NEOKILIANINA CONCAVA RAMALHO, 2015 AND NEOKILIANINA RAHONENSIS (FOURY & VINCENT, 1967): A DIMORPHIC PAIR OF UPPER JURASSIC LARGER BENTHIC FORAMINIFERA?

Abstract

The species Neokilianina concava Ramalho was described from the Kimmeridgian of Portugal found in the same (isochronous) levels as Neokilianina rahonensis (Foury & Vincent). The external morphology was indicated as the only difference between the two taxa, notably a pronounced concavity in the middle part of the cone base and a wider apical angle in N. concava against N. rahonensis. These differences can reasonably be considered as intraspe-cific variations, reflecting adult test dimorphism between the megalospheric (N. rahonensis) and microspheric specimens (N. concava), also suggested by their isochronous occurrence. The morphological features that were used for species discrimination are well recorded from the two generations (A-, B-forms) of other larger benthic foraminifera including the Orbitolinidae.