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

SGER：爱荷华州塔基奥谷地懒的挖掘、骨学和 DNA 测定

• 批准号: 0829393
• 负责人: Holmes Semken
• 金额: $ 2万
• 依托单位: University of Iowa
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-06-15 至 2010-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0829393&HistoricalAwards=false
• 关键词: SGER; Excavation; Osteology; DNA; Determination

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

爱荷华州塔尔基奥山谷的发掘、骨学和DNA测定。小塞姆肯PI摘要。 2001年，在一场大洪水之后，人们在爱荷华州西南部的一条河床上发现了一只非凡的成年冰河时代巨型地懒，巨爪龙。随后的挖掘，可能只有在流量减少的时期，产生了104个元素（约55%）的发现骨架。这个标本现在代表了第二个最完整的杰斐逊？已知的巨型地懒。这具成年标本的科学价值因随后发现的两具不同年龄的少年（目前有41具骨骼）与成年标本部分混合而大大增加。这是第一个成年巨爪龙与可能的后代的直接联系。含有树懒遗骸的池塘状沉积单元还含有植物大型化石、花粉、软体动物以及数量有限的微型脊椎动物。这些将提供有关死亡时的直接和区域环境的信息。树懒遗骸的上级保存表明，骨骼元素的同位素分析应该提供有关这些神秘生物的饮食信息以及死亡时间前后的温度值。良好的同位素分析的可能性得到了成人牙齿元素图的支持。碳已被确定为存在于牙列中，因此DNA也可能存在。如果存在，可以确定样本的性别、家庭关系和绝对年龄（放射性碳年）。该网站，最新更新世的年龄根据地层位置，是位于一个已知的距离冰川前（得梅因叶），并应提供洞察力的气候耐受性，这一广泛的分类在生态极端。很明显，繁殖发生在冰锋附近。树懒群体似乎生活在更新世末大型哺乳动物灭绝事件附近，这可能有助于寻找解释。塔尔基奥山谷生物协会提供了一个无与伦比的机会，以提高我们的生理学和古生态学的巨爪龙的知识。一个拥有孢粉学、稳定同位素、植物大型化石、微型脊椎动物、分子生物学、考古学和第四纪地层学专业的学者团队渴望指导学生对该协会进行全面分析。然而，在对标本及其古环境关系进行全面分析之前，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单和骨骼学分析，（3）确定是否可以对塔尔基奥标本进行比较DNA分析。部分发现位于塔尔基奥山谷北岸8米厚的覆盖层下，其他部分位于河床下方，骨床延伸到南部4米厚的滑塌块下。 北岸已被清理，但需要重型设备来暴露河床，并揭露南岸下的含骨沉积物。一旦完成全部挖掘，将准备一份完整的元素清单、骨骼学分析和骨骼分布图，为所有未来调查提供必要的基本数据。在塔尔基奥山谷遗址的探索工作的最后阶段是确定是否保存了足够的DNA来建立遗址上个体树懒之间的关系。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的冰河时代大型哺乳动物协会之一。这一发现通过一个网站、巡回展览、讲座和志愿者参与，使该地区成千上万的人感到兴奋。外联实习生将提供即时更新，并更好地协调所有这些活动。活动可在以下网址查阅：www.uiowa.edu/~nathist/Site/sloth/index.html