The cave of bones: A story of solenodon survival

By Rebecca Morelle
Science reporter, BBC News, Sierra de Bahoruco, Dominican Republic


Conservationists are in the Dominican Republic attempting to save one of the world's most strange and ancient mammals - the Hispaniolan solenodon.

While trying to track down one of these creatures, The Last Survivors team is also trying to find out exactly how this animal has been able to survive for a remarkable 76 million years.

It is pitch black.

Splashes of light from our torches illuminate patches of the vast cavern we are standing in, every now and then highlighting bats as they swoop above.

Fine dust swirls, coating everything.

The last few remains of a human skeleton sit ominously close to the entrance - but that is not why the scientists are here.

Image caption,
Bones - including some human ones - are easy to find in the cave

It is the piles of tiny bones poking out, here and there, on the sediment and bat dropping caked floor that are attracting all the attention.

We are in a cave nestled in a cliff face in the Dominican Republic's tropical forests. It is reached by a startlingly steep ascent, then a deep drop into darkness.

Scientists think it could hold one of the keys to finding out how the Hispaniolan solenodon has been able to survive for so long, while nearly all other life around it has died out.

'Living fossil'

But before we get to the cave, we need to rewind a little.

Seventy-six million years, in fact. To the time when dinosaurs roamed the Earth.

This is when a hunk of land attached to the great landmass that today forms North America broke away, taking with it some insectivorous mammals - the ancestors of the solenodon.

These creatures might not have looked much different to the animal we are hoping to spot on this expedition.

Conservation palaeontologist Sam Turvey, from the Zoological Society of London who is working on The Last Survivors project and the Edge of Existence Programme, says: "There is this concept of the solenodon being a 'living fossil', because it does seem to have retained certain, potentially ancient, features."

One of these is the groove in its teeth, which allows it to inject venom into passing insect prey - a unique feature, among today's mammals.


This lump of land carrying these strange animals, would later, after a few more breaks and fractures, become the island of Hispaniola, which contains the Dominican Republic and Haiti.

But just 11 million years after it slowly began to drift away from the supercontinent, devastation hit nearby.

Image caption,
This image of a solendon jaw bone shows the groove in its tooth

A colossal space rock, 10-15km across, smashed into the Earth at the northern edge of what is now the Yucatan Peninsula, wiping out the dinosaurs that had dominated the world until that point.

Dr Turvey says: "The Caribbean islands were much closer to the mainland then, and this would have been close to 'ground zero'."

In the immediate aftermath, the impact would have caused massive rises in temperature and giant tsumamis. Later, the planet would have been shrouded in darkness, casting a devastating shadow over any animal hoping to survive.

Yet, while the dinosaurs and much other prehistoric life perished, somehow - and theories abound that it might have been because it burrowed - the solenodon survived.

Image caption,
The impact crater from the giant space rock is buried under Mexico's Yucatan Peninsula and is visible from space

Skip forward a few more tens of millions of years, and the solenodon proves itself a champion survivor once again. First, by coping with the super-hot "greenhouse Earth" of the Eocene Period, then major changes in global ecosystems, and later, the Ice Age.

But stop the clock at 6,000 years ago, and suddenly the plucky mammal had to contend with one of the biggest threats to Caribbean fauna to date - humans.

Before humans arrived, there were about 25 land mammals on the island. But one by one they died out, leaving only the solenodon and a rodent called the The Last Survivors Hispaniolan hutia as the last mammals standing.

What had happened?

Dr Turvey says: "If you want to find the smoking gun responsible for these extinctions, you need to find out exactly when these animals actually disappeared."

And so, back to the cave.

Within just a few moments of entering the dusty tomb, hidden away in a dark corner, we stumble across a fossil treasure trove.

Image caption,
These pygmy sloth bones were discovered in the cave

As the layers of dust are carefully swept away, tiny bones begin to emerge.

"A giant hutia… That's a pygmy sloth… Here's a spiny rat," exclaims Dr Turvey

All several thousand years old. And all now extinct.

Finds like this provide a window into the past: through carbon dating, the researchers can find out exactly when the different species died out.

And then they can see whether the extinctions can be linked to humans or other changes on the island.

No bones?

In his extensive trawls through caves like this one, Dr Turvey has noticed a strange anomaly - a lack of solenodon bones.

He has only found a couple of tiny fragments of ancient solenodons, despite months and months of searching. But fossil finds of now-extinct species have been much more common.

Image caption,
Dr Turvey found few solenodon fossils, such as this tooth

Dr Turvey says: "This raises a lot of important questions - and rightfully so.

"Why did these species die out while the solenodons survived? What were the key ecological differences between these species?"

In their more recent history, solenodons have faced greater threats still.

When Christopher Columbus arrived in Hispaniola in 1492, rats began to leap off his ships onto the island, causing havoc.

But, while others perished, the solenodon survived the rat onslaught.

Dr Turvey thinks the venomous beasts may have been so resilient thanks to what he describes as the "Goldilocks hypothesis".

Very small mammals, such as the now-extinct pygmy shrew, could have easily have become the victims of the black rats.

Whereas the solenodon, which is close to rabbit-sized, probably had fewer problems with rats thanks to its heftier bulk.

Image caption,
The rat invasion can be traced to the arrival of the first Europeans

But while the solenodon is bigger, it is not too big, which according to Dr Turvey, means it probably escaped the attention of hungry humans.

He explains: "If you are hunting something for dinner, you're more likely to go for something like a sloth or a monkey."

So, he says, it is possible that solenodon is a sort of "halfway house" - not too small and not too big.

He adds: "Like in Goldilocks, they're just right."

Ultimate survivors

Whatever happened to make the solenodon the ultimate survivor, allowing it to hang on against all the odds, the researchers fear that more modern problems like deforestation and the threats from very recent introductions, such as mongoose and dogs, could put a stop to its 76-million-year story.

But researchers say that delving into the solenodon's history could help to ensure its future.

As we emerge from the darkness of the cave and begin to prepare for our next night-trek into the forest, where we will try to come face to face with one of these fanged furballs, Dr Turvey takes a last look back into the cave.

Trying to piece together the puzzle of what happened to Hispaniola's mammals in the past, he says, might just help us to figure out how to save these last survivors today.

The Last Survivors project involves Jersey's Durrell Wildlife Conservation Trust, the Zoological Society of London (ZSL), the Hispaniolan Ornithological Society (SOH) and the Dominican Republic's national zoo and environment ministry. It is funded by a grant from the UK Government's Darwin Initiative.

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