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Species Globorotalia fohsi Cushman & Ellisor 1939 | ||||||
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| Discussion / Comments: | ||||||
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Bolli & Saunders (1985): The Early Middle Miocene G. fohsi represents one of the best documented evolutionary sequences of gradual morphological change known in the planktic foraminifera. To stress the close relationship between the taxa into which the lineage is split it is natural to give them subspecific rank within the species fohsi. Such treatment is also advantageous for their use in stratigraphy in that it offers more flexibility in their application. Such taxonomic treatment on the subspecific level was proposed by Bolli (1950, and later publications) and followed e.g. by Stainforth et al. (1975). In contrast Blow & Banner (1966) gave species rank to the taxa distinguished within the lineage and, furthermore, placed them in the two subgenera Turbororotalia (forms without peripheral keel) and Globorotalia (forms with a peripheral keel). The principal morphological changes that characterize the subspecies of the fohsi lineage from the earliest peripheroronda to the end form robusta are: (1) Increase in test size from about 0.3 mm in peripheroronda to about 0.7 mm in lobata and robusta. (2) Development of a peripheral keel from the non carinate peripheroronda via peripheroacuta to the keeled fohsi, praefohsi, lobata and robusta. (3) Increase in the number of chambers forming the last whorl from 5-6 in peripheroronda, peripheroacuta and fohsi to 6 1/2- 8 in praefohsi, lobata and robusta. (4) Distinctly lobate periphery in lobata. Following their recognition as morphological stages of an evolutionary sequence, and their application to biostratigraphy in Trinidad (Bolli, 1950, 1951, 1957), the Globorotalia fohsi subspecies have found wide application for the subdivision of the tropical subtropical Middle Miocene. After having been successfully used in this sense for some 15 years, the G. fohsi group became the subject of some controversy as to the best method of taxonomic subdivision (Banner & Blow, 1965b; Blow & Banner, 1966; Jenkins, 1966; Bolli, 1967; Beckmann et al., 1969; Olsson, 1972). These differing views and interpretations were clearly reviewed in Stainforth et al. (1975). Bolli (1950) distinguished four fohsi subspecies. Blow & Banner(1966) proposed for G.fohsi barisanensis, as interpreted by Bolli, the new species G. (T.) peripheroronda, and a G. (T) peripheroacuta for specimens with an acute periphery that previously were regarded as transitional between G. fohsi barisanensis and G. fohsi fohsi. G. fohsi fohsi was subdivided by these authors into G. (G.) fohsi and G. (G.) praefohsi. The subspecies lobata and robusta were by them relegated to 'formae' of G. fohsi. Bolli (1967) agreed to the additional splitting of the early part of the fohsi lineage into four instead of the original two taxa, but maintained as subspecies the morphologically characteristic, readily recognizable and stratigraphically significant lobata and robusta. Stainforth et al. (1975) described and figured the six taxa on a subspecies level, as did Bolli (1967), but preferred to recognize only the four subspecies peripheroronda, fohsi, lobata and robusta, and treat peripheroacuta and praefohsi as infrasubspecific. The morphological changes referred to above under (1) to (4) are gradual through time. Therefore, limits between recognized taxa remain to some extent subjective, progressively more so the closer the lineage is subdivided into separate taxa. Such tolerances must also be taken into account when delimiting the zonal boundaries that are determined by these taxa. For example, the presence or absence of an imperforate peripheral keel in the chambers of the last whorl would appear to be a distinct and easily recognizable feature. However, transitional stages do occur between forms with an acute periphery and those with an imperforate keel as they do between forms with rounded and acute peripheries. Particularly in poorly preserved specimens the presence or absence of an imperforate partial or even full keel may be difficult to determine. This is also the opinion of Stainforth et al. (1975). Stratigraphic significance: The value of the Globorotalia fohsi series for stratigraphic subdivisions in the lower and middle part of the Middle Miocene is generally agreed, especially by those working on low latitude faunas, As reviewed above, divergent opinions concern only the nomenclature of the taxonomic units to be used. In the present work we retain the four fold zonation established by Bolli, as this has proved of value not only in the Caribbean but also in the Gulf of Mexico, Java and in Atlantic and Indo Pacific DSDP sites. As regards the two subspecies