Abstract
The taxonomy and phylogeny of the Miocene to Recent genus Sphaeroidinellopsis have been documented in previous studies, but the evolution of this lineage remains unclear. Some authors have debated this genus in the past, choosing a variety of parameters to discriminate the morphospecies. Here we present new scanning electron microscope analyses of specimens from Ocean Drilling Program (ODP) Site 925 (Ceara Rise, western equatorial Atlantic) and ODP Site 959 (Deep Ivorian Basin, eastern equatorial Atlantic). Our study reveals transitional individuals Sphaeroidinellopsis disjuncta–Sphaeroidinellopsis kochi, a speciation event never described previously. These transitional specimens are characterized by extreme morphological features such as elongated and sac-like final chambers, requiring amendments to the current classification and taxonomy of these morphospecies. In this paper, an alternative hypothesis is presented and discussed, to assess these new observations within the evolutionary mosaic of Sphaeroidinellopsis.
Highlights
The genus Sphaeroidinellopsis ranges from the early Miocene to Pliocene. Kennett & Srinivasan (1983) considered Sphaeroidinellopsis to be composed of four morphospecies, S. disjuncta, S. seminulina, S. kochi and S. paenedehiscens
This study focused on the taxonomical evolution of Sphaeroidinellopsis disjuncta and S. kochi through scanning electron microscope (SEM) analyses of planktonic foraminifera in oceanic cored sediments
Planktonic foraminifera assemblages from Ocean Drilling Program (ODP) Site 959 show high diversity, while the overall preservation is moderate to good through the uppermost lower Miocene to Holocene
Summary
The genus Sphaeroidinellopsis ranges from the early Miocene to Pliocene. Kennett & Srinivasan (1983) considered Sphaeroidinellopsis to be composed of four morphospecies, S. disjuncta, S. seminulina, S. kochi and S. paenedehiscens. The genus was erected by Banner & Blow (1959) for low trochosphiral species that lacked a supplementary sutural aperture. The genus Sphaeroidinella, by contrast, was erected by Cushman in 1927, and amended by Banner & Blow in 1959 to include globigeriniform taxa with thick walls covered by a shiny cortex and possessing supplementary openings on the spiral side. While the two genera have been placed in a single evolutionary lineage by some authors (Banner & Blow 1959; Kennett & Srinivasan 1983; Aze et al 2011; Spezzaferri et al 2015, among others), Be (1965) and Bandy et al (1967) considered them bathypelagic forms of at least two different species of Globigerinoides. On the other hand, Spezzaferri et al (2015) reported Sphaeroidinella and Sphaeroidinellopsis as potential
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