Catalog - Eoglobigerina extensa

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Eoglobigerina extensa

Citation: Eoglobigerina? extensa Blow 1979

Type specimens: PM PF 63726 (holotype); PM PF 63685 paratype)

Type age (chronostrat): Lower Paleocene, lower Danian, Zone P. I (Globorotalia (Turborota/ia) pseudobulloides/ Eoglobigerina eobulloides simplicissima concurrent-range zone). Ranges down into lowermost Danian, zone P.a (Globorotalia (Turborotalia) longiapertura partiaI-range zone).

Type locality: Zone P1, DSDP Hole 47.2/11/3, 0-5 cm, Shatsky Rise, NW Pacific Ocean

The small test is coiled in a distinct, tightly expressed, trochospire with 9-10 chambers comprising the spire and with four chambers in the last whorl. In dorsal aspect, the chambers are inflated, closely appressed, closely-set and quite strongly embracing and the dorsal intercameral sutures are subradially to sinuously disposed. The dorsal and ventral intercameral sutures are depressed to moderately incised. In ventral aspect, the chambers are inflated, subglobular, but embracing. The umbilicus is closed and the aperture extends from the umbilicus
extensively towards the anterior side of the last chamber and is a widely open, almost rectangular, opening bordered by a weakly developed but thickened porticus. The equatorial profile is strongly lobulate but almost circular in outline whilst the axial profile shows the distinct early trochospire and subglobular nature of the later chambers. The wall is very finely perforate and the mural-pores are very widely and sparsely developed; the mural-pores do not open into pore-pits but the wall bears fine pustules which may be the bases of normal spines.

Maximum diameter of holotype 0.198 mm as measured electronically.

The paratype illustrated in fig. 7 shows a form with a slightly open umbilicus and a more strongly developed porticus. However in other characters of the test this paratype agrees with the conditions seen in the holotype. This form is comparatively rarely occurring and since it has thinly developed walls is often seen broken. The generic assignation of the taxon to Eog[obigerina Morozova, emend. Blow, 1979, may be questioned since the wall structure and texture is much more characteristic of that seen in forms referred to the genus Globastica Blow, 1979. However, the apertural system of E. extensa Blow, 1979, is not typical of Globastica but is of the same general pattern as seen in Eoglobigerina. The importance of this form lies in the recognition of its very finely perforate wall, which, together with the specimens referable to Eoglobigerina? Iodina Blow, 1979, could be interpreted as forming part of a group of 'smooth walled' eoglobigerinids distinct from the normally perforate, cancellate or reticulate, wall of the eobulloides - trivialis - edita group. Thus, although both extensa and fodina (which both have very strange apertural systems) are provisionally placed in the genus Eoglobigerina, it is doubtful if this generic assignation will be maintained following more work on the very stratigraphically early Cainozoic forms. However, in order to clearly delimit the characters of Globastica, the writer decided that fodina and extensa would be best placed in Eoglobigerina for the time being at least.

References:

Blow, W. H. (1979). The Cainozoic Globigerinida: A study of the morphology, taxonomy, evolutionary relationships and stratigraphical distribution of some Globigerinida (mainly Globigerinacea). E. J. Brill, Leiden. 2: 1-1413. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Eoglobigerina? extensa Blow 1979

Eoglobigerina extensa

References:

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