Orbitolina hensoni Simmons, Whittaker & Jones 2000

Orbitolina hensoni Simmons, Whittaker & Jones 2000 View in CoL

1948 Orbitolina cf. concava – Henson, p. 61-64; pl. 4, fig. 5-10; text fig. 10. “Cenomanian” (late Albian), subsurface Iraq.

? 1978 Orbitolina (Orbitolina) cf. concava qatarica – Berthou & Schroeder, p. 76, pl. 4, fig. 8-12. Early Cenomanian, Portugal.

? 1985 Orbitolina (Orbitolina) sefini – Schroeder in Schroeder & Neumann, pl. 30, fig. 4-8. Late Albian, Spain.

1986 Orbitolina (Orbitolina) sefini – Schroeder et al., p. 383-385, text fig. 2a-g. Late Albian, SW England.

1990 Orbitolina (Orbitolina) concava – Weidich & Al-Harithi, p. 605-606, pl. 5, figs. 1-10. Albian – Cenomanian transition, Jordan (age in part based on this occurrence).

1992 Orbitolina sefini – Simmons & Williams, pl. 1, figs. 3-5. Late Albian, south-west England.

T 2000 Orbitolina hensoni n. sp. – Simmons et al., p. 423, pl. 2, fig. 1-2; pl. 4, fig. 9. Late Albian, subsurface Iraq.

Diagnostic features: An Orbitolina with a proloculus of max diameter c. 0.25mm. The proloculus is not well known in published illustrations but appears concave upwards. The embryonic apparatus diameter is c. 0.60mm and generally has a flat base. The supra-embryonic zone is highly subdivided. The sub-embryonic zone is thin, and less strongly subdivided than the supra-embryonic zone. Radial zone chamber passages are distinctive and exclusively equilateral triangular in shape.

Remarks: Following their reappraisal of Orbitolina sefini , Orbitolina hensoni was introduced by Simmons et al. (2000) for Orbitolina with exclusively triangular chamber passages. An embryonic apparatus with a diameter of 0.6 mm and a flat-based, upwards concave proloculus is a supplementary defining feature, although the proloculus shape is poorly known.

Specimens of “ O. (O.) sefini ” from the late Albian of Spain illustrated by Schroeder in Schroeder & Neumann (1985) that may be better referred to O. hensoni (note triangular chamber passages) have a cup-shaped or spherical proloculus. The embryonic apparatus is a little larger (diameter 0.7-0.8 mm; proloculus diameter 0.2 mm) than the type material of O. hensoni . Specimens of “ O. sefini ” from the late Albian of southwest England ( Schroeder et al., 1986; Simmons & Williams, 1992) have clearly triangular chamber passages and an embryonic apparatus in the size range of O. hensoni , although its morphology is slightly different.

See discussion of O. sefini for issues surrounding chamber passage shape that differ between macrospheric and microspheric generations (Cherchi & Schroeder, 1999). Conceptually, this might be a difference that mistakenly led Simmons et al. (2000) to separate O. hensoni from O. sefini but cannot be proved without a review of better topotype material.

Stratigraphic range: Latest Albian (confident and common) – (uncertain)?earliest Cenomanian. With type material from the Naftah-1 well in Iraq, the range was tentatively regarded as late Albian. The only other named record of the species is that of Farsi et al. (2022) who provided indeterminate illustrations from the (late Albian) Mauddud portion of the Sarvak Formation from the Iranian Zagros (Kuh-e-Genu) .

The species may have been recorded from the early Cenomanian of Portugal as “ Orbitolina (Orbitolina) cf. concava qatarica ” (Berthou & Schroeder, 1978). Specimens of “ Orbitolina (Orbitolina) concava ” illustrated by Weidich & Al-Harithi (1990) from the Albian/Cenomanian transition of Jordan fit well with the identity of O. hensoni in terms of embryonic apparatus size and chamber passage shape.

Palaeogeographic distribution: Confirmed records (notwithstanding issues concerning identity) range from Jordan and Iraq to the UK with possible records also from Iran and the Iberian Peninsula. Consequently O. hensoni as interpreted herein appears to be the most widespread of the Orbitolina species.