LATE CRETACEOUS TERRESTRIAL VERTEBRATES FROM MADAGASCAR: IMPLICATIONS FOR LATIN AMERICAN BIOGEOGRAPHY¹

The Mahajanga Basin Project, initiated in 1993 and centered in Upper Cretaceous strata of northwestern Madagascar, has resulted in the discovery of some of the most complete, well-preserved, and significant specimens of Late Cretaceous vertebrate animals from the Southern Hemisphere and indeed the world. Among the most important finds are various specimens of crocodyliforms, non-avian dinosaurs, and mammals; these finds have the potential to provide key insights into the biogeographic and paleogeographic history of Gondwana. Madagascar has been physically isolated from Africa for over 160 million years and from all other major landmasses for more than 85 million years. The closest known relatives of many of the Late Cretaceous Malagasy taxa are penecontemporaneous forms from South America (primarily Argentina) and India, thus documenting a previously unrecognized high level of cosmopolitanism among Gondwanan vertebrates near the end of the Cretaceous. The family-level taxa that are shared among Madagascar, South America, and the Indian subcontinent are not known from penecontemporaneous horizons in mainland Africa, but it cannot yet be confidently determined if this is due to differential extinction, poor sampling, true absence (i.e., the taxa were never present on Africa), or some combination thereof. Nonetheless, currently available geologic and paleontologic data are most consistent with the Africa-first model, suggesting that Africa was the first of the major Gondwanan landmasses to be fully isolated prior to the Albian/Cenomanian boundary, and that its terrestrial vertebrate faunas became progressively more provincial during the Cretaceous, while those on other Gondwanan landmasses remained relatively cosmopolitan until the later stages of the Late Cretaceous.