120-Million-Year-Old Fossil Frog Found With Salamander in Stomach

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What did ancient animals eat?

It's a question that's usually answered with indirect evidence, like the shape of a creature's jaw, the structure of its teeth, or by inferring from the diets of modern-day descendants. Rarely do scientists dig up direct evidence of past eating habits.

Yet researchers Lida Xing, Kecheng Niu, and Susan Evans struck fossil gold with a specimen of a long-extinct frog, Gerobatrachus baoshanensis, discovered with a nearly complete salamander skeleton lodged inside the animal's gut. They recently described the find in the journal Scientific Reports.

The fossil (pictured top) was originally unearthed in 120-125 million-year-old sediment deposits of the Guanghua Formation in northeastern China, then subsequently brought to the Yingliang Stone Nature History Museum in Nan’an. The frog is about 7.4 centimeters-long from snout to pelvis. Its consumed salamander prey is clearly visible when looking at the frog's underside, taking up a significant portion of the gut. You can see the salamander's tail jutting across the frog's spine.

Reconstruction of the frog and salamander, roughly to scale, in silhouette. The frog image is based on the extant Alytes, and the salamander image on the extant Hynobius.

As the researchers described:

"The salamander skeleton... is largely intact with its bones in association. This suggests it had been caught and swallowed whole, apparently tail first given the position of the skeleton (with the head lying proximally in the gut) and presumably still alive, not long before the frog died and was buried. Predator and prey were of comparable size, and although the salamander was more gracile in its build, there must have been a struggle."

In a delicious juxtaposition, salamanders of today are more known for eating frogs than vice versa.

Source: Lida Xing, Kecheng Niu & Susan E. Evans. "Inter-amphibian predation in the Early Cretaceous of China. Scientific Reports volume 9, Article number: 7751 (2019) https://doi.org/10.1038/s41598-019-44247-7

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