Sloths are no slouches when it comes to evolution

Sep 16, 2014

By Science Daily

Today’s sloths might be known as slow, small animals, but their ancestors developed large body sizes at an amazing rate, according to an evolutionary reconstruction published in the open access journal BMC Evolutionary Biology. The fast rate of change suggests that factors such as environmental conditions, or competition with other species must have strongly favored the bigger sloths, before they died out.

Scientists from UCL (University College London) and University College Dublin looked at existing models for reconstructing how sloths diversified, with some species as large as elephants, and some shrinking down to their current small sizes from a large ancestor. The study showed that some sloth lineages increased in size by over 100 kilos every million years — some of the fastest rates of body size evolution known for mammals.

Dr Anjali Goswami (UCL Earth Sciences), an author on the paper, said: “Today’s sloths are really the black sheep of the sloth family. If we ignore the fossil record and limit our studies to living sloths, as previous studies have done, there’s a good chance that we’ll miss out on the real story and maybe underestimate the extraordinarily complex evolution that produced the species that inhabit our world.”

9 comments on “Sloths are no slouches when it comes to evolution

  • To access the continuation of RDF articles, click grey triangle abreast “source”. Further, hyperlinks to original research can be found within (usually).

    Sir David and sloths



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  • @OP- Scientists from UCL (University College London) and University College Dublin looked at existing models for reconstructing how sloths diversified, with some species as large as elephants, and some shrinking down to their current small sizes from a large ancestor. The study showed that some sloth lineages increased in size by over 100 kilos every million years — some of the fastest rates of body size evolution known for mammals.

    Because of the need for re-engineering hearts, limbs which carry more weight, metabolism, and diet, evolving larger takes 10 times longer than evolving smaller.

    From minute to massive – mammal size evolution explained – http://monash.edu/news/show/evolutionary-biologists-animal-size-is-brood-skewed

    The researchers found that species that matured more quickly and produced a larger mass of young each year relative to body weight were able to evolve to a larger maximum size. Further, they are likely to reach that size in fewer generations.

    “The blue whale is the largest animal to have evolved, even larger than dinosaurs, and it reached this size at the fastest rates we recorded. Key to this success is that they produce large young that mature quickly, reaching around 30 metres in eight to 10 years,” Dr Evans said.

    The study also linked maximum size to mortality rate. Because larger animals tend to breed less frequently than smaller animals, if the mortality rate doubles, the maximum size is predicted to be 16 times smaller.

    “It points to why many of the large animals went extinct after the last Ice Age, as changing climates probably increase mortality rates. Large animals are also at high risk of extinction in modern environments because it takes a long time for their population to rebound from disasters.”



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  • Because of the need for re-engineering hearts, limbs which carry more
    weight, metabolism, and diet, evolving larger takes 10 times longer
    than evolving smaller.

    Could that also be because sloths the size of elephants need bloody great trees to climb on so if big trees are suddenly in short supply, as in the disasters mentioned, rebounding should be impossible?



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  • It was a little tongue in cheek Alan because I am still struggling with the claws. The explanation given with the comparison to the anteater just doesn’t sit well in my mind but I will have to do more reading on that one. So far, my mechanical mind is saying they might have maybe just climbed the trunks of the tree to reach higher branched.



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