Humans make use of many other animal species for food (including meat, eggs and dairies), for materials (such as leather, fur and wool), as pets and as working animals for transportation, and services. In modern times, the biological classification of animals relies on advanced techniques, such as molecular phylogenetics, which are effective at demonstrating the evolutionary relationships between taxa. In 1874, Ernst Haeckel divided the animal kingdom into the multicellular Metazoa (now synonymous with Animalia) and the Protozoa, single-celled organisms no longer considered animals. Carl Linnaeus created the first hierarchical biological classification for animals in 1758 with his Systema Naturae, which Jean-Baptiste Lamarck expanded into 14 phyla by 1809. Historically, Aristotle divided animals into those with blood and those without. 6,331 groups of genes common to all living animals have been identified these may have arisen from a single common ancestor that lived 650 Mya during the Cryogenian period. Nearly all modern animal phyla became clearly established in the fossil record as marine species during the Cambrian explosion, which began around 539 million years ago (Mya), and most classes during the Ordovician radiation 485.4 Mya. Precambrian life forms interpreted as early complex animals were already present in the Ediacaran biota of the late Proterozoic, but fossils of primitive sponge and other speculative early animals have been dated to as early as the Tonian period. and the deuterostomes, which include the three phyla echinoderms, hemichordates and chordates, the latter with the vertebrates being its most successful subphylum. Extant bilaterians include the basal group Xenacoelomorpha, but the vast majority belong to two large superphyla: the protostomes, which include phyla such as arthropods, molluscs, flatworms, annelids and nematodes, etc. Most living animal species belong to the infrakingdom Bilateria, a highly proliferative clade whose members have a bilaterally symmetric body plan. The scientific study of animals is known as zoology, and the study of animal behaviors is known as ethology. They have complex ecologies and interactions with each other and their environments, forming intricate food webs. It has been estimated there are as many as 7.77 million animal species on Earth.

With few exceptions, animals consume organic material, breathe oxygen, have myocytes and are able to move, can reproduce sexually, and grow from a hollow sphere of cells, the blastula, during embryonic development.Īs of 2022, around 2.16 million living animal species have been described-of which around 1.05 million are insects, over 85,000 are molluscs, and around 65,000 are vertebrates. Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia.

Elephant head outline drawing