Paleontologists have unearthed a multitude of fossil footprints in sediments in northwest Argentina, and now there is a burning question they would love to answer: What left the tracks?
At first glance, the answer's easy. The imprints are remarkably similar to those left by modern shorebirds, says Ricardo N. Melchor, a geologist at National University in La Pampa, Argentina. Most of the fossil tracks show three slender toes tipped by small claws, but some also bear the imprint of a small, rear-facing toe called a hallux. Because the th