Mississippian Fossil Tetrapods from Midcontinental USA and Early-Tetrapod Phylogeny

陆栖脊椎动物的最早历史，从3.7亿年到3.2亿年前的现在，代表了极少数地区的极少数化石。这些化石大多保存不善，残缺不全，这给古生物学家解释陆生脊椎动物早期历史带来了困难。从对目前可用的化石的研究中已经学到了很多，从少数几个可用的例子中仍然可以学到更多的东西。然而，在了解陆生脊椎动物最早的历史方面取得的进一步进展将主要来自新化石的发现。1985年，在爱荷华州东南部靠近德尔塔镇的一个新地点发现了大量早期陆地脊椎动物的化石。据地质学家测定，三角洲遗址大约有3.4亿年的历史，这使它成为美国最古老的早期陆地动物所在地，也是世界上最古老的地点之一。在三年的时间里，收集了600多个标本，其中包括大约50具部分骨架，其中一些几乎是完整的；这些藏品的大部分保存在菲尔德自然历史博物馆，还有一些保存在爱荷华大学。这些化石保存完好，是早期陆地脊椎动物地区中数量最多的好标本。至少存在三个新物种，每个物种都非常原始。这三个物种代表了这类早期陆地脊椎动物已知数量的大约20%的增长。因此，三角洲化石构成了数十年来最重大的古生物发现之一。野外博物馆的化石制作者已经在三角洲标本上花费了3000多个工时。对这一研究项目的支持将为另外700小时的技术帮助提供资金。这项工作的大部分时间(560小时)将集中在为科学研究准备三角洲地区最丰富物种的额外关键标本。剩余的时间(140小时)将用于制作该物种的科学插图以供出版。

The earliest history of land-living vertebrates, from 370-320 million years before present, is represented by a very few fossils from a handful of localities. Most of these fossils are poorly preserved and incomplete, which makes it difficult for paleontologists to interpret the early history of terrestrial vertebrates. Much has been learned from study of the currently-available fossils, and more can still be learned from the few available examples. However, further progress in understanding the earliest history of land-living vertebrates will come primarily from the discovery of new fossils. In 1985, a new locality containing numerous fossils of early land vertebrates was discovered in southeastern Iowa near the town of Delta. The Delta site has been dated by geologists at about 340 million years old, which makes it the oldest early-land-animal locality in the United States, and one of the oldest in the world. Over a periods of three years, more than 600 specimens including about 50 partial skeletons, some nearly complete, were collected; most of this collection is stored in the Field Museum of Natural History, and some at the University of Iowa. The fossils are well-preserved and the collection represents the largest number of good specimens of any early-land-vertebrate locality. At least three new species are present, each very primitive. These three species represent an increase of about 20% in the known number of such early land vertebrates. The Delta fossils thus comprise one of the most significant paleontological discoveries in decades. Field Museum fossil preparators have already spent over 3,000 person-hours on Delta specimens. Support for this research project will fund a further 700 hours of technical help. The majority of this effort (560 hours) will be focused on preparing additional key specimens of the most abundant species in the delta collection for scientific study. The remainder (140 hours) will be used to produce scientific illustrations of this species for publication.