Antarctic Tertiary Progonocytheridae: The last refuge of Majungaella, the survivor of a long lineage, a geographical and physiological migration from low to high latitudes

Abstract

Majungaella Grekoff is shown to be the only member of the once dominant ostracod family Progonocytheridae, Progonocytherinae to survive the Jurassic and also to survive the Cretaceous–Tertiary boundary event. In the Jurassic, Majungaella had a northeastern gondwanine distribution, occurring only in India, Africa and Madagascar. However, during the Neocomian it appears in South America where it extends to the Maastrichtian, while in Australia it first appears in the Aptian and ranges up to the Campanian. Its last records in Africa are in the Cenomanian of South Africa and the Santonian of south-western Africa. This southward shift into higher latitudes was probably due to an increasing cryophilia and, although this may have also been prompted by competitive exclusion by better adapted, newly evolved taxa, it is difficult to demonstrate this due to the universal distribution of most Late Mesozoic ostracod genera. Whatever the reason, Majungaella seems to have become, during the Cretaceous, increasingly adapted to living in high-latitude shallow seas and this adaptation is advanced as the prime reason why the genus, alone among the progonocytherids was able to survive both the post-Cretaceous global cooling and Antarctic palaeoenvironments into the Late Neogene. Eocene, Oligocene and Pliocene occurrences of Majungaella in the Antarctic are investigated and it is concluded that the genus is in situ in all instances and that, especially in the two latter cases, it lived in water temperatures very much lower than those of its Mesozoic forebears.