The sloth lemurs (family Palaeopropithecidae) were the most species-rich group of the subfossil lemurs, with four genera and eight species. The common name is due to strong similarities in morphology with arboreal sloths, or in the case of Archaeoindris, with giant ground sloths. They ranged in size from some of the smallest of the subfossil lemurs, such as Mesopropithecus, weighing as little as , to the largest, Archaeoindris, weighing approximately . Their characteristic curved finger and toe bones (phalanges) suggest slow suspensory movement, similar to that of an orangutan or a loris, making them some of the most specialized mammals for suspension. Their day vision was very poor, and they had relatively small brains and short tails. Their diet consisted mostly of leaves, seeds, and fruit; dental wear analysis suggests they were primarily folivorous seed-predators.
