Catalog - Chiloguembelina fusiformis

This page provides data from the catalog of type descriptions. The catalog is sorted alphabetically. Use the current identification link to go back to the main database.

Chiloguembelina fusiformis

Citation: Chiloguembelina fusiformis Kim 1987

Type specimens: Plate 1, Figures 1-6. Holotype and Paratypes are on deposit at the U.S. National Museum (nos. 419238-419241), Washington D.C. Paratypes except the paratype B (Fig. 4, PI. 1) are also in the Stanford University

Type sample (& lithostrat): Sample KBJ 8-3 of Kim (1987); friable yellow sandstone of the San Gregorio Formation

Type age (chronostrat): Late Oligocene; P22

Type locality: west side of Mexico Highway 1, 6.5 km south of the town of El Cien, Baja California Sur, Mexico. 24° 16'38"N, 110° 57' 54"W:

Type repository: Washington, USNM

Test small, elongate, tapering toward both ends, biserial, periphery rounded, compressed. Chambers distinct, slightly inflated, of rather uniform shape except the last pair, usually 8 to 13 in number, biserially arranged, rapidly increasing in size up to the 5th pair of chambers, decreasing in breath and thickness from the 6th pair in the adult. Sutures oblique to almost parallel, depressed. Wall calcareous, finely perforate, slightly roughened. Aperture high and narrow opening, asymmetrical, bordered by distinct rim, running from the base of the last· formed chamber.

Length 0.15-0.22 mm, breath 0.1-0.14 mm, thickness 0.1 mm.

Remarks: Chiloguembelina fusiformis is easily distinguished from other species of this genus by its fusiform shape in mature specimens (Figs. 1-4, Pl. 1) after which its name is taken. Juveniles of this species (Figs. 5-6. PI. 1) differ from C. tenuis (Todd, 1957) in having fewer pairs of chambers (5 pairs) and are without a polished wall. The juveniles of C. fusiformis can also be distinguished from C. parallela Beckmann (1957) by their nearly parallel sutures and asymmetrical aperture.

C fusiformis comprises the entire foraminiferal assemblages in Sample KBJ 8-3 (more than 300 specimens).

Age: Zone P22 (Blow, 1969) of late Oligocene. Although C. fusiformis was not found with other age diagnostic taxa at its type locality, additional specimens of this species were collected from the upper San Hilario section of the San Gregorio Formation located 7.3 km northeast of the type locality (Kim, 1987). Among the additional 12 specimens of this species, 11 are obtained from Sample SH-6 together with Globigerinita glutinata whose range is P22 to Recent (Kennett and Srinivasan, 1983) and one from Sample SH-7 located approximately 25 cm below Sample SH-6. Sample SH-7 represents the lower boundary of the P22 Zone of the San Hilario section based on the first occurrence of G. glutinata and cooccurrence of typical constituents of the P22 Zone assemblage including Globigerina angulisuturalis, G. angustiumbilicata, G. ciperoensis, G. praebulloides, and Globoquadrina venezuelana etc. (Kim, 1987). Sample SH-7 is approximately 3.3 m below the white tuff bed, dated by Hausback (1984) as 25.5 ± 0.4 Ma.

Evolutionary position: Chiloguembelina fusiformis appears to be the descendant of C. victoriana. Comparing the younger Oligocene form and the older Eocene form of C. victoriana of Beckmann's (1957) original figures, several evolutionary patterns can be recognized, i.e. aperture elongating and last chamber thinning in addition to Beckmann's (1957) note on becoming stout. The same evolutionary trends continue from early Oligocene C. victorina through to late Oligocene C. fusiformis.
The shape and position of aperture has been one of the most important bases for grouping species of Chiloguembelina (Beckmann, 1957; Samanta, 1969; Resig and Kroopnick, 1983; Poore and Gosnell, 1985). Considering apertural forms of Oligocene species of this genus, two kinds of divergence trends can be recognized from high and wide apertural shape of Paleocene C. midwayensis midwayensis (Fig. 2). C. fusiformis and C. victoriana represent a trend in which the height to width ratio of aperture increases whereas C. cubensis represents the contrary trend.
Chiloguembelina fusiformis is one of the youngest species of this genus reported yet.

Paleoecology: Chiloguembelina fusiformis occurs together with tropical to warm subtropical species such as Catapsydrax dissimilis and Globoquadrina venezuelana which are abundant in samples SH-6 and SH-7 of the San Hilario section of the San Gregorio Formation (Kim, 1987). Thus, it is assumed that C. fusiformis preferred a warm subtropical setting.

See http://www.dbpia.co.kr/Journal/ArticleDetail/NODE01385574

References:

Beckmann, J. P. (1957). Chiloguembelina Loeblich and Tappan and related foraminifera from the Lower Tertiay of Trinidad, B.W.I. In, Loeblich, A. R. , Jr., Tappan, H., Beckmann, J. P., Bolli, H. M., Montanaro Gallitelli & E. Troelsen, J. C. (eds) Studies in Foraminifera. U.S. National Museum Bulletin . 215: 83-95. gs

Kim, W. H. (1987). Chiloguembelina fusiformis n. sp. and its paleontological significance. Journal of the Paleontological Society of Korea. 3: 71-77. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Chiloguembelina fusiformis Kim 1987

Chiloguembelina fusiformis

References:

Add Comment

Comments