Venomous Shrew That Survived the Dinosaurs Is Sequenced, Just in Time

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Hispaniolan solenodon (Solenodon paradoxus) is one of the only extant venomous mammals. Its species separated from other insectivores at the time of the dinosaurs.
Hispaniolan solenodon (Solenodon paradoxus) is one of the only extant venomous mammals. Its species separated from other insectivores at the time of the dinosaurs.Credit: Eladio Fernandez / Caribbean Nature Photography

After enormous aggravation, geneticists have managed to sequence the genome of a poisonous shrew-like rodent that thrived between dinosaurs' toes and laughed off the meteor that devastated life on the planet 66 million years ago.

One of the lead authors of the report published today in Gigascience, Dr Juan Carlos Martinez-Cruzado, noted that "local resources are absolutely necessary for this kind of work; only they truly know their animal's behavior." Or, as they elaborated: they appreciate the "local guides who helped them track and ambush passing solenodons at night." In the jungle. In the dark.

Just in time, too. After having outlived the dinosaurs, the last solenodons alive are dwelling in jungle pockets in two islands, Hispaniola and Cuba. That's it.

There are several reasons Hispaniola solenodons hadn't been sequenced yet. One: they're rare. Two: They're nocturnal. Three, four and five: They're not big, though large males can reach a couple of feet in length including the tail; they're venomous; and the few left breathing are doing so on the islands of Cuba and Hispaniola, both Caribbean locations apparently more conducive to holidaying than DNA analysis. Both islands are large but solenodons only live in isolated pockets.

Did we also mention that they burrow? So you have a small animal that you can't find and if you do, it may try to kill you.

But now they have been sequenced. The draft genetic sequence of the Hispaniola solenodon (Solenodon paradoxus)  was published late last week by an international team lead by Dr. Taras Oleksyk from the University of Puerto Rico. Yes, they concluded that the solenodon survived that meteor strike and no, it isn't multiple species on Hispaniola, just one.

Don't stick your finger in its mouth

Solenodons are the only known survivor of a mammalian branch that split off from insectivores (moles, hedgehogs and true shrews) at the time of the dinosaurs, around (it seems) 74 million years ago.

Mammals have been around for over 200 million years, though their real time only arrived after the dinosaurs mostly died off around 66 million years ago.

Early mammals seem to have looked a lot like our solenodon (i.e., ratty). Like it, the first mammals lived at night and ate insects.

Today venom is largely the fief of reptiles like snakes, and fish. But among the mammals of the Cretaceous, venom was apparently a thing, and today's mammals with venom are considered to have retained that characteristic from this extremely distant ancestor.

The solenodon's poison, which seems to be not unlike a snake's neurotoxin, is produced by modified salivary glands and administered by grooves in its lower fangs. It won't kill you, but who needs it.

The Cuban solenodonCredit: New York Zoological Society

Other examples of poisonous mammals include the male platypus, which has a poisonous hind claw; the loris, a primitive primate that licks an arm gland that secretes toxin to render their saliva poisonous; and some shrews.

Other solendon primitive weirdness includes impressively large claws, a protruding, flexible snout with a ball-and-socket joint not unlike the coatimundi, and "oddly positioned teats, which are on their rear," write the scientists. Yes: the mother's nipples are on her butt.

Not having fun

The team seems to crave appreciation. "Carrying out genomics research in remote parts of the Caribbean provided a challenge, particularly in transporting high quality DNA to the lab," the paper says, and goes on to complain that because the DNA couldn't hold out and budgets were scanty, "the commercial lab used to carry out the sequencing turned out a very low coverage per individual."

As said, Hispaniola turns out to have just one species of this ratlike mammal, but it has two subspecies that split – according to this genetic analysis – around 300,000 years. Ergo, the northern and southern populations should be treated as two separate conservation units and may need independent breeding strategies, the scientists suggest.

But with all due respect to breeding strategies, not only does the solenodons' limited range surrounded by (rising) oceans augur ill for these intriguing animals. After tens of millions of years of isolation, the scientists say we have to assume that they're inbred. It is an axiom of genetics that inbreeding reduces diversity which reduces the animal's potential ability to adapt, including for instance to change in climate.

Finally, some might mistake the solenodon for a rat – it's no smaller, and also has a naked tail. They can be quite long-lived, with the Hispaniola variety clocked in at 11 years in captivity and counting. Like rats, they will eat pretty much anything not nailed down or that is nailed down and do not balk at eating earthworms. But though one might think they'd conveniently eat the garbage, they're not ideal pets: they secrete a musk from their little groins that reportedly makes skunks smell pretty good. If you have one, don't hug it.