Island Of The Giant Rats
Giant Rats as Large as an American Black Bear



 
Island Of The Giant Rats
Giant Rats as Large as an American Black Bear

 
Island gigantism is a biological phenomenon in which the size of animals isolated on an island increases dramatically in comparison to their mainland relatives.

Many rodents grow larger on islands, whereas carnivores, proboscideans and artiodactyls usually become smaller.


The giant hutias are an extinct group of large rodents known from fossil and subfossil material in the West Indies.

One species, Amblyrhiza inundata, is estimated to have weighed between 50 and 200 kg (110 and 440 lb), big specimens being as large as an American Black Bear.


This is much larger than Capybara, the largest rodent living today, but still much smaller than Josephoartigasia monesi, the largest rodent known. These animals may have persisted into historic times and were probably used as a food source by aboriginal humans.

All giant hutias are in a single family Heptaxodontidae, which contains no living species; this grouping seems to be paraphyletic and artificial however.

One small species, Quemisia, may have survived as late as the days when the Spanish were beginning to conquer North America. Some of their smaller relatives from the family Capromyidae, known as hutias, survive in the Caribbean Islands.


Island gigantism is a biological phenomenon in which the size of animals isolated on an island increases dramatically in comparison to their mainland relatives.

Large mammalian carnivores are often absent on islands, due to their large range requirements and/or difficulties in over-water dispersal.

In their absence, the ecological niches for large predators may be occupied by birds or reptiles, which can then grow to larger-than-normal size.

For example, on prehistoric Gargano Island in the Miocene-Pliocene Mediterranean, on islands in the Caribbean like Cuba, and on Madagascar and New Zealand, some or all apex predators were birds like eagles, falcons and owls, including some of the largest known examples of these groups.

However, birds and reptiles generally make less efficient large predators than advanced carnivorans. Since small size usually makes it easier for herbivores to escape or hide from predators, the decreased predation pressure on islands can allow them to grow larger.

Small herbivores may also benefit from the absence of competition from missing types of large herbivores. Thus, island gigantism is an evolutionary trend resulting from the removal of constraints related to predation and/or competition.

In contrast, the complementary phenomenon of island dwarfism results from the imposition of constraints associated with the limited area and food supply available on islands. As opposed to island dwarfism, island gigantism is found in most major vertebrate groups and in invertebrates.

With the arrival of humans and associated predators (dogs, cats, rats, pigs), many giant island endemics have become extinct.