Praemurica nikolasi


Classification: pf_cenozoic -> Truncorotaloididae -> Praemurica -> Praemurica nikolasi
Sister taxa: P. uncinata, P. inconstans, P. pseudoinconstans, P. taurica, P. nikolasi, P. sp.,

Taxonomy

Citation: Praemurica nikolasi Koutsoukos 2014
Rank: Species
Synonyms:
Taxonomic discussion: The new species is placed within the genus Praemurica by the development of a microperforate, nonspinose, weakly cancellate praemuricate wall texture. Despite variations in spire height (e.g., holotype USNM 545300, Fig. 13.1, and paratype USNM 545301, Fig. 13.2) all specimens assigned to Pr. nikolasi n. sp. consistently share the same chamber arrangement, with 4½–5 subglobular chambers, an inflated, balloon-shaped, subglobular last chamber projecting over the umbilicus with a well- developed apertural lip largely obscuring it, and an umbical-extraumbilical aperture. The variety of morphotypes probably has established phylogenetic roots from which are derived all the subsequent earliest Danian cancellate species (see below).
Despite the high degree of morphological variablity, which can be observed among early Danian Globigerinina, Pr. nikolasi n. sp. is quite a stable morphospecies. It remarkably exhibits a consistent expression of its main morphological characters and common occurrence throughout the studied Danian interval, and can be easily distinguished from other globigerinacean species. [Koutsoukos 2014]

NB Arenillas & Arz. (2017) dispute the interpretation of P. nikolasii as an early Danian species.

Catalog entries: Praemurica nikolasi

Type images:

Distinguishing features: Very small trochospiral test, 4½–5 subglobular chambers in the last whorl; equatorial periphery lobate; ; very small umbilicus; last chamber inflated, with well-developed apertural lip projecting over the umbilicus and covering most of it.

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


Wall type: Wall calcareous, microperforate, circular pores ,0.3–1.0 mm in diameter, with a nonspinose, weakly developed cancellate praemuricate texture, in varying developmental stages, from pustules coalescing around pores (Fig. 13.1d) to well-formed honeycomb ridges surrounding pores of a rather coarsely cancellate wall texture, distinctive under the SEM (Fig. 13.3b). Detailed high-magnification SEM analyses of well-preserved specimens reveal a few scattered structures similar to primitive small pores developed next to pustules and occasionally to larger well-defined pores (see Figs. 13.1d, 14.6b). These small pores are not spine holes, are not related to the dissolution process, and are commonly obscured in specimens with better developed cancellate walls and by gametogenic overgrowth calcification. [Koutsoukos 2014]

Test morphology: Very small trochospiral test with 10–12 chambers, commonly with 4½–5 subglobular chambers in the last whorl, increasing gradually in size. Trochospire varying from low to moderately high; equatorial periphery lobate; axial periphery moderately compressed; very small, hardly discernible umbilicus; chambers on the spiral side are rounded to slightly elongate-oval, drawn out in the direction of coiling; chambers on the umbilical side are broadly triangular, somewhat angular in disposition; last chamber is inflated, balloon-shaped, subglobular, slightly offset toward the umbilicus, with a well-developed apertural lip projecting over the umbilicus and covering most of it. Sutures distinct, depressed, radial on the umbilical side, oblique to curved in the direction of coiling on the spiral side. Aperture developed as a low, wide umbilical-extra- umbilical arch, bordered by a moderately thin, wide imperforate lip covered by scattered small pustules with a hispid/corrugated margin. [Koutsoukos 2014]

Size: 130-170 µm

Character matrix

test outline:Subquadratechamber arrangement:Trochospiraledge view:Equally biconvexaperture:Umbilical-extraumbilical
sp chamber shape:Globularcoiling axis:Lowperiphery:N/Aaperture border:Thick lip
umb chbr shape:Inflatedumbilicus:Narrowperiph margin shape:Moderately roundedaccessory apertures:None
spiral sutures:Moderately depressedumb depth:Shallowwall texture:Cancellateshell porosity:Finely Perforate: 1-2.5µm
umbilical or test sutures:Strongly depressedfinal-whorl chambers:4.5-5.0 N.B. These characters are used for advanced search. N/A - not applicable

Biogeography and Palaeobiology


Geographic distribution: The occurrence of Praemurica nikolasi n. sp. in a deep-water core of the Campos Basin implies a preference for tropical to subtropical oceanic water masses at low to middle latitudes, but this needs to be confirmed from other sites. [Koutsoukos 2014]

Isotope paleobiology: Currently unrecorded. [Koutsoukos 2014]

