Bipolar molluscs and their evolutionary implications

• Published in: Journal of Biogeography
• Main Author: Crame, J. A.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Wiley 1993
• Subjects: Arctic; Canada; Antarc*; Antarctica; Siberia
• Online Access: http://nora.nerc.ac.uk/id/eprint/517674/; https://doi.org/10.2307/2845668

The phenomenon of bipolarity, one of the major disjunct distribution patterns on the face of the earth, has been investigated repeatedly since the mid-nineteenth century. Running through the many hypotheses that have been put forward to account for its occurrence, it is possible to detect two persistent themes: it is usually interpreted within a dispersal framework, and it is generally believed to be of comparatively recent origin. To many authors, the phenomenon is intimately linked to the Plio-Pleistocene glaciations. Recent palaentological investigations have extablished that bipolarity can now be traced back to at least the Early Jurassic period (i.e. 200 m.y.a.). Here it is well marked in the Pliensbachian stage by a variety of pectinacean bivalve taxa. Further bivalves indicate probable Middle Jurassic examples, but the phenomenon is more clearly seen in the Late Jurassic, especially in the Tithonian stage. At this time, in-oceramid, buchiid and oxytomid bivalve occurrences at northern hemisphere localities such as arctic Canada, N.W. Europe, Siberia, N.E. USSR and Japan can be matched with those in southern South America, Antarctica and Australasia. A striking Early Cretaceous (Aptian-Albian) bipolar pattern for the oxytomid Aucellina may be complemented by several infaunal bivalves, brachiopods and at least one gastropod. There is strong circumstantial evidence to suggest that bipolar molluscs continued to develop through the Cenozoic era. Such is the level of generic and subfamilial differentiation within certain living forms as to suggest that they must be the product of a considerable evolutionary history. It is likely that present-day distribution patterns of prosobranch gastropod groups such as th whelks (Buccinidae), together with certain fissurellids, littorinids, naticids and turrids, can be related to a late Paleogene-early Neogene phase of bipolarity. Many amphitropical taxa, in both the marine and terrestrial realms, have probable late Neogene-Pleistocene origins. It is possible to set the ...