Trilobatus Spezzaferri, Kucera, Pearson, Wade, Rappo, Poole, Morard & Stalder 2015

Genus Trilobatus Spezzaferri, Kucera, Pearson, Wade, Rappo, Poole, Morard, & Stalder, 2015

Type species. Globigerina triloba Reuss, 1850.

Diagnosis. Type of wall: normal perforate, spinose, coarsely cancellate ‘ sacculifer -type’ wall texture, though commonly obscured by a heterogeneous secondary, ‘gametogenic’ calcite. Test morphology: test low trochospiral, three to four usually globose, near-spherical chambers in the final whorl, generally high chamber expansion rate; sutures distinct, depressed, slightly straight to curved on both sides; umbilicus typically narrow; primary aperture usually extraumbilical-umbilical, generally a low arch, numerous apertures on spiral side, one per chamber, placed at the sutures of the preceding chamber and third-previous chamber (see Spezzaferri et al. 2015 for further detail).

Remarks. Trilobatus is discerned from its ancestor Globoturborotalita Hofker, 1976 by possessing one or more supplementary apertures on the spiral side. Globigerinoides Cushman, 1927 also possesses supplementary apertures but differs from Trilobatus as the latter possesses a strictly sacculifer - type wall texture, whereas the former exhibits a ruber- or ruber / sacculifer - type wall texture (see Hemleben & Olsson 2006 for wall texture classification). Morphospecies of Globigerinoides also show a tendency towards higher arched primary apertures, whilst those of Trilobatus generally have low-arched, often slit-like primary apertures. Globigerinoidesella differs in having digitate protuberances on the final chamber(s) and usually exhibits a larger test size compared to Trilobatus. See also Spezzaferri et al. (2015, table 2) for comparison of morphological characters.

Trilobatus was erected to encompass the ‘ sacculifer lineage’ (sensu Spezzaferri et al. 2015), and distinguish it from the ‘ ruber lineage’, which were both formerly part of Globigerinoides Cushman, 1927. Spezzaferri et al. (2015) demonstrated that the two lineages developed independently and thus placed the two groups in separate genera to avoid polyphyly (see Introduction for further detail).

Range. Latest Oligocene to Recent.