RUI/SG: Phylogenetic Relationships of Archaic "Ungulates" and Their Implications for the Timing and Rate of Divergence of Placental Mammal Clades

“髁状突”是生活在恐龙灭绝后的头2000万年左右的不同哺乳动物化石家族的集合。不同种类的髁状突一直被认为是某些早期哺乳动物谱系的祖先或近亲，特别是各种有蹄哺乳动物。最近利用活着的哺乳动物的DNA进行的研究让我们更好地了解了活着的哺乳动物的不同谱系是如何进化的，但他们也让人不太清楚髁状突之间的关系。这项研究的目的是阐明髁突与其他哺乳动物，特别是那些幸存至今的谱系之间的关系。由于它们生活在化石记录中出现各种现存哺乳动物谱系的时代，了解髁突与现存哺乳动物的进化关系将有助于我们更好地了解不同哺乳动物谱系的起源。这将有助于解决一个长期存在的问题，即大多数哺乳动物的谱系是在恐龙灭绝之后多样化，还是在恐龙灭绝之前很久(正如一些哺乳动物的DNA研究所提出的那样)。因此，这将有助于我们理解哺乳动物为什么进化成包括我们自己的物种在内的这么多形式的原因。这项研究将专门关注四个主题：1)髁状突分类群与现存哺乳动物谱系的系统发育亲缘关系；2)是否有任何髁状突动物科形成自然(单系)群；3)有蹄类动物是否是自然类群；以及4)髁状突进化如何影响不同哺乳动物谱系的分化时间的解释。来自髁状突骨骨解剖的数据将与广泛的现存和灭绝的胎盘哺乳动物的形态和分子数据相结合。简约法、似然法和贝叶斯方法将被用来评估髁突的系统发育位置，几种新的途径和方法将被用来估计分化时间。这一结果将有助于评估湿疣的系统发育地位和分类，重新评价湿疣对于胎盘哺乳动物起源的意义，并根据湿疣的系统发育重新评估现存胎盘血统的分化时间。

"Condylarths" are a collection of different families of fossil mammals that lived during the first 20 million years or so after the extinction of the dinosaurs. Different kinds of condylarths have been considered to be ancestors or close relatives of certain early lineages of mammals, especially the various groups of hoofed mammals. Recent studies using DNA from living mammals have given us a better understanding of how the different lineages of living mammals evolved, but they have also made the relationships of the condylarths less clear. This research aims to clarify how condylarths are related to other mammals, particularly those lineages that have survived to the present. Because they lived during a time when the various lineages of living mammals appeared in the fossil record, understanding the evolutionary relationships of condylarths to living mammals will help us better understand the origins of different mammal lineages. This will help resolve a longstanding issue as to whether most mammal lineages diversified after the dinosaurs went extinct or well before the dinosaur extinction (as some DNA studies of mammals have proposed). As a result, it will help us understand the reasons why mammals diversified into so many forms that we see today, including our own species.This study will focus specifically on four topics: 1) the phylogenetic affinities of condylarth taxa to extant mammalian lineages; 2) whether any condylarth families form natural (monophyletic) groups; 3) whether ungulates (hoofed mammals) are a natural group; and 4) how condylarth evolution affects the interpretation of divergence times for various mammal lineages. Data from the skeletal anatomy of condylarths will be combined with morphological and molecular data for a broad range of extant and extinct placental mammals. Parsimony, likelihood, and Bayesian methods will be used to evaluate the phylogenetic positions of condylarths, and several new approaches and methods will be used to estimate divergence times. The results will assess the phylogenetic position and taxonomy of condylarth taxa, re-evaluate the significance of condylarths for the origins of placental mammal lineages, and re-evaluate divergence times of extant placental lineages based on condylarth phylogeny.