U.S. researchers have identified two dozen new species of lizards on the Caribbean islands, and about half of them may be extinct or close to extinction.

Blair Hedges, a professor of biology at Penn State University, led the study in the New Zealand journal Zootaxa that was published Monday and co-authored by Caitlin Conn, a researcher at the University of Georgia.

Skinks typically have small smooth round scales, thick bodies, strong necks and short legs or snake-like bodies. The team identified 39 types of skink — six of which were already recognized and nine named long ago but considered invalid until now – by examining museum specimens, DNA sequences and the animals themselves.

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The Jamaican skink is one of the newly identfied species that is under threat. (Joseph Burgess/Penn State University)

The creatures range in size, with the some up to six time larger than others.

The discovery of new reptile species is relatively common, with about 130 added to the global species count each year, but the authors note that researchers haven’t identified more than 20 species at a time since the 1800s.

The lizards will, however, join an unappealing club. Of more than 3,000 reptiles listed as endangered by the International Union for Conservation of Nature, the skinks are likely to join the quarter classified as being threatened with extinction.

"The mongoose is the predator we believe is responsible for many of the species' close-to-extinction status in the Caribbean," said Hedges, adding that the mongoose was introduced from India in 1872 to control rats in sugar cane fields.

Mongooses have been spreading across the islands for decades and, Hedges says, have "nearly exterminated this entire reptile fauna, which had gone largely unnoticed by scientists and conservationists until now."

Skinks produce a human-like placenta and gestate offspring for up to a year, which makes them unique among lizards but may also make pregnant females more vulnerable to predators. 

New data may guide conservation efforts

Hedges and Conn added that human activity, especially the removal of forests, is also contributing to the decline of many island species.

The new data may help guide conservation efforts, as well as further research on the geographic distribution and adaptation techniques of the lizards.

"We were completely surprised to find what amounts to a new fauna, with co-occurring species and different ecological types," said Hedges.  

"Now, one of the smallest groups of lizards in this region of the world has become one of the largest groups."