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Skeleton of Malta's extinct Palaeoloxodon falconeri, the smallest known species of elephant. Adult males measured about one meter in shoulder height and weighed about 305 kg. Females were considerably smaller.

Insular dwarfism, a form of phyletic dwarfism,[1] is the process and condition of large animals evolving or having a reduced body size[a] 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 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 effect" or "Foster's rule", which posits that when mainland animals colonize islands, small species tend to evolve larger bodies (island gigantism), and large species tend to evolve smaller bodies.

Possible causesEdit

There are several proposed explanations for the mechanism which produces such dwarfism.[3][4]

One is a selective process where only smaller animals trapped on the island survive, as food periodically declines to a borderline level. The smaller animals need fewer resources and smaller territories, 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. Smaller size is also advantageous from a reproductive standpoint, as it entails shorter gestation periods and generation times.[3]

In the tropics, small size should make thermoregulation easier.[3]

Among herbivores, large size confers advantages in coping with both competitors and predators, so a reduction or absence of either would facilitate dwarfing; competition appears to be the more important factor.[4]

Among carnivores, the main factor is thought to be the size and availability of prey resources, and competition is believed to be less important.[4] In tiger snakes, insular dwarfism occurs on islands where available prey is restricted to smaller sizes than are normally taken by mainland snakes. Since prey size preference in snakes is generally proportional to body size, small snakes may be better adapted to take small prey.[5]

Dwarfism versus gigantismEdit

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

The process of insular dwarfing can occur relatively rapidly by evolutionary standards. This is in contrast to increases in maximum body size, which are much more gradual. When normalized to generation length, the maximum rate of body mass decrease during insular dwarfing was found to be over 30 times greater than the maximum rate of body mass increase for a ten-fold change in mammals.[6] The disparity is thought to reflect the fact that pedomorphism offers a relatively easy route to evolve smaller adult body size; on the other hand, the evolution of larger maximum body size is likely to be interrupted by the emergence of a series of constraints that must be overcome by evolutionary innovations before the process can continue.[6]

Factors influencing the extent of dwarfingEdit

For both herbivores and carnivores, island size, the degree of island isolation and the size of the ancestral continental species appear not to be of major direct importance to the degree of dwarfing.[4] However, when considering only the body masses of recent top herbivores and carnivores, and including data from both continental and island land masses, the body masses of the largest species in a land mass were found to scale to the size of the land mass, with slopes of about 0.5 log(body mass/kg) per log(land area/km2).[7] There were separate regression lines for endothermic top predators, ectothermic top predators, endothermic top herbivores and (on the basis of limited data) ectothermic top herbivores, such that food intake was 7 to 24-fold higher for top herbivores than for top predators, and about the same for endotherms and ectotherms of the same trophic level (this leads to ectotherms being 5 to 16 times heavier than corresponding endotherms).[7]


Non-avian dinosaursEdit

Recognition that insular dwarfism could apply to dinosaurs arose through the work of Ferenc Nopcsa, a Hungarian-born aristocrat, adventurer, scholar, and paleontologist. Nopcsa studied Transylvanian dinosaurs intensively, noticing that they were smaller than their cousins elsewhere in the world. For example, he unearthed six-meter-long sauropods, a group of dinosaurs which elsewhere commonly grew to 30 meters or more. Nopcsa deduced that the area where the remains were found was an island, Hațeg Island (now the Haţeg or Hatzeg basin in Romania) during the Mesozoic era.[8][9] Nopcsa's proposal of dinosaur dwarfism on Hațeg Island is today widely accepted after further research confirmed that the remains found are not from juveniles.[10]


Example Species Range Timeframe Continental relatives
A. atacis Ibero-Armorican Island Late Cretaceous / Maastrichtian Nemegtosaurid sauropods
E. holgeri Lower Saxony Late Jurassic / Middle Kimmeridgian Brachiosaurs
M. dacus Hateg Island Late Cretaceous / Maastrichtian Rapetosaurus
P. nalatzensis Hateg Island Late Cretaceous / Maastrichtian Epachthosaurus


Example Species Range Timeframe Continental relatives
Langenberg Quarry torvosaur
Unnamed Lower Saxony Late Jurassic / Middle Kimmeridgian Torvosaurus
T. transsylvanicus Hateg Island Late Cretaceous Hadrosaurids
T. insularis Trieste province Late Cretaceous Jintasaurus
T. antiquus Southern England Late Triassic / Rhaetian Plateosaurus

Z. robustus

Z. shqiperorum
Hateg Island Late Cretaceous Camptosaurus



In addition, the genus Balaur was initially described as a Velociraptor-sized dromaeosaurid (and in consequence a dubious example of insular dwarfism), but has been since reclassified as a secondarily flightless stem bird, closer to modern birds than Jeholornis (thus actually an example of insular gigantism).


