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.”