Collaborative Research: Mesozoic Therians from Central Asia: The Basal Radiation of Tribosphenic Mammals and Their Impact on the Higher-Level Relationships of Therian Mammals

合作研究——中亚中生代兽类：摩擦生哺乳动物的基础辐射及其对兽类哺乳动物高级关系的影响美国自然历史博物馆的Novacek博士、路易斯维尔大学的Rougier博士和卡内基自然历史博物馆的Wible博士获得了一项资助，对白垩纪（1.45亿至6500万年前）兽类哺乳动物的辐射进行全面研究。兽类包括现存的有袋动物和胎盘动物以及它们已灭绝的近亲。今天有超过4600个物种代表着兽类，几乎涵盖了所有现存哺乳动物的多样性，除了三种产卵的单孔目动物。动物之间进化关系的研究已经用分子生物学（DNA结构）和比较解剖学（现存和灭绝形式的结构）的数据来解决。由这两种方法得出的家谱（系统发育）并不完全一致，也没有表明现存蜥蜴主要谱系的起源时间相同。然而，分子和解剖学工作者都同意，类虫食动物是therian辐射的基础。博士可用。Novacek， Rougier和Wible是他们项目的核心研究小组，他们在蒙古戈壁沙漠著名的恐龙和哺乳动物化石床上收集了保存完好的8000万年前的食虫化石，其中一些与胎盘动物有关，另一些与有袋动物有关。这些化石是由美国博物馆和蒙古科学院最近的联合考察收集的。与绝大多数白垩纪恐龙化石不同的是，这些化石只是孤立的颌和牙齿，它们几乎是完整的骨架。他们将为研究白垩纪龙及其现存后代之间的进化关系提供迄今为止最全面的解剖学数据库，并评估DNA和解剖学结果之间有争议的差异。被研究的大多数白垩纪龙都是鼩鼱大小，因此单凭肉眼无法有效地研究。对这些小形态进行解剖研究需要两种工具：标准立体显微镜和高分辨率计算机断层成像（ct扫描）。两者都是可用的，后者在宾夕法尼亚州立大学的国家科学基金会支持的设施。Drs。Novacek、Rougier和Wible将利用他们在现存和灭绝哺乳动物解剖方面的专业知识，以及美国博物馆、卡内基博物馆和其他机构的藏品，建立一个比较信息的解剖数据库。家谱将通过各种可用的计算机程序从这个数据库生成，并与以前根据其他信息发布的家谱进行比较。这些精美的蒙古化石是一种独特的资源，最终将被归还给它们的原产国。现在对这些化石进行仔细的研究和广泛的记录是至关重要的，这样才能使它们广泛地用于科学进步。这项研究的副产品将是一个标准化的龙骨解剖学术语；目前，研究特定兽系的研究人员使用不同的术语，往往是不一致的。这项研究也提供了教育和培训新的科学家在前和博士后水平的机会。最后，这些化石中包含的有价值的科学知识将通过美国博物馆和卡内基博物馆的展览和教育项目为公众翻译。

Collaborative Research - Mesozoic therians from Central Asia: the basal radiation of tribosphenic mammals and their impact on the higher-level relationships of therian mammals A grant has been awarded to Dr. Novacek at the American Museum of Natural History, Dr. Rougier at the University of Louisville, and Dr. Wible at the Carnegie Museum of Natural History for a comprehensive study of the Cretaceous (145 to 65 million-years-ago) radiation of therian mammals. Therians include living marsupials and placentals plus their extinct relatives. Therians are represented today by more than 4600 species accounting for nearly all the diversity of living mammals, the exception being the three species of egg-laying monotremes. The study of the evolutionary relationships among therians has been addressed with data from molecular biology (the structure of DNA) and comparative anatomy (the structure of living and extinct forms). The family trees (phylogenies) that result from these two approaches are not entirely congruent nor do they suggest the same time of origin of the major lineages of living therians. However, both molecular and anatomical workers agree that insectivore-like forms are at the base of the therian radiation. Available to Drs. Novacek, Rougier, and Wible as the core study group for their project are exquisitely preserved, 80 million-year-old insectivore-like fossils, some related to placentals and others to marsupials, collected from the famed dinosaur and fossil mammal beds of Mongolia's Gobi Desert by recent joint expeditions from the American Museum and the Mongolian Academy of Sciences. Unlike the vast majority of Cretaceous therian fossils, which are merely isolated jaws and teeth, these are nearly complete skeletons. They will provide the most comprehensive anatomical data base to date for studying the evolutionary relationships among Cretaceous therians and their living descendants, and evaluating the controversial difference between DNA and anatomical results. Most of the Cretaceous therians to be studied are shrew-sized and, therefore, cannot effectively be investigated with the naked eye alone. Two tools are needed for the anatomical study of these small forms: standard stereoscopic microscopy and high-resolution computer tomographic imaging (CT-scanning). Both are available, the latter at a National Science Foundation supported facility at Pennsylvania State University. Drs. Novacek, Rougier, and Wible will use their expertise in the anatomy of living and extinct mammals, and the collections at the American Museum, Carnegie Museum, and other institutions to build an anatomical data base of comparative information. Family trees will be generated from this data base by various available computer programs and compared with those previously published based on other information. These exquisite Mongolian fossils are a unique resource that ultimately will be returned to their country of origin. Careful study and extensive documentation of these fossils now is critical in order to make them widely accessible for scientific advancement. A by-product of this study will be a standardized anatomical terminology for the therian skeleton; currently, researchers studying particular therian lineages employ different terms that are often incongruent. This study also affords the opportunity for educating and training of new scientists at both the pre- and postdoctoral level. Finally, the valuable scientific knowledge contained in these fossils will be translated for the public through the exhibits and educational programs of the American Museum and Carnegie Museum.