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

点击翻译按钮获取中文摘要

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.