Insular dwarfism, a form of
phyletic dwarfism, is the process and condition of the reduction in size of large animals over a number of generations when their population's range is limited to a small environment, primarily islands. This natural process is distinct from the intentional creation of dwarf breeds, called
dwarfing. This process has occurred many times throughout evolutionary history, with examples including
dinosaurs, like
Europasaurus, and modern animals such as
elephants and their relatives. This process, and other "
island genetics" artifacts, can occur not only on traditional islands, but also in other situations where an ecosystem is isolated from external resources and breeding. This can include
caves, desert
oases, isolated valleys and isolated mountains ("
sky islands"). Insular dwarfism is one aspect of the more general "
island rule", which posits that when mainland animals colonize islands, small species tend to evolve larger bodies, and large species tend to evolve smaller bodies.