Resolving the phylogeny and biogeographic history of early Crocodylia through total evidence analysis and exceptionally preserved Eocene fossils from Vietnam

鳄鱼的代表，包括现代短吻鳄、凯门鳄、鳄鱼和大腹鳄，在古近纪形成了低地生态系统的主要组成部分，并有大量的化石记录。这使它们成为解决宏观进化中广泛问题的极好模型分支，例如深时间生物多样性的环境驱动因素。特别令人感兴趣的是它们的生物地理历史，因为始新世温暖的高纬度气候促进了它们的多样化，洲际扩散在其中发挥了重要作用。古近系鳄鱼的生物地理历史在很大程度上仍然是不确定的，因为包括化石在内的系统发育由于采样有限而不稳定。最关键的问题包括亚洲明显贫乏的古近系化石记录，仅从当今的多样性来看，亚洲大陆显然在鳄鱼的进化中发挥了重要作用。另一个主要因素是在结合现存和灭绝物种的形态学进行系统发育推断时分子数据的利用有限。在此，我们建议通过增加<s:1>宾根大学在越南的DFG BO 1550/11- 1,2资助项目中收集的未描述的始新世鳄鱼的化石数据来广泛扩展采样。丰富的数量、特殊的保存和多样性（代表了三个主要的现存谱系和几个个体发育阶段）使这个新的化石组合成为迄今为止亚洲古近纪鳄鱼动物群中最重要的。新发现的化石是北美和欧洲保存最完好的化石之一，因此，这是第一次可以对整个劳亚的动物进行有意义的比较。为了阐明鳄鱼的早期多样化和Laurasian生物地理历史，我们将结合来自越南分类群和欧洲和北美关键物种的最新骨学资料与分子资料。研究结果对早古近纪洲际古地理重建和动物交换具有重要意义。

Representatives of Crocodylia, the group including modern-day alligators, caimans, crocodiles, and gharials, formed a major element of lowland ecosystems during the Paleogene and have an extensive fossil record accordingly. This makes them an excellent model clade for addressing a broad range of questions in macroevolution such as the environmental drivers of biodiversity in deep time. Of particular interest, is their biogeographic history as intercontinental dispersals played a major role in their diversification facilitated by the warm high-latitude climate of the Eocene. The Paleogene biogeographic history of crocodylians remains largely uncertain because phylogenies including fossils are instable due to limited sampling. The most critical issues include the markedly poor Paleogene fossil record of Asia, a continent that evidently had a major role in the evolution of Crocodylia based on present-day diversity alone. Another major factor is the limited utilization of molecular data in phylogenetic inference in combination with morphology from extant and extinct species. We here propose to extensively expand sampling by the addition of fossil data from undescribed Eocene crocodylians collected by the University of Tübingen during a DFG BO 1550/11-1, 2 - funded project in Vietnam. The abundance, exceptional preservation, and diversity (representing each of the three major extant lineages with several ontogenetic stages) makes this new fossil assemblage by far the most important among crocodylian faunas from the Paleogene of Asia. The new material ranks among the best-preserved fossils from North America and Europe thereby, for the first time, allowing meaningful comparisons of faunas across Laurasia. Novel osteological data from the Vietnamese taxa as well as key species from Europe and North America will be combined with molecular data in order to elucidate the early diversification and Laurasian biogeographic history of Crocodylia. The expected results will have important implications for intercontinental paleogeographic reconstruction and faunal interchange during the early Paleogene.