Uppermost Miocene Lamniform Selachians (Pisces) from the Alvalade basin (Portugal)

Abstract

Key-words: Selachians; Lamnifonns; Alvalade Basin; Uppermost Miocene; Paleoecology. This paper deals with Lamnifonn teeth collected in deposits from the Esbarrondadoiro Fonnation, Alvalade Basin in Southern Portugal. The following genera were recognized: Carcharias, Pseudocarcharias, Alopias, Isurus and Carcharocles. The species Carcharias acutissima is by far the most predominant, all other taxa being rare or very rare. This situation points to neritic, tropical to subtropical, rather shallow waters not far away from the coast. This is corroborated by the rarity of the associated, mainly pelagic taxa. The ratio between C. acutissima and the remaining Lamnifonns as a whole is markedly uneven between Esbarrondadoiro and the localities of Santa Margarida and Vale de Zebro. This suggests quite different environmental conditions, a matter that will require a more thorough examination taking into account all palaeontologic and geologic data.