ORIGIN AND EARLY EVOLUTION OF WHALES IN EOCENE TETHYS (PAKISTAN)

摘要古生物学和分子生物学证据表明，早期鲸鱼与偶蹄目陆地哺乳动物关系最为密切，很可能是与现存河马祖先相近的早期炭疽偶蹄目哺乳动物。从形态上看，始新世考古动物演化的两个阶段是众所周知的：(1)以4700万年前的早中始新世Rodhoctus为代表的早期原生生物阶段；(2)以3700万年前的中到晚始新世Dorudon为代表的广泛化的担子鲸阶段。2004年与巴基斯坦地质调查局合作进行的野外工作表明，有可能从上伊普里统至普里亚布里亚沉积在特提斯东部的普里亚伯统地层中收集到保存完好的几乎完整的古八头鲸骨骼，现在暴露在巴基斯坦中部的苏莱曼山脉。这里提出的新的野外和实验室研究包括连续三次前往巴基斯坦的年度野外考察，目的有两个：1.从巴基斯坦中部边缘-海相低海平面巴斯卡组4800万-5000万年前的地层中恢复和研究原始古生物的关节骨骼。需要检验的假设是，白鲸级别的鲸鱼是陆生的。无论假说是否得到证实，这一时期的良好骨骼遗骸都将极大地增强我们对鲸目动物从陆地向海洋过渡的理解。巴基斯坦中部浅海上多曼达Pir Koh组和下Drazinda组3800万-4500万年前地层中原生生物到担龙化石的关节骨骼的恢复和研究。需要检验的假设是，像Georgiacus这样的高级原生生物完全是水生的，缺乏骨盆腰带和脊椎的连接，无法在陆地上支撑它们的重量。无论这一假说是否得到证实，这一时期的良好骨骼遗迹都将极大地提高我们对从原始原生动物那样的足力游泳转变为像霸王龙和现代鲸鱼那样的尾巴游泳的理解。现场方法是标准的GPS/GIS增强方法，化石的制备和复制将在密歇根大学最先进的准备设施中进行，与活的和灭绝的半水栖哺乳动物相比，分析将涉及广泛的定量描述和功能解释。这项研究的智力价值是恢复鲸鱼早期进化的新的形态和临时中间阶段的有形证据，从而能够评估鲸鱼对水中生活的许多方面的适应。这些新的证据对于促进早期鲸鱼进化的知识和加强我们对跨越适应带的宏观进化(在这种情况下是从陆地到海洋的过渡)的理解是必不可少的。该项目的广泛影响包括通过发现代表鲸鱼进化阶段的新骨骼来加强研究和教育的基础设施，而这些阶段目前鲜为人知。该项目将为美国和外国民族提供国际研究经验。最大的影响可能是通过更好的地质和古生物学证据来加强公众对进化的理解，这是人们广泛关注的主要进化转变之一。以前的探险收集的鲸骨现在在博物馆展出，在教科书中插图，并在世界各地的教室里讨论。

AbstractPaleontological and molecular evidence indicates that early whales are most closely related toartiodactyl land mammals, probably early anthracothere artiodactyls that were close to the ancestry ofliving hippos. Two stages of Eocene archaeocete evolution are now well known morphologically: (1) anearly protocetid stage represented by 47 million-year-old early middle Eocene Rodhocetus; and (2) ageneralized basilosaurid stage represented by 37 million-year-old middle-to-late Eocene Dorudon.Field work carried out through 2004 in collaboration with the Geological Survey of Pakistandemonstrates that it is possible to collect well-preserved and virtually-complete skeletons of archaeocetewhales from upper Ypresian through Priabonian strata deposited in eastern Tethys and now exposedspectacularly in the Sulaiman Range of central Pakistan. New field and laboratory research proposedhere includes three successive annual field expeditions to Pakistan, with two objectives:1. Recovery and study of articulated skeletons of primitive archaeocetes from 48-50 million-yearoldstrata of the marginal-marine low-sea-stand Baska Formation of central Pakistan. Thehypothesis to be tested is that whales of Pakicetus-grade were terrestrial. Whether the hypothesisis corroborated or not, good skeletal remains from this interval will greatly enhance ourunderstanding of the cetacean transition from land to sea.2. Recovery and study of articulated skeletons of protocetid-to-basilosaurid archaeocetes from 38-45 million-year-old strata of the shallow marine upper Domanda, Pir Koh, and lower Drazindaformations of central Pakistan. The hypothesis to be tested is that advanced protocetids likeGeorgiacetus were fully aquatic and lacked connection of the pelvic girdle to the vertebralcolumn, precluding support of their weight on land. Whether the hypothesis is corroborated ornot, good skeletal remains from this interval will greatly enhance our understanding of thetransition from foot-powered swimming like that of primitive protocetids to tail-power swimminglike that of basilosaurids and modern whales.Field methods to be employed are standard GPS/GIS-enhanced methods, preparation and replication offossils will take place in a state-of-the-art preparation facility at the University of Michigan, and analysiswill involve extensive quantitative description and functional interpretation in comparison with livingand extinct semiaquatic mammals.The intellectual merit of this research is recovery of tangible evidence of new morphologicallyand temporally intermediate stages of early whale evolution that enable assessment of many aspects ofadaptation to life in water. Such new evidence is essential for advancing knowledge of early whaleevolution and for enhancing our understanding of macroevolution across adaptive zones (in this case inthe transition from land to sea).Broader impacts of this project include enhancement of infrastructure for research and educationthrough discovery of new skeletons representing stages of whale evolution that are presently poorlyknown. The project will provide international research experience for American and foreign nationals.The greatest impact may be enhanced public understanding of evolution through better geological andpaleontological evidence for one of the principal evolutionary transitions of wide interest. Whaleskeletons collected by previous expeditions are now exhibited in museums, illustrated in textbooks, anddiscussed in classrooms all over the world.