pforams@mikrotax - Falsotruncana loeblichae

Citation: Falsotruncana loeblichae (Douglas, 1969)

Basionym: Praeglobotruncana loeblichae

Taxonomic discussion: The spiny surface ornamentation of this species and the radially arranged spines on the umbilical side are features suggestive of the genus Rugoglobigerina. However, the species does not possess tegilla, and the primary aperture is a single extraumbilical-umbilical opening with a narrow bordering lip. These features indicate relationship to the rotaliporids rather than to members of the Globotruncanidae. The species exhibits the diagnostic features of the genus Praeglobotruncana but has a somewhat distinctive wall structure.

The diagnostic features of the genus Praeglobotruncana, are 1) an imperforate margin and 2) a single interiomarginal extraumbilical-umbilical aperture with bordering porticus. On the basis of the presence of these features the species is assigned to this genus. However, the expression of these features in the species is somewhat distinct from that in common examples of the genus such as Praeglobotruncana stephani (Gandolfi) [Globotruncana stephani, 1942].

The axial margin of most species of Praeglobotruncana is acute, with a distinct carina constructed of a thin band of clear imperforate calcite. The margins of P. loeblichae are truncate to somewhat rounded, and in some specimens axial sections of the wall reveal that the marginal band is penetrated by an occasional pore. On both the spiral and umbilical sides near the edges of the marginal band, and more rarely within the marginal band, pores may be observed which appear to have been plugged by the later addition of shell material. The margins of the test were apparently originally rounded and slightly porous, as in Hedbergella, but became imperforate and truncate during the ontogeny of the organism as more material was added to the surface of the shell.
The aperture of typical Praeglobotruncana is a narrow arched opening which extends from the margin to the umbilicus. The outer edge of the aperture is bordered by a flap (or porticus) which partly covers the opening and extends into the umbilical area. In P. loeblichae the aperture is typical of the genus, but none of the specimens examined (ca. 300) possessed or suggested the former presence of an apertural flap. Also, the umbilical depression of the species is distinctly broader and shallower than in other species of the genus.
One feature which sets off this form from other species of Praeglobotruncana is its spinose or rugose surface. The surface of the spiral side is covered with short spines or rugae or both. In axial section the ornamentation on the older chambers is built up by layers of shell material, so that the larger spines have a laminar structure. The surface of the last-formed chamber is usually smooth, particularly on the umbilical side, indicating that the ornamentation is largely a secondary development. In occasional specimens spines may become interconnected and develop ridges similar to those found in Rugoglobigerina. [copied from Chronos database]

Original description: Test free, low trochospiral; spiral side gently convex; umbilical side nearly flat; equatorial periphery lobate; axial periphery semiovate to broadly truncate, covered with large spines. Chambers subglobular, 5 to 6 in final whorl, compressed, subrectangular on spiral side, sectorial on umbilical side. Sutures radial and depressed, slightly curved on spiral side. Wall calcareous, perforate; surface spiny to rugose; surface spines tangentially arranged on spiral side; coalesced surface spines radially arranged on umbilical side. Umbilicus wide and shallow. Aperture a low interiomarginal arch extending from umbilicus nearly to margin, bordered by narrow apertural lip.

Geological Range:
Last occurrence (top): within M. schneegansi zone (89.91-92.56Ma, top in Turonian stage). Data source: [copied from Chronos database]
First occurrence (base): within H. helvetica zone (92.56-93.52Ma, base in Turonian stage). Data source: [copied from Chronos database]

References:

Caron, M. (1981). Un nouveau genre de Foraminifere planctonique du Cretace: Falsotruncana nov. gen. Eclogae Geologicae Helvetiae. 74(1): 65-73. gs

Douglas, R. G. (1969). Upper Cretaceous planktonic foraminifera in northern California. Part 1 - Systematics. Micropaleontology. 15(2): 151-209. gs

test outline:	Lobate	chamber arrangement:	Trochospiral	edge view:		aperture:	Umbilical-extraumbilical
sp chamber shape:	Petaloid	coiling axis:	Low	periphery:	Double keel	aperture border:	Thin lip
umb chbr shape:	Trapezoidal	umbilicus:	Wide	periph margin shape:	Subangular	accessory apertures:	Relict
spiral sutures:	Moderately depressed	umb depth:	Shallow	wall texture:	Coarsely pustulose	shell porosity:
umbilical or test sutures:	Moderately depressed	final-whorl chambers:	6-6.5	N.B. These characters are used for advanced search. N/A - not applicable

Falsotruncana loeblichae

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