Abstract
The Alcântara Formation, an important stratigraphic unit from the early Cenomanian of Brazil, was deposited under transitional (estuarine) conditions, and its fossil record includes fragmentary remains of plants, fishes, crocodylomorphs, pterosaurs and dinosaurs, with a noteworthy diversity of dipnoiformes tooth plates. The dipnoiformes material reported here comprises a new taxon, Equinoxiodus alcantarensis, gen. et sp. nov. Most of the identified morphotypes of continental vertebrates collected in the Alcântara Formation are similar to chronocorrelative faunas from Northern Africa, but this new genus of Dipnoiformes indicates some degree of paleogeographic isolation and endemism. This was probably caused by the widening of the equatorial Atlantic Ocean during the early Cenomanian, which may have selectively affected some species.
Highlights
In 1994, a multiple layered bone-bed within iron-oxide cemented conglomeratic layers, alternating with sandstone levels, was discovered on the eastern side of the Cajual Island (2◦28 53, 4 S and 44◦27 41, 3 W) in northern Maranhão State, northeastern Brazil (CorrêaMartins 1997)
The material collected at the Laje do Coringa fossiliferous site, Cajual Island, northern Maranhão State, northeastern Brazil (Figs. 1 and 2), comprises a series of 10 dipnoiformes isolated tooth plates with no supporting bones preserved
The specimens are deposited in the fossil collection of the Universidade Federal do Maranhão (UFMA), in the city of São Luis, Brazil
Summary
In 1994, a multiple layered bone-bed within iron-oxide cemented conglomeratic layers, alternating with sandstone levels, was discovered on the eastern side of the Cajual Island (2◦28 53, 4 S and 44◦27 41, 3 W) in northern Maranhão State, northeastern Brazil (CorrêaMartins 1997). The tidal range exceeds six meters causing the beach to be frequently swept by waves that expose and free up the fossils from the rock matrix Deposits in this region were considered as belonging to the São Luís Basin. The bone-bed (Fig. 2), named Laje do Coringa (Corrêa-Martins 1997), is a sequence within the Alcântara Formation (Itapecuru Group) located on the eastern beach of the Cajual Island. It is unique in Brazil because it crops out in a very restricted area exposed only during the low tide that has yielded thousands of bones, teeth and petrified plants as conifers and ferns. Trunks of conifers and ferns were distinctly fossilized by a combination of silica and iron oxides and probably have a more complex taphonomic history
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