lobata and robusta, these have proved to have virtually worldwide distribution with lobata appearing first and robusta marking the final phase of the plexus when this is ideally developed. Comparison with nannofossil zonal schemes has shown the two forms to have real time significance and not to be'highly variable in the time sense from one area to another' as Blow (1969) stated. Thus we retain them, as do Stainforth et al. (1975) and also continue to advocate the use of the two zones named after them. G. fohsi peripheroronda, the earliest of the subspecies, has a distinctly wider latitudinal distribution than the later subspecies. It is present not only in today's tropical subtropical belt but extends in the northern hemisphere as far as the Mediterranean area, where the later forms are no longer present. From this it has been deduced that the later, and particularly the keeled forms, were restricted to tropicalsubtropical waters and that water temperatures of, for example, the Middle Miocene Mediterranean Sea, became too low for their survival. Whether the non keeled peripheroronda persisted longer under cooler water conditions during at least part of the time when in warmer waters the acute and keeled forms began to develop has still to be verified. A re study of zonal type locality material from Trinidad, made by us revealed that the first distinct representatives of the G. fohsi lineage appear no earlier than the Globigerinatella insueta Zone and not, as had previously been thought as early as the Globorotalia kugleri Zone (Bolli, 1957) or the N 4 Globigerinoides primordius Zone (Blow, 1969). Seemingly transitional specimens that possibly could have branched off from the G. mayeri stock do occur in the underlying Catapsydrax stainforthi Zone. Coiling trends: The worldwide coiling pattern of the G.fohsi subspecies is random in peripheroronda but changes with the appearance of peripheroacuta to a strong preference for sinistral coiling, a direction that persists until the extinction of the last subspecies, robusta (Bolli, 1950, 1971) Chaisson & Leckie (1993): Remarks: We did not distinguish between Globorotalia fohsi fohsi, G. fohsi lobata, and G. fohsi robusta in this study. One reason for lumping these subspecies is the fact that the "cockscomb-like" chambers characteristic of the fully carinate G. fohsi lobata also occur on large specimens of partially carinate G. praefohsi (see discussion by Bolli and Saunders, 1985). Similar species: Globorotalia fohsi s.l. has an imperforate band and/or a thin raised keel around the entire final whorl of its test that distinguishes this group from G. praefohsi, which has an imperforate band and/or a keel on only the last two or three chambers of the final whorl. In this distinction between G. fohsi and G. praefohsi, we follow Kennett and Srinivasan (1983) but differ from Bolli and Saunders (1985). Transitional specimens occur as low as Core 130-806B-49X-CC (e.g., see Plate 3, Figs. 8-10). |
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| Systematics: | ||||||
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1 Superregnum Eukaryota Regnum Protoctista Phylum Ciliophora Subphylum Postciliodesmatophora Ordo Globigerinida Superfamilia Globorotaliaceae Superfamilia Nonionacea Familia Globorotaliidae Genus Globorotalia Species Globorotalia fohsi |
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| Synonym list: | ||||||
| Bolli & Saunders (1985): 1985 Globorotalia fohsi Cushman & Ellisor. - Bolli & Saunders : p.212
Chaisson & Leckie (1993): 1939 Globorotalia fohsi Cushman & Ellisor. - Cushman & Ellisor : p.12 pl. 2; fig. 6a-c
1949 Globorotalia lobata Bermudez. - Bermudez : p.286 pl. 22; fig. 15-17
1950 Globorotalia fohsi robusta Bolli. - Bolli : 84, 89 pl. 15; fig. 3a-c
1983 Globorotalia (Fohsella) fohsi fohsi Cushman & Ellisor. - Kennett & Srinivasan : p.100 pl. 23; fig. 1-3
1983 Globorotalia (Fohsella) fohsi lobata Bermudez. - Kennett & Srinivasan : p.100 pl. 21, fig. 2;
pl. 23, fig. 4-6
1983 Globorotalia (Fohsella) fohsi robusta Bolli. - Kennett & Srinivasan : p.102 pl. 23; fig. 7-9
1993 Globorotalia fohsi sensu lato Cushman & Ellisor. - Chaisson & Leckie : p.171 pl. 3; fig. 1-4
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| Was used in synonym list of: | ||||||
| Stratigraphy - absolute ages: | ||||||
| LAD: 12.7 ± 0 [Ma], Berggren et al. (1995) |
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| References: | ||||||
Cushman,J.A. and Ellisor,A.C. (1939): Bermudez,P.J. (1949): Bolli,H.M. (1950): Kennett,J. and Srinivasan,M.S. (1983): Bolli,H.M. and Saunders,J.B. (1985): Chaisson,W.P. and Leckie,R.M. (1993): Berggren,W.A.; Kent,D.V.; Swisher,C.C. and Aubry,M.P. (1995): |
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| Anonymous: Unedited TaxonConcept data | ||||||
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