Catalog - Alanlordella

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Alanlordella

Citation: Alanlordella BouDagher-Fadel 1995

Type species: Alanlordella banneri BouDagher-Fadel 1995

Test planospiral, nearly involute, chambers globular, sutures depressed, wall muricate in early whorls, macroperforate, the macroperforations become sunk into perforation depressions (see Pl.2, fig.12) and the rims of these depression fuse to give the later chambers a cancellate texture. Periphery rounded, sometimes compressed in the early stage but never developing a keel. Aperture interiomarginal, equatorial, symmetrical, extending laterally into each umbilicus, final aperture and relict apertures are usually furnished with portici.

The generic name Alanlordella is in honour of Prof. Alan Lord, in recognition of his support and constant help throughout the research.

The genus at present is considered to have two species: A. banneri (type species) and A. praebuxtorfi Wonders (1975). Alanlordella is different from Globigerinelloides in being macroperforate and muricate and from Planomalina in lacking a muricocarina. It does not show the biseriality of Biglobigerinella of the Late Cretaceous (Campanian- Maastrichtian) (which seems to be restricted only to the United States).
Alanlordella develops in the Late Aptian from the planospiral, rnicroperforate, sometimes with perforation cones, Globigerinelloides by acquiring macroperforations and muricae. Then (probably only in the area of the United States) in the latest Aptian and Albian, they develop terminal biseriality which is characteristic of Biglobigerinella. However, these terminally biserial forms range up into the Campanian-Maastrichtian as (Biglobigerinella multispina). They are unique among the Hedbergellidae in their terminal biseriality and their latest Cretaceous range and must be distinguished on the generic level from all of the rest.

Alanlordella should be placed in the Planomalinidae because it is planospiral, compressed laterally, macroperforate and never develops perforation cones (which only occur in the Praehedbergellidae), but frequently develops muricae. When muricae appear, they first occur on the earliest part of the last whorl adjacent to the aperture as in Alanlordella banneri (Pl.2, figs 10-12), where they could disintegrate the food particles carried by the extrathalamous cytoplasm directly to the aperture. By the Cenomanian almost all species of the planospiral forms possess muricae on all chambers of the last whorl and a peripheral fused muricocarina (or keel). There is a gradual spread of the muricae during Aptian-Albian- Cenomanian evolution, from partially murico-carina as in Alanlordella to fully keeled as in Planomalina. The transition between these genera is essentially gradual. They are retained because of their stratigraphical value. The boundary between them is arbitrary and they have been differentiated because of their utility in describing the phylogenetic evolution of the Globigerinacea in this part of the Cretaceous (an article tracing this evolution is in preparation). The Planomalinidae are planospiral and possess strong muricae (at least on the early chambers of the last whorl) and can develop a peripheral murico-carina. Alanlordella lacks a murico-carina except on the earliest chambers of the last whorl, and true Planomalina has a murico-carina on all chambers of the last whorl.

Stratigraphy: Albian.

References:

BouDagher-Fadel, M. K. (1995). The planktonic Foraminifera of the Early Cretaceous of Tunisia compared to those of western and central Tethys. Paleopelagos. 5: 137-159. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Alanlordella BouDagher-Fadel 1995

Alanlordella

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