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

论文研究：冈瓦纳大陆的新白垩纪哺乳动物及其对中生代哺乳动物类系统学的影响

• 批准号: 1501497
• 负责人: Erik Seiffert
• 金额: $ 1.61万
• 依托单位: SUNY at Stony Brook
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-05-01 至 2017-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1501497&HistoricalAwards=false
• 关键词: DISSERTATION; RESEARCH; New; Cretaceous; Mammals

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.

到侏罗纪中期（大约 1.65 亿年前），哺乳动物已经在地理上广泛分布，并且生活在生态多样化的栖息地中。最近的发现表明，早期哺乳动物会攀爬、挖洞、游泳，一些哺乳动物甚至吃恐龙。尽管化石中的解剖学信息大量增加，但仍有一个问题仍未得到解答：哺乳动物何时起源？该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大规模的系统发育分析中来研究哺乳动物的起源。详细的形态描述、字符矩阵、插图和 3D 重建将可通过 MorphoBank 和 MorphoSource 公开获取。这项工作已经与高中生进行了合作，并成为石溪大学为科学与工程专业本科女性提供的课程的一部分。更具体地说，该项目以一种称为异兽亚纲（Allotheria）的早期哺乳动物类群为中心（包括冈瓦纳兽亚目（Gondwanatheria）、哈拉米亚目（Haramiyida）、真兽亚目（Euharamiyida）和多瘤亚目（Multituberculata）。最近，异兽亚目成为哺乳动物起源争论的焦点，因为它可能包括比先前已知的最古老的哺乳动物化石还要早5000万年以上的物种，将哺乳动物的起源推回三叠纪。异兽有特殊的牙列，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原始的爬行动物样牙齿，要么发展出前三蝶齿列或三蝶齿列（现代胎盘动物和有袋动物中常见的模式）。异兽亚纲的进化枝不符合这一方案，但这是否是由于共同起源或趋同进化所致尚不确定。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，一些异兽类几乎完全由高度特化的牙齿和颌骨代表。幸运的是，在中国发现了基本完整的多瘤动物、真哈拉米动物和哈拉米动物的骨骼，而在马达加斯加发现了完整且保存异常完好的冈瓦纳兽类哺乳动物的骨骼。连同来自马达加斯加的冈瓦纳兽的完整头骨，这些非凡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，最终将有可能对冈瓦纳动物、Haramiyida、Euharamiyida 和 Multituberculata 相对于现存哺乳动物谱系的位置提供更可靠的测试。在更广泛的范围内，对 AToL 哺乳动物生命树矩阵中 1,500 多个字符的先前未采样样本进行评分将对该项目的持续发展做出重大贡献。