Globigerinatheka mexicana

Classification: pf_cenozoic -> Globigerinidae -> Globigerinatheka -> Globigerinatheka mexicana
Sister taxa: G. semiinvoluta, G. tropicalis, G. luterbacheri, G. euganea, G. index, G. curryi, G. barri, G. korotkovi, G. kugleri, G. mexicana, G. subconglobata, G. sp.,


Citation: Globigerinatheka mexicana (Cushman 1925)
Rank: Species
Basionym: Globigerina mexicana
Variants: sm
Taxonomic discussion: As reported by Bolli (1972, p. 129), Cushman’s species mexicana “has been misinterpreted more than any other of the Globigerinatheka” (see the synonymy list) owing to the inadequate original description and illustrations and to the fact that specimens with different features and of much larger sizes than the holotype have been identified as mexicana, including by Cushman himself (1927). Saito (1962), in emending mexicana, regarded it as being very closely related to barri, which he interpreted as the bullate form of the former. Saito’s view was followed by Bolli (1972, p. 129) who, based on Beckmann’s observation of the original types, considered mexicana s. s. and barri as subspecies of Globigerinatheka mexicana. Bolli (1972) also included in mexicana his species kugleri, again as a subspecies of it, based on his finding intermediate forms, a view rejected here (see above). For instance, the specimen illustrated by Bolli (1972, pl. 2, fig. 5, the spiral view) as G. mexicana mexicana for its subtriangular outline is attributable to G. kugleri. Toumarkine (1978) illustrated as G. mexicana mexicana some specimens that do not possess the last large enveloping chamber and have a rather short, not flat initial spire; they may be closer to G. barri. The specimen attributed by Samanta (1970, pl. 2, figs. 20-21) to G. barri in our opinion exhibits a large last chamber that is more characteristic of G. mexicana. Blow (1979, p. 789) referred Globigerinatheka kutchensis Singh and Tewari, 1967 to G. mexicana mexicana because it possesses abortive chambers and not true bullae. Blow and Saito (1968a) regarded mexicana as synonymous with semiinvoluta, whilst Blow (1979) considered mexicana as synonymous with tropicalis. We recognise all these species as separate taxa (also see Bolli, 1972 for discussion). [Premoli Silva et al. 2006]

Catalog entries: Globigerina mexicana, Globigerinatheka kutchensis

Type images:

Distinguishing features: Test nearly spherical. Last chamber large (ca ½ test), inflated. Sutures not vey distinct.

NB These concise distinguishing features statements are used in the tables of daughter-taxa to act as quick summaries of the differences between e.g. species of one genus.
They are being edited as the site is developed and comments on them are especially welcome.


Diagnostic characters: Globigerinatheka mexicana is characterized by its nearly spherical test and large inflated last chamber that comprises about half of the entire test. It differs from G. semiinvoluta by its less embracing last chamber and smaller secondary apertures that lack a rim, from G. barri by its larger hemispherical last chamber, less depressed sutures throughout, spherical outline and less common bullae, and from G. kugleri by its more spherical test and less distinct sutures. [Premoli Silva et al. 2006]

Wall type: pores about 4 mm in diameter.

Test morphology: Test very close to spherical, early chambers arranged in a low trochospire composed of at least 6 subglobular chambers initially gradually increasing in size as added, then increasing much more rapidly; last chamber hemispherical constituting almost half of the entire test totally covering the umbilical side of the earlier chambers; sutures poorly visible except between the last two to three chambers where they are very slightly depressed; three visible apertures at the base of the last chamber, small to medium-sized arches close to subcircular, apparently located at the junctions of previous chambers. [Premoli Silva et al. 2006]

Size: The diameter of the holotype measures 0.30 mm, much smaller than that indicated by Cushman (1925, diameter 0.40-0.60 mm). [Premoli Silva et al. 2006]

Character matrix

test outline:Circularchamber arrangement:Envelopingedge view:Equally biconvexaperture:Biapertural
sp chamber shape:Globularcoiling axis:Lowperiphery:N/Aaperture border:N/A
umb chbr shape:Globularumbilicus:Narrowperiph margin shape:Broadly roundedaccessory apertures:None
spiral sutures:Weakly depressedumb depth:Deepwall texture:Spinoseshell porosity:Macroperforate: >2.5µm
umbilical or test sutures:Weakly depressedfinal-whorl chambers:3.0-3.5 N.B. These characters are used for advanced search. N/A - not applicable

Biogeography and Palaeobiology

Geographic distribution: Low to mid latitudes. [Premoli Silva et al. 2006]

Isotope paleobiology: Globigerinatheka mexicana has oxygen and carbon isotopic ratios indicative of a mixed layer habitat (Boersma and others, 1987; Wade, 2004). [Premoli Silva et al. 2006]

Phylogenetic relations: Bolli (1972, p. 114) stated that mexicana “branched off from G. subconglobata micra near the base of G. subconglobata subconglobata Zone (= upper part of Zone E8), while the subspecies barri and kugleri originated from mexicana s.s. in subsequent order always within the G. subconglobata subconglobata Zone”. Besides Bolli (1972), other authors (i.e., Stainforth and others, 1975; Blow, 1979; Toumarkine, 1983) all agree that mexicana appears first, followed slightly later by barri. Consequently, G. mexicana probably descended from the G. subconglobata plexus close to the E8/E9 zonal boundary. Through Zone E13, the sutures of G. mexicana become less pronounced, the final chamber more spherical and apertures semicircular to circular in outline. In uppermost Zone E13 and lowermost E14 in the western North Atlantic (ODP Site 1052), transitional forms are evident to G. semiinvoluta (Plate 7.8, Fig. 11). [Premoli Silva et al. 2006]

Most likely ancestor: Globigerinatheka subconglobata - at confidence level 3 (out of 5). Data source: Premoli Silva et al. 2006 f7.1.
Likely descendants: Globigerinatheka semiinvoluta;

Biostratigraphic distribution

Geological Range:
Notes: Globigerinatheka mexicana appears in the lower middle Eocene and its first occurrence was used to identify the base of Zone P11 (=E9) sensu Stainforth and others, 1975; Blow, 1979; Toumarkine, 1983. Although the appearance of G. mexicana is poorly calibrated it seems it occurs very close to that of G. kugleri. It ranges up to the topmost part of E14. [Premoli Silva et al. 2006]
Last occurrence (top): within E14 zone (35.89-37.99Ma, top in Priabonian stage). Data source: Premoli Silva et al. 2006 f7.1
First occurrence (base): within E9 zone (43.23-43.85Ma, base in Lutetian stage). Data source: Premoli Silva et al. 2006 f7.1

Plot of occurrence data:

Primary source for this page: Premoli Silva et al. 2006 - Eocene Atlas, chap. 7


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Globigerinatheka mexicana compiled by the pforams@mikrotax project team viewed: 8-7-2020

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