An international team of researchers has identified three new species of the world's smallest salamander and warned that the rare creatures are in danger of dying out.
The species, from the enigmatic genus Thorius, the adults of which are smaller than a matchstick, are the smallest four-legged tailed organism on Earth, and their miniaturized bodies are highly unusual for vertebrates.
Once extremely abundant and now rarely found in nature, populations of Thorius have declined precipitously over the last 30 to 35 years. The latest findings were made in remote mountains of Oaxaca, Mexico, and published on Tuesday in the journal PeerJ.
"Salamanders of the highlands of Mexico are closer to extinction than any other on Earth," said David Wake, a University of California, Berkeley, professor in the Department of Integrative Biology and a co-author of the paper. "The main factors are habitat conversion and new infectious diseases."
First discovered in the 19th century, Thorius were believed to be a single species for the next 75 years. Nine additional species were discovered between 1940 and 1960, but the adults are so small that the species were hard to tell apart.
A breakthrough came in the 1970s, when biologists discovered that many species, while anatomically similar, could be told apart by using molecular techniques. Since then, more species have been discovered and the three newly found species bring the current total to 29.
The new species were discovered in southern Mexico by the team of researchers from the United States, Mexico and Spain through decades of fieldwork and using a combination of sophisticated molecular analyses, including deoxyribonucleic acid (DNA) sequencing; digital imaging, such as X-ray computed tomography; and statistical analysis of external and internal anatomy.
"We have known about the salamanders we have described for decades, at a time when they were exceedingly common, but only recently have we obtained evidence that they are indeed new species, though now critically endangered," Wake was quoted as saying in a news release from UC Berkeley.
"This is a common experience with other high-altitude species in Mexico, and a biological disaster is facing us."
For at least the last 30 years, the number of valid named amphibian species worldwide has increased at a rate of about 3 percent per year. Whereas in 1985, biologists thought there were around 4,000 species of amphibians, today they recognize more than 7,700. More new ones are being discovered almost daily.
However, the discovery and documentation of amphibian diversity coincides with the precipitous decline of amphibians globally.
Many once-abundant species have gone extinct in the last 50 years, and others are likely doomed to a similar fate barring effective steps to save them.
Of the nearly 30 species of Thorius now recognized, almost all are regarded as endangered or critically endangered by the International Union for the Conservation of Nature. Indeed, the researchers said, Thorius may be the world's most endangered genus of amphibians.