Alligator's favourite snack was snails
The closest relatives of the rare Chinese alligator live in North America. But this was not always the case. However, the diet of the fossilised relative is quite surprising.
Compared to earlier times, only a pitiful remnant of crocodile species survives today: depending on the count, there are up to 26 species worldwide; at their peak, there were probably hundreds. And scientists are constantly coming across new representatives of these reptiles, such as Alligator munensis, whose partially fossilised skull was found in Ban Si Liam, Thailand, in 2005. A team led by Gustavo Darlim from the University of Tübingen describes the new species in "Scientific Reports" based on this find.
With an age of the fossil of around 230,000 years, these alligators became extinct in geologically relatively recent times. Alligator munensis was named after the River Mun, which flows near the site where the fossil was found. It is probably closely related to the endangered Chinese alligator from the Yangtze River, which is the only surviving representative of this group in Asia: the entire family, including the caimans, is otherwise found in America.
"The skull from Thailand is reminiscent of that of a bulldog. It has some special features that are missing in all other species," says Márton Rabi, who was involved in the study. The large skull had a short, very broad and low-set snout, a reduced number of dental cavities and the nostrils were far away from the tip of the snout. The research team estimates the overall body length at one and a half to two metres, which is similar to that of the Chinese alligator.
Because of the similarity between the two Asian alligators, the research team suspects that both had a common ancestor that lived in the lowlands of the Yangtze-Xi and Mekong-Chao Phraya river systems. When the Himalayan Mountains then began to rise and other mountain ranges subsequently rose, at least two populations were separated 23 to 5 million years ago, which then diverged.
"The large dental cavities in the skull of A. munensis indicate that it had large teeth in the back of its mouth, which could also be used to crush the shells of snail shells, for example," says Rabi. In the evolutionary past, spherically flattened large teeth with a similar function were common in crocodiles, which also include alligators, and had developed several times independently of each other. However, this type of jaw is no longer found in species living today.
Scientists attribute the extinction of so many crocodile species a few hundred thousand to millions of years ago primarily to the beginning of the Ice Age. Crocodiles are ectothermic, they cannot regulate their own body temperature like mammals, for example - so cold brought them death. The northernmost recent species are the alligators in China and the USA; they can survive sub-zero temperatures for short periods. In Africa, numerous species disappeared around ten million years ago when the Sahara spread at the expense of the extensive wetlands that existed at the time. In contrast, the formation of the South American Andes led to the end of most of the species that existed in the Amazon basin at the time: The mountain range caused the region's mega swamps to be drained. For oceanic crocodile species, on the other hand, sea level fluctuations played a decisive role: when the oceans retreated during the ice ages because water was trapped in the ice, many species also became extinct.
Spectrum of Science
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Cover image: © Márton Szabó (detail) This illustration shows Alligator munensi, whose fossilised remains were found in Thailand. It is closely related to the Chinese alligator.
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