DISSERTATION RESEARCH: New Cretaceous Mammals from Gondwana and their implications for the systematics of Mesozoic Mammaliaformes

到了中侏罗纪（约1.65亿年前），哺乳动物已经在地理上分布广泛，生活在生态多样的栖息地。最近的发现表明，早期的哺乳动物会攀爬、挖洞、游泳，有些哺乳动物甚至吃恐龙。尽管来自化石的解剖学信息有了巨大的增加，但有一个问题仍然没有答案：哺乳动物是什么时候起源的？这个项目将调查哺乳动物的起源，将几个骨骼材料，直到最近，鲜为人知的早期哺乳动物到一个大规模的系统发育分析。详细的形态描述，字符矩阵，插图和3D重建将通过MorphoBank和MorphoSource开放访问。这项工作已经与高中学生合作，并已成为斯托尼布鲁克大学为科学和工程专业的女本科生开设的课程的一部分。更具体地说，这个项目集中在一个早期的哺乳动物群称为异兽（包括冈瓦纳兽，Haramiyida，Euharamiyida和Multituberculata）。最近，异兽目成为关于哺乳动物起源的争论的焦点，因为它可能包括比最古老的哺乳动物化石早5000万年的物种，将哺乳动物的起源推回到三叠纪。异兽有专门的齿系，比任何其他早期哺乳动物更类似于现代啮齿动物。大多数早期哺乳动物要么保留了原始的爬行类牙齿，要么发展出了一种前楔齿或楔齿的齿系（在现代胎盘动物和有袋动物中看到的模式）。异兽亚目的分支并不符合这一模式，但这是由于共同的起源还是趋同进化尚不确定。对它们的系统发育关系进行严格的测试是不可能的，因为直到最近，几种异兽动物几乎都只有高度特化的牙齿和颌骨。幸运的是，在中国发现了基本完整的多瘤兽、真哈拉米兽和哈拉米兽的骨骼，而在马达加斯加发现了一个完整的、保存得非常好的冈瓦纳兽类哺乳动物的骨骼。这些惊人的发现，再加上来自马达加斯加的冈瓦纳兽的完整头骨，提供了大量以前无法获得的形态学数据。通过将这些信息纳入生命树（AToL）矩阵，最终将有可能提供更可靠的测试冈瓦纳兽，Haramiyida，Euharamiyida和Multituberculata相对于现存哺乳动物谱系的位置。在更广泛的范围内，为AToL哺乳动物生命树矩阵中的1,500多个字符对以前未采样的标本进行评分将大大有助于该项目的持续发展。

By the Middle Jurassic (about 165 million years ago), mammals were already geographically widespread and lived in ecologically diverse habitats. Recent discoveries reveal that early mammals climbed, dug holes, swam and some mammals even ate dinosaurs. Despite the tremendous increase in anatomical information from fossils, one question still remains unanswered: when did mammals originate? This project will investigate the origin of mammals by incorporating skeletal material of several, until recently, poorly known early mammals into a broad-scale phylogenetic analysis. Detailed morphological descriptions, character matrices, illustrations, and 3D reconstructions will be openly accessible through MorphoBank and MorphoSource. This work has already generated collaborations with high school students and has formed part of a course offered to undergraduate Women in Science and Engineering at Stony Brook University. More specifically, this project centers on an early mammalian grouping called Allotheria (including Gondwanatheria, Haramiyida, Euharamiyida, and Multituberculata). Recently, Allotheria became a focal point in the debate on the origin of mammals as it may include species that are more than 50 million years older than the oldest, previously known mammalian fossils, pushing the origin of mammals back into the Triassic. Allotheria have specialized dentition which is more similar to that of modern rodents than any other early mammal. Most early mammals either retained primitive reptilian-like teeth or developed a pre-tribosphenic or tribosphenic dentition (a pattern seen in modern placental and marsupials). The clades of Allotheria do not fit this scheme, but whether this is due to a common origin or to convergent evolution is uncertain. Rigorous tests of their phylogenetic relationships have not been possible, because several allotherians were, until recently, represented almost solely by highly specialized teeth and jaws. Fortunately, largely complete skeletons of basal multituberculates, euharamiyids, and haramiyids have been found in China, while a complete and exceptionally well-preserved skeleton of a gondwanatherian-like mammal has been found in Madagascar. Together with a complete skull of a gondwanatherian from Madagascar, these remarkable discoveries provide a tremendous amount of morphological data that was previously unavailable. By including this information into the Tree of Life (AToL) matrix, it will finally be possible to provide more robust tests of the position of Gondwanatheria, Haramiyida, Euharamiyida, and Multituberculata relative to extant mammalian lineages. On a broader scale, scoring previously unsampled specimens for more than 1,500 characters in the AToL Mammal Tree of Life matrix will contribute significantly to the ongoing growth of that project.