The giant panda belongs to Carnivora but eats almost nothing except plants
Being a carnivoran and being a carnivore are different things. The giant panda sits in the order Carnivora yet lives almost entirely on plants, while whales eat nothing but animals and are not carnivorans at all. Meat-eating itself goes back perhaps billions of years, to cells swallowing other cells.
A carnivore, from Latin words for flesh and devouring, is any animal or plant that meets its energy and nutrient needs by eating animal tissue, whether it kills the prey or scavenges it. The mammal order Carnivora causes endless confusion because its members, properly called carnivorans, are not all meat-eaters. Cats are obligate carnivores, but bears span the range: polar bears get over 90% of their food from meat, most other bears are omnivores, and the giant panda is almost wholly vegetarian. Meanwhile cetaceans all eat animals without belonging to the order.
Diet percentages give another yardstick. Hypercarnivores take in more than 70% meat, mesocarnivores 30 to 70%, and hypocarnivores under 30%, though no sharp ratio separates a flexible meat-eater from an omnivore. Specialists get their own names: insectivores for insects, vermivores for soft invertebrates, piscivores for fish. Any flesh-eater at the top of its food chain counts as an apex predator. Carnivory also appears in plants, fungi that trap nematodes and springtails, and single-celled protists.
True carnivores cannot properly digest plants. Cats sometimes chew grass simply to make themselves vomit, and their bodies cannot manufacture retinol, arginine, taurine or arachidonic acid, so in the wild they must eat flesh; in captivity, carefully processed plant and synthetic foods can in principle supply everything. Meat-eaters tend to have short guts, since they skip cellulose, and mammalian predators nearly all have forward-facing eyes for depth perception, unlike most reptilian and amphibian hunters. Snakes, spiders, scorpions and some wasps subdue prey with venom.
Predation began with microbes engulfing other cells, somewhere between 1 and more than 2.7 billion years ago, and partially digested prey surviving inside hosts may have helped give rise to complex cells. Stronger predators may have contributed to the loss of the Ediacaran fauna, and Cambrian radiodonts such as Anomalocaris became the first apex hunters. Later came giant nautiloids, sea scorpions, armoured placoderms like Dunkleosteus, and eventually land-going temnospondyls preying on other four-limbed animals.
Source: Carnivore
