Umbilical Structures of Globotruncana fornicata Plummer and. G. contusa (Cushman) in Exceptionally Well-preserved Material from Blake Escarpment (D.S.D.P. ...
Cretuceous Research (1983) 4, 211-214
Short Communication Umbilical Structures of Globotruncana fornicata Plummer and G. contusa (Cushman) in Exceptionally Well-preserved Material from Blake Escarpment (D.S.D.P. Leg 44, Site 39oA)
Whether or not the planktic foraminifera of the Globotruncana fovnicata group truly belong to the genus Globotruncana as originally defined by Cushman (1927, 1950) and emended by Bronnimann & Brown (1956) depends on their umbilical structures. S.E.M. photographs of Maastrichtian material from Blake Escarpment indicate that this question should be answered negatively. On Leg 44 of the D.S.D.P. in 1975 a core was taken at Site 390A, in which a Cretaceous-Tertiary sequence was recovered (F. Gradstein, in Benson et al., 1978). The Maastrichtian part of this section is being studied at the Department of Micropaleontology, State University of Utrecht. The planktic foraminifers prove to be exceptionally well preserved. Umbilical features of the Globotruncaninae, rarely visible in the common state of preservation of Cretaceous material, are often completely present. In the original definition of the genus Globotruncana by Cushman (1927) no mention is made of any particular feature in the umbilical region. Pulvinulina arca Cushman was appointed genotype species. In the 1950 edition of Cushman’s “Foraminifera” the description mentions: ‘L. . . aperture ventral, in well preserved specimens with a thin, plate-like structure over the umbilical area, . . .” and in their emendation of Globotvuncana Bronnimann & Brown (1956, page 538) state: “ . . . Long apertural flaps extend into the umbilicus, and in later chambers form a protruded, imperforate, umbilical cover-plate with accessory apertures. ... Globotruncana has been previously described many times as possessing only one aperture. This is probably because the protruded, umbilical cover-plate along which accessory apertures open, is commonly not preserved. . . . Nevertheless, a protruded imperforate, umbilical cover-plate with accessory apertures is apparently a morphologic character common to all species of Globotruncana”.. Such a “cover-plate” with accessory infra-laminal and/or intra-laminal apertures is generally called a tegilla, and the individual flaps in the singular tegillum (Loeblich & Tappan, 1964, page C64). “Distinctly asymmetrical apertural flaps, originally defined as being imperforate (e.g. Ticinellu, Praeglobotruncana)” (Loeblich & Tappan, 1964, page C62) are to be called “portici” (singular: porticus). The presence or absence of such apertural features is considered to be distinguishing on the generic level (Loeblich & Tappan, 1964; Pessagno, 1967; Robaszynski & Caron, 1979). The point has been raised whether or not Globotruncana fornicata Plummer and its derivatives, e.g. G. contusu (Cushman), belong to the genus in which they are habitually classified. In normally preserved Late Cretaceous material these species are generally characterized by having a large, open umbilicus (if not obscured by sedimentary fill) showing, at best, some indistinct remains of apertural flaps [see, for instance, the excellent figures in Postuma (1971, pages 31 and 39)]. However, such is very often the case in most recovered globotruncanids, the difference being that many species do occasionally show more or less well preserved tegillar structures. Material from site D.S.D.P. 390A provides conclusive evidence that globotruncanids from the fornicutu group never have a true tegillum (Figures 1 and 2) whereas representatives of virtually all other species of Globotruncunu show 0195-6671/83/020211+04
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Figure 1. (a) and (b) Abatho+zalus mayavoensis (Bolli). Core 12, section 1, Site 390a, D.S.D.P. (a) Umbilical side; (b) spiral side. (c)-(e) “Globotruncana” contwa (Cushman). Core 12, section 1, Site 390a, D.S.D.P. (c) Umbilical side; (d) oblique lateral view; (e) spiral side. (f) and (g) “Globotruncana” fornicata (Plummer). Core 12, section 2, Site 390a, D.S.D.P. (f) Umbilical side; (g) spiral side. All x 50.
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Figure 2. (a) and (b) “Globotruncanu” fornicutu (Phnnmer). Core 13, section 6, Site 390a, D.S.D.P. (a) Umbilical side; (b) spiral side. (c) and (d) “Globotruncuna” fornicuta (Plummer). (c) Umbilical side; (d) spiral side. (e) and (f) “Globotruncunu” fornicuta (Plummer). Core 12, section 2, Site 390a, D.S.D.P. (e) Umbilical side; (f) spiral side. (g) Rugoglobigerina rugosu (Plummer). Core 14, section 5, Site 390a, D.S.D.P. Umbilical side, showing perfect preservation of tegilla. (h) Globotruncunu linneunu (d’orbigny). Core 14, section 4, Site 390a, D.S.D.P. Umbilical side, showing perfect preservation of tegilla. (g) x 62.5, remainder x 50.
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excellently preserved tegilla as demonstrated by S.E.M. photographs of Abathomphalus mayaroensis (Bolli): Figure l(a) and (b); Rugoglobigerina rugosa (Plummer); Figure 2(d); G. Zinneana (d’orbigny); Figure 2(e). The fornicata group on the other hand is distinguished by possessing a well-developed system of portici, often of rather irregular shape, that in a very few instances tends to fuse in the centre [Figures l(f) and (g), Figure 2(a)] but never forms a true tegillum. If the definition of the genus Globotruncana is accepted, the fornicata-contusa group should then be placed in a different, presently un-named genus.
E. Mulder P. Marks Nutuurhistorisch
Museum Denekamp The Netherlands
Instituut
VOOY
Aardwetenschappen RU Utrecht The Netherlands
References Benson, W. E. & Sheridan, R. E. (Eds) 1978. Sites 389 and 390. In Initial Reports of the Deep Sea Drilling Project, Volume 44. Washington, D.C.: U.S. Government Printing Office. Bronnimann, P. & Brown, N. K. 1956. Taxonomy of the Globotruncanidae. Eclogae geologicae Helvetiae 48 (2), 503-561. Cushman, J. A. 1927. An outline of a reclassification of the Foraminifera. Contributions of the Cushman Laboratory Foraminijeral Research 3 (l), l-105. Cushman, J. A. 1950. Foraminijera, Their Classification and Economic Use (fourth edition), pp. l-589. Cambridge, Massachusetts: Harvard University Press. Loeblich, A. R. & Tappan, H. 1964. Protista 2. Sarcodina, chiefly Thecamoebians and Foraminifera. Treatise on Invertebrate Paleontology, Part C, Volume 1. University of Kansas Press. Pessagno, E. A. 1967. Upper Cretaceous planktonic foraminifera from the Western Gulf Coastal Plain. Palaeontograjica Americana 5 (37), 245-445. Postuma, J. A. 1971. Manual of Planktonic Foraminijera, pp. l-420. Amsterdam: Elsevier. Robaszynski, F. & Caron, M. (Eds) 1979. Atlas de Foraminiftres planctoniques du CrttacC moyen. Cahiers de Micropaliontologie 1979-1, l-181. Paris: Centre National du Recherche Scientifique.
