Globigerinella obesa

Globigerinella obesa (Bolli, 1957) Pl. 7, figs. 9–10

Globorotalia obesa Bolli, 1957, p. 119, pl. 29, figs 2–3.

Globigerina praebulloides Blow, 1959, pl. 8, fig. 47; Kender, 2007, p. 202, pl. 49, fig. 7.

Globigerinella obesa Bolli et al., 1985, p. 206, fig. 26.44; Kennett & Srinivasan, 1983, p. 234, pl. 59, figs 2–5; Kender et al., 2008, p. 202, pl. 29, fig. 4; Spezzaferri et al., 2018a, p. 198, pl. 6.1, figs. 14–17; pl. 6.8, figs. 1–23.

Description: The wall surface is cancellate-spinose. The test is trochospirally arranged with the chambers globular in shape, which rapidly enlarge towards the terminal end. Four chambers are visible in the final whorl in umbilical view, with straight depressed sutures. The test is biconvex in marginal view and has a lobate outline in umbilical view.A thin imperforate lip may border the apertural arch. The aperture extends from the umbilical to extra-umbilical region, forming an arched shape visible in the peripheral margin view.

Remarks: The relative abundance of G. obesa in this study is trace (<1%) in samples of all three cores. The tests are relatively moderate in size, measuring up to 0.5 mm in diameter.

G. obesa is ancestral to Globigerinella siphonifera, which later gave rise to Globigerinella calida. This species evolved from G. archaeobulloides and is different from that species in its aperture, which is more umbilical to extraumbilical towards the margin of the test. It also differs from G. bulloides in this way and has a more inflated terminal chamber compared to its initial chambers. G. obesa is different from G. praesiphonifera in having four chambers in the last whorl, whereas G. praesiphonifera has five (Spezzaferri et al., 2018a). Globigerina praebulloides is synonymised and now accepted as G. obesa.

Environmental preferences: G. obesa has been identified as a warm to temperate species (Bicchi et al., 2003).

Global stratigraphic range: G. obesa has been recorded in Oligocene to lower Pliocene strata (Kennett & Srinivasan, 1983).

Regional occurrence: This species has been recorded to occur in middle Miocene strata from the Congo Basin (Kender et al., 2008) to the northern Namibian outer continental shelf, south of the Kunene River mouth (this study).