These physical differences are signs that two-toed and three-toed sloths found their own ways to adapt to a lifestyle in the trees. ‘(But) they have different numbers of toes on their forelimbs and the way the muscles connect from the body to the bones in the arms is also different,’ she said. ‘When you look at them hanging in the trees, the two look very similar,’ said Dr Marcela Uliano da Silva, a computational biologist at the Leibniz Institute for Zoo and Wildlife Research in Berlin, Germany. They are an example of what is known in biology as convergent evolution – a process where species develop similar adaptations to a habitat through different evolutionary routes. Modern sloths, however, are thought to have avoided the extinctions that wiped out their larger relatives because they ascended into the trees.īut what makes their survival more extraordinary is that the two types of modern sloths – the two-toed and the three-toed sloths – are thought to have adapted to life in the trees entirely independently of each other. Many of their extinct cousins were giants – some larger than elephants – that spent most of their time on the ground before they died out 10,000 years ago at the end of the last ice age. Yet the sloths that creep through the rainforest canopies of Central and South America are the last remaining members of a group of animals that has roamed the Earth for at least 30 million years and once boasted hundreds of species.
Hanging lazily from tree branches where they barely move for hours on end, sloths hardly seem like born survivors.
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