In the early Miocene (about 24 mya), castorids evolved a semiaquatic lifestyle. Members of the subfamily Castoroidinae appeared around this time and included giants like "Castoroides" of North America and "Trogontherium" of Eurasia. Members of this group appear to have been less specialized for aquatic life than modern beavers. "Castoroides" is estimated to have had a length of and a weight of . Fossils of one genus in Castoroidinae, "Dipoides", have been found near assemblages of chewed wood, though it appears to have been a rather poor woodcutter compared to "Castor". Researchers suggest that modern beavers and Castoroidinae shared a bark-eating common ancestor. Dam and lodge-building likely developed from bark eating and allowed beavers to survive in the harsh winters of Arctic latitudes. There is no conclusive evidence for this behavior occurring in non-"Castor" species.