An alarming new study has bad news for us, and other relatively large vertebrates — we probably would get wiped out in a mass extinction event. But tiny critters would fare a lot better.

But why is that? A fascinating new study is shedding some new light on that based on fish that died 350 million years ago after the so-called Hangenberg event wiped out a huge number of species, according to a Christian Science Monitor report.

Scientists at the University of Pennsylvania found that large vertebrates get wiped out in mass extinction events, and the only creatures to survive in the ocean after this event were about the size of a sardine — not a single whale to be found.

So what’s the difference? It’s not because they can more easily find food or shelter — it’s because they reproduce way faster than bigger creatures, and that’s the key to survival in extreme conditions.

Smaller creatures tend to have shorter lifespans and tend to breed much quicker, making them ideally suited for more hostile environments where life is short. Large vertebrates, meanwhile, must spend several years raising young to the point where they can fend for themselves, and that puts them at a unique disadvantage. It’s also why we’d be extremely vulnerable to a mass extinction event.

One theory suggests that larger vertebrates come about as life settles down on the planet and a species can “focus” on growing in size in order to better avoid predation and live longer lives. Another theory suggests that as oxygen increases or as the temperature drops, creatures will tend to get bigger.

Either way, the findings are certainly concerning for us humans, especially since scientists think we may be on the verge of a sixth mass extinction. And it’s all our fault, too.

Still, if we can get our act together with better and more aggressive conservation efforts, perhaps we can avoid this extinction and save ourselves in the process.