）的咬合力普遍较弱，而角龙类（ceratopsids）与鸭嘴龙类（hadrosaurids）的咬合力相对较强；后两类类群均具备机械优势，其咬合力可达收肌收缩产生力量的2至3倍。角龙类与鸭嘴龙类这两类后期类群所共有的高效颌骨力学机制，是在各自演化谱系中独立、逐步形成的。现有初步证据显示，结节龙类（nodosaurids）的咬合力要强于甲龙科（ankylosaurids），但恐龙公园组巨型植食恐龙类群整体的力学多样性较低，这表明颌骨力学差异在食性生态位分化中仅起到辅助作用。这种力学保守性可能是自然选择所青睐的性状，也可能仅仅反映了演化约束所带来的局限性。无论其成因如何，在恐龙公园组巨型植食时代动物群（megaherbivore chronofauna）约150万年的演化历程中，其力学差异模式始终保持稳定。补充数据——本文可于www.tandfonline.com/UJVP免费获取补充材料。