Greater Caribbean land frogs (aka robber frogs; genus Eleutherodactylus) are the most numerous group of amphibians in the region with over 240 known species. Of these, possibly the most well known species is the common coquí (Eleutherodactylus coqui), considered as a symbol of national pride in Puerto Rico, but a nuisance in other places where they have been introduced, like Hawaii and California. With so many different species spread across the Caribbean it makes one wonder, how long did they arrive to the region? Well, today (April 8, 2020) we published a new discovery that can help answer that question.
Today my colleagues David Blackburn, Rachel Keeffe and Maria Camila Vallejo-Pareja from the Florida Museum of Natural History and I described a fossil that represents the oldest fossil frog from the Caribbean region! In this work, published in the scientific journal Biology Letters, we describe in great detail a small bone that represents the oldest record of a frog belonging to the genus Eleutherodactylus or coquí frog, as they are known in Puerto Rico. The fossil was discovered in a locality in northwestern Puerto Rico, in sediments that were deposited between 31-29 million years ago. This new locality is very close to the one that yielded the oldest Caribbean rodents, which was published last February. Prior to our discovery, the oldest record of a fossil Eleutherodactylus was from the early Miocene of the Dominican Republic (~20-15 Ma), thus our find extends the record of this group by about an additional 10 million years.
Top: map of Puerto Rico showing the distribution of Oligocene-Miocene deposits.
Center: the fossil site (left) and the fossil humerus (right) described in our paper.
Bottom: interpretive illustration of the fossil coqui from Puerto Rico.
The fossil consists of the distal end of a humerus (arm bone) which shows diagnostic characteristics that allowed us to identify it as a frog, and more specifically as a member of the genus Eleutherodactylus. This species-rich group of frogs share common ancestors with other groups of frogs from South America, where there are other species of Eleutherodactylus as well. With few exceptions, this is consistent with a South American origin for the majority of terrestrial vertebrates in the Antilles. One of those rare exceptions is the presence of the salamander Palaeoplethodon hispaniolae a group that is completely absent in the region and whose closest relatives are in North America.
|Comparison of the fossil coquí from Puerto Rico with other species of Eleutherodactylus (top) and other related subgenera (bottom). (Modified from Figure S1 of our work).|
|Comparison of the fossil coquí from Puerto Rico with representatives of other Eleutherodactylus subgenera and with other Caribbean anurans. (Modified from Figure 2 of our work).|
Finding the oldest coquí frog sure is exciting, as it represents a unique record that extends the presence of this group to the early Oligocene. Based on this discovery, in combination with some molecular divergence estimates, we can hypothesize that the initial colonization of Eleutherodactylus in the Caribbean likely took place under the same conditions which facilitated the arrival of other terrestrial vertebrates, like sloths and rodents, during the late Eocene-early Oligocene, as discussed in this previous post.
|A male common coquí (Eleutherodactylus coqui) guarding its egg clutch.|
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