Phyletic dwarfism is the decrease in average size of animals of a species. There are a few circumstances that often lead to species doing this. Lack of

predators Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...

of smaller creatures can allow smaller members of a species to survive. The lack of resources to sustain a large population of larger animals can pick off the largest specimens. Available resources being more beneficial for smaller creatures can also do so. These circumstances are common on islands, making

insular dwarfism Insular dwarfism, a form of phyletic dwarfism, is the process and condition of large animals evolving or having a reduced body size when their population's range is limited to a small environment, primarily islands. This natural process is disti ...

the most common form of phyletic dwarfism. Examples of this are the Channel Island fox, extinct

dwarf elephant Dwarf elephants are prehistoric members of the order Proboscidea which, through the process of allopatric speciation on islands, evolved much smaller body sizes (around ) in comparison with their immediate ancestors. Dwarf elephants are an example ...

s of Crete, and ''

Brookesia micra ''Brookesia micra'', also known as the Nosy Hara leaf chameleon is a species of chameleons from the islet of Nosy Hara in Antsiranana, Madagascar. At the time of its discovery, it was the smallest known chameleon and among the smallest reptiles ...

'', a minuscule chameleon from Madagascar. An noninsular example is the evolution of dwarfed marmosets and tamarins among New World monkeys. Phyletic dwarfism may have also helped give rise to birds from their much larger dinosaur ancestors.

References

Evolution of animals Animal size Dwarfism {{zoology-stub