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The term "fish" describes any non-tetrapod chordate, (i.e., an animal with a backbone), that has gills throughout life and has limbs, if any, in the shape of fins. [8] Unlike groupings such as birds or mammals, fish are paraphyletic, since the tetrapod clade is within the clade of lobe-finned fishes. [9] [10]
The vertebrates include mammals, birds, amphibians, and various classes of fish and reptiles. The fish include the jawless Agnatha, and the jawed Gnathostomata. The jawed fish include both the cartilaginous fish and the bony fish. Bony fish include the lobe-finned fish, which gave rise to the tetrapods, the animals with four
Marine animals are further informally divided into marine vertebrates and marine invertebrates, both of which are polyphyletic groupings with the former including all saltwater fish, marine mammals, marine reptiles and seabirds, and the latter include all that are not considered vertebrates.
Reptiles are generally considered less intelligent than mammals and birds. [31] The size of their brain relative to their body is much less than that of mammals, the encephalization quotient being about one tenth of that of mammals, [ 125 ] though larger reptiles can show more complex brain development.
In order to be considered fully domesticated, most species have undergone significant genetic, behavioural and morphological changes from their wild ancestors, while others have changed very little from their wild ancestors despite hundreds or thousands of years of potential selective breeding. A number of factors determine how quickly any ...
A mammal (from Latin mamma 'breast') [1] is a vertebrate animal of the class Mammalia (/ m ə ˈ m eɪ l i. ə /).Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three middle ear bones.
A fish (pl.: fish or fishes) is an aquatic, anamniotic, gill-bearing vertebrate animal with swimming fins and a hard skull, but lacking limbs with digits.Fish can be grouped into the more basal jawless fish and the more common jawed fish, the latter including all living cartilaginous and bony fish, as well as the extinct placoderms and acanthodians.
Aquatic animals generally conduct gas exchange in water by extracting dissolved oxygen via specialised respiratory organs called gills, through the skin or across enteral mucosae, although some are evolved from terrestrial ancestors that re-adapted to aquatic environments (e.g. marine reptiles and marine mammals), in which case they actually ...