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Species Dentoglobigerina tripartita Koch 1926 | ||||||
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| Diagnosis / Definition: | ||||||
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Pearson et al. (2006): DESCRIPTION.- Type of wall: Cancellate, normal perforate, nonspinose, Globoquadrina-type wall texture. Test moyphology: Test trochospiral, compact, globular, subcircular to subquadrate in outline, chambers ovoid; in spiral view 3-3 ovoid chambers in ultimate whorl, increasing rapidly in size, ultimate chamber often a low, elongate oval shape ("cap-like") that projects or hangs over the umbilicus, sutures moderately depressed, slightly curved; in umbilical view 3-3 1/2 ovoid chambers increasing rapidly in size, sutures deeply depressed, straight, umbilicus moderate in size, sometimes overlapped by ultimate chamber, aperture centered over the umbilicus, bordered by a thin irregular, subtriangular-shaped lip; in edge view oval in outline, chambers ovoid in shape, embracing, ultimate chamber extends over the umbilicus,. Size: Maximum diameter of holotype 0.47 mm, thickness 0.42 mm. |
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| Discussion / Comments: | ||||||
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Pearson et al. (2006): DISTINGUISHING FEATURES.- The species is characterized by its compact, subcircular to subquadrate test, embracing chambers, a cap-like ultimate chamber that extends over the umbilicus, and an umbilically centered aperture that is bordered by an irregular, subtriangular-shaped lip that projects over the umbilicus. DISCUSSION.- Blow (1979) included tripartita in a group of related taxa that he derived from galavisi in his new genus Dentoglobigerina. He characterized (p. 1310) the development of D. tripartita from D. galavisi "by increasing tightness of the trochospiral coiling-mode, increasing tangential lengthening of the later chambers combined with some increased degree of appression of these ontogenetically later chambers". Blow and Banner (1962) refigured the holotype of Globigerina bulloides var. tripartita (here reproduced on Pl. 13.3, Figs. 1-3) and noted that the ultimate chamber was "misshapen" . In their study of populations of this taxon they noted (p. 97) "large numbers of specimens with aborted end- chambers. These aborted final chambers usually retain their normal position in the progression of the spire but reduced in volume, are variable in shape....". The Use of the term "misshapen" applied to the holotype of tripartita apparently was referring to what they regarded as an aborted end-chamber. Blow (1979) later added (p. 1311) 'the last chamber is somewhat deformed and mishapen". Blow and Banner (1962) and Blow (1979) selected specimens (here reproduced on Pl. 13.3, Figs. 5,6) that they believed showed normal last chambers. It is now well known that during the adult and gametogenetic stages of the life cycle of modern planktonic foraminifera the final chamber may be reduced in size and variable in shape, but is not aborted. In the case of D. tripartita the final chamber of the holotype would appear to be a full expression of the morphology of this taxon. The final chamber has a caplike shape and projects over or hangs over the umbilicus. Specimens with a similar although somewhat less extreme morphology are shown on Plate 13.3, Figs. 4 and 15. Other specimens on Plate 13.3 compare with Blow and Banner's and Blow's concept of this taxon. Figure 13 on Plate 13.3 illustrates a specimen with a reduced final chamber, the so-called "aborted end-chamber". Blow (1969) suggested that D. tripartita was the ancestor of a number of important Oligocene and lower Miocene species. Fleisher (1974) referred tripartita to the genus Globoquadrina because he regarded it as ultimately ancestral to the type species of the genus, Globoquadrina dehiscens (Chapman, Parr and Collins). Blow (1979) placed tripartita in Dentoglobigerina in a lineage leading to Dentoglohigerina