Paleontological Study of Hemphillian (Late Miocene to Early Pliocene) Vertebrate Localities in Central Mexico

已知的晚中新世(早上新世)陆生脊椎动物遗址在墨西哥很少见，显然，该国任何地方都没有明确的早中新世化石(这些时代的化石在整个中美洲极其罕见)。在目前拟议的研究范围之外，只有三个地点被报道为希米利亚晚期：伊达尔戈州的特胡奇拉；米却肯州的拉戈莱塔(可能包含更多的布兰坎时代的化石)；以及奇瓦瓦州北部的伊波梅拉。前两个遗址没有很好的地层学记录，尽管第三个也是产量最高的遗址有。然而，它位于美国和墨西哥边境以南约150英里处。目前拟议的研究区域位于墨西哥中部瓜纳华托州的中东部，据报道，在该区域内有两个嗜血虫脊椎动物遗址。其中一种名为El Ocote，已在几份报告中讨论过；另一种名为Coecillo，尚未得到很好的收集或研究。第三种是新发现的Rinconada。最后一处遗址包含非常丰富、保存完好的化石，这些化石似乎代表了早期和晚期的西半球形式。了解中美洲早期的脊椎动物很重要，原因有几个。这些措施包括更好地了解晚新生代北美和南美洲之间最早的扩散时间，确定扩散是否是间歇性的而不是连续性的，比较中美洲相对鲜为人知的嗜血动物群和美国的知名动物群，以及关于突然出现在美国大平原地区的一些哺乳动物属和物种的起源和多样性的有价值的信息，这些物种可能是在墨西哥高原上进化的。这些属和种包括马和蟋蟀类等重要类群。此外，在拟议研究期间收集的数据将提供关于在重要时间间隔期间气候和生态条件变化的宝贵信息。这项拟议研究的主要目标是仔细收集Rinconada和Coecillo遗址的地层背景下的化石和数据。化石的屏幕清洗将是行动的一部分。然后将对化石进行准备和研究，以获得与上述物品有关的知识。

Known late Hemphillian (Early Pliocene) terrestrial vertebrate sites are rare in Mexico, and apparently, unequivocal early Hemphillian fossils (Late Miocene) have not yet been reported from anywhere in the country (fossils of these ages are extremely rare in all Central America). Outside the area of the presently proposed study only three localities of late Hemphillian age have been reported: Tehuichila in the state of Hidalgo; La Goleta in the state of Michoacan (which probably contains more Blancan than Hemphillian age fossils); and Yepomera in the northern state of Chihuahua. The first two sites have not been well documented stratigraphically, although the third, and most productive site, has. It is, however, only about 150 miles south of the U.S.-Mexican border. Inside the presently proposed study area, which lies within the east- central part of the state of Guanajuato in central Mexico, are two reported Hemphillian vertebrate sites. One, El Ocote, has been discussed in several reports; the other, Coecillo, has not been well collected or studied. A third, Rinconada, is newly discovered. The last site contains very abundant, well preserved fossils which appear to represent early as well as late Hemphillian forms. Knowledge of early Hemphillian vertebrates from Central America would be important for several reasons. These include a better understanding of the earliest times of dispersals in the Late Cenozoic between North and South America, determination whether dispersals were episodic rather than continual, comparison of relatively poorly known Hemphillian faunas in Central America with well known ones in the United States, and valuable information concerning the origin and diversification of a number of mammalian genera and species which appeared suddenly in the United States' Great Plains area that probably evolved on the Mexican Plateau. These genera and species include such important groups as horses and cricetid rodents. Additionally, data gathered during the proposed research would provide valuable information on changing climatic and ecologic conditions during an important time interval. The major objective of this proposed research is to carefully collect fossils and data in a stratigraphic context at the Rinconada and Coecillo sites. Screen washing for fossils would be part of the operation. Fossils would then be prepared and studied in order to obtain knowledge relevant to the items stated above.