Streptochilus tasmanense


Classification: pf_cenozoic -> Benthic origins -> Streptochilus -> Streptochilus tasmanense
Sister taxa: S. globulosum, S. globigerum, S. latum, S. subglobigerum, S. inglei, S. macdougallae, S. cetacense, S. mascarenense, S. pristinum, S. rockallkiddense, S. tasmanense, S. martini, S. sp.,

Taxonomy

Citation: Streptochilus tasmanense Smart and Thomas, 2018
Rank: species
Taxonomic discussion:

Similar to the Miocene S. mascarenensis Smart and Thomas, but S. tasmanensis n. sp. does not become parallel-sided, has less curved sutures and has pore mounds. [Smart & Thomas 2018]

Streptochilus is a neuter noun (Smart & Thomas 2018, p.501) so the correct form of the species name is mascarenense , although it was given as mascarenensis in the original description.

Catalog entries: Streptochilus tasmanensis

Type images:

Distinguishing features: Test narrows towards apertural end, occasionally flared, laterally compressed, surface ornamentation of scattered circular pore mounds.

NB These concise distinguishing features statements are used in the tables of daughter-taxa to act as quick summaries of the differences between e.g. species of one genus.
They are being edited as the site is developed and comments on them are especially welcome.

Description


Diagnostic characters:

Distinguished by often becoming narrower towards apertural end, occasionally flared, laterally compressed, surface ornamentation with scattered circular pore mounds. According to the terminology of Georgescu and others (2011), S. tasmanensis n. sp. displays scattered incipient to well-developed pore mounds (2.8-3.7 µm) with circular pores (0.8-1.8 µm). Streptochilus tasmanensis n. sp. is distinguished from Chiloguembelina ototara by the more compressed test, surface ornamentation of scattered pore mounds, and presence of a toothplate. Streptochilus tasmanensis n. sp. differs from S. martini, S. pristinum and S. rockallkiddensis by surface ornamentation of scattered pore mounds. It differs from S. martini and S. pristinum by the narrowing of the test towards the apertural end. [Smart & Thomas 2018]


Wall type: Microperforate, surface scattered with circular pore mounds.[Smart & Thomas 2018]


Test morphology: Test small, biserial, elongate, increasing regularly in size, often narrowing towards apertural end, occasionally flared, rarely twisted, occasionally slightly curved; laterally compressed, periphery broadly rounded and lobulate; usually 5-8 pairs of chambers, rarely more, slightly inflated, wider than high, increasing gradually in size as added; sutures slightly curved and depressed; aperture high-arch shaped, offset slightly to one side of test, extending from the base of the last chamber onto apertural face, bordered by a thickened rim/collar along the top and outer side of the arch, the opposite side is turned inward to a plate connecting with the top of the collar and the in-turned portion of the preceding foramen; no obvious differences between micro- and megalospheric specimens. [Smart & Thomas 2018]

Size: Holotype length 0.20 mm, width 0.10 mm; length range 0.10-0.32 mm (mean 0.16 mm, St. Dev. 0.033, n = 207), width range 0.07-0.14 mm (mean 0.09 mm, St. Dev. 0.011, n = 207), thickness range 0.04-0.07 (mean 0.05 mm, St. Dev. 0.007, n = 42).

[Smart & Thomas 2018]

Character matrix

test outline:Subtriangularchamber arrangement:Biserialedge view:Compressedaperture:Interiomarginal
sp chamber shape:Subrectangularcoiling axis:N/Aperiphery:N/Aaperture border:Thin flange
umb chbr shape:Subrectangularumbilicus:N/Aperiph margin shape:Narrowly roundedaccessory apertures:None
spiral sutures:Weakly depressedumb depth:N/Awall texture:Smoothshell porosity:Microperforate: <1µm
umbilical or test sutures:Weakly depressedfinal-whorl chambers:2.0-2.0 N.B. These characters are used for advanced search. N/A - not applicable

Biogeography and Palaeobiology


Geographic distribution: Currently only known from South Tasman Rise, off Tasmania (ODP Site 1170). [Smart & Thomas 2018]

Isotope paleobiology: Late Oligocene δ18O values of S. tasmanensis n. sp. from Site 1170 (samples ODP 1170A/43X/3, 56-57 cm and ODP 1170A/43X/5, 57-58 cm, table 19.1) overlap with those of surface dwelling planktonic foraminifera (“Globigerina” cf. bulloides) indicating high (surface) water temperatures (text-figure 19.2), and are lighter than those of benthic foraminifera (Cibicidoides kullenbergi, Oridorsalis umbonatus and Bolivina huneri). δ13C values of S. tasmanensis n. sp. are lighter than the values for other planktonics, and overlap with, or are heavier than, those of benthics in the same samples. [Smart & Thomas 2018]

Phylogenetic relations: It has been shown that some Recent biserial foraminifera are able to live tychopelagically implying a similar lifestyle for fossil species, and polyphyletic evolution of planktonic from benthic biserial groups (Darling and others, 2009). It is likely that the distribution of S. tasmanensis n. sp. represents a separate expatriation event from the coastal benthos to the pelagic zone (Darling and others, 2009). [Smart & Thomas 2018]

Most likely ancestor: benthic ancestor - at confidence level 2 (out of 5). Data source: .

Biostratigraphic distribution

Geological Range:
Notes: Upper Oligocene Zone O7 to lower Miocene (Zone M1) (ODP Hole 1170A), pending further investigations. [Smart & Thomas 2018] [Smart & Thomas 2018]
Last occurrence (top): within M1 zone (21.12-22.96Ma, top in Aquitanian stage). Data source: Smart & Thomas 2018
First occurrence (base): within O7 zone (22.96-25.21Ma, base in Chattian stage). Data source: Smart & Thomas 2018

Plot of occurrence data:

Primary source for this page: Smart & Thomas 2018 - Olig Atlas chap.19 p.504

References:

Darling, K. F., Thomas, E., Kasemann, S. A., Seears, H. A., Smart, C. W. & Wade, C. M. (2009). Surviving mass extinction by bridging the benthic/planktic divide. Proceedings of the National Academy of Sciences, U.S.A.. 106: 12629-12633. gs :: ::

Georgescu, M. D., Quinney, A. E. & Anderson, K. D. (2011). New data on the taxonomy, evolution and biostratigraphical significance of the Turonian–Coniacian (Late Cretaceous) planktic foraminifer Huberella Georgescu 2007. Micropaleontology. 57: 247-254. gs :: ::

Premec Fucek, V., Hernitz Kucenjak, M. & Huber, B. T. (2018). Taxonomy, biostratigraphy, and phylogeny of Oligocene Chiloguembelina and Jenkinsina. In, Wade, B. S. , Olsson, R. K. , Pearson, P. N. , Huber, B. T. & Berggren, W. A. (eds) Atlas of Oligocene Planktonic Foraminifera. Cushman Foundation for Foraminiferal Research, Special Publication. 46(Chap 17): 459-480. gs :: ::

Smart, C. W. & Thomas, E. (2018). Taxonomy, biostratigraphy, and phylogeny of Oligocene Streptochilus. In, Wade, B. S. , Olsson, R. K. , Pearson, P. N. , Huber, B. T. & Berggren, W. A. (eds) Atlas of Oligocene Planktonic Foraminifera. Cushman Foundation for Foraminiferal Research, Special Publication. 46(Chap 19): 495-511. gs :: ::


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Streptochilus tasmanense compiled by the pforams@mikrotax project team viewed: 2-7-2020

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