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
本研究以产自拉腊米迪亚（Laramidia）晚白垩世的巨型植食性恐龙类群为研究对象，以恐龙公园组（Dinosaur Park Formation）化石组合为验证案例，探讨颌骨力学差异在推动其生态位分化中所发挥的作用。我们采用系统发育推断（phylogenetic inference）方法重建了该类群的下颌收肌（mandibular adductor musculature）结构，随后基于此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）的咬合力整体偏弱，而角龙科（ceratopsids）与鸭嘴龙科（hadrosaurids）的咬合力相对较强；两类群均具备机械优势，其产生的咬合力可达下颌收肌收缩力的2~3倍。后两类类群共有的高效颌骨机制在各自演化支系中独立、逐步演化而来。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性恐龙整体的力学分异度较低，这表明颌骨力学差异在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青睐的结果，亦或仅仅反映了演化约束所带来的性能极限。无论成因如何，在恐龙公园组巨型植食性恐龙时代动物群约150万年的演化历程中，机械分异度格局始终保持稳定。

补充数据——本文可通过www.tandfonline.com/UJVP免费获取补充材料。