Discriminating terrestrial, semiaquatic and fully aquatic life styles: The unresolved question of Triassic marine archosauromorphs.

由于形态和发现情况的模棱两可(即在海洋沉积物中)，一些已灭绝的始祖龙的生活方式引起了争议。始龙形体通常被认为是陆生四足动物，但出现在二叠纪，令人惊讶的是，它经常出现在特提斯王国西部和东部以及太平洋地区的三叠纪海洋沉积物中。由于陆生和水生生物的存在，争论的焦点是这些动物是被冲进海里的，还是各自海洋动物群中的完全水生成员。因此，除了三叠纪期间非始祖龙形态的海洋爬行动物的巨大多样性和陆生始祖龙的蓬勃发展外，明确的海洋始祖龙的存在尚不清楚。然而，一个悬而未决但至关重要的问题是，为什么像始祖龙这样成功的种群不应该生活在海洋环境中，即完全是水生的，除了中生代的地中海鳄鱼血统。中国中三叠世浅海沉积中发现了始龙形原龙类、双头龙类、始龙类、千尾龙等。人们一致认为，这些分类群至少有一种基于形态特征的半水生生活方式，但并不清楚地接受完全的海洋生物生活方式。对于其他原龙，如来自浅海沉积物的上二叠统原龙和中三叠世坦尼斯特罗夫龙，来自意大利阿尔卑斯山三叠纪的Rauisuchian始祖龙Ticinosuchus ferox，以及来自不列颠哥伦比亚省全海洋(即远洋)Pardonet组的Sikannisuchus Husky，其生活方式普遍存在争议。在奥古斯塔山脉(美国内华达州)中三叠世最开阔的海洋(即远洋)沉积物中发现了一种始祖龙，其生活方式也显示出一种模棱两可的形态。这一新发现将被详细描述，并将在该项目过程中测试其系统发育关系。为了解决始祖龙的生活方式问题，将编制一个基于形态、组织学和显微解剖学特征及其组合的数据集，以区分陆生、半水生和全水生生活方式的特征(例如，通过线性判别分析)。Terrestrisuchus和恐龙是陆地生活方式的基准分类群，现代鳄鱼是半水生生活方式的基准分类群，海生生物是海洋生活方式的基准分类群。由此产生的判别模型将应用于生活方式有问题的化石分类群。然而，一旦建立了模型，就可以应用于任何分类单元，这些分类单元保存得足够好，可以收集必要的形态、组织学和显微解剖学数据。

Because of an equivocal morphology and find situation (i.e. in marine sediments), the life style of some extinct archosauromorphs is controversially discussed. Archosauromorphs are generally considered terrestrial tetrapods but occur in Permian and surprisingly frequently in Triassic marine sediments of the western and eastern Tethyan realm as well as in the Pacific realm. Due to the presence of terrestrial and aquatic characters alike, the debate focusses around the question if these animals had been washed into the sea or were fully aquatic members of the respective marine faunas. Thus, besides a huge diversity of non-archosauromorph Triassic marine reptiles and a flourishing radiation of terrestrial archosauromorphs during the Triassic, the existence of unambiguous marine archosauromorphs is not clear. It is however, an unresolved but crucial question why such a successful group as the archosauromorphs should not have inhabited the marine environment, i.e. had been fully aquatic, with the exception of the Mesozoic crocodile lineage of Thalattosuchia. The archosauromorph protorosaur Dinocephalosaurus, the archosauriform Litorosuchus, and the archosaur Qianosuchus are all found in shallow marine sediments in the Middle Triassic of China. There is an agreement that these taxa have had at least a semiaquatic life style based on morphological characters but a fully marine life style is not clearly accepted for them. For other Protorosauria such as the Upper Permian Protorosaurus and the Middle Triassic Tanystropheus, both from shallow marine sediments, for the rauisuchian archosaur Ticinosuchus ferox from the Alpine Triassic of Italy as well as for Sikannisuchus husky from the fully marine (i.e. pelagic) Pardonet Formation of British Columbia, the life style is in general discussed controversially. A new find of an archosauriform from the most open marine (i.e. pelagic) sediments from the Middle Triassic of the Augusta Mountains (Nevada, USA), also shows an equivocal morphology in terms of its life style. This new find will be described in detail and its phylogenetic relationships will be tested in the course of this project. To solve the question of life style in archosauromorphs, a dataset based on morphological, histological, and microanatomical characteristics and combinations thereof of archosaurs with a clear life style will be compiled to classify characteristics of terrestrial, semiaquatic, and fully aquatic life styles (e.g. by linear discriminant analysis). Terrestrisuchus and dinosaurs are bench mark taxa for a terrestrial life style, modern crocodiles for the semiaquatic life style and thalattosuchians for the marine life style. The resulting discrimination model will be applied to fossil taxa with a questionable life style. However, once established the model can be applied to any taxon, which is good enough preserved to gather the necessary morphological, histological and microanatomical data.