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North to South or South to North: The dispersal direction of major mammal groups

Beginning in 1876 when Alfred Russel Wallace speculated on the biogeography of major mammalian groups in his seminal work, “The Distribution of Animals, with a study of the Earth’s Surface”, biogeographers have noted that the major groups of terrestrial mammals originated in the Northern Hemisphere and dispersed south. These dispersals supposed took place in the Mesozoic. With preponderance of relevant fossils in the Northern Hemisphere during that era and few from Gondwana, this hypothesis was strengthened with the collection of additional specimens over the last 150 years.

A handful of fossils discovered in the Southern Hemisphere during the past quarter century, indicate caution. Early Jurassic Argentine fossils of stem therians occur 50 million years earlier than undoubted therians (marsupials/placentals) in the Northern Hemisphere. Cimolodontan multituberculates are the most common Late Cretaceous mammals in the Northern Hemisphere, persisting until the Eocene. The oldest cimolodontan occurs in the late Early Cretaceous of Australia {two lower jaw fragments}, about 8 million years prior to appearance in the Northern Hemisphere.

Dispersal between South and North America was likely across the Panamanian region. From Australia to Asia dispersal may have been by island hopping as Australia was much further south in the late Mesozoic than at present.

Whether less than a dozen fossils is a harbinger of a replacement of a well-established biogeographic hypothesis will only be known when further specimens in the Southern Hemisphere come to light.

Details

Author
Thomas Rich1, Patricia Vickers-Rich2, Michael Hall2, Lesley Kool2
Institutionen
1Museums Victoria, Melbourne, Australia; 2Monash University, Melbourne, Australia
Veranstaltung
GeoSaxonia 2024
Datum
2024
DOI
10.48380/78cs-hw19