Data from: Rigorous approaches to species delimitation have significant implications for African crocodilian systematics and conservation

Accurate species delimitation is a central assumption of biology that, in groups such as the Crocodylia, is often hindered by highly conserved morphology and frequent introgression. In Africa, crocodilian systematics has been hampered by complex regional biogeography and confounded taxonomic history. We used rigorous molecular and morphological species delimitation methods to test the hypothesis that the slender-snouted croco- dile (Mecistops cataphractus) is composed of multiple species corresponding to the Congolian and Guinean biogeographic zones. Speciation probability was assessed by using 11 mitochondrial and nuclear genes, and cranial mor- phology for over 100 specimens, representing the full geographical extent of the species distribution. Molecular Bayesian and phylogenetic species deli- mitation showed unanimous support for two Mecistops species isolated to the Upper Guinean and Congo (including Lower Guinean) biomes that were supported by 13 cranial characters capable of unambiguously diagnos- ing each species. Fossil-calibrated phylogenetic reconstruction estimated that the species split + 6.5 – 7.5 Ma, which is congruent with intraspecies diver- gence within the sympatric crocodile genus Osteolaemus and the formation of the Cameroon Volcanic Line. Our results underscore the necessity of com- prehensive phylogeographic analyses within currently recognized taxa to detect cryptic species within the Crocodylia. We recommend that the com- munity of crocodilian researchers reconsider the conceptualization of crocodilian species especially in the light of the conservation ramifications for this economically and ecologically important group.

准确的物种界定是生物学的核心前提之一，在鳄形目（Crocodylia）等类群中，这一研究过程常因形态高度保守与频繁的基因渐渗而受阻。在非洲区域，鳄形类的系统学研究长期受复杂的区域生物地理格局与混乱的分类学历史掣肘。本研究借助严谨的分子及形态学物种界定方法，检验了狭吻鳄（Mecistops cataphractus）可划分为对应刚果生物地理区与几内亚生物地理区的多个物种这一假说。研究覆盖该物种分布的全部地理范围，通过11个线粒体及核基因序列与100余份标本的颅骨形态学特征，评估物种形成概率。分子贝叶斯物种界定与系统发育物种界定分析均一致支持，狭吻鳄属存在两个独立物种，分别局限于上几内亚生物区与刚果（含下几内亚）生物区，且二者可通过13项颅骨特征实现明确的物种鉴别。经化石校准的系统发育重建结果估算，两物种的分化时间约为650万至750万年前，这与同域分布的奥塞内尔鳄属（Osteolaemus）类群的种内分化时间以及喀麦隆火山带（Cameroon Volcanic Line）的形成时间相吻合。本研究结果凸显了对当前已认定的类群开展全面系统地理学分析，以侦测鳄形目中隐存物种的必要性。鉴于这一类群在经济与生态层面均具有重要价值，我们建议鳄形类研究学界重新审视鳄形类物种的概念界定，尤其需结合该类群所涉及的保护影响进行考量。