A new siderolitid from the late Maastrichian of Italy

Abstract

During the latest Cretaceous, many representatives of the larger benthic foraminifera (LBF) community reached a high level of “maturation”, developing large-sized shells with complex architectures. Increasing size and complexity in a relatively short period of time can be interpreted as a rapid response to biologic competition for space and resources with other LBF (like for instance fabularids, lacazinids, alveolinids, rotaliids, orbitoidids) in the shallow carbonate to mixed carbonate-clastic platforms. A paradigm of this type of fast evolution is the group of the Siderolitidae, lamellar-perforate LBF with a complex canal system that were abundant in shallow-water platforms during the late Cretaceous (Campanian-Maastrichtian). Five genera have been described up to now that represent five different steps of evolution in terms of complexity: Arnaudiella, Praesiderolites, Pseudosiderolites, Wannierina and Siderolites. In broad terms, the species ascribed to these genera replace each other in time, offering a good tool for high resolution biostratigraphy. Recent studies on material from the late Maastrichtian of Italy have yielded a siderolitid with a singular architectural pattern that differs from its relatives. The new morphotype has a very large test with large canaliferous spines and a very complex enveloping canal system. This new morphotype is the youngest siderolitid known so far. Strontium isotope stratigraphy indicates a late Maastrichtian age of 66.4 ±1.5 Ma, very close to the K-Pg boundary. The large size and very high complexity shown by the new morphotype are in accordance with the general evolutionary trends of LBF.