Intensive predepositional bone modification is described from fossil vertebrate remains. The bone material is derived from terrestrial Pliocene deposits exposed in the Laetoli area (Northern Tanzania), which represents predominantly vulcanoclastic material. The modifications described are shallow grooves with a U-shaped profile, as seen using scanning electron microscopy. The grooves form clusters of radially arranged grooves with 3–8 mm diameter that randomly cover bone surfaces forming broad surface erosion and lining subcortical cavities in the compact bone. Because of the paired arrangement of isolated grooves constituting the clusters, the modifications are attributed to yet unknown insects. Termites are tentatively suggested as possible producers of the marks.