Original Description Shape of test low to medium high trochospiral, wider than high; e~1atorial periphery strongly lobate. Wall calcareous, perforate, surface of well preserved specimens covered with very short spines. Chambers spherical, 10-12, arranged in about 2 whorls, the 4 chambers of the last whorl, in particular the ultimate one, rapidly increasing in size. Sutures on spiral and umbilical side radial, incised. Umbilicus wide and distinct. Aperture of the last chamber a very large more or less semicircular arch bordered by a distinct though thin rim, interiomarginal, umbilical. Large aperture of penultimate chamber as a rule also clearly visible. Size: Largest diameter of holotype 0.35 mm. Etymology: The new species is named in honor of Prof. Frances de Rivero of the
Escuela de Geologia, Universidad Central de Venezuela, Caracas. Extra details from original publication Remarks: Globigerina riveroae is characterized by its globular form and in particular by its very large, nearly semicircular aperture of the ultimate chamber. The new species most closely resembles Globigerina bulloides d'Orbigny but differs from it in the larger size of the above-mentioned aperture. Further, Globigerina riveroae is stratigraphically and geographically much more restricted than Globigerina bulloides. So far, the species has only been observed in the upper part of the Globorotalia margaritae Zone and in the Globoquadrina altispira altispira/Globorotalia crassaformis Zone of the Cerro Negro member, Cubagua formation, coastal northeastern Venezuela. It seems to have lived there under only moderately warm water conditions. Globigerina riveroae is no longer present in the Pliocene Cumana and Playa Grande formations of the same area and is also not known from the Recent. It is possible that Globigerina riveroae branched off from Globigerina bulloides in the late Miocene under ecological conditions that existed, as far as known, only in a restricted area around coastal north-eastern Venezuela. It became extinct there at about the close of the Miocene. Locally the new species is thus a good index fossil for the Cerro Negro member of the Cubagua Formation:
Kennett & Srinivasan (1983) regarded Globigerina riveroae Bolli and Bermudez, 1965 to be a phenotypic variant of Globigerina bulloides. However, new SEM images of the holotype of riveroae Bolli and Bermudez indicate a cancellate wall, and therefore riveroae does not belong in the genus Globigerina (Bridget Wade, November 2017).
Bolli, H. M. & Bermudez, P. J. (1965). Zonation based on planktonic foraminifera of middle Miocene to Pliocene warm-water sediments. Bol. Informativo, Asoc. Venez. Geol., Min. Petrol. 8(5): 121-149. gs
Globigerina riveroae compiled by the pforams@mikrotax project teamviewed: 5-6-2023