Revision of the Eocene artiodactyls (Mammalia, Placentalia) from Aumelas and Saint-Martin-de-Londres (Montpellier limestones, Hérault, France) questions the early European artiodactyl radiation

The fossiliferous localities of Aumelas and Saint-Martin-de-Londres in the Montpellier limestones (Hérault, France), known since the 1960s and 1980s, were originally dated as late middle Eocene (Lutetian), close to the European Mammal Palaeogene Reference Level 13 (MP13). This period is a key time interval in the initial radiation of European endemic mammals. We present here a systematic revision of the artiodactyl fauna from Aumelas and Saint-Martin-de-Londres in order to propose a biochronological revision of these localities. We identified five artiodactyl species: <i>Aumelasia gabineaudi</i>, <i>Dichobune</i> aff. <i>robertiana</i>, <i>Eurodexis</i> cf. <i>russelli</i>, Eurodexeinae indet. and <i>Lophiobunodon minervoisensis</i>. Two of these species are known in both localities. Comparisons with other European localities support an earlier dating than late middle Eocene for Aumelas and Saint-Martin-de-Londres. These localities seem to be close to the Ypresian/Lutetian boundary and could constitute a rare record of this period in Europe. The age of these localities is critical for discussing the initial radiations of endemic European artiodactyl families (Cebochoeridae, Choeropotamidae, Mixtotheriidae, Anoplotheriidae, Xiphodontidae, Cainotheriidae and Amphimerycidae). This systematic revision allows us to test the validity of phylogenetic relationships between these families using cladistic analyses. Our results question the monophyly of Dichobunidae and Choeropotamidae but support the older concept of Haplobunodontidae. This study, which constitutes a first step towards a better understanding of their evolutionary history, suggests that the European artiodactyl radiation took place close to the Ypresian/Lutetian boundary.

法国埃罗省蒙彼利埃灰岩地层中的奥梅拉（Aumelas）与圣马丁德隆德雷斯（Saint-Martin-de-Londres）产化石地点，自20世纪60年代、80年代起便为学界所知，最初被判定为中始新世晚期（路特阶），时代接近欧洲哺乳动物古近纪参考层位13（MP13）。该时段是欧洲特有哺乳动物最初辐射演化的关键时期。本研究对上述两地的偶蹄目（Artiodactyla）动物群开展系统厘定，以期对该类产化石地点的生物年代学框架进行修订。本次研究共鉴定出5种偶蹄目动物：<i>Aumelasia gabineaudi</i>、<i>Dichobune</i> aff. <i>robertiana</i>（亲近<i>robertiana</i>）、<i>Eurodexis</i> cf. <i>russelli</i>（比较<i>russelli</i>）、Eurodexeinae indet.（未定亚科）以及<i>Lophiobunodon minervoisensis</i>。其中2个物种在两处地点均有发现。通过与欧洲其他产化石地点的对比，本研究认为奥梅拉与圣马丁德隆德雷斯的时代早于中始新世晚期。两处地点的时代似乎接近伊普雷斯阶/路特阶界限，或可作为欧洲该时段罕见的化石记录。上述地点的时代对于探讨欧洲特有偶蹄目各科：塞波猪科（Cebochoeridae）、猪形兽科（Choeropotamidae）、混合兽科（Mixtotheriidae）、无防兽科（Anoplotheriidae）、剑齿兽科（Xiphodontidae）、凯诺兽科（Cainotheriidae）及两栖鹿科（Amphimerycidae）的初始辐射演化至关重要。本次系统厘定工作使得我们能够通过分支系统学分析，检验上述各科之间系统发育关系的合理性。本研究结果对双锥齿兽科（Dichobunidae）与猪形兽科（Choeropotamidae）的单系性提出了质疑，但支持单锥齿兽科（Haplobunodontidae）的旧有分类概念。本研究作为深入理解偶蹄目演化历史的第一步，表明欧洲偶蹄目动物的辐射演化事件恰好发生在伊普雷斯阶/路特阶界限附近。