Taxonomic reassessment and palaeobiogeographical patterns of some Miogypsinidae species, larger benthic foraminifera

Abstract

Abstract. The Miogypsinidae comprise orbitoidal larger benthic foraminifera with generally eccentric position of the nepionic stage and a fan of equatorial chamberlets; the members of this family are widely used in biostratigraphy of upper Oligocene–middle Miocene deposits. Here, a taxonomic review of the genus Miogypsinella Hanzawa, 1940 (type species: M. borodinensis Hanzawa, 1940) and Miogypsinoides lateralis Hanzawa, 1940 is presented based on the reassessment of the type specimens. The palaeobiogeographical patterns of these taxa are discussed based on a compilation of the geographical and stratigraphical ranges of all their reported occurrences including illustrations. The computed tomography (CT)-scan analysis of the type material of M. borodinensis, from the Chattian of the central Indo-Pacific (Kitadaito Jima), indicates that it is a valid species different from Miogypsinoides complanatus. Two Miogypsinella species (M. borodinensis, M. ubaghsi) are widespread in the Chattian–Aquitanian of the Indo-Pacific region and one species (M. bermudezi) in the Aquitanian of the eastern Pacific (Mexico). Miogypsinella appeared in the Chattian in the central Indo-Pacific, reached Central America, and disappeared in the Aquitanian in both areas. The American Oligocene faunas of larger benthic foraminifera were, therefore, not distinctly isolated as previously proposed. Miogypsinoides lateralis is a clearly distinct species that is an exception to the presumed morphological trend within the Miogypsinoides species lineage. Miogypsinoides lateralis possesses morphometric values comparable to those of the Burdigalian–Langhian M. indica but occurring earlier, in the Aquitanian. The latest Aquitanian initiation of the Indonesian Seaway restriction and widespread drowning of former carbonate platforms likely brought about the extinction of Miogypsinella borodinensis, M. bermudezi, M. ubaghsi, and Miogypsinoides lateralis.