Madagascar is known for its highly endemic Recent fauna. However, the full deep-time temporal context of Madagascar's endemicity is not completely understood, due to the patchy fossil record of the island. The Upper Cretaceous deposits of the Maevarano Formation in northwestern Madagascar provide insight into this issue due to their rich vertebrate fauna, including dinosaurs, crocodylians, frogs, turtles, snakes, mammals, and fishes. The Maevarano Formation consists of fluvial and alluvial deposits and accompanying debris flows, and exhibits excellent fossil preservation. Fossil fishes from the formation represent coastal marine and freshwater taxa, some of which have been identified in earlier reports. This study focuses on identifying teleosts present within the Maevarano Formation, and the resulting implications for Gondwanan biogeography. The teleosts are first identified to the most precise taxonomic unit possible, and their distributions during the Late Cretaceous are analyzed. Several of the fish taxa present extend the known temporal and/or geographic ranges of significant teleost clades (e.g. Elopomorpha, Characiformes, and Cypriniformes). Parsimony Analysis of Endemism and Simpson's and Jaccard's similarity indices showed some fossil fish taxa (e.g. elopomorphs) as rather cosmopolitan and less affected by continental geographical relationships. The presence of the identified fishes from the Late Cretaceous of Madagascar fishes shows major turnover in fish diversity in Madagascar from the Triassic to the Recent, and how the faunal composition changed with the progressive isolation of Madagascar. Comparison at the ordinal level between the Triassic, Late Cretaceous, and Recent fish faunas show that the dramatic change in fish diversity is comparable with what has occurred in the strictly terrestrial vertebrate taxa over the last 200 million years of Madagascar's history. This information supports the likelihood of successive waves of immigrations of vertebrate taxa after the isolation of the island, some of which presumably would have had large enough establishing populations to persist on the island and diversify. These waves have resulted in a higher degree of endemicity in the island's fauna today, relative to the fauna which existed on Madagascar throughout its geological history. These results highlight the complexities of deciphering fish biogeography, due to their transient nature and their ability to disperse across marine environments that act as barriers to fully terrestrial groups.
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