In a paper published this week in the journal Scientific Reports, paleontologists have described an extinct genus and species of frog, Electrorana limoae, preserved in mid-Cretaceous (99 million years old) amber from Myanmar.
Four amber-preserved specimens of Electrorana were acquired in the area of Angbamo in Kachin Province of northern Myanmar in 2015.
They provide the earliest direct evidence of frogs living in a wet tropical forest ecosystem and are oldest-known examples of frogs preserved in amber, with the only two previous reports from Cenozoic amber deposits of the Dominican Republic.
“It’s almost unheard of to get a fossil frog from this time period that is small, has preservation of small bones and is mostly 3D. This is pretty special,” said co-author Dr. David Blackburn, associate curator of herpetology at the Florida Museum of Natural History.
“But what’s most exciting about this animal is its context. 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.”
Electrorana limoae is a very small frog, about 0.8 inches (2.2 cm) in snout-vent length.
Clearly visible in the amber are the frog’s skull, its forelimbs, part of its backbone, a partial hind limb and the unidentified beetle.
“Electrorana raises more questions than it answers,” Dr. Blackburn said.
“Many characteristics herpetologists use to discern details of a frog’s life history and determine how it’s related to other frogs are either missing or were not yet fully developed in the juvenile frog.”
“The existing bones provide clues about Electrorana’s possible living relatives, but the results are puzzling: species that have similar features include fire-bellied toads and midwife toads — Eurasian species that live in temperate, not tropical, ecosystems.”
“The discovery of Electrorana helps add to our understanding of frogs in the Cretaceous period, showing they have inhabited wet, tropical forests for at least 99 million years,” the researchers said.
Lida Xing et al. 2018. The earliest direct evidence of frogs in wet tropical forests from Cretaceous Burmese amber. Scientific Reports 8, article number: 8770; doi: 10.1038/s41598-018-26848-w