Chapter 19: TAXONOMY, BIOSTRATIGRAPHY, AND PHYLOGENY OF OLIGOCENE STREPTOCHILUS
Published:January 31, 2018
Christopher W. Smart, Ellen Thomas, 2018. "TAXONOMY, BIOSTRATIGRAPHY, AND PHYLOGENY OF OLIGOCENE STREPTOCHILUS", Atlas of Oligocene Planktonic Foraminifera, Bridget S. Wade, Richard K. Olsson, Paul N. Pearson, Brian T. Huber, William A. Berggren
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Our investigation of the taxonomy, biostratigraphy, and phylogeny of the microperforate Oligocene species generally included in the planktonic genus Streptochilus documents that biserial planktonic foraminifera occur in the upper Oligocene, despite previous descriptions of a global gap in occurrence of such taxa over that interval. We describe a total of 4 distinct morphological species, namely Streptochilus martini (Pijpers), Streptochilus pristinum Brönnimann and Resig, Streptochilus rockallkiddensis Smart and Thomas, and Streptochilus tasmanensis Smart and Thomas n. sp. Some Recent biserial foraminifera (Streptochilus globigerus) live tychopelagically, i.e., the species lives in the plankton but is genetically identical to the neritic benthic species Bolivina variabilis. Fossil species could have had a similar lifestyle, from which they could have evolved into true planktonic species, implying polyphyletic, multiple evolution of planktonic from benthic biserial groups. It is likely, therefore, that the stratigraphic distribution of the genus Streptochilus represents one or more expatriation events from the coastal benthos to the pelagic zone, and that not all or no species traditionally placed in the genus Streptochilus are descended from the genus Chiloguembelina. The name Streptochilus has been used for species which morphologically cannot be distinguished from species in the benthic genus Bolivina but live planktonically, and the genus thus is polyphyletic. We do not have sufficient information on evolutionary patterns to define clades of biserial planktonic species, and here propose to keep the name Streptochilus provisionally for biserial planktonic species until evolutionary relations have been clarified. We assign the genus to the Superfamily Bolivinoidea.
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Atlas of Oligocene Planktonic Foraminifera
The taxonomy, biostratigraphy, distribution, paleoecology and phylogenetic systematics of Oligocene planktonic foraminifera are treated in an illustrated atlas format. One hundred and twenty-eight species are recognized, including three species of Catapsydrax, eight species of Globorotaloides, two species of Protentelloides, twelve species of Paragloborotalia, two species of Parasubbotina, three species of Globigerina, eight species of Globigerinella, two species of Quiltyella Coxall and Spezzaferri n. gen., four species of Ciperoella Olsson and Hemleben n. gen., fifteen species of Globoturborotalita, seven species of Globigerinoides, seven species of Trilobatus, nine species of Subbotina, sixteen species of Dentoglobigerina, one species of Globoquadrina, two species of Turborotalita, three species of Acarinina, two species of Pseudohastigerina, two species of Turborotalia, two species of Dipsidripella, two species of Globigerinita, four species of Tenuitella, four species of Chiloguembelina, two species of Jenkinsina, two species of Cassigerinella, and four species of Streptochilus.
We name fourteen new species: Chiloguembelina adriatica Premec Fucek, Hernitz Kucenjak and Huber n. sp., Chiloguembelina andreae Premec Fucek, Hernitz Kucenjak and Huber n. sp., Dentoglobigerina eotripartita Pearson, Wade and Olsson n. sp., Globigerina archaeobulloides Hemleben and Olsson n. sp., Globigerinella roeglina Spezzaferri and Coxall n. sp., Globigerinoides neoparawoodi Spezzaferri n. sp., Globigerinoides joli Spezzaferri n. sp., Globoturborotalita eolabiacrassata Spezzaferri and Coxall n. sp., Globoturborotalita paracancellata Olsson and Hemleben n. sp., Globoturborotalita pseudopraebulloides Olsson and Hemleben n. sp., Globorotaloides atlanticus Spezzaferri and Coxall n. sp., Subbotina projecta Olsson, Pearson, and Wade n. sp., Streptochilus tasmanensis Smart and Thomas n. sp. and Trilobatus altospiralis Spezzaferri n. sp. The following new genera are named: Ciperoella Olsson and Hemleben n. gen. and Quiltyella Coxall and Spezzaferri, n. gen.
Over 2000 scanning electron micrographs images, including the type specimens of more than 60 species are illustrated for the first time, providing fresh comprehension of the shell architecture and wall texture, particularly for species that were poorly illustrated when first described. The biostratigraphic occurrences and phylogenetic relationships of all species of Oligocene planktonic foraminifera are reviewed. Analysis of wall textures, based on well-preserved material (much of which is illustrated for the first time) provides the basis for the higher taxonomy. Accordingly, Oligocene normal perforate planktonic foraminifera are divided into the Families Globigerinidae, Truncorotaloididae, and Globanomalinidae. Oligocene microperforate species, are placed in the Families Globigerinitidae, Chiloguembelinidae, Guembelitriidae, and Cassigerinellidae.