Example Binomial Name Native Range Status Continental relatives
Cozumel curassow[11] Crax rubra grisconi Cozumel Unknown Great curassow
Kangaroo Island emu[12]
Dromaius novaehollandiae baudinianus Kangaroo Island, South Australia Extinct (c. AD 1827) Emu
King Island emu[13]
Dromaius novaehollandiae minor King Island, Tasmania Extinct (AD 1822)
Cozumel thrasher[11] Toxostoma gluttatum Cozumel Critically endangered Typical thrashers


Example Binomial Name Native Range Status Continental relatives
Madagascar dwarf chameleon
Brookesia minima Nosy Be island, Madagascar Endangered Madagascar leaf chameleons
Nosy Hara chameleon[14]
Brookesia micra Nosy Hara island, Madagascar Vulnerable
Roxby Island tiger snake[5] Notechis scutatus Roxby Island, South Australia Unknown Tiger snake
Dwarf Burmese python Python bivittatus progschai Java, Bali, Sumbawa and Sulawesi, Indonesia Unknown Burmese python
Tanahjampea python[15] Python reticulatus jampeanus Tanahjampea island, between Sulawesi and Flores Unknown Reticulated python



Example Binomial Name Native Range Status Continental relatives
Pygmy three-toed sloth
Bradypus pygmaeus Isla Escudo de Veraguas, Panama Critically endangered Brown-throated sloth
A. antillensis

A. odontrigonus

A. ye
Cuba, Hispaniola and Puerto Rico Extinct (c. 3000 BC) Megalonyx
Imagocnus I. zazae Cuba Extinct (Early Miocene)
M. rodens

M. zile
Cuba and Hispaniola Extinct (c. 2700 BC)
Neocnus spp. Cuba and Hispaniola Extinct (c. 3000 BC)


Example Binomial Name Native Range Status Continental relatives
Cretan mammoth
Mammuthus creticus Crete Extinct Mammuthus
Channel Islands mammoth
Mammuthus exilis Santa Rosae island Extinct (Late Pleistocene) Columbian mammoth
Sardinian mammoth Mammuthus lamarmorai Sardinia Extinct (Late Pleistocene) Steppe mammoth
Saint Paul Island woolly mammoth[16][17] Mammuthus primigenius Saint Paul Island, Alaska Extinct (c. 3750 BC) Woolly mammoth
Siculo-Maltese elephants
Palaeoloxodon antiquus leonardi

P. mnaidriensis

P. melitensis

P. falconeri
Sicily and Malta Extinct Straight-tusked elephant
Cretan elephants Palaeoloxodon chaniensis

P. creutzburgi
Crete Extinct
Cyprus dwarf elephant Palaeoloxodon cypriotes Cyprus Extinct (c. 9000 BC)
Naxos dwarf elephant Palaeoloxodon sp. Naxos Extinct
Rhodes and Tilos dwarf elephant Palaeoloxodon tiliensis Rhodes and Tilos Extinct
Japanese stegodon[18] Stegodon aurorae Japan and Taiwan[19] Extinct (Early Pleistocene) Chinese Stegodon
Larger Flores dwarf stegodon[3] Stegodon florensis Flores Extinct (Late Pleistocene) Sundaland Stegodon
Javan dwarf stegodon[20] Stegodon hypsilophus Java Extinct
Mindanao pygmy stegodon[21] Stegodon mindanensis Mindanao and Sulawesi Extinct (Middle Pleistocene)
Sulawesi dwarf stegodon[20] Stegodon sompoensis Sulawesi Extinct
Lesser Flores dwarf stegodon[3] Stegodon sondaari Flores Extinct (Middle Pleistocene)
Sumba stegodon[22] Stegodon sumbaensis Sumba, Indonesia Extinct (Middle Pleistocene)
Timor dwarf stegodon[20] Stegodon timorensis Timor Extinct
Sambungmacan dwarf stegodon[20] Stegodon sp. Kalibeng Island (now part of Java) Extinct (Early Pleistocene)
Bumiayu tetralophodon[20] Tetralophodon bumiajuensis Bumiayu Island (now part of Java) Extinct (Early Pleistocene) Tetralophodon


Example Binomial Name Native Range Status Continental relatives
Nosy Hara dwarf lemur[23] Cheirogaleus sp. Nosy Hara island off Madagascar Unknown Dwarf lemurs
Flores Man[24]
Homo floresiensis Flores Extinct (Late Pleistocene) Homo erectus
Callao Man Homo luzonensis[25][26] Luzon, Philippines Extinct (Late Pleistocene)
Modern pygmies of Flores[27] Homo sapiens Flores Extant Humans
Early Palau modern humans (disputed)[28] Homo sapiens Palau Extinct (?)
Homo sapiens Andaman Islands Extant
Sardinian macaque[31]
Macaca majori Sardinia Extinct (Pleistocene) Barbary macaque


