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

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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.