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Biogeography
The number of species of Spelaeogriphacea is unfortunately sparse. Despite this, their distribution suggests a potentially interesting set of biogeographical scenarios. The known recent forms are restricted to the southern hemisphere, suggesting their geographic pattern is a remnant of a Gondwanan distribution: P. brasiliensis found in Brazil, S. lepidops in South Africa, and the as-yet-unnamed spelaeogriphacean from Australia. However, each of the known fossil taxa is located in the northern hemisphere, with A. novascotica found in eastern Canada, L. quadripartitus in China, and the as-yet-unnamed Cretaceous form in Spain (Figure 6). Schram (1977, 1982) , with only one fossil species in the Carboniferous, suggested an early Laurentian origin with later Gondwanan ‘diversification.‘ This pattern of Laurentian origin with Gondwanan dispersal (most likely occurring at the time of the formation of the Pangean supercontinent in the Permian) seems reasonable and finds reflection perhaps in other malacostracan taxa. The new species from Australia would seem to support the prediction of Schram (1974) that with further research, living spelaeogriphaceans would be found "in the Gondwana areas."
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Fig. 6. World map showing distributions of Recent (indicated by ‘o’) and fossil (indicated by ‘x’) spelaeogriphacean taxa. |
Nevertheless, the new Cretaceous form from Spain, in combination with our Late Jurassic species from China might suggest an alternative scenario for the evolution of Spelaeogriphacea. Might we look to the bathynellacean syncarids for another model? The distributional pattern of all spelaeogriphaceans with their relatively late persistence in northern continents, could be one of world wide ubiquity. Under such a scenario we would be tempted to predict that future discoveries of spelaeogriphaceans will not be confined to Gondwana localities, but will conform to a distribution more akin to that shown by the bathynellaceans. These crustaceans are currently found in ground-water habitats world-wide, and are believed to have originated in the Laurentian from a primitive syncarid eumalacostracan in the late Palaeozoic. The bathynellaceans later dispersed throughout northern and southern regions with the formation of Pangaea in the Permian (Schram 1986 ). We believe that such a distribution pattern may eventually become evident for the Spelaeogriphacea, with expanded exploration of ground-water systems world-wide.