Catalog - Eoglobigerina appressa

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Eoglobigerina appressa

Citation: Eoglobigerina appressa Blow 1979

Type age (chronostrat): Basal Paleocene, lowermost Danian, zone Pa (Globorotalia (Turborotalia) longiapertura partial-range zone); paratype (fig. 9) from lower Danian, Zone P. I (Globorotalia (Turborotalia) pseudobulloides/ Eoglobigerina eobulloides simplicissima concurrent-range zone).

Type locality: DSDP Site 47/2, cored at a depth of 2689 meters on the Shatsky Rise, lat. 32.26.9' N. , long. 157. 42.7' E., northwestern Pacific Ocean; holotype (fig. 5) and three paratypes (pl. 60, figs. l, 6, 7) from sample I l4, 148-150 cm; paratype (pl. 65, fig. 7) from sample I l3, 148-150 cm; paratype (fig. 9) from sample I ll , 148-150 cm.

The small test is coiled in a low trochospire with about 12 chambers comprising the spire and with four chambers in the last whorl. The penultimate whorl of chambers, as seen in dorsal aspect, are inflated, subglobular and sensibly equidimensional but the dorsal aspect of the last whorl of chambers shows that they become appressed, closely-set and much longer tangentially than broad radially. The dorsal intercameral sutures are depressed, not deeply incised but radially disposed. In ventral aspect, the chambers are tangentially much longer than broad, radially depressed and without any considerable ventral inflation. The umbilicus is quite widely open but shallow and not well defined by the umbilical shoulders of the chambers of the last convolution of the test. The aperture is markedly asymmetrically umbilical-extraumbilical but is a quite distinctly arcuate opening with a clearly well defined portical structure. The equatorial profile is lobulate, oval in outline, with the test elongated in the direction which includes the last chamber; the chambers of the last whorl increase more rapidly in size as added in the progression of the trochospire as compared to the earlier, subglobular, chambers of the penultimate whorl. The axial-apertural profile shows a distinct early trochospire but the later chambers are axial compressed. The wall is perforate but the mural-pores are widely spaced and do not open into distinct pore-pits.

Maximum diameter of holotype 0.11 mm as measured electronically.

Remarks. - This very small taxon is quite distinctive but is difficult to assess as to its correct generic assignation. The morphotype is the most 'turborotaliid' of the forms included in Eoglobigerina Blow (See catalogue sheet) in this work. However, in particular, the dorsal aspect is probably more typical of forms included in the genus Eoglobigerina and the possession of an open, arcuate, aperture appears to support reference to Eoglobigerina. The later evolutionary relationships of the morphotypes are quite unknown, nevertheless, specimens of the taxon may be considered as showing some interrelationship between the very stratigraphically early eoglobigerinid and 'turborotaliid' [sensu Blow, 1979, op. cit., p. 448] morphotypes. In some ways the chamber arrangement, and even the apertural position, is reminiscent of forms included in Rugoglobigerina macrocephala Brönnimann (group).
The paratype figured on pl. 65, fig. 7, shows a very strongly developed porticus and a slightly smaller umbilicus than seen for the holotype. Superficially, the ventral aspect of such forms might suggest relationship to Subbotina triloculinoides triloculinoides (Plummer) [Globigerina triloculinoides, 1926]. However, the axially (dorsoventral) rather compressed later chambers, which are also tangentially longer than broad, mitigate against such a relationship. The paratype shown in fig. 9 shows what probably is a slight abortively produced last chamber and a smaller, less asymmetrically developed, less extensive, aperture but which still possesses a well marked porticus. This specimen also shows more axial compression of the later chambers than as compared to the condition seen in the holotype.
The paratypes figured on pl. 60, figs. 6 and 7, show similar characters to the holotype but fig. 6 possesses less rapidly enlarging chambers whilst fig. 7 possesses more rapidly enlarging chambers than seen for the holotype.

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 appressa Blow 1979

Eoglobigerina appressa

References:

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