Distant Relative of North American Rodents Lived in Puerto Rico 29 Million Years In the past | Paleontology

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

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

Caribeomys merzeraudi lived in Puerto Rico about 29 million years ago during the Oligocene.

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

His discovery challenges the view that all extinct and living Antilles rodents originated in South America.

“This discovery shows that water spread from North America was also a possible route to the Caribbean,” said Dr. Jorge Velez-Juarbe, paleontologist at the Natural History Museum of Los Angeles County.

“This calls into question what we thought we knew about the origins of the land mammals of the Antilles.”

“The teeth from Caribeomys merzeraudi were so unusual that the researchers initially had difficulty identifying what type of animal they came from,” said Lazaro Vinola Lopez, a graduate student at the Florida Museum of Natural History.

“We didn’t know what it was for several months. We wondered if this might be another rodent from the Caribbean or even a strange fish. It was so puzzling because they are not comparable to everything we have found in this region. “

The paleontologists eventually found several tooth features characteristic of rodents known as geomorphs, a group that includes kangaroo rats, pocket mice, and gophers.

Caribeomys merzeraudi is the first geomorph to be found outside of North America.

“Among other features, Caribeomys merzeraudi differs from its relatives in that it has an exceptionally thick layer of tooth enamel and could suggest that these rodents belonged to a particular West Indian branch that evolved in isolation over millions of years,” said Vinola Lopez.

The new species joins two other animal species – an extinct rhinoceros-like species and bizarre, venomous shrews known as solenodons – the only known examples of Caribbean land mammals with North American roots.

“The discovery of Caribeomys merzeraudi opens up the tantalizing possibility that Caribbean mammals of North American origin may not be as extraordinary as previously thought,” said Vinola Lopez.

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

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

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Laurent Marivaux et al. An unforeseen Ancient Colonization of the West Indies by North American Rodents: Dental Evidence of a Geomorph from the Early Oligocene from Puerto Rico Papers in Paleontology, published online July 15, 2021; doi: 10.1002 / spp2.1388