TERRESTRIAL VERTEBRATE FOSSILS FROM THE CENOZOIC OF MADAGASCAR

The origin and evolutionary history of Madagascar's modern vertebrate fauna remains an intriguing mystery. Despite an ever-increasing wealth of fossil material from both the Mesozoic and subfossil communities, little is known from the intervening interval of approximately 70 My during which the island was isolated and presumably colonized by the ancestors of its extant vertebrates. The subfossil record is so recent (26,000 years) as to be uninformative with regards to the origin and evolution of the highly endemic modern fauna, which are absent in the well-sampled Mesozoic communities. This "gap" in Madagascar's evolutionary history has left little indication of how, when and from where modern Malagasy vertebrates originated; any Cenozoic fossils found would lead to a greater understanding of this significant period of time in the evolution of this unique modern fauna.

Rocks of Cenozoic age have been mapped and described in Madagascar, but little paleontological reconnaissance has been undertaken. Deposits putatively mapped as "Pliocene continental" in the Mahajanga Basin of northwestern Madagascar were reassessed in July of 2001 and prospected for fossils. This survey revealed a complex interfingering relationship between marine and terrestrial deposits overprinted by erosion and redeposition of sediments by fluvial processes.

Fossils discovered include invertebrates as well as representatives of other vertebrate groups, including fish, sharks, rays, crocodiles and turtles. These fossils are the first vertebrates to be recorded from this gap in the fossil record of Madagascar, and will certainly provide a window into the origin and evolution of the modern vertebrate fauna. This mixed assemblage of terrestrial and marine vertebrates from nearshore marine mudstones and sandstones of Cenozoic age will be the focus of successive field studies.