Data from: Do convergent ecomorphs evolve through convergent morphological pathways? Cranial shape evolution in fossil hyaenids and borophagine canids (Carnivora, Mammalia)

Cases of convergent evolution, particularly within ecomorphological contexts, are instructive in identifying universally adaptive morphological features across clades. Tracing of evolutionary pathways by which ecomorphological convergence takes place can further reveal mechanisms of adaptation, which may be strongly influenced by phylogeny. Ecomorphologies of carnivorous mammals represent some of the most outstanding cases of convergent evolution in the Cenozoic radiation of mammals. This study examined patterns of cranial shape change in the dog (Canidae) and hyena (Hyaenidae) families, in order to compare the evolutionary pathways that led to the independent specialization of bone-cracking hypercarnivores within each clade. Geometric morphometrics analyses of cranial shape in fossil hyaenids and borophagine canids provided evidence for deep-time convergence in morphological pathways toward the independent evolution of derived bone-crackers. Both clades contained stem members with plesiomorphic generalist/omnivore cranial shapes, which evolved into doglike species along parallel pathways of shape change. The evolution of specialized bone-crackers from these doglike forms, however, continued under the constraint of a full cheek dentition and restriction on rostrum length reduction in canids, but not hyaenids. Functionally, phylogenetic constraint may have limited borophagine canids to crack bones principally with their carnassial instead of the third premolar as in hyaenids, but other cranial shape changes associated with durophagy nevertheless evolved in parallel in the two lineages. Size allometry was not a major factor in cranial shape evolution in either lineage, supporting the interpretation of functional demands as drivers for the observed convergence. The comparison between borophagines and hyaenids showed that differential effects of alternative functional “solutions” that arise during morphological evolution may be multiplied with processes of the “macroevolutionary ratchet” already in place to further limit the evolutionary pathways available to specialized lineages.趋同演化案例，尤其是在生态形态学（ecomorphological）语境下，对于识别不同演化支（clades）间具有普遍性的适应性形态特征具有重要指导意义。追溯驱动生态形态趋同的演化路径，可进一步揭示适应性演化机制——此类机制往往受到系统发育（phylogeny）的强烈影响。食肉哺乳动物的生态形态特征，是新生代（Cenozoic）哺乳动物辐射演化中最具代表性的趋同演化案例之一。本研究聚焦犬科（Canidae）与鬣狗科（Hyaenidae）的颅骨形态（cranial shape）变化模式，旨在对比两个演化支中独立演化出碎骨特化超食肉动物（bone-cracking hypercarnivores）的路径。针对化石鬣狗类（fossil hyaenids）与恐犬亚科犬类（borophagine canids）的颅骨形态开展几何形态测量学（Geometric morphometrics）分析，结果证实二者在通向特化碎食者的形态演化路径上存在深层趋同。两个演化支均包含具有祖征（plesiomorphic）广食性/杂食性（generalist/omnivore）颅骨形态的基干类群，二者均沿平行的形态变化路径演化出类犬物种。然而，从类犬形态向特化碎食者的演化过程中，犬科类群受到完整颊齿列与吻长缩短（rostrum length reduction）受限的演化约束，而鬣狗科类群则无此限制。从功能层面来看，系统发育约束可能使得恐犬亚科犬类主要通过裂齿（carnassial）啃咬骨头，而非鬣狗科类群所用的第三前臼齿，但二者与硬食性（durophagy）相关的其他颅骨形态变化仍呈现平行演化特征。大小异速生长（size allometry）并非两个类群颅骨形态演化的主要影响因素，这一结果支持“功能需求是观测到的趋同演化的驱动因素”这一学术解读。对恐犬亚科类群与鬣狗科类群的对比分析显示，形态演化过程中出现的不同功能“解决方案”所产生的差异化效应，可与已存在的“宏观演化棘轮（macroevolutionary ratchet）”过程共同作用，进一步限制特化演化支可选择的演化路径。