[LUM#14] On the Trail of the Rodents of the West Indies
700 kilos of soil to sift through and examine 5 grams at a time. That’s the scale of the project that Pierre-Olivier Antoine and his fellow paleontologists have undertaken on the island of Puerto Rico. It’s a painstaking task with an ambitious goal: to understand how the first land mammals arrived on the Caribbean islands.
“This question is now one of the most challenging mysteries in the natural sciences,” notes the paleontologist fromthe Montpellier Institute of Evolutionary Sciences (Isem*). A mystery that hides another: how were these islands formed from a geological perspective? “We’ve already outlined the broad patterns, but paleontology allows us to refine the scenarios, ” explains Philippe Münch of the Montpellier Geosciences Laboratory**.
Accompanied by paleontologist Laurent Marivaux (CNRS) fromISEM, the twoUM Professors UM an international team in February 2019 in Puerto Rico, where a fossilized rodent incisor, dated to approximately 30 million years ago, had already been unearthed in the early 2010s. Although not very informative, this small tooth revealed the indisputable presence of these animals in the Greater Antilles during that very distant era… But what kind of rodent was it?
The answer turned up in the sieves: armed with patience, the scientists were fortunate enough to discover three more teeth—molars—also dated to 30 million years ago. So rodents were indeed present in those distant times, but where did they come from? Most likely from the South American continent. “These are the oldest known rodents from the Caribbean islands, and they are close, now-extinct cousins of a strictly South American group, the one that includes chinchillas, ” explains Laurent Marivaux.
A valuable clue for geologists. Because if these tiny creatures were able to make the journey, it’s clear there was a passage… “This means that at that time there was a more or less continuous land bridge between the mainland and the islands, or perhaps a myriad of closer islands that would have allowed them to reach Puerto Rico and the rest of the Greater Antilles, ” explains Philippe Münch. The team of geologists is therefore actively searching the islands and the depths of the Caribbean Sea for evidence of these ancient islands that have since disappeared. And paleontologists continue to delve into the question. “Puerto Rican rodents haven’t revealed all their secrets, ” says Pierre-Olivier Antoine.
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*Isem (UM UM CNRS – IRD – EPHE)
**Géosciences Montpellier
(UM CNRS – University of the Antilles) Marivaux, L., Vélez-Juarbe, J., Merzeraud, G., Pujos, F., Viñola López, L. W., Boivin, M., Santos-Mercado, H., Cruz, E. J., Grajales, A., Padilla, J., Vélez-Rosado, K. I., Philippon, M., Léticée, J.-L., Münch, P., and Antoine, P.-O. (2020). Early Oligocene chinchilloid caviomorphs from Puerto Rico and the initial rodent colonization of the West Indies. Proceedings of the Royal Society B.