PAUL D STEWART / SCIENCE PHOTO LIBRARY PAUL D STEWART / SCIENCE PHOTO LIBRARY
Comparison of the femur of a modern three toed sloth and extinct giant sloth Scleidotherium spp. Scelidotherium (including the femur) was famously found by Darwin. The discovery of these giant extinct relatives of species still living in similar geographic regions was listed by Darwin as one of the major influences in realising the theory of evolution by natural selection.
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