Caribeomys merzeraudi: Distant Relative of North American Rodents Lived in Puerto Rico 29 Million Years Ago

Friday, July 16, 2021

This artist’s reconstruction shows the likely position of the fossil molars in the skull of Caribeomys merzeraudi. Image credit: Jorge Velez-Juarbe.

A new genus and species of extinct rodent has been identified from two fossilized teeth found in Puerto Rico.

Caribeomys merzeraudi lived in Puerto Rico during the Oligocene Epoch, some 29 million years ago.

About the size of a mouse, it is the Caribbean’s smallest known rodent and one of the region’s oldest.

Its discovery challenges the view that all extinct and living Antillean rodents derived came from South America.

“This discovery demonstrates that overwater dispersal from North America was also a potential pathway to the Caribbean,” said Dr. Jorge Velez-Juarbe, a paleontologist at the Natural History Museum of Los Angeles County.

“This challenges what we thought we knew about the origins of Antillean terrestrial mammals.”

“The teeth of Caribeomys merzeraudi were so unusual that researchers initially struggled to discern what kind of animal they had come from,” said Lazaro Vinola Lopez, a doctoral student at the Florida Museum of Natural History.

“We didn’t know what it was for several months. We wondered whether this could be some other rodent from the Caribbean or even some kind of strange fish. It was so puzzling because they’re not similar to anything else we had found in that region.”

The paleontologists eventually pinpointed several tooth characteristics that are hallmarks of rodents known as geomorphs, a group that includes kangaroo rats, pocket mice and gophers.

Caribeomys merzeraudi is the first geomorph found outside North America.

“An exceptionally thick layer of tooth enamel, among other features, sets Caribeomys merzeraudi apart from its relatives and could indicate these rodents belonged to a distinct West Indian branch that evolved in isolation over several million years,” Vinola Lopez said.

The new species joins two other types of animals — an extinct rhinoceros-like species and bizarre, venomous shrews known as Solenodons — as the only known examples of Caribbean land-dwelling mammals with North American roots.

“Discovering Caribeomys merzeraudi opens up the tantalizing possibility that Caribbean mammals with North American origins may not be as exceptional as previously thought,” Vinola Lopez said.

“But there’s only one way to find out: ‘Go back to the locality and see what else we can find’.”

The discovery of Caribeomys merzeraudi is reported in the journal Papers in Palaeontology.


Laurent Marivaux et al. An unpredicted ancient colonization of the West Indies by North American rodents: dental evidence of a geomorph from the early Oligocene of Puerto Rico. Papers in Palaeontology, published online July 15, 2021; doi: 10.1002/spp2.1388