praedehiscens (Blow and Banner) and then to Globoquadrina dehiscens Finlay. Kennett and Srinivasan (1 983) rejected Blow's placement of tripartita in Dentoglobigerina because they believed that there were two distinct lineages, one leading to G. dehiscens and the other to D. altispira (Cushman and Jarvis). They placed tripartita in the Globoquadrina lineage but they were uncertain of the taxonomic status of this taxon, grouping it with G. sellii (Borsetti), written as Gq. tripartita/sellii (p. 178). However, Bolli and Saunders (1985) clearly separated the two species as morphologically distinct taxa. The Globoquadrina lineage according to Kennett and Srinivasan began with Gq. tripartita/sellii, but no indication was made of an ancestor species. As discussed above the ancestor species is D. galavisi and we agree that there may be two separate lineages, as partly outlined by Kennett and Srinivasan and followed by Spezzaferri (1994), but we accept Blow's placement of tripartita in Dentoglobigerina because it lacks the distinctive morphology exemplified in Globoquadrina. PHYLOGENETIC RELATIONSHIPS.- Dentoglobigerina tripartita developed from D. galavisi by the development of more embracing, elongate ovoid chambers and, in some specimens, a cap-like final chamber that overhangs the umbilicus in adult specimens. STRATIGRAPHIC RANGE.- Zone E13? to Zone 06 (=P22). Banner and Blow (1962) and Fleisher (1974) suggested that the first occurrence of tripartita was in the Truncorotaloides rohri Zone and Zone P14 respectively, which correlate to Zone E13 of this study. Pearson and others (2001) also recorded it from this level in the upper part of the middle Eocene of Tanzania and the Adriatic Sea. According to Spezzaferri (1994), the species persists into the lower Miocene. GEOGRAPHIC DISTRIBUTION.- Known from low and mid latitude locations. STABLE ISOTOPE PALEOBIOLOGY.- Oligocene specimens from ODP Hole 758A registered among the heaviest ò18O of planktonic assemblages indicating a deep habitat, although earliest Oligocene specimens may have had a shallower water preference (Van Eijden and Ganssen, 1995). |
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| Systematics: | ||||||
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35 Ordo Foraminiferida Superfamilia Globigerinaceae Familia Globoquadrinidae Genus Dentoglobigerina Species Dentoglobigerina tripartita |
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| Synonym list: | ||||||
| Pearson et al. (2006): 1926 Globigerina bulloides var. tripartita Koch. - Koch : p.742 fig. 21a, b [middle Tertiary, unterer Teil der Globigerinenmergel Sadjau-Njak, southeast Bulongan, East Borneo]
1962 Globigerina tripartita Koch. - Blow & Banner : p.96 pl. 10; fig. A-C (reillustration of holotype), fig. D-F [upper Eocene Cribrohantkenina danvillensis Zone,
Sample FRCM 1923, Lindi area, Tanzania]
1969 Globigerina tripartita Koch. - Blow : p.322 pl. 16; fig. 6 [upper Eocene Zone El4, Sample FRCM 1645, Lindi,
Tanzania]
1979 Dentoglobigerina tripartita Koch. - Blow : p.1310 pl. 244; fig. 3, 4 [upper Eocene Zone E15/16, Sample FCRM 1923, Lindi, Tanzania]
1985 Globigerina tripartita Koch. - Bolli & Saunders : p.181 fig. 14.13a-c (reillustration of holotype by Blow and Banner,
1962, pl. 10, figs. A-C)
2006 Dentoglobigerina tripartita Koch. - Pearson et al. : p.409 pl. 13.3; fig. 1-16 (Pl. 13.3, Figs. 1-3; reillustration of holotype of
Globigerina bulloides var. tripartita Koch)
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| Specimen: | ||||||
| National Museum of Natural History, Basel, Inventory number: slide 59 |
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| References: | ||||||
Koch,R. (1926): Blow,W.H. and Banner,F.T. (1962): Blow,W.H. (1969): Blow,W.H. (1979): Bolli,H.M. and Saunders,J.B. (1985): Pearson,P.N.; Olsson,R.K.; Hemleben,C.; Huber,B.T. and Berggren,W.A. (2006): |
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| Anonymous: Unedited TaxonConcept data | ||||||
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