Brown-throated sloth

A brown-throated sloth grips a slender branch in the canopy near Santa Cruz, Bolivia, its curved claws hooked over the wood and its limbs wrapped around it at several points. This species has the lowest field metabolic rate ever measured in a mammal, lower even than the giant panda's. A wild individual burns roughly three-quarters of the energy that a mammal of its size is predicted to need at rest, and it lets its body temperature swing by as much as 10 °C over a day, warming back up by moving into sunlight.

The broad palmate leaves framing it are almost certainly cecropia, a fast-growing pioneer tree that springs up on cleared ground and city edges. Cecropia is also a documented favourite food of three-fingered sloths, and reddish new growth is visible around the animal.

Digesting it is slow work. Sloths ferment leaves in a multi-chambered stomach, an arrangement that arose independently from the one cattle use, and their digestion is the slowest measured in any mammal. Published estimates of how long a meal takes to pass through range from about a week to well over a month, and the true figure is still unsettled.