Back when dinosaurs stomped the Earth, dinky mammals scurried about in their shadows. The little furballs, hiding out in underground burrows, provided a fresh niche for a novel reptile: the snake. Skinny snakes could squeeze into the homes of mammals and gobble them up.

At least, that's how the dawn of snakes is imagined by Marc Tollis, an evolutionary biologist at Northern Arizona University in Flagstaff. No one knows for sure. Like the creatures themselves, the snake fossil record is long and thin, leaving gaps in snaky history. Major questions, such as where they got their start and who their closest relatives are, remain unanswered.

Today, new fossils and modern techniques are updating the story of snakes. Starting about 125 million years ago, snakes used their flexible body plans to diversify like crazy, conquering regions that now make up six continents, plus the Indian and Pacific Oceans — and Tollis would not be surprised to find snake fossils in once-balmy Antarctica, either.