Newly Discovered Amber Fossil Preserved the Oldest Known Prehistoric Tropical Frog

Mindy Sparks
June 17, 2018

David C. Blackburn, accompanied by Linda Xing, a researcher at the University Of Geosciences in China, examined the four excellently preserved ancient frogs fossils captured in amber, discovered in northern Myanmar (also called Burma in the past). A comparative analysis of the ancient frogs, dubbed Electrorana limoae, with similar species living today revealed more similarities than differences; it seems frogs haven't changed all that much across the millennia.

"Our comparisons of the skeleton of these new frog fossils indicate that these amber-preserved frogs were "true frogs" but may represent one of the most ancient lineages seen today", said Blackburn. This is why the new 99-million-year-old amber fossils are so important to scientists - they provide a very rare insight into the lives of ancient frogs that used to live in wet environments. "These frogs were part of a tropical system that, in some ways, might not have been that different to what we find today - minus the dinosaurs".

Frogs in amber are quite rare, with previous examples found in the Dominican Republic and Mexico and dating back to only about 40 million and 25 million years, respectively.

"Whilst Electrorana doesn't preserve much soft tissue, unlike some unbelievable lizard specimens from the same deposits, its well-preserved skeleton represents the oldest record of a frog from a tropical forest, which is a very important modern habitat for frogs", says Michael Pittman, a paleontologist at the University of Hong Kong. According to the researchers, published in the journal Scientific Reports, the discovery shows that the frogs, who were trapped in the sticky resin of a tree, lived in tropical forests before the dinosaurs disappeared.

"Lizards and frogs in amber are certainly not unheard of, but ones this old are exceptional".

More than a third of the 7,000-odd living species of frogs and toads are found in rain forests around the world.

The study determined that frogs, which emerged about 200 million years ago, were living in soggy forested areas at least 100 million years ago. "But surprisingly, we have nearly nothing from the fossil record to stay that's a longstanding association".

The four frog fossils were not dated directly. "There could be a lot more fossils coming", he said.

The piece of amber contains the frog's head, forelimbs, part of its spine, and part of one of its hindlimbs, as well as an unidentified beetle. Found it was among the amber of Myanmar, which has also found other unique remains of the era: tailed spiders and ants-vampires. But these are Eurasian species that live in temperate, not tropical, ecosystems.

Many characteristics herpetologists use to discern details of a frog's life history and determine how it's related to other frogs-wrist bones, the pelvis, hip bones, the inner ear, the top of the backbone-are either missing or were not yet fully developed in the juvenile frog.

"We don't have a lot of single-species frog communities in forests".

But Electrorana raises more questions than it answers, Blackburn says.

The awesome fossil and species descriptions were published today in Nature's Scientific Reports.

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