University Of Tübingen Experts Find Chinese Alligator’s Asian Relatives Around 200,000 Years Ago

An almost completely fossilized alligator skull that was found in 2005 in Ban Si Liam, Thailand and is no more than 230,000 years old, belongs to a previously unknown species. Márton Rabi and Gustavo Darlim from the University of Tübingen in cooperation with the Chulalongkorn University of Thailand and the Department of Mineral Resources there. They named the newly discovered species Alligator munensis after the Mun River, which flows near the site. The research team assumes that the species once split off from the Chinese alligator, which is still alive today. Their study was published in the journal Scientific Reports .

The Chinese alligator ( Alligator sinensis ) is the only living member of the caiman and alligator family found outside of the Americas. “We compared the skull with this one, as well as with the American Mississippi alligator and remains of four extinct alligator species,” reports Rabi. “The skull of the A. munensis from Thailand is reminiscent of that of a bulldog. It possesses some distinctive features absent from all other species.” The skull is large, the alligator had a short, very broad and deep-set snout, a reduced number of tooth cavities, and the nostrils were far from the tip of the snout. The research team estimates the overall body length at one and a half to two meters – similar to that of the Chinese alligator.

hypothesis on evolution
“The new species shares most of its similarities with the Chinese alligator,” says PhD student Gustavo Darlim. The researchers believe the two species are closely related and have hypothesized that they may have shared a common ancestor that lived in the lowlands of the Yangtze-Xi and Mekong-Chao Phraya river systems. They speculate that at some unspecified point during the uplift period of the southeastern Tibetan plateau, 23 to 5 million years ago, different populations separated and eventually evolved into two separate species. While the Chinese alligator survived to this day, the alligator munensis became extinct .

“The large tooth cavities in the skull of A. munensis indicate that it had large teeth in the back of the mouth, which could also be used to crush shells such as snail shells,” says Rabi. In the evolutionary past, spherically flattened large teeth with a similar function were common in crocodiles, including alligators, and evolved independently several times. However, such a type of teeth is no longer found in the species living today.

pieces of a puzzle
The Chinese alligator is critically endangered , unlike its Southeastern American cousin, the Mississippi alligator . It only occurs on the lower Yangtze River. “How and when the alligators spread from North America to Asia is not known. So fossils from Asia are important to further piece the puzzle together,” says Darlim. The discovery of the new species suggests that alligators were widespread in southern Thailand until around 200,000 years ago. It is therefore possible that areas outside of China could also be included in a protection program for the Chinese alligator.