Morozovella acuta


Classification: pf_cenozoic -> Truncorotaloididae -> Morozovella -> Morozovella acuta
Sister taxa: M. caucasica, M. crater, M. aragonensis, M. lensiformis, M. subbotinae, M. marginodentata, M. formosa, M. gracilis, M. aequa, M. apanthesma, M. angulata, M. praeangulata, M. edgari, M. allisonensis, M. velascoensis, M. acuta, M. occlusa, M. pasionensis, M. acutispira, M. conicotruncata, M. sp.,

Taxonomy

Citation: Morozovella acuta (Toulmin 1941)
Rank: Species
Basionym: Morozovella
Synonyms:
Taxonomic discussion: Considerable controversy surrounds the characterization and recognition of this, and closely related, forms of the velascoensis group. The "typical" M. acuta is generally believed to be distinguishable from M. velascoensis in its average smaller size, more rapid increase in chamber growth, proportionately larger final chamber, more subdued periumbilical ornamentation, and reduced number of chambers in the final whorl (Loeblich and Tappan, 1957a; Luterbacher, 1964; Blow, 1979). Other authors (Bolli, 1957a; Hillebrandt, 1962; Proto  Decima and Zorzi, 1965, among others) believe these (and other) forms are linked by continuous gradations and consider them synonymous.
At the same time, another commonly cited form is Globorotalia velascoensis parva (auct. non) that we believe shares a close morphologic relationship with M. acuta. Whether the forms illustrated by various authors as parva are, indeed, referable to Rey's taxon is a moot point, however. Luterbacher (1964) showed that the typical parva from the type sample from Morocco has four large, nearly equal-sized chambers in the final whorl, slightly raised and beaded sutures on the spiral side, and a relatively narrow umbilicus lacking the periumbilical ornament characteristic of the velascoensis -acuta forms. We concur with his analysis that forms identified as, parva by Bolli and Cita (1960), Gartner and Hay (1962), and Gohrbandt (1963) differ from the type-level specimens of
parva by possessing a heavy keel and a flat spiral side. The individuals illustrated by Aubert (1962) as velascoensis parva (pl. 1: fig. 2a-c) and acuta (pl. 1: fig. 3a-c), respectively, from Koudiat Bou Khelif, Morocco, are virtually identical, and the individual illustrated as acuta by Blow (1979, pl. 104: fig. 2) is virtually indistinguishable from the one he figured on pl. 95: fig. 6 as parva. We believe that the two morphotypes parva (auct) and acuta are virtually indistinguishable in late Paleocene assemblages.
 [Olsson el. 1999]

Catalog entries: Globorotalia velascoensis parva; Globorotalia wilcoxensis acuta;

Type images:

Distinguishing features: Conicotruncate, distinctly muricocarinate test with (typically) 5 chambers in last whorl; intercameral sutures radial, depressed on umbilical side and strongly recurved and tangential, distinctly ornamented on, and flush with, spiral side; periumbilical collar weakly to moder- ately well-ornamented with muricae; umbilicus (typically) wide and open but narrow in more tightly coiled individuals; aperture interiomarginal, umbilical-extraumbilical with (typically) well-developed, triangular, circumumbilical "teeth.

NB These concise distinguishing features statements are used in the tables of daughter-taxa to act as quick summaries of the differences between e.g. species of one genus.
They are being edited as the site is developed and comments on them are especially welcome.

Description


Diagnostic characters:

Conicotruncate, distinctly muricocarinate test with (typically) 5 chambers in last whorl; intercameral sutures radial, depressed on umbilical side and strongly recurved and tangential, distinctly ornamented on, and flush with, spiral side; periumbilical collar weakly to moder- ately well-ornamented with muricae; umbilicus (typically) wide and open but narrow in more tightly coiled individuals; aperture interiomarginal, umbilical-extraumbilical with (typically) well-developed, triangular, circumumbilical "teeth. [Olsson el. 1999]

