LET'S GO LARGE

FEE-FI-FO-FUM! IT MAY not make a great deal of grammatical sense, but this phrase is certain to conjure up mental images of magic beans, rampant beanstalks and one very angry giant.

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Colossal-sized humans and beasts are the stuff of our oldest legends, our favourite fairy tales and our scariest films. But as is often the case in the natural world, fact is stranger - and far more interesting - than fiction. While car-sized ants, a skyscraper-scaling ape, and a physics-defying mosasaur from a certain Hollywood dinosaur franchise may be scientific impossibilities, the physiology, anatomy and ecology of supersize wildlife are still fascinating, full of rules that nature ignores at its peril.

Before exploring why it is impossible for an elephant-sized cat - or even a cat-sized ant - to exist, it is worth looking at why a species might find itself on an evolutionary pathway to becoming huge. The main advantage of biological gigantism is likely to be reduced predation. If you find yourself among the ranks of the mega-sized, you're more likely to be able to defend yourself, or you'll simply be too large to consume.

A bigger body also means a bigger digestive system, enabling larger animals to exploit a different dietary niche, subsisting on lower-quality food simply by eating more of it. For instance, by developing multi-chambered stomachs and increasing the surface area of the gastrointestinal tract via the addition of specific internal structures - or even just increasing the overall length of the digestive tract - large dinosaurs could eat trees such as the infamously unpalatable monkey puzzle (Araucaria araucana). Giant African ungulates, meanwhile, including the ancient rhinoceros relative Paraceratherium, could make a fair meal from the tough bark and nutritionally poor leaves of the acacia.