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Species Globorotalia velascoensis Cushman 1925


Diagnosis / Definition:
Bolli (1957):
Shape of test very low trochospiral, spiral side flat; umbilical side strongly convex; in large specimens the outer wall of the chambers of the last whorl may be somewhat concave; equatorial periphery nearly circular; axial periphery angular with distinct keel which maybe spinose. Wall calcareous, perforate, surface smooth, around umbilical area often rugose. Chambers angular, inflated; 12-18, arranged in 2 1/2 -3 whorls, the five chambers of the last whorl increasing moderately in size. Sutures on spiral side curved, may be slightly raised; on umbilical side radial, depressed. Umbilicus narrow and deep in small specimens, becoming wider in large specimens. Aperture a low arch; interiomarginal, extraumbilical umbilical. Coiling random in the upper part of the Globorotalia pusilla pusilla zone, becoming sinistral in the Globorotalia pseudomenardii and Globorotalia velascoensis zones (about 95 percent). Largest diameter of figured hypotypes 0.49 mm. (pl. 20, figs. 1-3), and 0.27 mm. (pl. 20, fig. 4).
Discussion / Comments:
Bolli (1957):
Globorotalia velascoensis (Cushman) shows considerable variety in size and shape (especially of the umbilical area). Material studied from a Velasco shale sample of Mexico shows every intermediate stage between very small forms with a narrow umbilicus (G. wilcoxensis var. acuta Toulmin group) and large specimens with a wide umbilicus (G. velascoensis, s. s., group). The same has been observed throughout the life range of the species in Trinidad sections. Forms belonging to both these groups are therefore regarded as G. velascoensis, of which G. wilcoxensis var. acuta is a synonym. This confirms Grimsdale (1951) who regards G. wilcoxensis var. acuta as a variety of G. velascoensis. Globorotalia velascoensis appears in the upper part of the G. pusilla pusilla zone where it may have branched off from the G. angulata (White) group though no clearly intermediate forms have been observed. At the end of the G. velascoensis zone, the species becomes extinct in Trinidad together with numerous other planktonic and benthonic forms. The author's previous assumption (Bolli, 1952) that G. velascoensis occurs in the upper Lizard Springs and may be regarded as the ancestor of G. aragonensis Nuttall is no longer maintained. G. velascoensis is in fact restricted to the lower Lizard Springs; the forms previously described under this name from the upper Lizard Springs are now regarded as a new species (G. formosa gracilis Bolli, new species, new subspecies, and G. formosa formosa Bolli, new species, new subspecies) probably developing from the G. aequa Cushman and Renz group. This is supported by the coiling ratios of the species under discussion. G. velascoensis coils almost exclusively sinistrally before its extinction at the end of the Globorotalia velascoensis zone. G. aequa and G. formosa both coil predominantly dextrally in the Globorotalia rex and Globorotalia formosa formosa zones of the upper Lizard Springs.
Systematics:

20
 Genus Globorotalia
  Species Globorotalia angulata
   Species Globorotalia velascoensis
Synonym list:
Bolli (1957):
1925 Pulvinulina velascoensis Cushman. - Cushman : p. 19 pl. 3, figs. 5a-c
1941 Globorotalia wilcoxensis var. acuta Toulmin. - Toulmin : p. 608 pl. 82, figs. 6-8
1949 Globorotalia wilcoxensis var. acuta Toulmin. - Cushman & Bermudez : pp. 39-41
1957 Globorotalia velascoensis Cushman. - Bolli : pl. 20, figs. 1-4
Was used in synonym list of:
Morozovella velascoensis Cushman 1925
Globorotalia formosa formosa Bolli 1957
Morozovella caucasica Glaessner 1937
Morozovella formosa Bolli 1957
References:

Cushman,J.A. (1925):
Some new foraminfera from the Velasco Shale of Mexico . Contributions from the Cushman Foundation for Foraminiferal Research Vol. 1 p. 18-23

Toulmin,L.D. (1941):
Eocene smaller foraminifera from the Salt Mountain limestone of Alabama . Journal of Paleontology Vol. 15 p. 567-611

Cushman,J.A. and Bermudez,P.J. (1949):
Some Cuban species of Globorotalia . Contributions from the Cushman Foundation for Foraminiferal Research Vol. 25 p. 26-44

Bolli,H.M. (1957):
The genera Globigerina and Globorotalia in the Paleocene-Lower Eocene Lizard Springs Formation of Trinidad, B.W.I . Bulletin of the U.S. National Museum Vol. 215 p. 61-82
Anonymous: Unedited TaxonConcept data
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