We introduce a novel approach using stable oxygen isotopes from crocodilian fossil teeth to unravel palaeohydrological changes in past continental contexts. Applying it to the Plio-Pleistocene Ethiopian Shungura Formation, we found a significant increase in δ¹⁸O in the last 3 million years, likely due to monsoonal shifts and reduced rainfall, and that the local diversity of waterbodies (lakes, rivers, ponds) became restricted.