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The skeleton of a dwarf elephant from the island of Crete.

Insular dwarfism, a form of Phyletic dwarfism,[1] is the process and condition of the reduction in size of large animals – typically mammals but also dinosaurs – when their population's gene pool is limited to a very 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.

There are several proposed explanations for the mechanism which produces such dwarfism, which are often considered likely to be co-contributing factors. One explanation is an evolved gene-encoded response to environmental stress. Another is a selective process where only smaller animals trapped on the island survive, as food declines to a borderline level. The smaller animals need fewer resources, and so are more likely to get past the break-point where population decline allows food sources to replenish enough for the survivors to flourish.

Contents

Examples

Among the most famous examples of insular dwarfism are:

There are also proposed instances of this process occurring among plant life, the appearance of dwarf sequoia / redwood trees being one such proposal.

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, and isolated valleys.

There is also an inverse process, island gigantism, wherein small animals breeding on isolated islands lacking the predators of large land masses may become much larger than normal. An excellent example is the dodo, the ancestors of which were normal-sized pigeons. There are also several species of giant rats, some extinct and some still extant, that coexisted with both Homo floresiensis and the dwarf stegodons on Flores.

Additional examples

Carnivora

Ungulates

Other

See also

References

  1. ^ Prothero, Donald R. & Sereno, Paul C. 1982 "Allometry and Paleoecology of Medial Miocene Dwarf Rhinoceroses from the Texas Gulf Coastal Plain" Paleobiology 8(1):16-30"
  2. ^ Extinct dwarf elephants from the Mediterranean islands
  3. ^ North American Extinctions v. World
  4. ^ Scientist to study Hobbit morphing, abc.net.au
  5. ^ Skull may identify tiny islanders who shrank to survive, The Independent

External links

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