Collaborative Research: Late Cretaceous Vertebrates from Madagascar: Implications for the Plate Tectonic and Biogeographid History of Gondwana

当前提案的目标是大幅增加对马达加斯加晚白垩纪脊椎动物动物群的了解，目前对这些动物群知之甚少。随着在马达加斯加西北部Mahajanga盆地发现和分析更多更完整的脊椎动物化石，将有可能解决三个关键的（但并非相互排斥的）假设，这些假设与晚白垩纪冈瓦纳东部各组成部分的物理和生物联系以及马达加斯加现存脊椎动物群的生物地理起源有关。马达加斯加、非洲和印度次大陆，由于地理位置接近，在白垩纪晚期共享着非常相似的脊椎动物群，在某些情况下在物种水平上非常相似。马达加斯加晚白垩纪的许多脊椎动物被认为与非洲和印度的脊椎动物密切相关，或者在某些情况下与之相同。相应地，地球物理学家普遍认为，此时印度次大陆靠近或毗邻马达加斯加的东部边缘。尽管在马达加斯加、非洲和印度的晚白垩纪脊椎动物动物群中有明显的相似性，但由于材料不足，很难进行详细的比较。为了进行这样的比较，需要从马达加斯加（以及印度和非洲）获得更完整的脊椎动物化石材料。假设二：印度次大陆在晚白垩纪后期从马达加斯加（和非洲）分离出来，在白垩纪晚期，包含了来自Laurasis（与欧亚大陆碰撞的结果）的元素，这些元素与马达加斯加（或非洲）没有共享。印度次大陆在白垩纪晚期已经与欧亚大陆发生碰撞，这一新近提出的有争议的假说得到了一些古生物学证据的支持。印度马斯特里赫特地区据称存在的劳亚人群体表明，在印度次大陆和欧亚大陆之间的地下路线可能在这个时候已经存在。然而，用于支持这一结论的材料是由孤立的、碎片的和鉴定可疑的稀有标本组成的。对Mahajanga盆地一些标本的初步鉴定表明，至少有一些在印度晚白垩纪发现的“月牙”分类群也出现在马达加斯加。如果这些鉴定得到证实，这些“Laurasian”元素更有可能是通过非洲和马达加斯加进入印度次大陆的，而不是来自欧亚大陆。假设三：在新生代开始之前，一些包含马达加斯加现存动物群的脊椎动物高级分类群（例如，狐猴目，触手科，虫草科）就在该岛上定居了。马达加斯加现存的高度地方性和不平衡的脊椎动物群的生物地理起源是未知的，几十年来一直是猜测辩论的主题。这在很大程度上是由于岛上几乎没有非海洋的、全新世以前的新生代地层。因此，阐明这一重大问题的最佳机会是在Mahajanga盆地富含化石的上白垩纪非海相地层中发现脊椎动物化石。这个项目的重要意义在于发现和了解更多关于白垩纪晚期生活在马达加斯加的脊椎动物。通过提议的两个野外季节获得的化石收集将远远超过之前所有的努力（总和），并将为“Maevarano”和“Marovoay”地层的脊椎动物多样性提供一个合理的估计。在收集和分析数据以验证上述假设的过程中，我们期望：1)对马达加斯加晚白垩世脊椎动物的多样性、解剖学和系统发育关系的知识做出实质性贡献；2)更好地约束化石层的岩石地层学和生物地层学（并正式定义“Maravoay”、“Maaevarano”和“Berivotra”组）。

Krause 9418816 The goal of the current proposal is to substantially increase knowledge of the Late Cretaceous vertebrate fauna of Madagascar, which is currently very poorly known. With the discovery and analysis of additional and more complete vertebrate fossils from the Mahajanga Basin of northwestern Madagascar, it will be possible to address three critical (but not mutually exclusive) hypotheses relating to the physical and biotic connections of the component parts of eastern Gondwana during the Late Cretaceous and the biogeographic origins of the extant vertebrate fauna of Madagascar: HYPOTHESIS I: Madagascar, Africa, and the Indian subcontinent, owing to their physical proximity, shared vertebrate faunas in the Late Cretaceous that were very similar, in some cases at the species level. Many of the vertebrates from the Late Cretaceous of Madagascar are thought to be closely related to or, in some cases, conspecific with those of Africa and India. Correspondingly, there is general agreement among geophysicists that the Indian subcontinent was close or adjacent to the eastern margin of Madagascar at this time. Despite apparent similarities in the Late Cretaceous vertebrate faunas of Madagascar, Africa, and India, detailed comparisons have been difficult due to inadequate material. More complete material of vertebrate fossils from Madagascar (as well as India and Africa) are needed for such comparisons to be made. HYPOTHESIS II: The Indian subcontinent was faunally isolated from Madagascar (and Africa) in the later stages of the Late Cretaceous and, in the latest Cretaceous, contained elements from Laurasis (as a result of collision with Eurasia) that were not shared with Madagascar (or Africa). Some of the evidence used in support of the recent and controversial hypothesis that the Indian subcontinent had already collided with Eurasia by the latest Cretaceous is paleontological. The presence of purportedly Laurasian groups in the Maastrichtian of India indicated that a ter restrial route between the Indian subcontinent and Eurasia may have existed by this time. However, the material used to support this conclusion consists of isolated, fragmentary, and rare specimens with questionable identifications. Preliminary identifications of some specimens form the Mahajanga Basin indicate that at least some of the "Laurasian" taxa found in the Late Cretaceous of India also occurred in Madagascar. If these identifications are confirmed, it is more likely that these "Laurasian" elements entered the Indian subcontinent by way of Africa and Madagascar, rather than from Eurasia. HYPOTHESIS III: Some vertebrate higher taxa that comprise the extant fauna of Madagascar (e.g., Lemuriformes, Tenrecidae, Cordylidae) colonized the island prior to the beginning of the Cenozoic. The biogeographic origins of the extant, highly endemic and imbalanced vertebrate fauna of Madagascar are unknown and have been the subject of speculative debate for many decades. This is largely the result of the virtual absence of nonmarine, pre-Holocene Cenozoic strata on the island. As a result, the best opportunity to shed light on this major problem is to discover vertebrate fossils in the richly fossiliferous Upper Cretaceous nonmarine strata of the Mahajanga Basin. Much of the significance of this project lies in discovering and understanding more about the vertebrates that lived in Madagascar during the Late Cretaceous. Fossil collections obtained through the proposed two field seasons will far exceed all previous efforts (combined) and will provide a reasonable estimate of the diversity of vertebrates in the "Maevarano" and "Marovoay" formations. In the process of accumulating and analyzing data to test the hypotheses above, we expect to: 1) contribute substantially to knowledge of the diversity, anatomy, and phylogenetic relationships of the Late Cretaceous vertebrates of Madagascar; and 2) better constrain the lithostratigraphy and biostratigraphy of the fossiliferous beds (and to de fine formally the "Maravoay", "Maaevarano", and "Berivotra" formations).