Abstract

Two new species, Tubulogenerina turonica and Colomia africana, are described from the Turonian of Tanzania, and the genus Colomia is emended. The genus Tubulogenerina was originally thought to have originated in Europe in the early Eocene. Our discovery of T. turonica indicates that the roots of the genus reach back to the middle Cretaceous, and argues against a previous conclusion that it originated in temperate European regions. A tropical/subtropical site of origination would be consistent with the observation that most Tubulogenerina species inhabited warm, shallow-water environments. Tubulogenerina turonica has a relatively simple morphology, suitable as a starting point for morphological trends in the genus during the Cenozoic, thus supporting its status as a plausible ancestral species.

In clay-rich middle Cretaceous sediments from Tanzania, foraminifera are exceptionally well preserved, and assemblages include a number of aragonitic taxa, including Colomia africana. This new species is distinguished from others of the genus by its aperture and toothplate structure and its dominantly biserial test without a well-developed uniserial growth stage. Morphologic similarities, however, indicate the close evolutionary relationship with other species of Colomia, so the genus is emended accordingly. Sufficient numbers of C. africana were found in multiple samples to characterize its stable carbon and oxygen isotope values relative to another aragonitic species (Epistomina chapmani) and calcitic species (Berthelina berthelini) from the same material. Results show an expected offset between calcitic and aragonitic tests that is partially explained by differential fractionation factors, but suggests vital or microhabitat effects contribute to values measured on C. africana.

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