West Indian rice rat, as big as a cat

Unique and diverse group of Caribbean mammals are all extinct

Two Central American rodents: Oryzomys couesi (top) and Tylomys panamensis (bottom). E.R. Alston - Alston, E.R. 1882. Biologia centrali-americana. Mammalia. R.H. Porter

Two Central American rodents: Oryzomys couesi (top) and Tylomys panamensis (bottom). E.R. Alston - Alston, E.R. 1882. Biologia centrali-americana. Mammalia. R.H. Porter

A record number of mammals have become extinct in the West Indies. European Colonisation was responsible for the destruction of native habitats, as plantations were developed, while cats and rats were introduced to the islands of the region. These factors led to the extinction of these unique species.

Unique

Of the 100 unique species only ten remain: two insectivores and eight rodents. The mammals which have become extinct were highly diverse and not necessarily closely-related. Their ancestors reached these islands, independently of each other, millions of years ago. That is the conclusion reached by a team of biologists published in the Proceedings of the Royal Society. Menno Hoogland is one of the authors.

The Caribbean is the only archipelago that was colonised extensively by terrestrial, non-flying, mammals. Monkeys, sloths, shrews and rodents all reached the islands, either by swimming there, or being carried by driftwood.

Island species are often vulnerable to extinction. Evolved in a predator-free environment, they are defenceless against introduced predators. A classic example is the plight of the dodo, which made its nest on the forest floor of Mauritius, an island off the coast of Africa. Once the island was colonised in the early 16th century, people introduced rats, cats, dogs and pigs. For these predators, the eggs and young of the dodo were easy pickings.

Colonisation

Biologists researched the colonisation by West Indian rice rats of the Lesser Antilles. Rice rats are a group of mainland South American rodents. Researchers sort to identify when, and on how many occasions, they reached the islands, and whether the Caribbean Indians had any part in their spread.

West Indian rice rats are now extinct. The best know species is the Desmarest's pilorie (Megalomys desmarestii) which was as big as a cat and a strong digger, and hence a threat to coconut plantations. The people of Martinique were fond of their meat, although cooking them was an elaborate process. The rat became extinct after the eruption of Mount Pelée in 1902, an event which also killed 30.000 people.

DNA

Biologist collected DNA of Rice rats from museum collections. Of the 42 specimens only eight yielded sufficient DNA for analysis. In the warm and moist Caribbean climate DNA deteriorates very rapidly.

The analysis shows that Rice rats colonised the West Indies on at least two occasions. The most widespread species were related to the their mainland oryzomyine cousins that frequent the swamps, river deltas and coasts of South America.

The Rice rats of Antigua en Guadeloupe however are an older split, and appear most closely related to the mainland South American genus Hylaeamys. These two species are now placed in the new genus Antillomys.

The ancestor of these groups made their way to the island 6.3 and 6.8 million years ago, when sea levels where much lower. The native peoples of the Caribbean do not seem have played a part in the spread of these mammals which were unique to every island.

Last Modified: 04-05-2015