COLLABORATIVE RESEARCH: Late Creataceous Vertebrates from Madagascar: Implications for Gondwanan Biogeography

小行星9706302 NSF资助的马达加斯加西北部Mahajanga盆地Maevarano组的野外工作，使岛上晚白垩世脊椎动物的多样性增加了四倍。 动物区系列表现在包括至少32种鱼类，青蛙，海龟，蜥蜴，蛇，鳄鱼，恐龙，鸟类和哺乳动物。 几个分类群的代表是几乎完整的，精美保存的骨骼。 本提案的主要目标是通过进一步发现脊椎动物化石，对新样本进行系统发育分析，阐明地层学、沉积学和埋藏学背景，以及测试与南方超大陆冈瓦纳大陆碎裂有关的各种地理学假设，来扩大这项工作。 冈瓦纳大陆在晚侏罗世和白垩纪分裂成许多孤立的陆块，对相关的生物群产生了巨大的影响。 对这一大陆碎片的重建几乎完全基于地球物理证据，并且在古生物学上仍然缺乏测试。 根据最近的模型，南极洲、澳大利亚、马达加斯加和印度次大陆在晚侏罗世（150-160 Ma）的某个时候作为一个单一的构造单元从非洲东部分离出来。 南极洲可能在整个中生代都与南美洲保持着物理联系。 在早白垩世（125-130 Ma），马达加斯加达到了目前的位置约400公里的非洲东海岸，并与印度次大陆，从舌到澳大利亚分开。 马达加斯加和印度次大陆持续作为一个独特的构造单元，直到~88马，早在沉积的Maevarano组。 从这种破碎模式中可以得出几个与马达加斯加岛地理历史有关的可检验的假说：（1）马达加斯加岛晚白垩世陆生动物群与同时代的非洲动物群没有更大的亲缘关系，而是与印度次大陆的动物群，其次是与南极洲、澳大利亚和南美洲的动物群有更大的亲缘关系;（2）相应地，印度次大陆晚白垩世动物群与马达加斯加等冈瓦纳大陆的系统发育相似性最大，而不是与亚洲;和3）马达加斯加高度地方性和不平衡的现存脊椎动物区系的大多数主要成分（例如，狐猴类灵长类动物）在晚白垩世与世隔绝后殖民了该岛。 本研究将解决这些假设，通过严格的系统发育（支序）分析晚白垩世的脊椎动物从马达加斯加和其他冈瓦纳大陆。 虽然最近从马哈赞加盆地的Maevarano地层中发现的脊椎动物遗骸为这些测试提供了重要的基础，但还需要更多的材料。 因此，建议继续在Maevarano组进行古生物和地质野外工作，并将其扩展到Mahajanga盆地的低层。 因此，这个项目的意义是两层的。 在区域层面上，我们的努力将继续提供重要的，基线的解剖学，古生物学和马达加斯加晚白垩世脊椎动物的系统发育关系的见解，以及把它们放在一个详细的年代地层和古环境背景。 在全球范围内，该项目将阐明冈瓦纳中生代脊椎动物的大规模历史和地理模式，从而提供独立的手段来测试地球物理模型的构造破碎。

9706302 Krause NSF-funded fieldwork in the Maevarano Formation of the Mahajanga Basin, northwestern Madagascar, has quadrupled the previously known diversity of Late Cretaceous vertebrates from the island. The faunal list now includes a minimum of 32 species of fishes, frogs, turtles, lizards, snakes, crocodyliforms, dinosaurs, birds, and mammals. Several taxa are represented by nearly complete, exquisitely preserved skeletons. The primary goal of the present proposal is to expand upon this work through additional discoveries of fossil vertebrates, phylogenetic analysis of the new samples, elucidation of the stratigraphic, sedimentologic, and taphonomic context, and testing of various biogeographic hypotheses related to the fragmentation of the southern supercontinent, Gondwana. Gondwana fragmented into a number of isolated landmasses during the Late Jurassic and Cretaceous, with dramatic consequences for associated biotas. Reconstructions of this continental fragmentation are based almost entirely on geophysical evidence, and remain poorly tested paleontologically. According to recent models, Antarctica, Australia, Madagascar, and the Indian subcontinent broke away as a single tectonic unit from eastern Africa sometime in the Late Jurassic (150-160 Ma). Antarctica likely retained physical connections with South America throughout the Mesozoic. During the Early Cretaceous (125-130 Ma), Madagascar attained its current position approximately 400 km off the east coast of Africa and, together with the Indian subcontinent, separated from Antarcto-Australia. Madagascar and the Indian subcontinent persisted as a distinct tectonic unit until ~88 Ma, well before deposition of the Maevarano Fm. Several testable hypotheses relating to the biogeographic history of Madagascar derive from this pattern of fragmentation: 1) Late cretaceous terrestrial faunas from Madagascar will share greater phylogenetic affinities not with coeval faunas from Africa, but with those from the Indian subcontinen t and, secondarily, Antarctica, Australia, and South America; 2) correspondingly, Late Cretaceous faunas from the Indian subcontinent will show greatest phylogenetic similarities not with Asia, but with Madagascar and other Gondwanan landmasses; and 3) Most of the major elements of the highly endemic and imbalanced extant vertebrate fauna on Madagascar (e.g., lemuriform primates) colonized the island after its isolation in the Late Cretaceous. The present study will address these hypotheses through rigorous phylogenetic (cladistic) analyses of Late Cretaceous vertebrates from Madagascar and other Gondwanan landmasses. While the vertebrate remains recently recovered from the Maevarano Formation of the Mahajanga Basin provide a crucial foundation for these tests, additional materials are required. It is therefore proposed that paleontological and geological fieldwork be continued in the Maevarano Formation, and expanded to lower horizons in the Mahajanga Basin. Thus, the significance of this project is two tiered. On a regional level, our efforts will continue to provide important, baseline insights into the anatomy, paleobiology, and phylogenetic relationships of Late Cretaceous vertebrates from Madagascar, as well as place them in a detailed chronostratigraphic and paleoenvironmental context. On a global level, this project will elucidate larger-scale historical and biogeographic patterns among Mesozoic vertebrates from Gondwana, and thereby provide independent means of testing geophysical models of tectonic fragmentation.