The Permian-Triassic (P-T) mass extinction is the largest extinction event of the Phanerozoic and has been causally related to eruption of the Siberian Traps (Siberia, Russia) through climatic and ecological effects of volcanically forced greenhouse gas emissions. Given anthropogenic changes to the atmosphere, documenting details of links between greenhouse warming and catastrophic biological consequences has significance beyond better understanding of the P-T boundary. Earliest Triassic warming is supported by modeling and isotopic studies; however, the empirical data are limited. In this paper we show that δ18O values of phosphate in therapsid tusks from the interior of Pangea (paleolatitude 60°S) were relatively constant through the latest Permian but increased by ∼2‰ during the earliest Triassic. Over the same interval, δ18O values of carbonate soil nodules increased by ∼5‰. The increases in both measurements and the disproportionately large shift among nodules indicate that the interior of Pangea warmed and became markedly more arid immediately after the P-T boundary.