Early Cretaceous Multituberculata (Mammalia) from North America and Asia

多结核目的地质范围为晚三叠世至早渐新世（约1.95 ~ 3500万年前）；因此，这一类群是已知的最长寿的哺乳动物目。除了它们的长寿之外，多瘤动物是白垩纪晚期和古新世（大约7500万到5800万年前）最丰富和最多样化的哺乳动物群体之一。然而，从晚侏罗世到晚白垩纪早期，间隔超过5000万年，对多瘤动物的进化史几乎一无所知。正是在这段时间内出现了多结节病的三个主要亚群中的两个。尽管早白垩纪时期的北美多瘤动物的大量发现已经超过35年，但它从未被描述过。这组标本来自德克萨斯州中北部，包括大约165颗独立的牙齿，大约处于我们对多瘤进化的认识中5000万年的中间阶段。最近在蒙大拿州中南部的野外工作揭示了北美西部另一个早白垩世多结核地区的存在。因此，本研究的目的如下：1)描述来自德克萨斯州的多瘤属植物，并评估其与其他多瘤属植物的系统发育关系；2)在蒙大拿州的新地点进行实地考察，试图从这一关键时期发现更多的多瘤标本，但来自北美的不同地理区域；3)详细分析早白垩世多瘤龙的牙齿功能和颌部运动，以确定其饮食倾向。

The geologic range of the mammalian order Multituberculata is from the Late Triassic to early Oligocene (approximately 195 to 35 million years ago); the group is therefore the longest- lived order of mammals known. In addition to their great longevity, multituberculates constituted one of the most abundant and diverse mammal groups during the Late Cretaceous and Paleocene (from approximately 75 to 58 million years ago). Almost nothing, however, is known about the evolutionary history of multituberculates from the Late Jurassic to the early Late Cretaceous, an interval of over 50 million years. It is during this interval that two of the three major subgroups of multituberculates arose. Although a large collection of North American multituberculates of Early Cretaceous age has been known for over 35 years, it has never been described. This collection, from north-central Texas, comprises approximately 165 isolated teeth and lies roughly in the middle of the 50 million year gap in our knowledge of multituberculate evolution. Recent field work in south-central Montana has revealed the presence of another Early Cretaceous multituberculate-bearing locality in western North America. The objectives of the research proposed here are therefore as follows: 1) to describe the collection of multituberculates from Texas and to evaluate their phylogenetic relationships to other multituberculates; 2) to conduct field work at the new locality in Montana in an attempt to find additional multituberculate specimens from this crucial interval of time but from a different geographic region within North America; and 3) to perform a detailed analysis of dental function and jaw movement of Early Cretaceous multituberculates to determine their dietary proclivities.