Over nine million years ago, a hedgehog-sized shrew nickamed “terror shrew” roamed southern Europe.

Its most distinct feature was its huge dagger-like lower incisor which could tear into the flesh of smaller mammals, possibly even other shrews.

This immense weapon allowed it to feast on more than just insects, which is what most smaller mammals were limited to at the time. That's perhaps where it got its scientific name from: Dinosorex.

Its teeth were also unusually strong, with iron particles naturally built into the enamel. 

And it was extremely successful, the species survived in the area for about three million years, much longer than most mammals are able to stick around for.  

A team led by Marc Furió of Barcelona's Institut Català de Paleontologia Miquel Crusafont, has now studied it in detail for the first time. They outline their analysis in the journal Comptes Rendus Palevol.

For several million years no other insectivore could face the terror shrew. It outsized all the other creatures it encountered, says Furio.

It was literally a jungle out there

One reason it was so successful was the lack of direct competition.

However, about 10 million years ago, new animal groups began to arrive in Europe. This was also when "the rules of the ecosystem changed", Furio says. And this led to some kind of death penalty for the terror shrew.

What exactly changed is not clear. It may be that the climate played a key role in their eventual disappearance.

Co-author Lars Ven Den Hoek Ostende of the Naturalis Biodiversity Center in the Netherlands says: "It was literally a jungle out there, a very tropical climate.

"As long as conditions remain the same, you are safe, but once that changes, and the real [modern-day] shrews start radiating into the success story they are today, you are simply doomed."

The terror shrew disappeared when the seasons began to change more dramatically. "Rather than having a year-round supply of the same food, animals had to adapt to larger differences between summer and winter," says Ostende.

This change could also have resulted in a major abrupt extinction that occurred in the area, the so called Vallesian crisis.

This crisis coincided with the terror shrew's absence from the fossil record, as well as the disappearance of many other mammal in Europe, including apes.

Another downfall for the terror shrew could have been that it did not mould itself to fit into its new environment.

Normally any pressure threatening an animal with extinction also forces it to adapt, but this one critter doesn’t seem to have evolved at all, says Ostende.

The team still don't know the exact reasons that led to the terror shrew's demise. It could simply be that the "true shew" was able to take over because its biological traits were more favourable at that time, adds Furio.

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