Not everything about the syncarids is clear. The vicariant patterns of intercontinental biogeographic links of these animals are also intriguing. For example, something peculiar (Fig. 3) seems to going on in South America with the distribution of both Bathynellacea as well as stygocaridine Anaspidacea (Lopretto and Marrone, 1998). Noodt (1978) was the first to comment on this disparity, observing that it appeared as if bathynellaceans had taken two different paths to occupy South America.
Fig. 3. Vicariant patterns of syncarid distributions in the southern hemisphere (from Lopretto and Morrone, 1998). Two tracks prevail: one apparently across the South Pacific, a relict of a pathway through Antarctica, and the other traversing the South Atlantic.
Several taxa link Australia, New Zealand, and the southern Andes. The genus Stygocaris has species that extend from Australia, through New Zealand, to Chile, and this pattern is paralleled by species of the virtually ubiquitous genus Bathynella. Similarly, the genus Atopobathynella has representatives in southeastern Australia, Tasmania, New Zealand, and Chile. Chilibathynella can be collected in southeastern Australia and Chile. Obviously, this link across the southern Pacific is a manifestation of an ancient path of dispersal, or vicariant track, that utilized Antarctica when Gondwanaland was intact.
This South Pacific pattern contrasts with a different set of bathynellacean taxa that link northeastern and eastern South America with Africa. Specifically, the genera Nannobathynella and Cteniobathynella have members in Brazil as well as Central Africa. This latter track represents the remnants of a pre-Atlantic union of that part of South America with Africa before the opening of the South Atlantic seaway.
There appears to be a peculiar disparity here. Gondwanaland began breaking apart 100 million years ago. Why, in all that time, have not the eastern/northeastern groundwater biotas of South America mixed with those of the southern Andes and southern freshwater basins of South America? What is the barrier across the central belt of South America that has inhibited this exchange? Right now, these are unanswered questions that must await further examination of the groundwater biota and paleogeography of South America.