Megalodon, mako shark and planktonic foraminifera from the continental shelf off Portugal and their age

摘要

A turbidite specimen collected by a fishing net off the Portuguese coast presents some fossils. A process of condensation is revealed by Late Pliocene and Quaternary typical foraminifera. The matrix is phosphatised and rather iron-rich with small quantities of manganese and zinc and even less copper. Based on planktonic foraminifera in depressions of cetacean skulls from the same area, the fossilization of shark and cetaceans is likely to have occurred in the uppermost Messinian to Early Pliocene. Lack of benthic foraminifera also point out to more or less deep environments, while a scallop, Mimachlamys varia, indicates nearby rocky environments. The occurrence of Megaselachus megalodon excludes an older than Miocene age and most probably, even an older than Middle Miocene age. Its very advanced evolution stage is consistent with a Pliocene age. The mako shark, Isurus cf. oxyrhinchus is recorded here for the first time. The shark association represents a seemingly moderately warm indicator as megalodon and Isurus are essentially temperate water dwellers, while no warm water form is known. Hence temperate to moderately warm conditions seem to have prevailed.