化石-形态-分子：有尾两栖类的综合系统分支演化研究

Urodela (salamanders) are a major group of modern amphibians (Lissamphibia), with a long evolutionary history that can be traced back to the Mesozoic dinosaur time. Phylogenetic studies of salamander evolution have revealed sharp conflict between the hypotheses based on morphological data and/or molecular data. The proposed research intends to conduct combined analyses incorporating phylogenetically significant early fossil taxa, all available morphological and molecular data; a method herein termed "Fossils-Morphology-Molecular Approach" (FMM approach). Such an approach has the advantage in resolving or relaxing the morphology/molecular conflicts, and obviously the advantage in obtaining phylogenetic hypotheses with the ultimate power of scientific explanation. Fossil discoveries from the Middle Jurassic to Early Cretaceous beds in northern China have provided the key material for understanding the origins and early evolution of modern salamander clades. The fossil material found includes the earliest known fossil record of two major salamander clades (Cryptobranchoidea and Salamandroidea), and the basal taxa of several modern salamander clades. These fossils, together with other Mesozoic fossils worldwide, not only increase the taxon sampling for the phylogenetic analyses to be conducted, but also represent new combinations of anatomical characters, many of which are ancestral to salamander evolution. Morphological data used will include characters of salamander osteology, soft anatomy and development from various sources. Characters are drawn both from careful examination of real specimens and from published literatures. Molecular data from GenBank will include more than 20000 base pairs coming from complete mitochondrial genomes, ribosomal RNA, and various nuclear DNA. These data will be analyzed both separately and combined. Analyses of smaller dataset (morphological dataset with/without fossil taxa) will be performed using PAUP, whereas analyses of molecular data using direct optimization and morphology/molecular combined dataset (with/without fossil taxa) will be performed using more powerful tools, including MrBayes and POY. Phylogenetic results of parsimony analyses will be compared with those of Maximum Likelihood and Bayesian analysis. Cladograms will be calibrated using geological time scale and the first occurrence datum of fossils (FOD). By doing so, both the relationships and the tempo of salamander evolution can be better understood. Research results will be submitted for publication to international journals, including PNAS (if warranted), Cladistics, Systematic Biology, and Proceedings of the Royal Society of London B.

蝾螈类是形态保守而又具有生态多样性的两栖动物，其进化史可追溯到恐龙时代。中国北方中生代地层中发现的化石已成为研究现代蝾螈支系起源与演化的关键材料。已发现的化石包括隐鳃鲵亚目和蝾螈亚目的最早记录，以及某些现生科的干群代表。此前的蝾螈类研究揭示出根据形态或分子特征的不同分支假说的尖锐冲突。本项研究拟融合化石、形态、分子诸方面的数据进行全证据分析（拟称FMM Approach）。这一方法可有效消解形态-分子特征间的冲突，并可获取最具科学争辩力的系统分支假说。所用形态特征包括骨骼、软体解剖及发育特征。分子数据将包括从GenBank获取的逾两万个碱基对（线粒体基因组、核糖体RNA、核DNA）。不同类型数据将应用PAUP软件分别分析，并用POY进行综合分析。简约分析结果将与ML及贝叶斯分析结果进行比较研究。分支图将根据地质年代和首现化石记录校准标定。研究成果将投稿于PNAS和RSPB等国际SCI刊物。

蝾螈类是体态保守而又具有生态多样性的两栖动物，其演化历史可追溯到恐龙时代。过去十几年来中国北方中生代地层中发现的化石已成为研究现生蝾螈类主要支系的起源与早期演化的关键性材料。已发现的化石包括隐鳃鲵亚目和蝾螈亚目的最早地史记录，以及小鲵科、隐鳃鲵科等现生科的干群代表。以往的蝾螈类分支演化研究揭示出根据形态或分子特征的不同分支假说的尖锐冲突。为消解这方面的冲突问题，本项研究推出融合化石、形态、分子诸方面的数据进行全证据分析（FMM Approach），以获取最具科学争辩力的系统分支假说。项目执行期间整理和发表了中国侏罗-白垩纪蝾螈类化石记录的分类多样性、地史分布和化石标本的特殊保存；对中国新近发现的隐鳃鲵亚目和蝾螈亚目的早期化石类型进行了分类演化研究；采用高精度CT扫描技术成功获取了一批化石和现生蝾螈类标本的三维重建图像；对隐鳃鲵亚目进行了化石-形态-分子全证据分析，所获成果正在成文。另有几篇论文正在待刊、评审或是撰写过程中，完成后将作为本项目的后续研究成果投稿发表。