Globigerinoides is represented by both hispid (Gds. primordius) and reticulate (Gds. quadrilobatus) forms at levels below the first appearance (FA) of Globoquadrina dehiscens dehiscens, that is within Zone N.4A, in northern Australia, and at levels approximating the FA of Gq. dehiscens dehiscens, that is at the base of Zone N.4B, in southern Australia. These levels are below the FA of Globigerina (Globoturborotalita) woodi woodi, an event which occurs above the FA of Gq. dehiscens dehiscens, within the upper part of Zone N.4B. The presence of Globigerinoides quadrilobatus in southern Australia coincides with an extra-tropical excursion of larger benthic foraminiferids together with the warm water planktic form Globorotalia (Fohsella) kugleri, and disappears with the warm water forms within the basal part of the range of Ga. (Go.) woodi woodi; Globigerinoides quadrilobatus reappears within Zone N.6, above the FA of Ga. (Go.) woodi connecta. In northern Australia Globigerinoides quadrilobatus is continuously present throughout the Early Miocene as are the larger benthic foraminiferids. During the Early Miocene, populations of Globigerinoides throughout Australia (and elsewhere) show wide phenotypic variation, a feature of both Ga. (Go.) woodi and Ga. (Ga.) praebulloides populations. Based on oxygen isotope data Globigerinoides quadrilobatus has been a warm, shallow water dweller throughout its history, an attribute supported by its co-occurrence with other warm water species. Ga. (Go.) woodi, when it occurs with Globigerinoides, dwelt at intermediate water depths, and so at lower temperatures; its published biogeography supports a warm temperate distribution. Present day distribution of the Ga. (Ga.) bulloides group also supports a temperate biogeographic range, although it is typical of upwelling zones in subtropical and tropical areas. Thus, during the Early Miocene the biogeographic distribution of the reticulate globigerines was closely related to temperature, with those with spiral apertures typical of subtropical to tropical conditions, and those without these apertures were typical of warm temperate areas. Modern species of Globigerinoides maintain a symbiotic relationship with algae, but this relationship is absent in present day representatives of both Ga. (Ga.) bulloides and Ga. (Globoturborotalita). Such a relationship likely existed throughout the history of Globigerinoides. The presence of symbionts in Ga. (Ga) falconensis, a close warm water relative of Ga. (Ga.) bulloides, suggests that a similar relationship may have developed in warm water populations of Ga. (Ga.) praebulloides, the probable ancestral form. Following this reasoning, one of the published proposals that Ga. (Ga.) praebulloides gave rise to the Globigerinoides quadrilobatus group is supported. This contrasts with the views of other workers that Ga. (Go.) woodi was the ancestral form. However, the presence of reticulate Globigerinoides at levels prior to the FA of Ga. (Go.) woodi strongly supports the first proposal. However, there also seems to be a demonstrable evolutionary relationship between Ga. (Go.) woodi and Globigerinoides quadrilobatus suggesting that there may have been a genetic relationship between the two species. In order to overcome this duality of phylogeny I suggest that Ga. (Go.) woodi is a cool water ecomorph of Globigerinoides quadrilobatus. Support for this proposal comes from the sudden appearance of Ga. (Go.) woodi and its lack of other ancestral forms.
