Microfossils in limestones of Eocene age can be split into two groups that reflect their original plate tectonic controlled distribution; a north-south pattern that has been complicated by the relatively recent collision of Australia with the Indonesian plates. One group is found on plate fragments and islands that used to be at low latitudes (Indonesia and the tropical Pacific) and the other around Australia, which was then about 2,000 kms further south. A few locations reviewed did not have detailed data, so in order to test this bio-geographic hypothesis a visit was made to one of these, at Christmas Island, half way between the two realms. The Christmas Island samples were a surprise as neither high or low latitude Eocene markers were found, but instead a "paratropical" genus is common here. This genus has only been found before in the northern hemisphere (Boreal Europe). The species on Christmas Island is new, but the presence of the distinctive genus tentatively suggests it was restricted to transitional (paratropical) Eocene locations.

This biogeographic character has applications in identifying the origin of some microplates along the complex collision zone between Indonesia and Australia, and therefore in clarifying the geological development of this economically important zone.