They predated the dinosaurs by hundreds of millions of years, and they've survived--albeit in vastly diminished numbers--down to the present day. Now, biologists are worried that the world's amphibians may be imperiled by something called the chytrid fungus, which quickly kills frogs, toads and salamanders. (Bear in mind that there are only 6,000 or so species of amphibians on earth today, so they're not exactly in abundant supply.)

In the past few years, according to British biologists, over 100 species of frog have been wiped out, and any further extinctions could resonate higher up the food chain (for example, many species of birds and snakes subsist on frogs and toads). Although the odds of the chytrid fungus wiping out all amphibians are small, this would be the biggest mass extinction of a single type of animal since the demise of the dinosaurs, 65 million years ago.