Heterostegina ocalana Cushman, 1921

Torres-Silva, Ana. I., Eder, Wolfgang, Hohenegger, Johann & Briguglio, Antonino, 2018, Morphometric analysis of Eocene nummulitids in western and central Cuba: taxonomy, biostratigraphy and evolutionary trends, Journal of Systematic Palaeontology 17 (7), pp. 557-595 : 586-587

Heterostegina ocalana Cushman, 1921

( Fig. 18A, B, D–H )

1921 Heterostegina ocalana Cushman , 130, pl. 21, figs 15–18.

1941 Heterostegina ocalana Cushman ; Cole: 32, pl. 11, figs 3–6.

1952 Heterostegina ocalana Cushman ; Cole: 13, pl. 4, figs 2–18.

1957 Heterostegina ocalana Cushman ; Puri: 136, pl. 6, figs 10, 11, pl. 7, fig. 16.

1993 Heterostegina (Vlerkina) ocalana Cushman ; Robinson & Wright: 335, pl. 31, fig. 4.

2017 Heterostegina ocalana Cushman ; Torres-Silva, Hohenegger, Cori ́́c, Briguglio, & Eder: 57, fig. 10B–D.

2017 Heterostegina ocalana Cushman ; Benedetti, Less, Parente, Pignatti, Cahizac, Torres-Silva, & Buhl: 14, fig. 10A–G.

Material. Twenty-seven megalospheric specimens in equatorial sections, comprising 14 from Loma Viǵıa (CA-216), nine from Loma Jabaco (LM-52) and four from Norona ( NOR-UN).

Description.

External features. The test is involute, becoming evolute in the last whorls, lenticular to flat, biconvex, and thin towards the periphery with oval contour. Tests of the megalospheric form range in diameter from 1.5 to 4.5 mm. The distinct central pile is situated near the embryonic chambers. The septal sutures are slightly curved, and towards the periphery the primary and secondary sutures form a characteristic reticulate network; this ornamentation is absent in the Loma Vigia populations. B forms are very rare and no significant difference was observed in the size of adults between the megalospheric and microspheric forms.

Internal features. Megalospheric generations in equatorial section are characterized by a small and subspherical proloculus 0.067–0.19 mm in diameter (mean 0.14 mm), followed by a second reniform chamber and a loosely coiled spiral. The number of post-embryonic undivided chambers ranges from two to four and they do not reappear after the first heterosteginid chamber. Primary septa, with weaker backbend angle, form arched chambers, subdivided into subrectangular chamberlets by complete septula. The first chamberlets along the inner spiral cord are 2 times wider than the others. The number of chamberlets and septula increases through ontogeny. A second megalospheric morphotype was found with proloculus size between 0.05 and 0.06 mm followed by 6–7 operculinid chambers, confirming the results of Eder et al. (2017a) on the extant Heterostegina depresa showing strong variability in both characters based on the mixture of two megalospheric generations. Morphological variability in H. ocalana has already been published by Cole (1953).

Occurrences. Late Eocene, NP17/19, Blanco Formation; late Eocene, NP19-20/CP 15 and?early Oligocene, O1/ P18 and NP 21/CP 16, Jabaco Formation.

Remarks. As the most widely recorded heterostegenid species in the American-Caribbean late Eocene, Heterostegina ocalana is distinguished by its small proloculi and the great variability in the number of operculinid chambers within specimens from different localities (Cole 1952; Torres-Silva et al. 2017). Occurrences of H. ocalana at Dowling Park (Florida) dated by strontium isotope stratigraphy correspond to the latest Priabonian, roughly fitting the E16 planktonic foraminiferal biozone and NP21 calcareous nanofossil zone ( Benedetti et al. 2017). This is also consistent with the possible early Rupelian age of samples with H. ocalana from the Norona section, in which this species appears to be significantly more highly evolved than the Priabonian specimens elsewhere.

Stratigraphical and geographical distribution. Late Eocene (Priabonian); Cuba, Florida, Panama, Jamaica, and Island of the Grenadines.

Figures

Figure 18. A, B, D–H, Heterostegina ocalana Cushman; A, Loma Viǵıa, CA-216-D1a; B, Norona, NOR-UN 15/14; D, Loma Viǵıa, CA-216-79; E, F, Loma Jabaco; E, LM-52-756; F, LM-52-752; G, H, Norona, NOR-UN 24. C, Heterostegina cubana Cizancourt, Loma candelaria, 98LC-1H-809. I, Heterostegina sp. indet., Loma Candelaria, 98LC-1H-808. A, B, A forms in axial section; C–G, I, A forms in equatorial section; H, external view.