Late Cretaceous domatia reveal the antiquity of plant-mite mutualisms in flowering plants.

Mite houses, or acarodomatia, are found on the leaves of over 2000 living species of flowering plants today. These structures facilitate tri-trophic interactions between the host plant, its fungi or herbivore adversaries, and fungivorous or predaceous mites by providing shelter for the mite consumers. Previously, the oldest acarodomatia were described on a Cenozoic Era fossil leaf dating to 49 Myr in age. Here, we report the first occurrence of Mesozoic Era acarodomatia in the fossil record from leaves discovered in the Upper Cretaceous Kaiparowits Formation (76.6-74.5 Ma) in southern UT, USA. This discovery extends the origin of acarodomatia by greater than 25 Myr, and the antiquity of this plant-mite mutualism provides important constraints for the evolutionary history of acarodomatia on angiosperms.