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THE HUNTERS AND THE HUNTED

Plant eaters

Forests offer an ever renewing, inexhaustible supply of food for evolving animals. The first vertebrateherbivores probably evolve to utilize and digest such vegetation. Herbivorousdinosaurs had fed on them, smashing saplings in the forests of ash, elm and beech in North America, crashing through the palms and lianas of the tropics. With the extinction of the dinosaurs, only invertebrates such as insects would continue, unobtrusively, to claim their share, gnawing at the wood, scissoring the leaves into fragments. A few lizardspecies would have teared away at leaf fronds, and birds, would have been acquiring a taste for the newly evolving fruit, and obliging the plants with distribution of their seeds. About 50 to 60 million years ago there appeared to be no large herbivores using these plants. Eating plants is no easy business. It demands particular skills and structures just like any other specialized diet. For one thing, vegetable matter is not particularly nutritious and great quantities of material needs to be extracted to obtain enough calories to sustain a large animal. Some dedicated vegetarians have to spend three quarters of their waking hours foraging. This in turn would expose an animal to risk by a predator. One way for an animal to minimise such a risk is to grab as much as possible, as quickly as possible, and to run of with it to somewhere safe a strategy that the African Giant Rat (Cricetomys gambianus) employs. This rodent emerges cautiously from its burrow at night and when it is sure that there is no danger, frantically loads its cheek pouches with anything that looks remotely edible. Seeds, nuts, fruits, roots, occasionally a snail or a beetle all go in. The pouches are very large and when they are crammed full it scurries back to its burrow.

A Giant African Pouch Rat learns to get rewarded to indicate the location of explosives.