| 英文摘要: | Cretaceous Vertebrates from Madagascar: A Window into the Biogeographic and Plate Tectonic History of Gondwana
David Krause, Stoneybrook, EAR-1528273
Patrick O'Conner, Ohio University, EAR-1525915
This proposal is jointly funded by the Sedimentary Geology and Paleobiology Program (EAR/GEO) and the Africa, Near East & South Asia Program/Office of International Science and Engineering (OD).
ABSTRACT
Non-technical Explanation
The latter half of the Mesozoic Era witnessed profound changes in the configuration of landmasses that comprised the southern supercontinent Gondwana, with dramatic consequences for the associated vertebrate faunas. Madagascar lay near the center of Gondwana as it fragmented into its component parts. This proposal seeks to continue a project designed to discover and describe vertebrate fossils in a sequence of Cretaceous strata on the island, to analyze their paleobiology, to place them in phylogenetic and geologic context, and to employ them in testing biogeographic and plate tectonic hypotheses related to Gondwana as a whole and Madagascar in particular. PIs work in the Cretaceous of Madagascar is only at the very beginning of reaching its potential. To date, they have quintupled the previously known species diversity of Late Cretaceous vertebrates from the island and have discovered some of the most complete and spectacularly preserved specimens of Late Cretaceous vertebrates from the southern hemisphere and, indeed, the world. Many new taxa have been named and described. But much remains to be done in the vast expanses of paleontologically and geologically unexplored Cretaceous rocks of Madagascar. Many taxa are known by only fragmentary remains; many others are still to be discovered. With continued work, PIs are confident that Madagascar's Cretaceous vertebrate fauna will become one of the best known and best contextualized from the southern hemisphere and one of the primary standards against which other Gondwanan faunas of Cretaceous age are compared.
Technical Description
PIs propose to continue collecting terrestrial and freshwater vertebrate fossils of latest Cretaceous age from the Berivotra Study Area of the Mahajanga Basin of northwestern Madagascar, which continues to produce exquisite material of poorly known taxa and specimens of new taxa. Although they have published many detailed anatomical, functional, and phylogenetic analyses of taxa known from this basin, many more have been initiated and remain to be completed (in particular, on albuloid and amiid fishes, crocodyliforms, pterosaurs, sauropod and abelisauroid theropod dinosaurs, birds and other paravian theropods, and mammals). Some of this work will entail histological sampling, thus enabling a comparative analysis of ecosystem-scale, inter-element histological variation within single vertebrate skeletons and testing of hypotheses related to possible responses and growth history adaptations of taxa that are phylogenetically constrained, but which exhibit a wide array of morphological and functional specializations.
PIs also propose to continue developing newly discovered field areas in the Mahajanga Basin, which are yielding new taxa of roughly the same age but from different paleoenvironmental settings. Finally, they propose to expand their efforts into the Morondava Basin of western Madagascar, where brief expeditions in 2010 and 2012 yielded important finds and demonstrated the potential for many more from strata older than those yielding fossils in the Mahajanga Basin. Discoveries from these earlier horizons will provide a deeper temporal context with which to address biogeographic and plate tectonic hypotheses. Indeed, PIs discoveries continue to have profound implications for the biogeographic history of the extant and extinct Malagasy fauna and for the relative importance of dispersal and vicariance during Gondwanan fragmentation. One of their overarching goals is to provide a key building block for reconstructing Gondwanan biogeographic history in the form of a temporally controlled, well-sampled vertebrate fauna from the Cretaceous of Madagascar analyzed in a rigorous phylogenetic framework, and within the context of accurate paleogeographic reconstructions.
It remains a priority to conduct detailed stratigraphic, sedimentologic, and taphonomic studies of all sampled horizons in order to provide temporal control as well as paleoenvironmental and paleoclimatic context. More specifically, PIs propose to conduct: (1) a comprehensive analysis of Maevarano Formation taphonomy that will provide taxonomic summaries and maps for each major quarry, and will detail the preservation of the Maevarano Formation?s exceptionally-preserved vertebrate record; (2) a comprehensive report on the geochemistry and micromorphology of exceptionally-preserved paleosols and associated fluvial sediments in the Masorobe and Anembalemba members of the Maevarano Formation, which will provide critical insights into paleoclimate; (3) a study focused on trace fossils discovered in the Maevarano Formation, specifically back-filled burrows associated with an entombed carcass (subterranean scavenging); and (4) a study clarifying and formalizing the lithostratigraphy of Upper Cretaceous horizons in the Morondava Basin. |