Catalog - Protentella clavaticamerata

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.

Other pages this level: P. clavaticamerata, P. molinae, P. navazuelensis, P. prolixa, P. rohiensis

Protentella clavaticamerata

Citation: Protentella clavaticamerata (Jenkins 1977)

Type specimens: Holtype - MPK 1357; paratypes MPK 1331, 1332, 1359.

Type age (chronostrat): Lower Miocene, Burdigalian Stage; Globigerinoides trilobus trilobus Zone.

Type locality: English Channel, Sealab Trial Borehole at latitude 49"10.73'N., longitude 7"27.86'W., sample at latitude 49"10.73'N., longitude 7"27.86'W., sample SAZ 1700, at 5.68 m. below seafloor.

Type repository: Keyworth Nottinghamshire, UK; British Geological Survey

Holotype description: Test free, small, involute, biumbilicate, peripheral outline lobate,periphery rounded.
Chambers spherical, appressed in earlier part of final whorl of five and one-half chambers with the last becoming radially elongate, and with the final whorl embracing previous whorls.
Sutures distinct, incised, radial to curved.
Wall calcareous, hispid,finely perforate, earlier chambers with thickened walls.
Aperture basal, equatorial, low arch, with a distinct protruding lip.

Remarks: Significant variation in the test morphology of the type population includes
(1)four and one-half to five and one-half chambers in the final whorl,
(2)normally the final chamber is larger but can be smaller than the penultimate chamber, and
(3)short spines, more visible on the unthickened final chambers but can still be detected on earlier chambers, and
(4)the aperture can be high- or low-arched.

Protentella clavaticamerata differs from the Middle Miocene Protentella prolixa Lipps, described only from California, in having a distinctly hispid wall, and it is easily distinguished from other species in the Trial Borehole by this feature, plus its evolute coiling.

Srinivasan and Kennett (1975) have examined by scanning electron microscope topotype specimens of P. prolixa and reported that the "Wall is smooth, finely and uniformly perforate without any sign of spine bases on the adult chambers."" Lipps (1964) had previously reported that ""A few specimens have slight knobs on the chambers which may represent the bases of large spines, although because of their rare occurrence their significance could not be determined.""
Srinivasan and Kennett (1975) were not able to confirm this observation.
The uniform pore pattern on the test of P. prolixa (see Srinivasan and Kennett, 1975, pl. 2, fig. 14) is different from the more irregularly arranged pores of Protentella clavaticamerata, which are interspersed with basal spines.
Quilty (1976) described as new Clavigerinella nazcaensis in Late Oligocene and lowermost Miocene at DSDP Site 320 from off the coast of Peru. Clavigerinella nazcaensis is distinguished from P.clavaticamerata in having extremely elongated chambers forming a much larger test estimated as 0.9 mm. in diameter and in having a rimless aperture.
Some of the illustrated specimens of C. nazcaensis appear to have spine bases on the test surfaces and it is suggested that it should be placed in the genus Protentella.

Origin and evolution: The similar wall structure of the low trochospirally coiled Globorotalia obesa Bolli (plate 3, figures 9-10) and the intermediate taxon Globorotalia cf. obesa (plate 3, figure 11 ) which occurs in all four samples containing P. clavaticamerata (table 1) strongly suggests that P. clavaticamerata evolved from G. obesa in the Lower Miocene. At its earliest appearance in samples SAZ 1707 and SAZ 1706, specimens of P. clavaticamerata and Globorotalia cf. obesa do not possess the well-developed lip found in later samples SAZ 1702 and SAZ 1700. Also, P. clavaticamerata shows a slight asymmetry in both coiling and apertural position in the two earlier samples.

An iterative Miocene trend toward the evolution of an involute test is thus demonstrated by G. obesa which also evolved in the Miocene into the densely hispid Globigerinella praesiphonifera ( Blow) (plate 2, figures 1-2) and eventually into G. aequilateralis (Brady).

Srinivasan and Kennett (1975) suggested that Protentella prolixa evolved from Protentella bermudezi (Bolli) in the lower part of the Middle Miocene on a study of ultrastructure and morphological features.
As an alternative speculation, it is here suggested that the Lower Miocene P. clavaticamerata evolved into the closely related P. prolixa by a progressive loss of spines coupled with a concomitant development of uniform pores and development of more radially elongate chambers.

Because of the hispid wall structure of P. clavaticamerata the statement by Srinivasan and Kennett (1975) that ""Bolliella and Beella differ from Protentella and Clavatorella in possessing fine hispid test surfaces resulting from presence of spine bases even in adult tests,"" is no longer valid.

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References:

Jenkins, D. G. (1977). Lower Miocene planktonic forminfera from the a borehole in the English Channel. Micropaleontology. 23(3): 297-318. gs

Spezzaferri, S., Coxall, H. K., Olsson, R. K. & Hemleben, C. (2018a). Taxonomy, biostratigraphy, and phylogeny of Oligocene Globigerina, Globigerinella, and Quiltyella n. gen. In, Wade, B. S., Olsson, R. K., Pearson, P. N., Huber, B. T. & Berggren, W. A. (eds) Atlas of Oligocene Planktonic Foraminifera. Cushman Foundation for Foraminiferal Research, Special Publication . 46(Chap 6): 179-214. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Protentella clavaticamerata (Jenkins 1977)

Protentella clavaticamerata

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