Many find sloths cute, while some find them just plain bizarre. In 'The Upside-Down Book of Sloths', Elizabeth Shreeve uncovers their less-well-known evolutionary history and how they became the beloved - and unique - creatures of today. She pairs and compares the six extant modern species, like the pygmy sloth, the brown-throated sloth, and the ai, with their prehistoric counterparts, such as Thalassocnus, the tough seafaring sloth; Paramylodon, which had armour-like skin and walked on the sides of its feet; and Megatherium, which could weigh up to 8,000 pounds. She even reveals how modern sloths have adapted to hang upside down, how they learned to swim and even how they poo!