Catalog - Praemurica nikolasi

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Praemurica nikolasi

Citation: Praemurica nikolasi Koutsoukos 2014

Type specimens: Holotype USNM 545300 and paratypes USNM 545301–545312 (in October 2011) and USNM 597403–597406 deposited at the National Museum of Natural History, Smithsonian Institution, Washington, D.C. Additional unpublished topotypes are deposited in the NMNH collections with the curatorial numbers USNM 597428–597437

Type sample (& lithostrat): 6-8cm from top of core; Tamoios Member of the Ubatuba Formation

Type locality: Piston Core from Campos Basin, offshore Brazil; -22.82N; -39.07E

Type repository: Washington, USNM

Description. Very small trochospiral test with 10–12 chambers, commonly with 4K–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. 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.

Holotype (USNM 545300; Fig. 13.1a–d): maximum diameter 139 µm, thickness 81 µm, proloculus indistinct; paratypes: diameter 127–166 µm (averaging 149 µm), thickness/height 74–97 µm (averaging 86 µm).

Globigerina fringa Subbotina. Smit, 1982, p. 339, pl. 2, figs. 11A–C.
‘‘Globorotalia’’ (Turborotalia) cf. tetragona (Morozova). Stott & Kennett, 1990, p. 559, pl. 1, figs. 12, 13.
Eoglobigerina fringa (Subbotina). Huber, 1991, p. 461, pl. 2, fig. 8.

Remarks. 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).
Specimens with a distinct low, nearly flat trochospire, somewhat resemble Globigerina (Eoglobigerina) theodosica Morozova, 1961 (holotype reillustrated in Olsson et al., 1999, p. 20, pl. 8, figs. 16–18), a 5–chambered species with a moderately low elevated spiral side and fine cancellate wall, assigned by Olsson et al. (1999) to the Eoglobigerina edita plexus. Praemurica nikolasi n. sp. differs by the characteristic shape of the last chamber, fewer numbers of chambers in the last whorl, closed umbilicus, and aperture that is a low and wide arch, with a rim commonly bordered by a broad, imperforate corrugated lip. Globigerina (Eoglobigerina) theodosica appears to be a morphotype of the E. edita plexus, as concluded by Olsson et al. (1999).
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.
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

Etymology. Named after Nikolas Alves Koutsoukos, my son, who accompanied me during two research visits (March– June 2009 and March–May 2012) in Heidelberg, Germany.

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).

Stratigraphic range. Zone P0–Zone P1c (lower Danian; Fig. 5); range truncated here by the top of the piston core.

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.

Stable isotope paleobiology. Currently unrecorded.

References:

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

CATALOG OF ORIGINAL DESCRIPTIONS: Praemurica nikolasi Koutsoukos 2014

Praemurica nikolasi

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