A new set of rotations is presented that describes a refined model for the early opening of the Weddell Sea between South America and Antarctica and the Mesozoic breakup of Gondwana. Published high-resolution aeromagnetic data from the eastern Weddell Sea and additional track data farther west in the Weddell Sea were used to constrain the new model for the opening of the Weddell Sea. Rotation parameters derived for the South America--Antarctica spreading regime were combined with constraints on the South America--Africa and Africa-Antarctica spreading systems to calculate a refined model for the Mesozoic breakup of Gondwana. Thereafter, at the time when the north-south oriented separation between Africa and Antarctica is initiated by rifting in the Somali and Mozambique basins (~167 Ma), stretching and extension takes place in a basin comprising continental crust of the Filchner-Ronne Shelf, the Falkland Island block and the Maurice Ewing Bank. The first true ocean floor in the Weddell Sea is formed at about 147 Ma, after rifting between the Antarctic Peninsula and southernmost South America occurred. This is about 15--20 Myr later than previously estimated. Separation between South America and Antarctica takes place at slow spreading rates (14--12 mm/yr half rate) from 147 to 122 Ma and after 122 Ma (M2) at ultraslow spreading rates (~8 mm/yr half rate) with little change in the NNW spreading direction throughout this time. A revised age range is proposed for the formation of the Explora Wedge (150--138 Ma), which is more than 30 Myr later than previously published (~183 Ma).