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

到中侏罗世(大约1.65亿年前)，哺乳动物已经在地理上广泛分布，并生活在生态多样化的栖息地。最近的发现表明，早期的哺乳动物攀爬、挖洞、游泳，一些哺乳动物甚至吃恐龙。尽管来自化石的解剖学信息大幅增加，但有一个问题仍然没有答案：哺乳动物是什么时候起源的？这个项目将通过将几种直到最近还鲜为人知的早期哺乳动物的骨骼材料纳入广泛的系统发育分析来调查哺乳动物的起源。详细的形态描述、字符矩阵、插图和3D重建将通过MorPhoBank和MorPhoSource公开访问。这项工作已经产生了与高中生的合作，并成为石溪大学为理工科本科生开设的课程的一部分。更具体地说，该项目以一种名为异种异体的早期哺乳动物群体为中心(包括冈氏原虫、哈拉米亚原虫、真原原虫和多瘤原虫)。最近，异形动物成为关于哺乳动物起源的辩论的焦点，因为它可能包括比先前已知的最古老的哺乳动物化石早5000多万年的物种，将哺乳动物的起源推回到三叠纪。异形动物有专门的牙列，这与现代啮齿动物的牙列比任何其他早期哺乳动物都更相似。大多数早期哺乳动物要么保留了原始的爬行动物般的牙齿，要么形成了摩擦性或摩擦性牙列(这种模式见于现代胎盘和有袋类动物)。异形异形的分支不符合这一方案，但这是由于共同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，几个同种动物几乎完全由高度专门化的牙齿和颌骨代表。幸运的是，在中国身上发现了基本完整的多瘤类、真哈拉米亚目和哈拉米亚目的骨骼，而在马达加斯加发现了一具完整的、保存异常完好的类刚毛目哺乳动物的骨架。再加上马达加斯加一只刚毛虫的完整头骨，这些令人惊叹的发现提供了大量以前无法获得的形态数据。通过将这一信息纳入生命树(ATOL)矩阵，最终将有可能提供更可靠的测试，以确定冈氏原虫、哈拉米亚原虫、真原原虫和多瘤类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超过1,500个字符的以前未抽样的样本评分将对该项目的持续增长做出重大贡献。

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.