Perfectly preserved fossil salamander even has last meal in gut-A Frog – via Herp Digest

By Richa Malhotra, New Scientist, 10/12/17 

The fossil of an extinct salamander is so exquisitely preserved that the remains of its last meal – a frog – can be seen in its gut.

The fossil comes from the site of the Quercy phosphorites in south-west France, which has thrown up many vertebrate fossils over the years. This is despite a large number of specimens probably being destroyed by phosphate mining in the 19th and 20th centuries.

The salamander fossil had remained largely forgotten in the French National Museum of Natural History for decades, until Jérémy Tissier of the JURASSICA Museum in Porrentruy, Switzerland, and his colleagues took a closer look.

They scanned the fossil using advanced imaging techniques, and named it Phosphotriton sigei after the phosphorus-rich sediments of Quercy. It is the only known fossil of this species, with a search in museums and sediment deposits coming up empty.

The salamander died 34 to 40 million years ago, yet aside from its skeleton, many of its soft tissues are preserved: an initial examination identified skin and a lung. These were protected by a process called permineralisation, sometimes loosely known as “mummification”. Under this mechanism, minerals from groundwater seep into a buried animal and fill any empty pockets, or even individual cells.

This type of soft tissue preservation is rare, says Dean Lomax at the University of Manchester, UK.

When Tissier and his colleagues revisited the scan, they spotted other tissues, including digestive tract, nerves, muscles and an unidentified organ. But the “big surprise” came when they examined the digestive tract and found frog bones inside.

Those bones comprised four vertebrae and a 5-millimetre-long limb bone. “It was clear that they didn’t belong to the salamander, because they were in the wrong position and too small,” Tissier says. He isn’t sure whether the frog bones all belong to the same individual, but they do not come from any fully developed adults.

Regardless, the finding makes P. sigei the only extinct salamander known to have consumed frogs. “We definitely didn’t expect frog bones,” says Tissier, because modern salamanders rarely eat those animals.

“The frog was really small, which may have made it easier for the salamander to catch it,” he adds. The prey was just 18-20 millimetres long, whereas the salamander may have been 150 mm – although the fossil is only about 60mm long because it is missing its head and parts of its tail and neck.

Most present-day salamanders feed on invertebrates, with their mouths too small to consume large vertebrates, says herpetologist Sara Viernum. “But if they can fit a vertebrate prey in their mouths, they typically will eat it.” The frog’s small relative size may have doomed it.

Journal reference: PeerJ, DOI: 10.7717/peerj.3861