ABSTRACT

Sabertooth craniodental adaptations have evolved numerous times amongst carnivorous mammals. Some of the most extreme sabertooth adaptations are found within the carnivoran subfamily Barbourofelinae. However, the evolutionary origins of this group have been uncertain for more than 170 years, with variable placement as an independent case of sabertooth acquisition, as a clade within the Nimravidae (Eocene to Oligocene ‘false sabertooth cats’), or as a member of the Machairodontinae (true sabertooth cats such as Smilodon). Here we present a novel approach to assessing the validity of three independent sabertooth clades within Carnivora. We performed a total-evidence Bayesian analysis in Beast2 across all major carnivoran families, using the fossilized birth-death (FBD) model and incorporating 223 morphological characters, nuclear and mitochondrial gene sequences, and stratigraphic occurrence data. Our results place barbourofelines as terminal members of the Nimravidae, sister to the Nimravini (0.91 posterior probability), a relationship not found in prior cladistic studies. Ancestral area estimation performed in the R package BioGeoBEARS best supports a primarily European paleobiogeographic center for the barbourofelines with multiple dispersal events to other continents, a finding in direct opposition to past hypotheses for this group. Furthermore, new patterns in convergence between nimravids and machairodontines were revealed via Bayesian ancestral state estimation in BayesTraits. Results support a hypothesis of cats copying nimravids, and nimravids cats in certain aspects of sabertooth morphology, and not total evolutionary independence of these features as typically envisioned.

摘要

剑齿虎的颅牙适应性在食肉哺乳动物中进化了很多次。在食肉动物亚科 Barbourofelinae 中发现了一些最极端的剑齿虎适应性。然而，170 多年来，这个群体的进化起源一直不确定，作为剑齿虎获得的独立案例，作为 Nimravidae 中的一个分支（始新世到渐新世“假剑齿虎”），或作为Machairodontinae（真正的剑齿虎，如Smilodon）。在这里，我们提出了一种评估食肉目中三个独立剑齿虎进化枝有效性的新方法。我们对所有主要食肉动物科的 Beast2 进行了全证据贝叶斯分析，使用化石生死 (FBD) 模型并结合了 223 个形态特征、核和线粒体基因序列以及地层发生数据。我们的结果将 barbourofelines 作为 Nimravidae 的终端成员，Nimravini 的姐妹（0.91 后验概率），这种关系在之前的分支研究中没有发现。在 R 包 BioGeoBEARS 中执行的祖先面积估计最能支持主要欧洲古生物地理中心的 barbourofelines 具有向其他大陆的多次扩散事件，这一发现与该群体过去的假设直接相反。此外，通过 BayesTraits 中的贝叶斯祖先状态估计揭示了 nimravids 和 machairodontines 之间收敛的新模式。结果支持猫复制 nimravids 的假设，并且 nimravids 猫在剑齿虎形态的某些方面，而不是通常设想的这些特征的完全进化独立性。