Animals

Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen and are able to move. They can be found in nearly all habitats on Earth.

Most known animal phyla appeared in the fossil record as marine species during the Cambrian explosion about 542 million years ago which is when most modern day phylum first emerged. Animals range in size from 8-200 micrometers such as planktonic creatures like rotifers to huge cetaceans such as blue whales measuring up to 33 meters long.

The study of animals is called zoology and includes classification, physiology, development and behavior among other topics; while studying their evolution over time leads into fields including ecology or ethology (the study of animal behavior). Since Aristotle’s time it has been argued that animals lack reason or intelligence although this view has changed throughout history with more sophisticated forms of cognition being discovered by biologists observing various species around the world .

The distinction between plants and animals often comes down to how they obtain energy for growth: photosynthesis versus ingestion/digestion respectively—although this difference alone doesn’t necessarily define an organism’s distinctness from another type nor does it cover every life form within each category (such as fungi). Therefore many scientists prefer not use any single criteria but instead rely upon different combinations including cellular structure , reproduction methods , way movement occurs etc..to classify them properly according to current scientific understanding .

In recent decades there have been large strides forward made concerning our knowledge base regarding animal biology due largely advances made through technology allowing researchers access microscopic levels never before seen – leading us towards uncovering mysteries still left unsolved today related everything from genetics right down cell structures & functions across multiple kingdoms .