The fossil Coqui from Puerto Rico receives the title of the oldest Caribbean frog

Researchers attribute a 29 million-year-old partial arm bone fossil to the genus Eleutherodactylus. An ancient frog that could resemble this reconstruction was less than half an inch long. Credit: Jorge Veles-Huarbe

The vibrant twitter of the shell frog, the national symbol of Puerto Rico, has probably sounded in the forests of the Caribbean for at least 29 million years.

New study published in Biology Letters describes the fragmented frog arm bone in the genus Eleutherodactylus, also known as rain frogs or coquís. The fossil is the oldest record of frogs in the Caribbean, and, oddly enough, it was discovered on an island where shells are most popular.

“This is a national treasure,” said David Blackburn, curator of the Florida Herpetology Museum and lead author of the study. "This is not only the oldest evidence of a frog appearing in the Caribbean, but also one of the frogs that are the pride of Puerto Rico and associated with the large Eleutherodactylidae family, which includes Florida's invasive greenhouse frogs."

Jorge Veles-Huarbe, assistant curator of marine mammals at the Los Angeles County Museum of Natural History, discovered a fossil on a river exposed in the municipality of San Sebastian in northwestern Puerto Rico. Veles-Juarbe and his colleagues, who had gathered earlier on this site, discovered fossil seeds, sea cows, turtles with a side neck and the oldest remains of burning and rodents in the Caribbean, dating back to the early Oligocene era, about 29 million years ago.

However, “there have been many visits from which I went empty-handed over the past 14 years,” he said. "I have always kept my expectations not too high for this series of exposures."

Coqu & amp; # 237; fossil from Puerto Rico receives the title of the oldest Caribbean frog

The frog’s fossil arm was found in Oligocene sediments along a river in the municipality of San Sebastian. Credit: Jorge Veles-Huarbe

On this trip in 2012, he combed the deposits for half a day without much luck, when he caught sight of a small bone, partially exposed in the sediment. He examined it with a lens.

“At the moment, I could not understand what it is,” said Velez-Juarbe. "Then, as soon as I got home, cleaned it with a needle to see better, and checked some recommendations, I realized that I had found the oldest frog in the Caribbean."

Ancient Coca crowds out fossil amber frog discovered in the Dominican Republic in 1987 for the title of oldest Caribbean frogWhile amber fossil was originally estimated to be 40 million years old, scientists now date Dominican amber about 20-15 million years ago, Blackburn said.

Based on genetic data and family trees, scientists hypothesized rain frogs He lived in the Caribbean during the Oligocene, but did not have any fossil evidence. Small, light bones of frogs are often poorly preserved, especially in combination with the hot humid climate of the tropics.

Comparing a single bone fragment with a genus or species is "not always an easy process," said Veles-Juarbe. It may also depend on finding the right expert. His search for help in identifying the fossil turned out to be empty until his visit to the Florida Museum in 2017, where he was once a doctoral student.

Coqu & amp; # 237; fossil from Puerto Rico receives the title of the oldest Caribbean frog

Today, frogs in the genus Eleutherodactylus, which include the common shell, dominate the Caribbean, varying in different shapes and sizes. This fossil shows that they have been in the region for at least 29 million years. Credit: Alberto Lopez Torres

“I need to talk to Dave about the projects, and the rest is history,” he said.

Perhaps, having arrived to the Caribbean for the first time on rafts from South America, frogs of the genus Eleutherodactylus dominating in the region today, numbering about 200 species.

“This is the most diverse two-order group in the Caribbean,” Blackburn said. “They diversified into all these different specialists with different shapes and sizes of the body. Several invasive species also come from this genus. All this raises the question of how they should be so. ”

One partial arm bone may not tell the whole story of coca evolution, but this is only the beginning.

“I am very pleased that little by little we will learn about the wildlife that lived in Puerto Rico 29-27 million years ago,” said Velez-Juarbe. "Such findings help us unravel the origin of the animals that we see today in the Caribbean."

Amber fossils are the oldest evidence of the appearance of frogs in tropical rainforests.

Additional Information:
The earliest record of Caribbean frogs: fossil coca from Puerto Rico, Biology Letters,….1098 / rsbl.2019.0947

The fossil Coqui from Puerto Rico receives the title of the oldest Caribbean frog (2020, April 7)
retrieved April 7, 2020

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