新疆南部巴楚地区中-晚奥陶世脊椎动物群研究

In the Yijianfang of the Bachu County, South Xinjiang (Tarim Basin), the Middle-Late Ordovician abundant agnathans fossils including about six new gen. and new sp. have been found first time by applicant. These fossils should be a special agnathan fauna, because of there is a pair of orbits, the pineal opening on the anterior part of the head shield, and the six pairs of external branchial openings on the ventral aspect. These characteristics of fossils are similar to Silurian and Devonian agnathan, but there is no distinct hypophysial opening on the anterior part of head shield. This agnathans fossils group has been named the Bachuiaspis elegans- Palaeogaleaspis platyrostrastus fauna. The relation between Early Cambrian Myllokunmingia、Haikouichthys (Shu D-G.et al.,1999)un-possessing the external dermal and the Ordovician agnathans possessing the carapace must be researched from the collection. In the world, there were found the Ordovician agnathans fossils which belong to the heterostracans, such as: in USA (Denison R.H.,1967),Canada (Elliuk L.S.,1973),South American (Gagnier P.Y.et al.,1986),Australia (Ritchie A. and Gilbert-Tomlinson J., 1977 ), and are different from those of the Tarim Basin possessing the six pairs of external branchial openings ,which is similar to the galeaspids (Liu, 1965).Certainly, the Ordovician agnathans fauna of Bachu County would be referred to a new subclass on the subdivision system of vertebrates paleontology, and a new Ordovician vertebrates paleongeographic province. In China, the knowledge of the Ordovician fish fossils is lacked for the vertebrate paleontologist, because there was no the fossil almost to be found. In Middle Ordovician Zhuozishan Formation of The Zhouzishan Region, Inner-Mongolia,there is an agnathan fossil fragment which is referred to heterostracans(Wang and Zhu, 1997).This is only one specimen before in China, and different from those of Bachu County. This is the gap for the development and evolution of the Ordovician vertebrates which very important significance for the vertebrate paleontologists. The Middle-Late Ordovician agnathans material is so great and the diversities of the genera so high in the fauna of Bachu County. Those fossils must be researched and described in detail and deal with the tissue slides, CT scanning, so that the systematic taxonomy and the evolutionary pedigree of Ordovician fossils are established. At present, the researches of the agnathans fossils are preliminary, the vertebrates biology, bio-stratigraphy, sedimentary-paleonenvironment and the division of the palaeobiogeographic province would be gradually and deeply.

全球奥陶纪脊椎动物化石研究是一个薄弱、急待探索的新领域。我国鲜有该领域成功开展研究的实例，由于对东特提斯洋（即塔里木-扬子地块）奥陶纪脊椎动物及其动物地理区系的了解甚少，制约了古生物学家对早期脊椎动物起源、演化及其地理区系的形成过程的认识，这是当前脊椎动物发展史研究的一个严重不足。申请者首次从新疆巴楚县一间房剖面中获得了较丰富的奥陶纪无颌类鱼类化石，命名为巴楚动物群，有望填补我国这一研究领域的空白。项目将在奥陶纪无颌类鱼化石全面、系统的生物学观察描述基础上，结合甲胄组织切片及高精度CT扫描等新技术分析其内部微细构造，对奥陶纪无颌类动物群进行系统分类学和生物学研究，揭示其总体生物面貌，确定它在谱系演化表中的位置；进而阐明其与寒武纪和志留纪脊椎动物的差异及演化关系。根据生物学特征及与国内外资料对比，将证实该动物群是我国特有的、新的鱼类动物群，而且极可能是属于早期脊椎动物独立的动物地理分区。

奥陶纪的古脊椎动物化石研究在国内外古生物界都是薄弱和亟待探索的未知领域。这一时代古脊椎动物化石的发现均属凤毛麟角、十分罕见。目前已知全球发现的化石总计为个位数，主要见于北美洲、南美洲及澳洲。国内仅报道1件，且不能排除为节肢动物外壳的可能性。自2011年起笔者在新疆巴楚地区发现较丰富的中晚奥陶世无颌类以来，引起各方关注；2014年得到国家自然科学基金的支持，立项深入研究该区的古脊椎动物化石。通过对化石的外部形态、组织切片、CT扫描、弱酸浸泡分析微体化石等方法观察分析，在获得理性和生物学的证据后，对化石进行了系统研究。首先对化石生物学特征进行研究，包括眶孔、松果孔、外鳃孔、感觉沟及鼻垂体孔等项，对化石切片进行内部组织结构分析；在此基础上，展开系统分类学研究，列出该化石群在无颌类生物谱系中的生物学位置及与寒武纪、志留纪-泥盆纪类型的演化关系；同时，依据分类学和生物学的划分对其古生态环境和独特的生物古地理区系进行剖析和定位。本批化石的研究是自寒武纪发现以软体印模为主要特征的脊椎动物之后，首次在国内对前志留纪的具外骨骼的脊椎动物外部形态特征进行详细报道，揭示了该地区晚奥陶世脊椎动物群具有的特殊性及独立性；根据生物学和系统发生特征，本项目对已发现和命名的巴楚鱼目巴楚鱼科的巴楚鱼属、短甲鱼属，古盔甲鱼目古盔甲鱼科古盔甲鱼属和目、科未定的圆头鱼属进行了系统的、较为详细的生物学描述和研究。据上述研究，本项目共发表学术论文和著作4篇（部），其中国际Sci文章1篇，著作1部。在研期间项目组成员4次在国际学术会议上将研究成果以口头或展板报告形式，与国际同行进行交流和讨论。研究表明，新疆巴楚地区奥陶纪古脊椎动物化石以其承上启下的过渡性、鱼类演化的中间链条的生物特征，具有不可替代性；同时，其外部形态和骨骼构造、结构与北美、南美和澳洲的无颌类具有很大差异，属于独立的古脊椎动物生物地理区系。