Streptochilus rockallkiddense


Classification: pf_cenozoic -> Guembelitrioidea -> Chiloguembelinidae -> Streptochilus -> Streptochilus rockallkiddense
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 rockallkiddense Smart and Thomas 2007
Rank: species
Basionym: Streptochilus rockallkiddensis
Synonyms:
Taxonomic discussion:

Streptochilus rockallkiddensis was called Bolivina spathulata (Williamson) by Thomas (1986, 1987), but it was not illustrated. Smart and Thomas (2007:84) noted that early Miocene forms were typically small, elongate, laterally slightly compressed, biserial becoming staggered uniserial, commonly rectilinear and often narrower towards apertural end, aperture with thickened rim and often obscured, surface ornamentation varying from smooth to granular. [Smart & Thomas 2018]

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

Catalog entries: Streptochilus rockallkiddensis,

Type images:

Distinguishing features: Parallel-sided / rectilinear, often becomes staggered uniserial, ornament variable, aperture may be obscured

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 its commonly elongate rectilinear shape, occasionally flared, laterally slightly compressed, surface ornamentation varying from smooth to granular. Streptochilus rockallkiddensis is distinguished from Chiloguembelina ototara by the more compressed, commonly elongate rectilinear test, tendency to become uniserial in some elongate specimens, common granular surface ornamentation, and presence of a toothplate. Streptochilus rockallkiddensis differs from S. martini, S. pristinum and S. tasmanensis n. sp. by its more elongate rectilinear shape which becomes occasionally staggered uniserial, and by its surface ornamentation which is often granular. [Smart & Thomas 2018]


Wall type: Microperforate, surface ornamentation varies from smooth to finely granular to coarsely granular. [Smart & Thomas 2018]

Test morphology: Test biserial, shape variable, commonly elongate, parallel-sided and rectilinear, occasionally flared, in some elongate specimens the later formed part of the test may narrow towards the apertural end, rarely twisted; laterally slightly compressed, periphery rounded and non-lobulate to lobulate; chambers increase regularly in size as added, slightly wider than high, initial chambers small and commonly obscured by granular surface ornamentation, number of pairs of chambers varies from 5-8 or more; sutures slightly curved and depressed; aperture low-arch shaped, offset to one side of test, with an internal plate formed by the infolding and downward extension of one margin of the rimmed aperture; no obvious differences between micro- and megalospheric specimens. In early Miocene specimens, the test is biserial and may become staggered uniserial in some elongate specimens, with final chamber often having a thickened rim (Smart and Thomas, 2007:84). [Smart & Thomas 2018]

Size: Holotype length 0.23 mm, width 0.08 mm; length range 0.12-0.26 mm, width range 0.07-0.10 mm, thickness range 0.06-0.07 mm. [Smart & Thomas 2018]

Character matrix

test outline:Elongatechamber arrangement:Biserialedge view:Compressedaperture:Terminal
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:Moderately depressedumb depth:N/Awall texture:Moderately pustuloseshell porosity:Microperforate: <1µm
umbilical or test sutures:Moderately 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: Known from the North and South Atlantic Ocean (Goban Spur, DSDP Site 548 and Rio Grande Rise, DSDP Hole 516F). [Smart & Thomas 2018]

Isotope paleobiology: The δ18O values of lower Miocene S. rockallkiddensis from Site 608 overlap with those of surface dwelling planktonic foraminifera in the same samples, indicating a mixed-layer habitat, and δ13C values are lighter than the values for other planktonics, and overlap with, or are lighter than, those of benthics in the same samples (Smart and Thomas, 2006). The light carbon isotope values were explained as resulting from rapid calcification in a region with variable upwelling conditions (Smart and Thomas, 2006). [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, suggesting polyphyletic evolution of planktonic from benthic biserial groups (Darling and others, 2009). The stratigraphic distribution of S. rockallkiddensis may represent numerous excursions of expatriated tychopelagic individuals from the coastal benthos to the pelagic zone (Darling and others, 2009), and its ancestor is unknown. [Smart & Thomas 2018]

Most likely ancestor: benthic ancestor - at confidence level 2 (out of 5). Data source: Smart & Thomas 2018.

Biostratigraphic distribution

Geological Range:
Notes: Lower Oligocene Zone O2/O3 (DSDP Site 516, South Atlantic) to upper Pliocene Zone PL6 (DSDP Site 610, North Atlantic Ocean, Thomas, 1987), intermittent. [Smart & Thomas 2018]
Last occurrence (top): within PL6 [Atl.] zone (1.88-2.39Ma, top in Gelasian stage). Data source: Smart & Thomas 2007
First occurrence (base): within O2 zone (30.28-32.10Ma, base in Rupelian stage). Data source: Smart & Thomas 2007

Plot of occurrence data:

Primary source for this page: Smart & Thomas 2018 - Olig Atlas chap.19 p.52;

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. Proc. Natl. Acad. Sci. U. S. A.. 106: 12629-12633. gs

Poag, C. W. & Low, D. (1985). Environmental trends among Neogene benthic foraminifers at DSDP Site 548, Irish continental margin. Initial Reports of the Deep Sea Drilling Project. 80: 489-503. gs

Smart, C. W. & Murray, J. W. (1994). An early Miocene Atlantic-wide foraminiferal/ palaeoceanographic event. Palaeogeography, Palaeoclimatology, Palaeoecology. 108: 139-148. gs

Smart, C. W. & Ramsay, A. T. S. (1995). Benthic foraminiferal evidence for the existence of an early Miocene oxygen-depleted oceanic water mass?. Journal of the Geological Society, London. 152: 735-738. gs

Smart, C. W. & Thomas, E. (2006). The enigma of early Miocene biserial planktic foraminifera. Geology. 34: 1041-1044. gs

Smart, C. W. & Thomas, E. (2007). Emendation of the genus Streptochilus Brönnimann and Resig 1971 (Foraminifera) and new species from the lower Miocene of the Atlantic and Indian Oceans. Micropaleontology. 53(01-Feb): 73-103, 103 figures, 113 lates, 101 table. 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: 495-511. gs

Thomas, E. (1986). Early to Middle Miocene benthic foraminiferal faunas from DSDP Sites 608 and 610, North Atlantic. In, Summerhayes, C. P. & Shackleton, N. J. (eds) North Atlantic Palaeoceanography. Geological Society Special Publication. 205-218. gs

Thomas, E. (1987). Late Oligocene to Recent benthic foraminifers from Deep Sea Drilling Project Sites 608 and 610, northeastern North Atlantic. Initial Reports of the Deep Sea Drilling Project. 94: 997-1031. gs


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Streptochilus rockallkiddense compiled by the pforams@mikrotax project team viewed: 21-7-2019

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