Phylogenetic relations: Phylogenetic relationships. The species is the earliest recorded member of the Truncorotaloididae and of the cancellate lineages. It appears to descend directly from Hedbergella monmouthensis, from which it differs by having a microperforate test with a nonspinose weakly developed cancellate praemuricate wall texture, a more closed umbilicus with the last chamber protruding into and covering most of the umbilical area, generally fewer chambers in the last whorl, and a progressively higher trochospire.
Morphologically, in chamber arrangement (viewed both dorsally and ventrally) and variability in spiral height, Praemurica nikolasi n. sp. appears to be intermediate between the genera Praemurica (nonspinose, Truncorotaloididae) on the one hand and Eoglobigerina and Parasubbotina (spinose, Globigerinidae) on the other. Indeed transitional morphotypes are commonly seen within the population (see below), in some instances in blooms coeval or just about preceeding the first occurrence of the probable derived species. It could very well be the common progenitor-ancestor-species stock from which all early Danian cancellate lineages were derived (see further discussion below). [Koutsoukos 2014]

Similar species: Specimens of Pr. nikolasi n. sp. with a moderately high to highly elevated trochospiral test are somewhat similar to Eoglobigerina tetragona Morozova, 1961 (holotype reillustrated in Olsson et al., 1999, p. 20, pl. 9, figs. 1–3), also placed within the E. edita plexus by Olsson et al. (1999). Praemurica nikolasi n. sp. also differs in apertural features and in having its characteristically offset, balloon-shaped last chamber projecting into the umbilicus.
The new species is practically homeomorphic with Turborotalita quinqueloba (Natland, 1938), which ranges from the Oligocene–Recent, and is very similar morphologically to Turborotalita praequinqueloba Hemleben & Olsson, 2006 (in Pearson et al., 2006, p. 165, pl. 6.20), a late Eocene species. It differs from T. praequinqueloba in having morphotypes typically with a low to highly elevated trochospire; 4½–5 (rather than 4–4½) globular chambers in the last whorl; chambers gradually increasing in size; a less lobate profile; an ultimate subglobular chamber nearly equal to or larger than the penultimate one (never reduced in size as often seen in T. praequinqueloba), typically projecting toward the umbilicus; an umbilical to slightly extraumbilical low-arched apertural opening commonly bordered by a thin corrugated imperforate lip; and a more weakly developed cancellate test, with minute circular pores (diameter ,0.3–1.0 mm). It differs from T. quinqueloba in having a less compact test, with a looser, more lobate equatorial periphery; a low to moderately high trochospire; and an invariably large final chamber. [Koutsoukos 2014]

Most likely ancestor: benthic ancestor - at confidence level 3 (out of 5). Data source: Koutsoukos 2014, p.138.
Likely descendants: Praemurica taurica;

Biostratigraphic distribution

Geological Range:
Last occurrence (top): in lower part of P1c subzone (30% up, 63.5Ma, in Danian stage). Data source: Koutsoukos 2014 (may range higher as core truncated)
First occurrence (base): at base of P0 zone (0% up, 66Ma, in Danian stage). Data source: Koutsoukos 2014

Plot of occurrence data:

Primary source for this page: Koutsoukos 2014

References:

Arenillas, I. & Arz, J. A. (2017). Benthic origin and earliest evolution of the first planktonic foraminifera after the Cretaceous/Palaeogene boundary mass extinction. Historical Biology. 29: 25-42. gs

Huber, B. T. (1991b). Maestrichtian planktonic foraminifer biostratigraphy and the Cretaceous/Tertiary boundary at ODP Hole 738C (Kerguelen Plateau, southern Indian Ocean). Proceedings of the Ocean Drilling Program, Scientific Results. 119: 451-465. gs

Koutsoukos, E. (2014). Phenotypic plasticity, speciation, and phylogeny in Early Danian planktic foraminifera. Journal of Foraminiferal Research. 44: 109-142. gs

Smit, J. (1982). Extinction and Evolution of planktonic foraminifera after a major impact at the Cretaceous/Tertiary boundary. In, Silver, L. T. & Schultz, P. H. (eds) Geological Implications of Impacts of Large Asteroids and Comets on the Earth, Geological Society of America Special Paper 190. 329-352. gs

Stott, L. D. & Kennett, J. P. (1990). The Paleoceanographic and Paleoclimatic signature of the Cretaceous/Paleogene boundary in the Antarctic: Stable isotopic results from ODP Leg 113. Proceedings of the Ocean Drilling Program, Scientific Results. 113: 829-848. gs


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Praemurica nikolasi compiled by the pforams@mikrotax project team viewed: 22-8-2019

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