The Ears Have It: First Snakes Were Burrowers, Not Swimmers

摘要

Did the first snakes crawl on the land or swim in the water? It's one of paleontology's sharpest debates, pitting those who think that four-legged snake ancestors lost their limbs to become more efficient swimmers against those who believe that the demands of burrowing were key. The final verdict has yet to come in, but a new study of snake inner ears, presented at a paleontology conference* here, bolsters the view that today's snakes evolved from terrestrial, burrowing ancestors. "We keep finding new evidence that keeps [the debate] alive," says paleontologist Thomas Holtz of the University of Maryland, College Park. Today, the majority of the world's 3500 species of snakes are terrestrial. But in 1997, paleontologist Michael Caldwell of the University of Alberta in Edmonton, Canada, and his colleagues reported the discovery of Pachyrhachis, a marine fossil snake that still had hind legs. They argued that the 100-million-year-old fossil pointed to extinct aquatic lizards-agile swimmers called mosasaurs-as the ancestors of snakes.