Origin of West Indian insect eater much older than previously thought

Solenodon

Researcher Mark Springer, a professor of biology at the University of California, Riverside, is part of a team that has traced the origins of the shrew-like Caribbean creatures, known as solenodons, to the Mesozoic era, making them contemporaries with the dinosaurs.

Springer, with colleagues in Maryland, Brazil and the Dominican Republic, examined parts of the genome of solenodons using DNA sequencing to determine that the animals branched off from their insect-eating brethren, which today includes moles, shrews and hedgehogs, some 76 million years ago. The findings were published in the June 10 issue of Nature.

The National Cancer Institute's Laboratory of Genetic Diversity in Frederick, Md., spearheaded the research the resulted in the paper. The institute is trying to put the human genome into context by studying the evolution of other mammals. The solenodon lineage is one of the oldest among placental mammals and is older than more familiar groups such as elephants and their relatives. They are now, however, endangered due to the deforestation of their habitat on the islands of Cuba and Hispaniola.

"For the first time we have a good idea of where solenodon fits into the phylogenetic tree," Springer said. "The timing of the divergence tells us a lot about early mammalian evolution."

For one thing, solenodon, whose last surviving relatives inhabit the Western Antilles, can trace their origins to the era of the dinosaurs, according to the Nature paper. Scientists still are unclear how the creatures ended up on the islands, why they have remained biologically and structurally so unchanged over millions of years, and how they managed to survive the cataclysmic asteroid strike thought to have killed off the dinosaurs about 65 million years ago. As the theory goes, an asteroid, about 10 kilometers in diameter, struck somewhere in what is now the Yucatan peninsula, not far from where solenodon lives today.

It has not been clear whether solenodons arrived in Cuba and Hispaniola via a land connection from North America, dispersed from North America to these islands (for example, by rafting across the sea on vegetation) or somehow managed to come across the ocean from Africa. Recent genetic testing does not completely resolve this issue, but rules out the possibility that the solenodons are related to African insectivores and makes a North American origin more likely.

The latest discoveries about solenodons suggest that scientists rethink their interpretations of the fossil record and closely reexamine the geological record

to see how these creatures got to their current habitat, and when, Springer said.

"It's like a puzzle with a few more pieces now answered but a lot of pieces still missing," he added.

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