Abstract
The chondrichthyan fauna from the Pirabas Formation is redescribed.Only thirteen nominal taxa are considered valid. From these taxa, ten were reassigned to extant taxa (Carcharhinus sorrah, Carcharhinus perezii,Galeocerdo cuvier, Rhizoprionodon lalandii, Sphyrna sp., Hemipristis elongatus, Carcharodon carcharias, Isurus oxyrinchus, Nebrius ferrugineus, and indeterminate Myliobatidae), confirming the Neogene age of this formation. This elasmofauna is compared with other Caribbean and African Tertiary faunas.
Highlights
The Pirabas Formation crops out in the Bragantina Region, State of Pará, Northern Brazil (White, 1887; Maury, 1924; Ferreira, 1967; Brito, 1993) (Figure 1), and is bounded by the Marajó Basin, the Maranhão coastal Zone and the low Parnaíba, in the Piauí State (Brito, 1979).The Pirabas Formation was originally defined by White (1887) who considered to be of Cretaceous age
In this study is considered a synonym of the recent species Hemipristis elongatus; this species is only found in the Indian Ocean and west Pacific (Compagno, 1984; 1988)
Compagno (1973; 1979) suggested that osteodont histological type of the recent species Hemipristis elongatus was derived from the orthodont type found at least in some of the fossil Hemipristis
Summary
The Pirabas Formation crops out in the Bragantina Region, State of Pará, Northern Brazil (White, 1887; Maury, 1924; Ferreira, 1967; Brito, 1993) (Figure 1), and is bounded by the Marajó Basin, the Maranhão coastal Zone and the low Parnaíba, in the Piauí State (Brito, 1979).The Pirabas Formation was originally defined by White (1887) who considered to be of Cretaceous age. The Pirabas Formation crops out in the Bragantina Region, State of Pará, Northern Brazil (White, 1887; Maury, 1924; Ferreira, 1967; Brito, 1993) (Figure 1), and is bounded by the Marajó Basin, the Maranhão coastal Zone and the low Parnaíba, in the Piauí State (Brito, 1979). Later studies of its fauna suggested a Miocene age for this unit, and a tropical environment (Ferreira, 1966). This lithostratigraphic unit display three distinct facies: Castelo, Capanema and Baunilha Grande. The Capanema facies, suggest reduced salinity and shallower waters, with a rich molluscan fauna. In some places this facies yields a coastal thanatocenosis, with terrestrial plants, malacostracans crustaceans and cirripedes, which are a typical hard-ground fauna. The Baunilha Grande facies suggests a swamp environment which is demonstrated by the abundance of fossil crabs (Brito, 1979; Fernandes, 1979)
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