The tufted ground squirrel or groove-toothed squirrel (Rheithrosciurus macrotis) is a species of rodent in the Sciuridae family. It is monotypic within the genus Rheithrosciurus. It is found only on the island of Borneo, which is divided between Indonesia, Brunei and Malaysia. It is reputed to be a ferocious carnivore that ambushes deer and attacks domestic chickens, draining their blood and eating their hearts and livers, though this behaviour has never been observed scientifically.