Tetrapods and Continents

Abstract

The affinities of modern land-living animals are intimately related to the positions and connections of continents, a fact nicely demonstrated by mammalian faunas throughout the world. The zoogeography of modern mammals has roots in the various distributions of mammals during Cenozoic time. In the Paleozoic and Mesozoic eras, the relationship between continental positions and tetrapod faunas is reflected by the distributions of extinct amphibians and reptiles. The early Triassic Lystrosaurus fauna, an example of this, originally described from South Africa, is now known in Antarctica, in peninsular India, and in western China. The distributions of this ancient tetrapod fauna, as well as of other later Mesozoic faunas, indicate that the regions in which they now occur were then intimately associated, allowing for the ready intermigrations of land-living vertebrates. This lends strong support to the theory of Gondwanaland, which supposes the southern hemisphere continents plus peninsular India to have been joined into a single supercontinent (the correlative theory of Laurasia supposes a similar connection of northern hemisphere continents), and to the theory of continental drift, which visualizes eventual fragmentation of these supercontinents, the fragments drifting throught time to the positions occupied by the modern continents. The changing relationships of continents due to the break-up of Pangaea (Gondwanaland plus Laurasia) and the drift of the great continental blocks to their present positions, presumably resulted in the shift of tetrapod faunas from the ancient pattern of northern and southern moieties, through intermediate conditions, seen in the dinosaurian faunas of middle and late Mesozoic time, to the zoogeographical distributions of Cenozoic mammals.