中国东北大兴安岭地区热河生物群鸟类化石新发现及其古地理意义

New Early Cretaceous fossil birds from the Morin Dawa Daur Autonomous Banner of Hulunbuir City, Inner Mongolia, represent the first occurrence of Mesozoic birds in the Great Khingan Range area. These new discoveries document the northernmost geographic distribution of Jehol birds in China. The new fossil locality is conveniently accessed and it contains relatively wide stratigraphic outcrops. In addition to birds and non-avian dinosaurs, many other preserved fossils have been discovered from this locality, including plants, insects, turtles, and amphibians. But, the exact lithostratigraphic unit is still contravertial. This project plans to carry out additional excavations in search of more birds and other fossils. The proposed field work has the objective to confirm the lithostratigraphic unit, to clarify the types, numbers, and fossiliferous beds of this locality. The field investigations will also provide important evidence for better understanding the bio-faces, taphonomy, paleogeography, and paleo-environment of this area, and for establishing comparisons with different sites of the Jehol Biota. Based on preliminary observations, we conclude that of the two fossil birds so far discovered, one belongs to Enantiornithes and the other to Ornithuromorpha. In order to describe their morphologies, to determine their ontogenetic phases, and to compare their characteristics with those of other Mesozoic birds, we plan to examine them through computer tomographic (CT) imaging methods and histologic analyses, and to fully prepare the specimens. Then, we will determine their taxonomic identities through standard comparative methods and their phylogenetic position through computational cladistics methods (TNT). The new materials provide important information for understanding the evolution, radiation, and geographic distribution of Jehol birds as well as the global evolutionary history of early birds.

中国内蒙古莫力达瓦地区新发现的鸟类化石是大兴安岭地区首次发现中生代鸟类化石，也是热河生物群鸟类化石在我国分布的最北部。新化石点交通比较便利，地层出露较好，目前已发现大量热河生物群代表化石，但地层分类单元仍存在争议。本项目计划对化石点开展清理挖掘工作，并对化石点周边地区开展详细的野外调查和地层对比研究，采集更多的鸟类化石及其他门类化石，厘定地层分类单元，理清该地区热河生物群组合面貌，探讨该地区与冀北-辽西地区早白垩世地层的区域对比问题。通过对已采集到的两件鸟类化石的初步观察，我们确定其分别属于反鸟类和今鸟型类。项目计划先对其进行CT扫描，然后再仔细修复并进行骨组织学分析，以便更好的进行形态描述和特征对比研究，并确定其个体发育阶段；我们将运用TNT分析软件对其进行分支系统学研究，确定其分类位置和谱系演化关系，探讨热河生物群鸟类演化、辐射及古地理分布问题。

本项目主要以内蒙古东部大兴安岭莫旗地区发现的热河生物群化石产地及鸟类和恐龙化石为研究对象。通过野外调查、锆石U-Pb测年及综合研究，项目组确定了莫旗地区热河生物群化石赋存层位为下白垩统龙江组，鸟类包括今鸟型类新属新种呼伦贝尔兴安鸟和反鸟类新属新种兴安北国鸟，恐龙为驰龙类新属新种王氏达斡尔龙。莫旗地区热河生物群化石产地岩石特征与冀北-辽西地区主要化石赋存层位相似，形成于火山活动影响下的湖相沉积。已发现的鸟类和恐龙化石均属于特异埋藏，不仅形态特征与发现于辽西地区的相关类群相似，而且亲缘关系较近，代表了热河生物群的后期演化阶段，为不同地区热河生物群对比研究提供了重要证据。通过对辽西地区热河生物群新发现的鸟类化石研究，项目组建立了3个新属新种，为热河生物群鸟类演化辐射研究提供了重要信息。