Tortoise shapes evolved to avoid 'turning turtle'
FOR a tortoise, being upside down is at best ignominious and at worst fatal. So to avoid it, some species have evolved a quite brilliant trick – perfectly shaped self-righting shells. Gabor Domokos and Peter Varkonyi at the Budapest University of Technology and Economics in Hungary modelled the geometry of turtle and tortoise shells of differing dome heights. Those with very tall domes, such as the star tortoise, effectively have just one stable orientation, right side up. Put another way, a star tortoise placed on its back will automatically roll back onto its front,