Olsson and others (2006a) suggested that Globorotaloides quadrocameratus evolved from Parasubbotina in lower Eocene Zone E2. We, however, observe Globorotaloides-like morphologies in the early Paleocene, including specimens that have been illustrated as Subbotina cancellata and ‘Globigerina fringa Subbotina’ (see below), suggesting an earlier ancestry. Morphologies closely comparable to modern Globorotaloides hexagonus Natland, which is frequently found (at low abundance levels) in plankton nets, make their first appearance in the upper Oligocene.

The tendency for a bulla to develop in Globorotaloides appears to be dependent on geologic age. Early and early middle Eocene G. quadrocameratus and G. eovariabilis are typically non-bullate. Late Eocene, Oligocene and Miocene populations contain morphotypes with and without bulla. In contrast, Quaternary and living examples of Globorotaloides hexagonus (Natland) and Globorotaloides trema Lipps always lack a bulla. Reflecting on these observations, we have consolidated the set of described species, including one previously placed in Catapsydrax (i.e. stainforthi) to produce a framework through which the lineage to G. hexagonus can be traced. An important distinction, as originally set out by Bolli (1957), is that in Catapsydrax the aperture is umbilical whereas in Globorotaloides it is typically umbilical-extraumbilical, becoming equatorial in Globorotaloides atlanticus n. sp. and Protentelloides.

Globorotaloides maintained a low diversity through the early Oligocene but the group diversified in the mid- to late Oligocene (Figure 4.1). Development of the distinctive bullate morphospecies G. stainforthi was used as a zonal marker by Bolli (1957) for the early Miocene biozone bearing the name. Owing to the low abundance and patchy distribution of the nominate species the zone has not been incorporated into more recent ‘N’ or ‘M’ zonation schemes. Major modifications to the bulla in one branch of the lineage resulted in the evolution of the clavate planispiral genus Protentelloides. So far records of this genus are limited to the equatorial Atlantic Ocean.

An unresolved question underlying the taxonomy and phylogeny is whether Globorotaloides is spinose. Small circular holes occurring at the junction of cancellate ridges in some Eocene Globorotaloides quadrocameratus and Parasubbotina varianta have been interpreted as spine holes and therefore evidence that these taxa were spinose (Hemleben and Olsson, 2006, pl. 4.4, figs. 9, 12; Olsson and others, 2006a, pl. 5.5, fig. 8; pl. 5.13, figs. 15, 16). In core-top sediments (Holocene-Pleistocene) G. hexagonus occasionally also show similar ‘apparent spine holes’ supporting this idea. Living G. hexagonus recovered from plankton nets, however, clearly lack spines (Parker, 1962; Hemleben and others, 1989; Kucera, unpublished). Due to the close morphological similarities of wall and coiling in Paleogene and living Globorotaloides it seems unlikely that the genus is polyphyletic. Therefore, it is possible that spines were lost during the evolutionary transition from G. eovariabilis to G. hexagonus and/or that the holes are small pores or dissolution pits. For this reason we continue to separate G. eovariabilis and G. hexagonus, although we acknowledge the close morphologic similarity, and we note the continuous intergradation between the two in the mid- to late Oligocene. [Coxall & Spezzaferri 2018]

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