World’s Oldest Rainforest Frogs Found Preserved in Amber

Rodiano Bonacci
Giugno 17, 2018

Together with the Lida Ching from the University of Geosciences in China Blackburn analyzed four amber fossils discovered in the field in the Northern part of Myanmar, the former Burma.

Because it's so young, and only partial, numerous skeletal characteristics herpetologists use to determine how a frog is related to other frogs are either not yet fully formed, or missing.

"It's nearly unheard of to get a fossil frog from this time period that is small, has preservation of small bones and is mostly three-dimensional", the study's co-author David Blackburn, the associate curator of herpetology at the Florida Museum of Natural History, said in a statement.

Since frogs are such an established tropical species nowadays, it's easy to assume that frogs have always been a tropical species, but this the first evidence scientists have to back that up. "These frogs were part of a tropical ecosystem that, in some ways, might not have been that different to what we find today - minus the dinosaurs".

But considering only a literal handful of fossilized frogs in amber have ever been discovered, with the oldest prior one being only 40 million years old, this Electrorana limoae is a great find for amphibian enthusiasts. However, frogs live in just about every habitat on Earth, from scorching deserts to dense tropical rainforests to suburban back yards.

Dr Stanley, from the Florida Museum of Natural History, called the fossil highly valuable because the frog is likely to have lived on the tree, therefore it would be hard for its body to survive for such a long time.

The study determined that frogs, which emerged about 200 million years ago, were living in soggy forested areas at least 100 million years ago. The yellow and vibrant shaped amber is visible and in which one could see the skeletal system with the limbs and the skull distinctively. Over time, the resin turned into amber, leaving the frog remarkably preserved.

One of the most well preserved amber fossils in the lot. Found it was among the amber of Myanmar, which has also found other unique remains of the era: tailed spiders and ants-vampires. "The presence of ribs and a bones in the cartilaginous plate that supports the tongue suggests an affinity with the species alive today, such as fire-bellied toads and midwife toads".

The fossil of Electrorana limoae. But these are Eurasian species that live in temperate, not tropical, ecosystems.

Numerous characteristics which herpetologists use to analyse a frog's evolutionary and life history - the wrist bones, the pelvis, hip bones, the inner ear, and the top of the backbone - are either missing from the fossil or were not yet fully developed in the juvenile frog.

There are still questions that need to be answered about this Cretaceous tropical frog.

In fact, so incomplete are the fossils that scientists gave them a new genus and species rather than attempt to tie them to a known one.

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

Scientific reference: Lida Xing et al, The earliest direct evidence of frogs in wet tropical forests from Cretaceous Burmese amber, Scientific Reports (2018).

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