Word Origin and History for semi-Expand before vowels sem-, word-forming element meaning half, part, partly; partial, imperfect; twice, from Latin semi-half, from PIE *semi-half (cf. Sanskrit sami half, Greek hemi-half, Old English sam-, Gothic sami-half).
Well-known rodents include mice, rats, squirrels, prairie dogs, porcupines, beavers, guinea pigs, hamsters, gerbils and capybaras. Other animals such as rabbits, hares, and pikas, whose incisors also grow continually, were once included with them, but are now considered to be in a separate order, the Lagomorpha.
Animals with backbones, like these zebras, are commonly referred to as vertebrates. Mammals, birds, fish, amphibians, and reptiles are all vertebrates. Zebras belong to the mammal order. Mammals, which also include humans, are the most complex animals in the animal kingdom.Fossils indicate that animals have existed on Earth for over 1.2 billion years, but our knowledge of past life is still incomplete.nimals belong to the largest and most diverse of the five kingdoms of living things. So far over two million animal species have been identified. All animals share certain features. Unlike plants, animals get the energy they need by eating food. They are all made up of many cells and many animals are highly mobile.