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

到中侏罗世（约1.65亿年前），哺乳动物已经在地理上广泛分布，生活在生态多样化的栖息地。最近的发现表明，早期哺乳动物会爬、挖洞、游泳，有些哺乳动物甚至吃恐龙。尽管从化石中获得的解剖学信息有了巨大的增长，但有一个问题仍然没有得到解答：哺乳动物是什么时候起源的？该项目将研究哺乳动物的起源，将几种直到最近才为人所知的早期哺乳动物的骨骼材料纳入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公开访问。这项工作已经与高中生进行了合作，并成为石溪大学科学与工程专业本科生课程的一部分。更具体地说，这个项目集中在一个叫做异源兽目的早期哺乳动物类群上（包括冈瓦那兽目、原源兽目、真源兽目和多结核兽目）。最近，异源兽门成为哺乳动物起源争论的焦点，因为它可能包括比已知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。异源兽有特殊的牙齿，与其他早期哺乳动物相比，与现代啮齿动物更相似。大多数早期哺乳动物要么保留了原始的爬行类牙齿，要么发展出了前摩擦齿或摩擦齿（在现代胎盘类和有袋类动物中看到的一种模式）。异源兽目的进化枝并不符合这一理论，但这是由于共同的起源还是趋同的进化尚不确定。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，一些异源兽几乎完全由高度特化的牙齿和颌来代表。幸运的是，在中国发现了基本的多结节类、真原足类和原足类的完整骨架，而在马达加斯加发现了一具完整的、保存得非常完好的类冈瓦纳兽类哺乳动物骨架。再加上一个来自马达加斯加的冈瓦那瑟类动物的完整头骨，这些惊人的发现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之树（AToL）矩阵，最终将有可能提供更可靠的测试，以确定冈瓦那亚目、原氏亚目、真原氏亚目和多结核亚目相对于现存哺乳动物谱系的位置。在更广泛的范围内，对AToL哺乳动物生命之树矩阵中超过1500个字符的先前未采样的标本进行评分将对该项目的持续发展做出重大贡献。

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.