Spurious migration

In what must be one of the most important contributions ever to ostracodology and paleobiogeography, Krommelbein (1970) and Krommelbein and Wenger (1966), demonstrated that the fresh-water Neocomian ostracod faunas of northeastern Brazil and Gabon shared a common geographical origin. Of the 40 species of ostracods known from the Cocobeach Formation of Gabon and 90 species from northeastern Brazil, 33 occur in both regions. This result was fundamental to establishing the existence of a land connexion between South America and Africa in the lowermost Cretaceous and for delineating the rift-controlled freshwater inland seas in the Gabon, Congo and northeastern Brazilian contact zones. It is stimulating to observe how Krommelbein gradually, over a spate of years, arrived by skilful deduction at the conclusion that the Brazilian and Gabon ostracod sequences had once inhabited the same sequence of rift-valley lakes and that the impression of lateral migration was not a viable concept. Transport by migrating birds as a possible mechanism was soon discredited since experience shows that birds migrate along a N-S-N axis and not in an E-W-E direction, which would be a pointless exercise from the bioclimatic standpoint (Hartmann 1988b). A referee suggested that this may not have been so in the past. Be this as it may, there is no evidence known to me that gainsays Krommelbein (1970) and Hartmann (1988) and, moreover, the question has scant bearing on the geological facts before us. The fact that a great number of the known Wealden ostracod species of Gabon and eastern Brazil are common to both areas was used by Reyment and Tait (1972) and Reyment and Dingle (1987) in their reconstruction of the rift-valley phase of the South Atlantic Ocean. They also compiled a detailed reconstruction of the relative geographical position and comparative sedimentology of the Sergipe-Alagoas and Gabonese basins prior to the Aptian marine episode (Reyment and Tait 1972, p. 81, Fig.5).

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