Data from: Testing adaptive hypotheses of convergence with functional landscapes: a case study of bone-cracking hypercarnivores

Morphological convergence is a well documented phenomenon in mammals, and adaptive explanations are commonly employed to infer similar functions for convergent characteristics. I present a study that adopts aspects of theoretical morphology and engineering optimization to test hypotheses about adaptive convergent evolution. Bone-cracking ecomorphologies in Carnivora were used as a case study. Previous research has shown that skull deepening and widening are major evolutionary patterns in convergent bone-cracking canids and hyaenids. A simple two-dimensional design space, with skull width-to-length and depth-to-length ratios as variables, was used to examine optimized shapes for two functional properties: mechanical advantage (MA) and strain energy (SE). Functionality of theoretical skull shapes was studied using finite element analysis (FEA) and visualized as functional landscapes. The distribution of actual skull shapes in the landscape showed a convergent trend of plesiomorphically low-MA and moderate-SE skulls evolving towards higher-MA and moderate-SE skulls; this is corroborated by FEA of 13 actual specimens. Nevertheless, regions exist in the landscape where high-MA and lower-SE shapes are not represented by existing species; their vacancy is observed even at higher taxonomic levels. Results highlight the interaction of biomechanical and non-biomechanical factors in constraining general skull dimensions to localized functional optima through evolution.

形态趋同（morphological convergence）是哺乳动物中已有充分文献记载的现象，学界通常借助适应性解释来推断趋同特征的相似功能。本研究借鉴理论形态学与工程优化的相关思路，对适应性趋同演化的假说进行检验，以食肉目（Carnivora）中的碎骨生态形态型为案例对象。既往研究显示，颅骨加深与加宽是趋同演化的碎骨类犬科与鬣狗科物种的核心演化模式。本研究构建以颅骨宽长比、深长比为变量的二维设计空间，用以探究两种功能属性的优化形态：机械优势（mechanical advantage, MA）与应变能（strain energy, SE）。通过有限元分析（finite element analysis, FEA）对理论颅骨形态的功能特性展开研究，并将结果可视化为功能景观。功能景观中实际颅骨形态的分布呈现出一条趋同演化轨迹：祖征性的低机械优势、中等应变能颅骨逐步演化至高机械优势、中等应变能的形态；对13件实际标本的有限元分析结果也佐证了这一趋势。尽管如此，功能景观中仍存在高机械优势与低应变能的形态区域，未被现生物种占据，甚至在更高分类阶元中也未发现此类形态。本研究结果揭示了生物力学与非生物力学因素间的相互作用，该作用通过演化过程将颅骨整体形态约束于局域功能最适点。