Heterostegina armenica ( Grigoryan, 1986 )

Less, György, Özcan, Ercan, Papazzoni, Cesare A. & Stockar, Rudolf, 2008, The middle to late Eocene evolution of nummulitid foraminifer Heterostegina in the Western Tethys, Acta Palaeontologica Polonica 53 (2), pp. 317-350 : 331-334

Heterostegina armenica ( Grigoryan, 1986)

Fig. 11A–I, M.

Emended diagnosis.—Involute, flat biconvex test with oval contour, central pile and slightly sigmoid septal sutures passing into an irregular sutural network in the edges. The proloculus is relatively large; the chamberlets (often with incomplete secondary septa) are rather irregularly arranged and characteristically polygonal. The number of undivided chambers is subjected to nepionic acceleration. Based on this, the species is subdivided into two chronosubspecies as follows:

H. armenica armenica X mean> 8

H. armenica tigrisensis ssp. nov. X mean <8

Description

External features ( Fig. 11A 2 , M).—The test is involute, biconvex, flat and medium−sized (3–6 mm) with oval contour. The distinct central pile is somewhat eccentrically placed. Septal sutures are slightly sigmoid, passing into a rather irregular hexagonal network of primary and secondary septal sutures in the peripheral zone of the adult whorls.

Internal features.—The equatorial section of A−forms: The relatively large proloculus is followed by the second chamber of similar size and then by a loosely coiled spiral. The chambers are high, densely spaced and almost evenly arched. The first appearance of chamberlets is stratigraphically controlled; undivided chambers may often reappear in the neanic stage of growth. The arrangement of the chamberlets is characteristically irregular, though becoming more regular in both higher onto− and phylogenetic levels. Their shape is also irregularly polygonal; the secondary septa are often incomplete, especially in the early stage of phylogenesis. Numerical features are tabulated in Table 5.

Microspheric specimens have not been found yet.

Species species sub- sample p[t(X)] Species species sub- sample p[t(X)] armenica armenica Keçili Azatek 3 0.043 0.691 helvetica Úrhida Úrhida Úrhida 8 9 7 0.075 0.336. H tigrisensis Keçili 11 reticulata Mossano Oberbergli 3 0.289 0.987 Keçili Prella 11 5 0.125 reticulata Mossano Şarköy 5+6 0.000 0.567 0.417 tronensis La Úrhida Trona 1 0.041 0.469 0.173 Heterostegina mossanensis Verona Úrhida, Felice 10 0.257 0.995 Siest Verona, hairpin reticulata hungarica Úrhida 2+3 0.000 0.909 Mossano Mossano 7 8 0.607 0.168 0.567 Heterostegina multifida P Mossano M. Aguilera. Cavro 2 0.008 0.594 0.360 italica Possagno Possagno Noszvaj 2 1 0.658 0.640 Úrhida 4+5 p[t(S)] 0.567 Possagno 1 0.103 helvetica Gschwänt Úrhida 6 0.611. gracilis Possagno Benidorm 2 0.973 Úrhida 7 0.754 H Biarritz, Cachaou 0.583

Axial section ( Fig. 11E): The test is flat, biconvex and involute with a flaring last whorl. The central pile is distinct. The subdivision of the chambers into chamberlets is hardly visible.

Remarks.—The forms described above can be identified with Grigoryan’s (1986) Grzybowskia armenica since we could investigate the material from Azatek, the type locality of this species. Its taxonomic validity is confirmed, since Heterostegina armenica differs from H. reticulata with similar degree of nepionic acceleration by the much less regular arrangement and shape of secondary chamberlets. The distinction is also confirmed by the significantly larger proloculus of H. armenica in comparison with the coeval H. reticulata (see also Fig. 10 ) as well as by the joint occurrence of the most advanced H. armenica (i.e., H. a. tigrisensis ) with the most primitive H. reticulata (i.e., H. r. tronensis ) in sample Keçili 11 where they could be separated biometrically (see also Fig. 8 ). Moreover, H. armenica is definitely flatter than H. reticulata .

Heterostegina armenica occurs together with the Operculina gomezi −group in all the localities known so far. The latter differs from H. armenica only in lacking complete secondary chamberlets and in having a significantly smaller (about 100 µm) proloculus. Since this involute Operculina appears first in lower stratigraphical levels than H. armenica (e.g., in the Keçili section, see Özcan et al. 2007), early members of the O. gomezi group may be considered as possible ancestors of H. armenica . The intraspecific evolution of H. armenica is expressed significantly in the decrease of parameter X and in the increasing density of the chamberlets (parameter S). The size of the proloculus (P) increases less distinctly. H. armenica either became extinct with no successors or gave rise to H. reticulata .

sections, paratype, ITU O/KEÇ.11−38 (G), holotype, ITU O/KEÇ 11−54 (H), paratype, ITU O/KEÇ.11−27 (I). M. Paratype, MÁFI E. 9508, A−form, axial section. J–L, N–R. Heterostegina reticulata tronensis ssp. nov., middle late Bartonian , SBZ 18 B. J, K. Keçili 11 (E Turkey), A−form, equatorial sections, ITU O/KEÇ.11−55 (J), ITU O/KEÇ.11−39 (K). L, N–Q. Vic (NE Spain), La Trona. L, N, O. A−form, equatorial sections , paratype, MÁFI E. 9509 (L), holotype, MÁFI E. 9510 (N), paratype, MÁFI E. 9511 (O). P. Paratype, MÁFI E. 9512, A−form, axial section. Q. Paratype, MÁFI E. 9513, external view. R. Prella 5 ( Switzerland), MCSNL P5/β−3, A−form, equatorial section .

Geographic and stratigraphic distribution.—Early and middle late Bartonian (SBZ 18 A–B) of Armenia and Turkey (Eastern Anatolia) as detailed at the particular subspecies.

Heterostegina armenica armenica ( Grigoryan, 1986) Fig. 11A–F.

1986 Grzybowskia armenica sp. nov.; Grigoryan 1986: 120–121, pl. 37: 1–4, 7.

Diagnosis.— Heterostegina armenica −populations with X mean exceeding 8. The equatorial section of A−forms.—Secondary chamberlets are rather disorderedly arranged and of irregularly polygonal shape. The secondary septa are often incomplete. For numerical features see Table 5.

Remarks.—The biometrical parameters of the Azatek (the type locality of Grigoryan’s 1986 Grzybowskia armenica ) population indicate that they belong to the more primitive evolutionary stage of the species; therefore the subspecific name

“ armenica ” is attributed to this stage. Geographic and stratigraphic distribution.—Early late Bartonian (SBZ 18 A) of Armenia (Azatek) and Eastern Anatolia, Turkey (the middle larger foraminiferal horizon in Keçili, sample Keçili 3)

Figures

Fig. 2. The measurement system in the equatorial section of megalospheric Heterostegina (see also text). Pre−heterosteginid chambers (X) are marked by solid circles, secondary chamberlets in chamber 14 (S) by asterisks.

Fig. 10. Distribution of the Eocene heterosteginid populations (mean values at the 95.44% confidence level) on the P–X (proloculus diameter versus number of undivided post−embryonic chambers) bivariate plot (X is on logarithmic scale)

Fig. 8. Distribution of heterosteginid specimens from sample Keçili 11 on the P–X (proloculus diameter versus number of undivided post−embryonic chambers) bivariate plot (X is on logarithmic scale). Solid circles, Heterostegina armenica; open circles, H. reticulata.