Animals are multicellular, symbiotic organisms in the microbial kingdom Eukarya. With few exceptions, all animals eat organic matter, breathe oxygen, can move, reproduce sexually, and utilize certain types of body tools like teeth, claws, and hooves. The vertebrates ( amphibians and reptiles), birds, small mammals such as rodents, non-mammal ungulates such as whales and hippos, fish, small aquatic ungulates such as aquatic crayfish, etc. The mammals generally belong to the Kingdom Homoeopathicia and are categorized as animals with a body system comprised of a single set of organs, anastomoses (protruders) that directly connect with the anorexiphoid for reproduction, metatherias (plants) with skin, anemones (worms) with olfactory organs, secreting chemical substances from their body. In some cases, humans have been classified as animals, although they actually did not evolve as animals.
All mammals belong to the Kingdom Prototheria and all of the different classes of mammals are further divided into five classes, namely: placental, pouched, terrestrial, aeriform, and marsupials. The placental is the class that includes all the mammals that lay eggs and only a few that give live birth. The pouched or placental mammal is the only one that can give live birth and it belongs to this class of animals only.
The word animal has three different meanings according to American English, all of which derive from the Latin word acus, meaning ‘afresh; newly born’. The other options’ b’ and ‘a’ respectively mean ‘of a new life’, ‘down’, ‘new creation’ and ‘ancestor’. Hence, the term ‘animal’ would therefore refer to any new life emerging from a parent plant or animal. The word fauna means a separate class on the basis of its having animals in it.
The welfare of animals has become very important for many reasons. Humans have an ethical responsibility towards us in relation to our treatment of animals, because we are creatures of the earth as well as creatures of the sky. We need to take care of the planet while we live among it. Animals too need ethics in relation to their well-being, because the planet cannot sustain us well-being without human interaction. It is in fact an ethical obligation for the scientist to participate in animal welfare work.
Recent studies have revealed that a multicellular eon existed more than million years ago. Called Protocera, this was the first eon that gave rise to all the different vertebrate animals we know today. These were the first animals to make use of the ocean and land surfaces to build nests and rear their young. Evidence discovered in South Africa indicated that this was the time when whales, hippos, crayfish, pre-carnivores and other large predatory marine mammals appeared on land. Evidence found at Zaire in Tanzania indicated that these mammals fed upon fish which were present at the time. This is considered to be the first food chain on earth.
Some palaeontologists have concluded from their studies that these mammals were probably not vegetarians because they used meat obtained from animal body parts such as horns, hooves and teeth for their diet. They used the marrow of animals to produce milk for their infants. A vegetarian diet would have been detrimental to the survival of these animals, therefore suggesting the conclusion that these were not a sexual reproduction species, but asexual reproduction only, therefore ruling out the theory of evolution by natural selection.