Example Binomial Name Native Range Status Continental relatives
Honshū wolf
Canis lupus hodophilax Japan (excluding Hokkaido) Extinct (AD 1905) Gray wolf
Sardinian dhole Cynotherium sardous Corsica and Sardinia Extinct Xenocyon (?)
Cozumel Island coati[11] Nasua narica nelsoni Cozumel Critically endangered Yucatan white-nosed coati
Zanzibar leopard
Panthera pardus pardus Unguja Island, Zanzibar Critically endangered or Extinct African leopard
Bali tiger
Panthera tigris sondaica Bali Extinct (c. AD 1940) Tiger
Javan tiger
Panthera tigris sondaica Java Extinct (c. AD 1975)
Cozumel raccoon
Procyon pygmaeus Cozumel Critically endangered Common raccoon
Channel Island fox
Urocyon littoralis Channel Islands of California Near Threatened Gray fox
Cozumel fox Urocyon sp. Cozumel Critically endangered or Extinct

Non-ruminant ungulatesEdit

Example Binomial Name Native Range Status Continental relatives
Malagasy hippopotamuses
Choeropsis madagascariensis

Hippopotamus lalouema

H. lemerlei
Madagascar Extinct (c. AD 1000) Pygmy hippopotamus

Common hippopotamus
Bumiayu dwarf hippopotamus[20] Hexaprotodon simplex Bumiayu Island (now Java) Extinct (Early Pleistocene) Asian hippopotamuses
Cretan dwarf hippopotamus
Hippopotamus creutzburgi Crete Extinct (Middle Pleistocene) European hippopotamus
Maltese dwarf hippopotamus
Hippopotamus melitensis Malta Extinct (Pleistocene)
Cyprus dwarf hippopotamus
Hippopotamus minor Cyprus Extinct (c. 8000 BC)
Sicilian hippopotamus
Hippopotamus pentlandi Sicily Extinct (Pleistocene)
Cozumel collared peccary[11] Pecari tajacu nanus Cozumel Unknown Collared peccary
Philippines rhinoceros[32] Rhinoceros philippinensis Luzon Extinct (Middle Pleistocene) Javan rhinoceros


Example Binomial Name Native Range Status Continental relatives
Sicilian bison[18] Bison priscus siciliae Sicily Extinct (Late Pleistocene) Steppe bison
Sicilian aurochs[33] Bos primigenius siciliae[18] Sicily Extinct (Late Pleistocene) Eurasian aurochs
Cebu tamaraw Bubalus cebuensis Cebu, Philippines Extinct Wild water buffalo
Lowland anoa
Bubalus depressicornis Sulawesi and Buton, Indonesia Endangered
Bubalus mindorensis Mindoro, Philippines Critically endangered
Mountain anoa
Bubalus quarlesi Sulawesi and Buton, Indonesia Endangered
Balearic Islands cave goat
Myotragus balearicus Majorca and Menorca Extinct (after 3000 BC) Gallogoral
Dahlak Kebir gazelle[34] Nanger soemmerringi ssp. Dahlak Kebir island, Eritrea Vulnerable Soemmerring's gazelle
Nesogoral[35] Nesogoral spp. Sardinia Extinct Gallogoral

Cervids and relativesEdit

Example Binomial Name Native Range Status Continental relatives
Cretan dwarf megacerine deer
Candiacervus spp. Crete Extinct (Pleistocene) Praemegaceros verticornis[9]
Ryukyu dwarf deer[36] Cervus astylodon Ryukyu Islands Extinct Sika deer (?)

Cervus praenipponicus (?)
Jersey red deer population[37] Cervus elaphus Jersey Extinct (Pleistocene) Red deer
Corsican red deer
Cervus elaphus corsicanus Corsica and Sardinia Near Threatened
Pleistocene Sicilian deer[18] Cervus siciliae Sicily Extinct (Late Pleistocene)
Hoplitomeryx spp. Gargano Island Extinct (Early Pliocene) Pecorans
Sicilian megacerine deer[18] Megaloceros carburangelensis Sicily Extinct (Late Pleistocene) Irish elk
Key deer
Odocoileus virginianus clavium Florida Keys Endangered Virginia deer
Sardinian megacerine deer[9]
Praemegaceros cazioti Sardinia Extinct (c. 5500 BC) Praemegaceros verticornis
Svalbard reindeer
Rangifer tarandus platyrhynchus Svalbard Unknown Reindeer
Philippine deer
Rusa marianna Philippines Vulnerable Sambar deer

See alsoEdit


  1. ^ An example of noninsular phyletic dwarfism is the evolution of the dwarfed marmosets and tamarins among New World monkeys, culminating in the appearance of the smallest example, Cebuella pygmaea.[2]


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External linksEdit