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P. eugubina Earliest Paleocene 65 Ma
P. eugubina, a low trochospiral individual
Scientific classification
Phylum:	Foraminifera
Class:	Globothalamea
Order:	Rotaliida
Family:	Guembelitriidae
Genus:	Parvularugoglobigerina Hofker, 1978 †

Parvularugoglobigerina

Parvularugoglobigerina is a genus of Phylum Foraminifera belongs to Superfamily Guembelitrioidea. The generic name Parvularugoglobigerina was first introduced by Hofker 1978, which includes the forms occur immediately above the Cretaceous-Tertiary boundary. The Parvularugoglobigerina group belongs to Planktonic Foraminifera. Various authors have identified this genus as Globigerina, Planorotalites and Turborotalia, however, the morphology and wall texture differentiate this genra from these other groups. Following the mass extinction event at Cretaceous- Tertiary boundary planktonic foraminifera saw a rapid recovery in the species diversity. However, the origin and evolution of the Parvularugoglobigerina species debated by various authors is unclear and not converging. The age of the species belonging to Parvularugoglobigerina is considered earliest Paleocene (65Ma), immediately above the K-Pg boundary. However, some authors has reported the occurrence of species such as P. eugubina about 20,000 years before the mass extinction event.

Description

The Parvularugoglobigerines are characterized by dominantly low trochospiral test with 8-12 sub-globular to globular chambers essentially. Chambers increase slowly in the inner whorl and rapidly in the final whorl with 4-7 in number and are seperated by sutures on both spiral and umbilical sides. The test size is variable and ranges in size from 80-150µm with fewer as large as 250µm. The wall texture is smooth, slightly rugose in few species due to calcite growth. The aperture is high and elongated in most tests. In low trochospiral forms the aperture is extraumbilical with or without aperture lip. The species of this group can be differentiated on the basis of low to high spiral height and position of the aperture.

Specie abundance of genus Parvularogoglobigerina and range of genra from K-Pg boundary at Al Kef, Tunisia.Adopted and modified from Li et al. 1991

Species

Five species have been possibly related and are grouped within the genus Parvularugoglobigerina. These includes:

1. Parvularugoglobigerina ''alabamensis'' Liu & Olsson, 1992 †
2. Parvularugoglobigerina ''alticonusa'' Li, McGowran & Boersma, 1995 †
3. Parvularugoglobigerina ''eugubina'' Luterbacher & Premoli Silva, 1964 †
4. Parvularugoglobigerina extensa Blow, 1979 †
5. Parvularugoglobigerina ''perexigua'' Li, McGowran & Boersma, 1995 †

Parvularugoglobigerina eugubina

Morphology and Distinguishing features

Specie P. eugubina tests with microperforate wall texture and few pore mounds. Image taken and modified from Olsson et al. 1999.

P. eugubina has a smooth wall texture and finely pustulate with scattered microperforations (<1µm) which may have a rugose appearance due to dissolution and re-crystallization. P. eugubina composed of 12-14 chambers, with final whorl containing 6 chambers gradually increasing in the size. The chambers are sub-globular to globular in shape with an increase of spire height while sub-triangular to oval in shape in compressed tests. The distinguishing feature of the P. eugubina is its elongated aperture. The aperture is high, umbilical to extraumbilical, crescent shaped opening and may be with or without a thin lip. Secondary aperture is also present on the spiral side of both the normal and inflated forms. These secondary apertures mostly occur on the basal sutures of the chambers in the final whorl. In some tests the areal aperture is present on the final chamber. The typical mounded to microperforate wall distinguishes the P. eugubina from Globigerina. The P. eugubina is widely distributed. The high abundance of the specie was inferred in the upwelling regions during the Danian age. It occurs rarely in polar areas or even absent. However, it is very abundant in samples from many localities such as Spain, Denmark, Italy and Tunisia reaching upto 50%.

P. eugubina with microperforate wall texture and scattered pore mounds. Adopted and modified from Olsson et al 1999

Micropaleontological studies of the sediments from North pacific locality suggest that P. eugubina and P. cretacea were the only species that survived the K-Pg extinction event. The δO¹⁸ and δC¹³ values of Globigerina eugubina from below and above the K-Pg boundary have a negligible difference. The δO¹⁸ values indicate relatively colder paleotemperatures as compared to co-existing species of planktonic foraminifera. Moreover, the δC¹³ values for P. eugubina were also lighter than other planktonic foraminifers species. This suggests that the P. eugubina might have lived in the cooler, shallow intermediate water masses advected from higher latitudes during the latest cretaceous cooling episodes.

Discussion

Since the temperate-warm climates were restored and new ecosystem developed in the oceans during the Danian age, the planktonic foraminifera rapidly evolved after the Creatacous-Paleogene extinction event which resulted in the rapid colonization and speciation at all latitudes. The species of Parvularugoglobigerina constituted in somewhat between 20 to 50 % of total fauna dominating in the mid-latitudes and upwelling regions. The small test size and typical elongate aperture of specie P. eugubina might be related to the fast reproduction and large populations. The P. eugubina is considered to be eutrophic colonizers due to their short life span as they occurred in early paleocene.