North to south or south to north: what was the dispersal direction of two Mesozoic mammal groups?

Abstract

Numerous mammalian biogeographers since the late 19th Century have envisioned that major mammalian groups originated in the Northern Hemisphere and subsequently dispersed to the Southern Hemisphere. A small number of Mesozoic mammalian fossils reported from the Southern Hemisphere since 1997 predate the oldest occurrence of two major mammalian groups, tribosphenidans and cimolodontan multituberculates, in the Northern Hemisphere. This suggests that dispersals of those two groups were from the South to the North rather than vice versa.