Catalog - Globorotalia (Hirsutella) eleonorae

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Other pages this level: G. (Hirsutella) eleonorae, G. (Hirsutella) scitula planaria, G. (Hirsutella) theyeri

Globorotalia (Hirsutella) eleonorae

Citation: Globorotalia (Hirsutella) eleonorae Riforgiato&Salvatorini 2012

Type specimens: Plate 1, figs. 1–13; Text-figure ; Holotype figure: text-fig. 3, 1a–d.

Type sample (& lithostrat): Sample AEB-7.3 from the Ain el Beida section.

Type age (chronostrat): N.17 Zone of Blow (1969)

Type locality: Ain el Beida (Bou Regreg valley, near Rabat, Morocco).

Type repository: Siena; Micropaleontology Laboratory of the Department of Earth Sciences, Siena University (Via Laterina 8, 53100 - Siena, Italy).

Test medium, compressed, with a low trochospire formed by an indeterminate number of chambers arranged in about three whorls. Six gradually enlarging chambers in the final whorl. Equatorial profile elliptical, equatorial periphery weakly lobulate. Spiral surface convex, the early whorls forming a low dome; umbilical surface slightly convex. Profile biconvex in axial view. Periphery acute with an imperforate keel bearing scattered pustules on earlier part.
Chambers longer than wide, weakly convex on the spiral and the umbilical sides; finely perforate but with pores absent in a semi-lunar area located in the proximal-posterior portion of each chamber on the spiral side. On the umbilical side, fine pores are sparse or altogether absent on the narrow apertural face and in the area surrounding the umbilicus. The outer margin of the last chamber is crescent and asymmetrical with an indistinct trailing section and a short, weakly convex leading section. The leading section of the inner margin is short and weakly concave, whereas the trailing section is elevated.
Spiral suture limbate; intercameral sutures curved, slightly incised, limbate on the spiral side, and weakly incised, with a slight gentle curvature in their distal portion on the umbilical side. Umbilicus punctiform. Aperture an umbilical-extraumbilical slit-like opening bordered by a distinct lip.
The surface is shiny, with a finely and intensely perforated wall texture and with scattered pustules confined to the earlier chambers of the outer whorl.

Intra-specific variability: sub-circular (especially in non-adult specimens) to more or less elliptical equatorial profile, equatorial periphery often entirely continuous or with a weak lobulation connected with the last suture(s). With respect to the holotype, the spiral surface can be more convex (spiroconical Globorotalia margaritae-like) or almost flat and the umbilical surface can be more convex, flatter or weakly concave. As a result, the axial profile may be symmetrically or asymmetrically biconvex, even concave-convex or spiroconvex. The keel can be more or less developed. The spiral surface of chambers in the last whorl is often flat and sometimes weakly convex in the early chambers of adult specimens. The leading section of the outer margin is rarely linear. Spiral intercameral sutures may be flat (in specimens with planar surface chambers) or weakly depressed (in specimens with convex surface chambers). The umbilicus may be narrow and closed. The last chamber, sometimes much smaller than the penultimate one (kummerform chamber), is rarely abortive. Specimens generally show five and a half-six chambers in the final whorl; a few have five or seven chambers.

Remarks: G. (H.) eleonorae differs from G. (H.) margaritae Bolli and Bermúdez (as neotypified by Bolli and Bermúdez 1978) in showing generally six rather than five chambers in the last whorl. The chambers increase less rapidly in size and are less flared on the spiral and umbilical sides. The test is less concave-convex, the keel is less developed. The pores are absent in a crescent-shaped area in the proximal-posterior portion of each chamber on the spiral side.

Globorotalia (H.) andalusiana Perconig, Martinez, Granados, a poorly known Tortonian-Messinian species considered to be the immediate ancestral form of G. margaritae according to Perconig et al. (1980), differs from G. (H.) eleonorae in having a higher growth rate and four to five chambers in the last whorl. The chamber surface is more convex on the umbilical side.

In the late Tortonian interval of the investigated sections we found no typical specimens of G. (H.) eleonorae n. sp. However, within populations of the scituline stock belonging to the G. (H.) margaritae lineage, we found specimens of an unidentified form possibly representing the first evolutionary step towards the development of our new species. These specimens differ from G. (H.) eleonorae in generally having five chambers in the last whorl and a more convex umbilical surface in both the test and individual chambers, and for the absence of an imperforate keel (a thin keel rarely develops on the last chambers) and of the peculiar imperforate areas in sectors of the spiral chambers surfaces. Spiral and intercameral sutures are non-limbate. The writers prefer to not give any definitive conclusion regarding these specimens, because they are revising the G. (H.) margaritae lineage from different sections. Although in the last decades various interpretative hypotheses have been suggested for this lineage, further study of the taxonomic units in the evolutionary sequence is required.

As for the origin of G. (H.) eleonorae, the species may have been the final component without descent of an evolutionary line branching out from the scituline stock of the G. (H.) margaritae lineage during the late Tortonian.

Stratigraphic range: Messinian (late Miocene). N.17 Zone of Blow (1969); from the N. acostaensis/G. lenguaensis Zone, M13 (the G. extremus/G. plesiotumida-G. lenguaensis Subzone, M13b, (Sub) Tropical) to the G. lenguaensis/G. tumida Zone, M14 and from the N. mayeri-G. conomiozea Zone, Mt9 to the G. conomiozea/G. mediterranea-G. sphericomiozea Zone, Mt10 (Transitional) of Berggren et al. (1995); within the G. lenguaensis/G. tumida Zone, M14 ((Sub) Tropical of Iaccarino et al. (2007). The First Occurrence of G. (H.) eleonorae is recorded in the Chron C3Bn and is astronomically dated at 7.204 Ma; the Last Occurrence of this species is found in the Chron C3An.1n and is astronomically dated at 6.232 Ma.

References:

Riforgiato, F. & Salvatorini, G. (2012). Globorotalia (Hirsutella) eleonorae, a new planktonic foraminifera species from the early Messinian. Micropaleontology. 58: 389-395. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Globorotalia (Hirsutella) eleonorae Riforgiato&Salvatorini 2012

Globorotalia (Hirsutella) eleonorae

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