Koalas have very long, very sharp claws. Both hands and feet have claws on every digit, except the big toe!
The claws of the hands are particularly sharp and strong. Several times I’ve seen a koala slip and almost fall off a branch. But if even one claw has good contact with the tree, the koala can usually haul itself back up.
The sharpness of the claws helps a koala to climb big trees. If the tree is larger than the koala’s arm reach, they have to use the claws like crampons on ice – they dig in to the surface and haul themselves up using brute arm strength. Sharp claws also aid in staying on slippery bark – many of the trees koalas prefer have smooth bark that becomes slippery after rain.
Compared to other large arboreal (tree-dwelling) animals, koalas claws are particularly long and sharp for their size. Orangutans, the world’s largest tree climbing mammal, have flat nails rather than sharp claws. See here: orangutan nails (picture credit Borneo Orangutan Survival Australia.)
Large monkeys, like the Black Howler Monkey of South America, also have nails.
Sloths have long curved claws that are not as sharp as koala’s, and not as dextrous. See here: sloth claws on a tree
Koala claws have the greatest similarities with their distant relatives – the Australian possums. Koalas and possums, though not closely related, are all diprotodonts (with the kangaroos, wallabies & gliders) so have similar basic anatomy. Koalas and possums share an arboreal existence, and both eat foliage, so both have to deal with similar conditions.
The first thing one learns if one ever has to capture a koala is how very strong their grip is. If a koala gets a good hold on a branch or cage, it takes a lot of effort to disengage them. Those claws can also be used in self defence. Never underestimate koalas! They have a very sweet, gentle demeanour until they are messed with, and then… look out!