Toward the Origin of Whales: Eocene Cetacea from Pakistan

The wissen 9526686这个项目研究鲸目动物(鲸鱼、海豚、鼠海豚)从陆栖四足动物到海洋游泳者的转变。这一转变是为数不多的有文献记载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，运动和听力，并评估其古生态背景。假设--将检验七个假设。其中两个预测了早期鲸目动物运动方式的变化。三种假说预测鲸目动物中耳和内耳的进化和功能。另外两个假说解决了这种转变发生的物理环境，做出了关于古生态的预测。将从巴基斯坦北部库尔达纳组和科哈特组的淡水和浅海沉积物中收集新的化石材料，库尔达纳组和科哈特组是唯一发现最早和最具半形性鲸目动物的地区。这份材料将允许对假设进行检验。库尔达纳/科哈特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，需要进行详细的地质研究。沉积学研究将阐明过渡的物理背景。相关的正在进行的工作包括对现代鲸目动物耳朵发育和功能的分析，以及基于稳定氧同位素的生理限制分析。意义--鲸目动物的起源是脊椎动物之间陆地-水过渡的最好记录之一，并展示了几个经历了普遍变化的形式-功能复合体。鲸目动物的游动从四足划桨进化到加宽尾巴的背腹摆动，Kuldana鲸目动物表现出中间模式。鲸目动物祖先的耳朵被调谐到中频空中传播的声音，而现代鲸目动物听到的是水下的高(齿形)或低(Mys Ticete)声音。Kuldana鲸目动物的位置尚不清楚，但它们的听觉形态与它们的陆生姐妹群和现代鲸目动物不同。根据现代水生哺乳动物提供的背景，在已建立的系统发育背景下解释的化石形态阐明了这些进化模式。研究记录了这些形态模式的岩石的沉积学，阐明了从陆地到水的转变的生态环境。本研究对哺乳动物的高等系统发育具有更广泛的意义。它将提供形态数据，以测试抹香鲸的亲缘关系以及鲸目动物与偶蹄类的关系(偶指目)。这些系统发育假说是在分子数据的基础上提出的，并且受到了形态学者的极大争议。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。地质数据驳斥了这一说法。这项研究将为始新世古生物资料提供关键的检验。

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.