Catalog - Conoglobigerina grigelisi

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Conoglobigerina grigelisi

Citation: Conoglobigerina grigelisi Gradstein 2017

Type sample (& lithostrat): Sample 24/2P taken in 1978 from the middle Tojeira Formation, Montejunto, Portugal; slightly above the thin limestone bed in Fig. 2.

Type age (chronostrat): Platyna through Platynota Zones, Early Kimmeridgian.

Type locality: Montejunto, Portugal

Type repository: Krakow; European Micropaleontological Reference Centre of the Micropress Foundation, AGH University, Krakow, Poland

Low to medium high conical test with a compact spire and 3.5–4 chambers in the last whorl. H/D ratio 0.5–1, rarely over 1. No preferred coiling direction observed. The chambers of the last whorl are large and have deeply incised sutures. Last whorl strongly embraces previous (? 2) whorls such that the earlier part of the test maybe hardly visible. Apex generally blunt, rarely pointed. Umbilical area depressed. Aperture generally a more or less symmetrical arch with lip, rarely comma-shaped. Specimens may have a small bulla over the umbilicus with one or two, low-arch apertures; it may resemble the bulla structure of Cenozoic Catapsydrax taxa. Wall microperforate, strongly pustulose; pustules form low and broken ridges that create an imperfectly reticulate pattern over the surface of the chambers.

Conoglobigerina grigelisi Gradstein sp. nov. is named after Algimantas Grigelis for his early study of Jurassic planktonic foraminifera.

Differential diagnosis: Conoglobigerina grigelisi sp. nov. differs from G. bathoniana in its more compact test, strongly embracing chambers in the last whorl, often wider last whorl and wider umbilicus, and by its densely pustulose, reticulate wall sculpture. The pustules form broken ridges that arrange in an imperfect, low reticulate pattern over the whole test. C. helvetojurassica has more spherical, globular chambers which do not so strongly overlap previous whorls as in C. grigelisi.
The specimens of C. grigelisi in shape somewhat resemble Globuligerina avariformis (Kasimova, 1984) from the Bajocian of Azerbaijan. This taxon is poorly documented, but the original description under the genus name Conoglobigerina by Kasimova and Aliyeva (1984) mentions a smooth test and low arch aperture. The original drawings of the holotype show that the last whorl much less embraces the test than in C. grigelisi sp. nov. Gorog and Wernli (2002) report common C. aff. avariformis from the middle and late Bathonian of Hungary.
The SEM illustration on Fig. 8.8–10 of a specimen of G. avariformis (Kasimova) from Simmons et al. (1997), donated by G. K. Kasimova to the Museum of Natural History, London, UK shows the rather smooth wall and compact test. The sutures are less incised than in our specimens of C. grigelisi sp. nov. Another key difference is that the Bajocian age specimens from Azerbaijan have a wall with low pustules and ridges, instead of a dense muricate and rather reticulate wall sculpture. In C. grigelisi the last whorl also is more embracing the older part of the test.
Görög and Wernli (2013) described a morphotype from the Kimmeridgian of SE France under the name C.? avariformis, using acetolysis, that strongly resembles C. grigelisi sp. nov.

Range: Common in the Tojeira Formation, Lower Kimmeridgian of Central Portugal, and observed with few, small specimens in slightly older strata on the Grand Banks. Likely occurs also in the Kimmeridgian of SE France.

Phylogeny: The more embracing test and more advanced wall texture of C. grigelisi sp. nov. compared to G. avariformis (Kasimova) may indicate an evolutionary trend from the latter to the former taxon in Late Jurassic time. A problem is the lack of record of the latter in Callovian through Oxfordian strata.

References:

Gorog, A. & Wernli, R. (2002). The Middle and Late Bathonian protoglobigerinids of Gyenespuszta (Bakony Mts., Hungary). Revue de Paléobiologie. 21(1): 21-34. gs O

Gradstein, F. M. (2017a). New and emended species of Jurassic planktonic foraminifera. Swiss Journal of Palaeontology. 136(2): 161-185. gs

Kasimova, G. K. & Aliyeva, D. G. (1984). Planktonic foraminifera of the Middle Jurassic deposits of Azerbaidzhan. In, Alizade, K. A. (ed.) Questions in the paleontology and stratigraphy of Azerbaidzhan. Elm (for Akad Nauk Azerbaidzhan. SSR, Inst Geol im I.M. Gubkinaa), Baku 1-12. gs

Simmons, M. D., Boudagher-Fadel, M. K., Banner, F. T. & Whittaker, J. E. (1997). The Jurassic Favusellacea, the earliest Globigerina. In, Boudagher-Fadel, M. K., Banner, F. T. & Whittaker, J. E. (eds) The Early Evolutionary History of Planktonic Foraminifera. British Micropalaeontological Society Publication Series . 17-30. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Conoglobigerina grigelisi Gradstein 2017

Conoglobigerina grigelisi

References:

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