A surprise finding: 99 million-year-old frog encased in amber

    Abdulaziz Sobh

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    At first glance, the strangely shaped specks that obscure a vibrant yellow piece of amber appear to be amorphous spots. But on closer examination, a form emerges.

    There are two previous extremities. At the end of each limb, there are four smaller bones, forming a shape clearly similar to a hand. Within the larger dark spot, which has a rounded top, the eye sockets become distinguishable. It is a skull.

    Enclosed within the soft piece of amber is the body of a young, small tropical frog. Scientists say the tiny bug, which is less than an inch long, lived about 99 million years ago before being buried in the sap of the sticky tree. At that time, the dinosaurs were still roaming the Earth.

    The fossil is one of four dating from the Cretaceous period, providing scientists with the earliest direct evidence that frogs inhabited humid tropical forests, according to a statement from the Florida Museum of Natural History. The findings were published Thursday in Nature's Scientific Reports.

    "It's almost unheard of to get a fossil frog from this time period that is small, has small bone preservation and is primarily three-dimensional," said study co-author David Blackburn, associate curator of herpetology at the Florida Museum of Nature. History, he said in a statement. "This is very special."

    The fossils include a skeleton of a frog that was complete enough for scientists to identify it as a new species, called Electrorana limoae, according to the study. The other fossils contain two hands and a footprint of a frog that probably rotted inside the amber.

    "Honestly, I'm still amazed that there are even frogs found in amber," Blackburn told Gizmodo. "It's a remarkable experience to hold these little gems and see the parts of the frogs that seem to have been there last month."

    While frogs have existed for more than 200 million years, their fossil record is sparse and usually biased towards arid and seasonal species, not small rainforest inhabitants, the statement said.

    But now, with the discovery of the four small lumps of amber originally excavated in northern Myanmar, Blackburn said scientists know that frogs have lived in environments similar to those of rainforests for at least 99 million years.

    "These frogs were part of a tropical ecosystem that, somehow, could not have been so different from what we found today, except dinosaurs," he said.

    In addition to giving scientists a glimpse into the life of ancient frogs, fossils are also the oldest known examples of frogs preserved in amber. The fossils previously found in the Dominican Republic date back to about 40 million years ago.

    The fossils were a "miraculous" find, Lida Xing, another of the study's authors and paleontologist at the Chinese University of Geosciences in Beijing, told BBC News.

    "In China, frogs, lizards, and scorpions are called three treasures of amber," Xing said.

    Beyond the rarity of the discovery, fossils are essential to help scientists learn more about the evolutionary history of frogs.

    "Our skeleton comparisons of these new frog fossils indicate that these frogs preserved in amber were 'real frogs' and may represent one of the oldest lineages seen today," Blackburn told Popular Science.

    Despite everything they have learned from tiny remains, Blackburn said, there are still many unanswered questions. Many features such as the bones of the wrist, pelvis, hip bones, inner ear and upper part of the spine are used by herpetologists to discover details of a frog's life and determine its relationship to other frogs says the statement. Unfortunately, in recently discovered fossils, those crucial parts either were missing or had not fully developed in the young frog.

    Blackburn said he continues to wait for other frogs to be discovered in amber.

    "We do not have many communities of frogs of a single species in the forests," he said. "It seems extremely unlikely that there is only one." There could be many more fossils on the way. "

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