SGER: Excavation, Osteology and DNA Determination of the Tarkio Valley, Iowa, Ground Sloths

爱荷华州塔基奥山谷的挖掘、骨学和DNA测定，地懒小霍姆斯·A·塞姆肯。图片摘要。2001年，在一场大洪水之后，在爱荷华州西南部的河床上发现了一种非凡的冰河时代的成年巨型地懒--巨型地懒。随后的挖掘只有在流量减少的时候才有可能，已经发现了104个元素(约55%)。这个标本现在代表了已知的第二完整的杰斐逊？S巨型地懒。这具成年标本的科学价值因随后发现的两具不同年龄的幼体(目前为41块骨骼)而大大增加，这些幼体部分与成体混合在一起。这是第一次将成年巨型甲鱼与可能的后代直接联系起来。含有树懒遗骸的池塘状沉积单元还包括植物大型化石、花粉、软体动物以及数量有限的微型脊椎动物。这些资料将提供有关死亡时的直接和区域环境的信息。树懒遗骸的出色保存表明，骨骼元素的同位素分析应该提供关于这些神秘生物的饮食信息，以及死亡时间附近的温度值。成人牙齿的元素图支持良好的同位素分析的可能性。碳已经被确定为存在于牙列中，所以DNA也可能存在。如果存在，可以确定放射性碳年标本的性别、家庭关系和绝对年龄。根据地层位置，该遗址的年龄是最晚的更新世，距离冰川前缘(得梅因河口)有一段已知的距离，应该可以洞察这个生态极端的大范围分类群的气候容忍度。很明显，繁殖发生在冰面附近。这一树懒群体似乎生活在更新世末期巨型哺乳动物灭绝事件附近，可能有助于寻找解释。塔基奥谷生物协会提供了一个无与伦比的机会，以增强我们对巨型甲鱼的生理学和古生态的了解。一个由孢粉学、稳定同位素、植物大型化石、微脊椎动物、分子生物学、考古学和第四纪地层学专业的学者组成的团队渴望在协会的总体分析中指导学生。然而，在对标本及其古环境关联进行全面分析之前，有必要(1)确保恢复所有剩余的骨骼元素，(2)完成每只树懒的骨骼清点和骨学分析，(3)确定是否有可能对塔尔基奥标本进行DNA比较分析。部分发现位于塔基奥山谷北岸8米厚的覆盖层下，其他部分位于河床下方，骨头床向南延伸到一个4米长的塌陷地块下。北岸已经清理完毕，但需要重型设备来暴露河床，并发现南岸下面的含骨沉积物。一旦全部挖掘完成，将准备一份完整的元素清单、骨学分析和骨骼分布图，为未来的所有调查提供必要的基本数据。在塔尔基奥山谷遗址进行的这项探索工作的最后阶段是确定是否保存了足够的DNA来建立该遗址中各个树懒之间的关系。这三个阶段的完成将使塔尔基奥山谷地区成为有记录以来最全面审查的冰河时代大型哺乳动物协会之一。这一发现通过网站、巡回展览、讲座和志愿者参与，使该地区成千上万的人兴奋不已。一名外展实习生将及时提供最新情况，并更好地协调所有这些活动。可在www.uiowa.edu/~nathist/site/sloth/index.html上查看活动。

Excavation, Osteology and DNA Determination of the Tarkio Valley, Iowa, Ground Sloths Holmes A. Semken, Jr. PIAbstract. An extraordinary adult ice-age giant ground sloth, Megalonyx jeffersonii, was discovered in a southwest Iowa stream bed in 2001 following a major flood. Subsequent excavations, possible only during periods of reduced flow, have produced 104 elements (about 55 percent) of the discovery skeleton. This specimen now represents the second most complete Jefferson?s giant ground sloth known. The scientific value of this adult specimen was compounded tremendously by the subsequent discovery of two juveniles (41 bones at present) of different ages partially intermingled with the adult. This is the first direct association of an adult Megalonyx with possible offspring. The pond-like depositional unit containing the sloth remains also contains plant macrofossils, pollen, mollusks as well as limited numbers of micro-vertebrates. These will provide information on the immediate and regional environments at the time of death. Superior preservation of the sloth remains suggests that isotope analyses of the skeletal elements should provide dietary information about these enigmatic creatures as well as temperature values around the time of death. The probability of good isotopic analyses is supported by elemental maps of an adult tooth. Carbon has been determined as present in the dentition so it is possible that DNA is also is present. If present, sex, family relationships and absolute age of the specimens in radiocarbon years may be determined. The site, latest Pleistocene in age based on stratigraphic position, is located a known distance from the glacial front (Des Moines lobe) and should provide insight on the climatic tolerances of this wide-ranging taxon at an ecological extreme. It is clear that breeding occurred near the ice front. It also appears that the sloth group lived close to the end-Pleistocene mega-mammal extinction event and may assist in the search for an explanation. The Tarkio Valley biotic association offers an unparalleled opportunity to enhance our knowledge of both the physiology and paleoecology of Megalonyx. A team of scholars with specialties in palynology, stable isotopes, plant macrofossils, microvertebrates, molecular biology, archaeology and Quaternary stratigraphy is eager to supervise students in the total analysis of the association. However, before a comprehensive analysis of the specimens and their paleoenvironmental associations, can be conducted, it is necessary to (1) ensure recovery all remaining skeletal elements, (2) complete a skeletal inventory and osteological analysis of each sloth and (3) ascertain if comparative DNA analyses of the Tarkio specimens is possible. Part of the find is located under eight meters of overburden on the north bank of the Tarkio Valley, others are just below the stream bed and the bone bed extends under a four meter slump block to the south. The north bank has been cleared but heavy equipment is required to expose the stream bed and uncover the bone-bearing deposits under the south bank. Once total excavation is accomplished, a complete element inventory, osteological analysis and bone distribution map will be prepared to provide the basic data necessary for all future investigations. The final phase of this exploratory effort at the Tarkio Valley site is to determine if sufficient DNA is preserved to establish relationships between individual sloths at the site. Completion of these three phases will then permit the Tarkio Valley locality to be one of the most comprehensively examined ice-age large mammal associations on record. This discovery has excited thousands of people regionally via a web site, traveling exhibits, lectures and volunteer participation. An outreach Intern will provide immediate updates and better coordinate all of these activities. Activities can be reviewed at: www.uiowa.edu/~nathist/Site/sloth/index.html