The sloth family tree once sported a dizzying array of branches, body sizes and lifestyles, from small and limber tree climbers to lumbering bear-sized landlubbers.  Why sloth body size was once so diverse, while today’s sloths are limited to just two diminutive tree-dwellers, has been a long-standing question. Scientists have proposed that sloths’ body size might be linked to a wide variety of factors: habitat preferences, diets, changes in global temperature, or pressure from large predators or humans. Sign up for our newsletter We summarize the week's scientific breakthroughs every Thursday. #sloths #once #came #dizzying #array