云南早泥盆世肺鱼类的形态学与分支系统学研究

Lungfishes are a highly derived group of sarcopterygian fishes that form the living sister group of the tetrapods. However, interrelationships among fossil lungfishes are debatable, particularly among the earliest forms. With fossil discoveries made in China since 1980, global studies on key areas of early lungfish evolution have made significant progress. The earliest and most primitive lungfish was discovered from the Lochkovian (Early Devonian) of South China; nevertheless, this assignment has been disputed due to morphological disparity with more recent fossil taxa. A recent discovery from the Early Devonian (Pragian) of Zhaotong, Yunnan Province, represents the first record of lungfishes from the Pragian of China. The new specimen preserves a combination of anatomical features that partially bridges the morphological gap between the primitive and more derived forms, providing a vital data on early lungfishes anatomy, evolution and paleogeography. High-resolution computer tomography will be conducted to the new material along with other primitive lungfishes from Yunnan to reveal details of the neurocranium that should contribute to our understanding of the early sarcopterygian braincase. To provide a convincing hypothesis of their early diversification, a phylogenetic analysis of early lungfishes will be performed employing different inferences such as maximum parsimony, maximum likelihood, and Bayesian analyses. The sum total of these studies should be a substantial increase in our knowledge of the early evolution of this important group of vertebrates.

肉鳍鱼类中的肺鱼类是与四足动物关系最密切的现生代表，该类群的研究一直受到学术界的广泛关注。早泥盆世是肺鱼类起源和辐射演化的关键时期，三十年来，我国云南曲靖地区的早泥盆世洛霍考夫期地层中报道了一批珍贵的肺鱼类化石，为研究肺鱼类乃至肉鳍鱼类的起源与早期演化提供了关键资料。近年来，云南昭通地区早泥盆世布拉格期地层中同样发现了重要的早期肺鱼化石新材料，这是我国肺鱼化石在布拉格期的首次出现。本项目拟对该新材料和已报道的发现于云南曲靖洛霍考夫期地层的目前已知最早的肺鱼- - 奇异鱼进行详细的形态学与比较解剖学研究；借助高精度断层扫描技术，通过对其内颅内部构造重建来揭示早期肺鱼类内颅内部特征；以分支系统学理论为基础，就肺鱼类的早期演化和特征演化序列等国际学术界高度关注的研究课题进行深入探讨，为揭示肺鱼类的起源、早期演化以及肺鱼类与其他肉鳍鱼类的系统发育关系提供更有说服力的化石证据或假说。

肺鱼类是肉鳍鱼类的的一支，也是与四足动物关系最密切的现生代表，该类群的研究一直受到学术界的广泛关注。早泥盆世是肺鱼类起源和辐射演化的关键时期，我国云南地区的早泥盆世洛霍考夫期地层中曾报道了一批珍贵的肺鱼类化石，为研究肺鱼类乃至肉鳍鱼类的起源与早期演化提供了关键资料。在此基础上，项目组研究了我国布拉格时期的首件肺鱼化石——产自云南昭通地区的云南古嵴鱼。研究显示，该化石材料是处于原始肉鳍鱼类与肺鱼类之间的过渡类型，为肺鱼类自接型头骨的演化过程研究提供了重要线索。系统发育分析结果显示：古嵴鱼与顶嵴鱼构成姊妹群，是除奇异鱼外最基干的肺鱼类群。古嵴鱼与顶嵴鱼的近亲关系说明华南板块和欧美板块在泥盆纪早期曾存在某种古地理联系。项目组还对两件奇异鱼标本进行了高精度层析扫描和三维重建，呈现了最古老、最基干的肺鱼类的脑腔形态。结果显示，奇异鱼的脑腔已经具备一些典型肺鱼类的特征，说明肺鱼类的脑腔特征在其起源之初便已形成，同时确定了奇异鱼的肺鱼属性，对了解肺鱼类起源研究具有重要作用。对卡思尔斯喙鱼和吮吻鱼的研究丰富了我国早泥盆世肺鱼的化石记录，同时为研究早期肺鱼类的演化和古动物地理分布提供了新的资料。在形态学研究的基础上，项目组重新认识和整理了肺鱼类的形态特征，建立了包括肺鱼类化石和现生肺鱼类的数据矩阵，这是迄今最完整的肺鱼类形态学矩阵。课题组还首次运用最大似然法对肺鱼类的演化进行了分析，并结合简约性原理、贝叶斯法等就肺鱼类的早期演化和特征演化序列进行探讨，为揭示肺鱼类的起源、早期演化以及肺鱼类与其他肉鳍鱼类的系统发育关系提供了更有说服力的演化假说。