Researchers have identified two new species of giant salamander -- one of which they suspect is the world's biggest amphibian -- using DNA from museum specimens collected in the early 20th century. Chinese giant salamanders, now classified as Critically Endangered, were once widespread throughout central, southern and eastern China, researchers noted.

They have previously been considered a single species (Andrias davidianus). However, the new analysis by researchers from the Zoological Society of London (ZSL) and London's Natural History Museum of 17 historical museum specimens and tissue samples from wild salamanders challenges this assumption. Record-Breaking Almost 10 inch Long Salamander Found in US.

Watch: Newly discovered giant salamander species is 'world's biggest amphibian'

The research, published in the journal Ecology and Evolution, found three distinct genetic lineages in salamanders from different river systems and mountain ranges across China. These lineages are sufficiently genetically different that they represent separate species: Andrias davidianus, Andrias sligoi, and a third species which has yet to be named, researchers said.

One of the newly identified species, the South China giant salamander (Andrias sligoi), was first proposed in the 1920s based on an unusual salamander from southern China that lived at the time at London Zoo, they said.

The idea was then abandoned but has been confirmed by this study, according to researchers. The team used the same animal, now preserved as a specimen in the Natural History Museum after living for 20 years at the Zoo, to define the characteristics of the new species. The other unnamed new species, from Huangshan (the Yellow Mountains), is still only known from tissue samples and has yet to be formally described.

"Our analysis reveals that Chinese giant salamander species diverged between 3.1 and 2.4 million years ago," said Professor Samuel Turvey of ZSL's Institute of Zoology. These dates correspond to a period of mountain formation in China as the Tibetan Plateau rose rapidly, which could have isolated giant salamander populations and led to the evolution of distinct species in different landscapes.

The decline in wild Chinese giant salamander numbers has been catastrophic, mainly due to recent overexploitation for food, researchers said. "We hope that this new understanding of their species diversity has arrived in time to support their successful conservation, but urgent measures are required to protect any viable giant salamander populations that might remain," Turvey said.

Salamanders are currently moved widely around China, for conservation translocation and to stock farms that cater for China's luxury food market. "Conservation plans must now be updated to recognise the existence of multiple giant salamander species, and movement of these animals should be prohibited to reduce the risk of disease transfer, competition, and genetic hybridisation," said Turvey.

Chinese giant salamanders are the world's biggest amphibians, researchers noted. They suggest that the newly discovered South China giant salamander -- which can reach nearly two metres -- is the largest of the three and is therefore the largest of the 8,000 or so amphibian species alive today.