Character matrix

test outline:Lobatechamber arrangement:Trochospiraledge view:Planoconvexaperture:-
umb chamber shape:Subtriangularcoiling axis:Highperiphery:Muricocarinateaperture border:Thin flange
sp chbr shape:Petaloidumbilicus:Narrowperiph margin shape:Subangularaccessory apertures:None
umbilical or test sutures:Strongly depressedumb depth:Deepwall texture:Spinoseshell porosity:Finely Perforate: 1-2.5µm
spiral sutures:Raised beadeddiameter mm:0.46width mm:0.37breadth mm:0.24
final-whorl chambers:4.0-5.0

Biogeography and Palaeobiology


Geographic distribution: Morozovella acuta is an essentially subtropical to tropical form with somewhat narrower biogeographic distribution than M. velascoensis (see also Loeblich and Tappan, 1957a). [Olsson el. 1999]
Aze et al. 2011 summary: Low to middle latitudes; based on Olsson et al. (1999)

Isotope paleobiology: Morozovella acuta has ∂180 and ∂13C similar to other species of Morozovella (M. occlusa, M. velascoensis). Morozovella acuta has more positive ∂13C and more negative ∂18O than Subbotina spp. (Shackleton et al., 1985). [Olsson el. 1999]
Aze et al. 2011 ecogroup 1 - Open ocean mixed-layer tropical/subtropical, with symbionts. Based on very heavy δ13C and relatively light δ18O. Sources cited by Aze et al. 2011 (appendix S3): Shackleton et al. (1985)

Phylogenetic relations:

This species evolved from M. velascoensis through a reduction in umbilical size and ornament and chamber number [Olsson el. 1999]

Most likely ancestor: Morozovella velascoensis - at confidence level 4 (out of 5). Data source: Olsson et al. (1999) f5a.

Biostratigraphic distribution

Geological Range:
Notes: Zone P4b to Zone E2 (top). [Berggren & Pearson 2006]
Zone P4b to Zone P5 (top). Several authors suggest that M. acuta occurs somewhat higher than M. velascoensis. We record its lowest occurence in Zone P4b and have not found it to extend above M. velascoensis at DSDP Site 213 (Indian Ocean). Shutskaya (1970a) gave the range of M. acuta as extending from the A. acarinata Zone (= Subzone P4b this paper) to the top of the G. aequa Zone (= top of Zone P5 this paper), which is, essentially, the same as observed herein. [Olsson el. 1999]
Last occurrence (top): at top of E2 zone (100% up, 55.2Ma, in Ypresian stage). Data source: Berggren & Pearson (2006) f11.1
First occurrence (base): near base of P4b subzone (10% up, 60.2Ma, in Selandian stage). Data source: Berggren & Pearson (2006) f11.1

Plot of occurrence data:

Primary source for this page: Olsson et al. 1999 - Atlas of Paleocene Planktonic Foraminifera, p. 55

References:

Berggren, W.A. & Pearson, P.N., (2006). Taxonomy, biostratigraphy, and phylogeny of Eocene Morozovella. In: Pearson, P.N. et al. (Editors), Atlas of Eocene Planktonic Foraminifera, Cushman Foundation Special Publication 41. Cushman Foundation Special Publication. 41 Allen Press, Lawrence, Kansas, pp. 343-376.

Olsson, R.K.; Hemleben, C.; Berggren, W.A. & Huber, B.T., (1999). Atlas of Paleocene Planktonic Foraminifera. Smithsonian Contributions to Paleobiology, 85. Smithsonian Institution Press, Washington, DC, 1-252 pp.

Rey, M., (1954). Description de quelques espèces nouvelles de foraminifères dans le Nummulitique nord-marocain. Société Géologique de France, Bulletin. 4(4-6):, 4(4-6): 1-209.

Toulmin, L., (1941). Eocene Smaller Foraminifera from the Salt Mountain Limestone of Alabama. Journal of Paleontology, 15(6): 567-611.


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Morozovella acuta compiled by the pforams@mikrotax project team viewed: 18-9-2018

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