It must have been a traumatic event for the little amphibian. No sooner had it hatched from its egg than something tried to eat it, tearing off its leg. It then landed in a sticky deposit of resin, to be preserved forever in amber. But the tiny salamander’s loss turned out to be researchers' gain, for this little fossil represents the only known evidence that salamanders ever lived in the Caribbean. Today, they are absent from the entire group of islands.
“I was shocked when I first saw it in amber,” said George Poinar Jr. of Oregon State University, an expert on insects, plants and other life forms found entombed in amber, and co-author of the study published in the journal Palaeodiversity. “There are very few salamander fossils of any type, and no one has ever found a salamander preserved in amber. And finding it in Dominican amber was especially unexpected, because today no salamanders, even living ones, have ever been found in that region.”
The researchers describe the species as a member of the Plethodontidae family, a widespread family of salamanders that mostly live in the Americas, ranging from Canada all the way down to Brazil, though a few species are still found in Europe and elsewhere. It is the largest living group of salamanders, with members characterized by their lack of lungs, meaning that they breathe mostly through their skin and the tissue in their mouth. Their living habits range widely; some are fully aquatic, while others reside in trees. But none had ever been found in the Caribbean before.
This artist's image shows what the only salamander ever preserved in amber might have looked like in real life. Credit: George Poinar, Jr./Oregon State University
The remarkable fossil is thought to be around 20-30 million years old, and was found in an amber mine in the northern mountain range of Cordillera Septentrional in the Dominican Republic. After studying the tiny specimen – measuring just 20 millimeters (2 centimeters) in length – the researchers were able to discover some intriguing aspects about its morphology. They were able to get a good look at the three legs that hadn't been gnawed off, which seem to be strangely undefined, almost completely webbed and lacking distinct digits. The researchers say that they’re undecided as to whether this is simply because the young amphibian wasn't fully developed, or if this hints that it wasn’t particularly arboreal – tree climbing – as a species.
What’s even more of a puzzle, though, is how they got there in the first place. The island of Hispaniola, of which the Dominican Republic forms the eastern half, does have many species of frog, so it’s not too difficult to imagine that if they made it there, maybe salamanders did too. There are two current theories: Either they crossed over when the island was still attached to North America around 50 million years ago, or they hitched a ride on floating vegetation.
But that’s not the only thing that intrigues Poinar. “The discovery of this fossil shows there once were salamanders in the Caribbean, but it's still a mystery why they all went extinct,” says Poinar. “They may have been killed by some climatic event, or were vulnerable to some type of predator.”