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，包括现代的鳄鱼、凯门鳄、鳄鱼和食人鱼，在古近纪形成了低地生态系统的主要组成部分，并因此有大量的化石记录。这使它们成为解决宏观进化中广泛问题的极佳模式分支，例如深层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史，因为洲际扩散在始新世温暖的高纬度气候促进了它们的多样化方面发挥了重要作用。鳄鱼的古近纪生物地理史在很大程度上仍然不确定，因为包括化石在内的系统发育由于样本有限而不稳定。最关键的问题包括非常糟糕的亚洲古近纪化石记录，单从今天的多样性来看，这块大陆显然在鳄鱼的进化中发挥了重要作用。另一个主要因素是分子数据在结合现存和灭绝物种的形态进行系统发育推断方面的利用有限。在此，我们建议通过添加未描述的始新世鳄鱼化石数据来广泛扩大采样范围，这些化石数据是由Tübingen大学在DFG BO 1550/11-1，2资助的越南项目中收集的。丰富、特殊的保存和多样性(代表了现存的三个主要谱系中的每一个都有几个个体发生阶段)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。这种新材料跻身于北美和欧洲保存最完好的化石之列，因此，这是第一次能够对劳拉西亚各地的动物群进行有意义的比较。来自越南分类群以及来自欧洲和北美的关键物种的新的骨学数据将与分子数据相结合，以阐明鳄鱼的早期多样性和劳亚生物地理史。这一预期结果将对早古近纪洲际古地理重建和动物群交换具有重要意义。

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.