Scientists have discovered that a modern venomous mammal—which has been described as a “giant rat with Freddy Krueger claws”—actually predates the dinosaurs.
The mammal, which is called the Hispaniolan solenodon, can only be found on (you guessed it) the island of Hispaniola, which includes Haiti and the Dominican Republic. It grows to be about a foot (30 cm) long, and is currently endangered thanks to the introduction of cats and dogs on the island—although it has been around for some 78 million years, having diverged from other living mammals at that time, according to the scientists.
An ancient mammal with an impressive track record
“It’s just impressive it’s survived this long,” said co-first author Adam Brandt, a postdoctoral researcher at Illinois, in a statement. “It survived the asteroid; it survived human colonization and the rats and mice humans brought with them that wiped out the solenodon’s closest relatives.”
Researchers from the University of Illinois and the University of Puerto Rico came to this conclusion after completely sequencing the DNA of solendons’ mitochondria—the part of the cell frequently referred to as its “powerhouse,” which comes complete with its own separate DNA.
Not that getting this DNA was easy—because of their endangered status, solenodon DNA is hard to come by. The team actually had to collect samples by laying on the ground and waiting for the venomous critters to crawl across their bodies. After it all was collected, the researchers then analyzed the samples two different ways in order to sequence the mitochondrial genome—both of which came up with completely identical results.
Then, an expert at Texas A&M used the genes to estimate when solendons diverged from other mammals, which resulted in the date of 78 million years.
This study, which can be found in Mitochondrial DNA, has also filled in the last major branch of the placental mammals on the tree of life by sequencing their mitochondrial DNA (mtDNA). Further, it has supported the notion that there are two genetically distinct subpopulations on Hispaniola, one in the north and one in the south, which should be conserved separately. The researchers also determined that the northern population is much more genetically diverse than the southern population.
Moreover, the date of their evolution fits nicely with a hypothesis regarding how the solendons came to live on Hispaniola. Some geologists have theorized that the island was part of a volcanic arc which was connected to what is now Mexico some 75 million years ago. Over time, it drifted eastward, away from the continent, until arriving where it is today.
“Whether they got on the island when the West Indies ran into Mexico 75 million years ago, or whether they floated over on driftwood or whatever else much later is not very clear,” added lead researcher Alfred Roca.
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