Some slender Australian lizards called skinks have gone from being five-fingered to legless (like most snakes) in just 3.6 million years, a new study finds. That's a blink of an eye in geologic time. For comparison, if a 1,000-sheet roll of toilet paper represented all of Earth's geologic history, it is only on the last square of paper that bipedal ancestors of Homo sapiens showed up — about 4.5 million years ago, said Penn State geologist Robert Giegengack, who was not involved in the study. There are 75 species of these fast-evolving skinks called Lerista. These skinks have been crawling and slithering around Earth for about 13.4 million years, and even today, some have five fingers, some have four and some have none, or tiny stubs for legs. So researchers from the University of Adelaide used genetic sequences to arrive at a new family tree for the skinks that showed when and how fast they had lost their fingers or entire legs throughout their evolution.