Data from: Character evolution and the origin of Caimaninae (Crocodylia) in the New World Tropics: new evidence from the Miocene of Panama and Venezuela

Alligators and caimans share a close relationship, supported by both molecular and morphological characters. The divergence between alligators and caimans has been difficult to discern in the fossil record. Two basal taxa have recently been described from the Miocene of Panama and Venezuela, but have not yet been presented in a joint phylogeny. Continued preparation of the type material of the Venezuelan Globidentosuchus brachyrostris has revealed new characters for scoring in a cladistic framework. In addition, the first lower jaw of the Panamanian Centenariosuchus gilmorei is described herein, and additional characters were scored. In total, we conducted five cladistic analyses to better understand the character evolution involved in the establishment of Caimaninae. In each case, Globidentosuchus appears as the basal-most of the caimanine lineage, followed by Culebrasuchus mesoamericanus from Panama. Stepwise character additions of synapomorphies define progressively more derived caimanines, but stratigraphic context creates ghost lineages extending from the Miocene to Paleocene. The persistence of two basal taxa into the Miocene of northern South America and Central America supports the concept of a relict basal population in this region. This further supports biogeographic hypotheses of dispersals in both directions between North and South America prior to full land connection.

短吻鳄（Alligators）与凯门鳄（Caimans）亲缘关系密切，该结论得到分子与形态学特征的共同支持。二者的分化事件在化石记录中始终难以厘清。此前已有两个基干类群（basal taxa）分别于巴拿马和委内瑞拉的中新世（Miocene）地层中被报道，但尚未被整合至联合系统发育分析（joint phylogeny）中。针对委内瑞拉Globidentosuchus brachyrostris的模式标本（type material）的后续制备工作，已揭示出一批可用于分支系统学框架（cladistic framework）下进行特征计分的新形态特征。此外，本文首次描述了巴拿马Centenariosuchus gilmorei的下颌骨，并新增了若干特征计分项。本研究共开展5次分支系统学分析，以深入解析凯门鳄亚科（Caimaninae）起源过程中涉及的特征演化规律。各次分析均显示，Globidentosuchus为凯门鳄亚科演化支中最基干的类群，其后依次为巴拿马的Culebrasuchus mesoamericanus。通过逐步添加共有衍征（synapomorphies），可逐步构建出衍征愈发特化的凯门鳄类群，但结合地层年代学背景，可发现存在从中新世延伸至古新世（Paleocene）的幽灵支系（ghost lineages）。两个基干类群延续至南美洲北部与中美洲的中新世地层，这一发现支持该区域存在孑遗基干种群的观点。该结果进一步支撑了"在完整陆地连接形成之前，南北美洲之间存在双向生物扩散"的生物地理学假说。