Toward the Origin of Whales: Eocene Cetacea from Pakistan

Thewissen 9526686 该项目调查鲸类动物（鲸鱼，海豚，鼠海豚）从陆地四足动物到专门的海洋游泳者的转变。 这种转变是少数几个古生物学记录的哺乳动物宏观进化变化的例子之一。 该项目将解释两个系统中的宏观进化变化模式，这两个系统经历了普遍的修改，运动和听觉，并评估其古生态环境。 Hypotheses.--将检验七个假设。 其中两个预测了早期鲸类动物运动模式的变化。 三种假说对鲸类中耳和内耳的进化和功能进行了预测。 另外两个假说则针对这种转变发生的物理环境，对古生态学进行了预测。 将从巴基斯坦北方的Kuldana组和Kohat组的淡水和浅海沉积物中收集新的化石材料，这是发现最早和最具拟形鲸目动物的唯一地区，这些材料将用于检验假设。 Kuldana/Kohat鲸目动物生活在各种沉积环境中，现在是一个结构复杂的地区，需要详细的地质研究。 沉积学研究将阐明过渡的物理背景。 正在进行的相关工作包括分析现代鲸目动物耳朵的发育和功能，以及根据稳定氧同位素分析生理制约因素。 Significance.--鲸类起源是脊椎动物中陆地-水过渡的最佳记录例子之一，并展示了几种经历普遍变化的形式-功能复合体。 鲸类的游泳从四足划水发展到宽尾的背腹振荡，Kuldana鲸类显示中间模式。 鲸类祖先的耳朵被调谐到中频空气传播的声音，而现代鲸类动物听到水下高（齿鲸）或低（mys ticete）的声音。 库尔达纳鲸类的位置尚不清楚，但它们的听觉形态与它们的陆地姐妹群和现代鲸类不同。 化石形态解释在一个既定的系统发育背景和现代水生哺乳动物提供的背景阐明了这些进化模式。 研究记录这些形态模式的岩石的沉积学，澄清了陆地向水过渡的生态背景。 这一研究对哺乳动物的高等生殖具有广泛的意义。 它将提供形态学数据，以测试抹香鲸（odotocete paraphyly）的亲缘关系以及鲸目动物与偶蹄动物（artiodactyl paraphyly）的关系。 这些系统发育假说是基于分子数据提出的，形态学家对此有很大争议。 动物群演化的研究表明，印度-巴基斯坦在白垩纪与亚洲接触。 地质数据反驳了这一说法。 本研究将为始新世古生物学资料提供一个重要的检验。

Thewissen 9526686 This project investigates the transition of cetaceans (whales, dolphins, porpoises) from terrestrial quadrupeds to obligate marine swimmers. This transition is one of the few paleontologically documented examples of macroevolutionary change in mammals. The project will interpret patterns of macroevolutionary change in two systems that underwent pervasive modifications, locomotion and hearing, and evaluate its paleoecological context. Hypotheses.-- Seven hypotheses will be tested. Two of these make predictions about changes in the modes of locomotion in early cetaceans. Three hypotheses make predictions about evolution and function of the cetacean middle and inner ear. Another two hypotheses address the physical environment under which this transition took place, making prediction about paleoecology. New fossil material will be collected from freshwater and shallow marine sediments of the Kuldana and Kohat Formations of Northern Pakistan, the only area where the earliest and most plesiomorphic cetaceans are found. This material will allow testing of the hypotheses. Kuldana/Kohat cetaceans lived across a variety of depositional environments in what is now a structurally complex area, requiring detailed geological study. Sedimentological study will elucidate the physical setting of the transition. Related, ongoing work includes analyses of modern cetacean ear development and function, and an analysis of physiological constraints, based on stable oxygen isotopes. Significance.-- Cetacean origins is one of the best documented examples of land-water transitions among vertebrates, and showcases several form-function complexes that underwent pervasive change. Cetacean swimming evolved from quadrupedal paddling to dorsoventral oscillation of the broadened tail, and the Kuldana cetaceans display intermediate modes. The ears of cetacean ancestors were tuned to mid-frequency airborne sounds, whereas modern cetaceans hear underwater high- (odontocete) or low- (mys ticete) sounds. The position of the Kuldana cetaceans is unclear, but their auditory morphology is different from their terrestrial sister group and modern cetaceans. Fossil morphologies interpreted in an established phylogenetic context and against a background provided by modern aquatic mammals elucidates these evolutionary patterns. Studying the sedimentology of the rocks that document these morphological patterns clarifies the ecological setting of the land-to-water transition. This study is of broader significance for the higher phylogeny of mammals. It will provide morphological data to test phylogenies of the affinities of sperm whales (odotocete paraphyly) and the relationship of cetaceans to artiodactys (artiodactyl paraphyly). These phylogenetic hypotheses were proposed on the basis of molecular data, and are greatly disputed by morphologists. Studies of faunal evolution have suggested that Indo-Pakistan contacted Asia in the Cretaceous. Geological data dispute this claim. This study will provide a critical test for the Eocene paleontological data.