About 170 million years ago, huge, long-necked dinosaurs called sauropods left hundreds of footprints on the floor of a shallow saltwater lagoon on a warm island in the midlatitudes. Now preserved in ancient layers of limestone and sandstone that are exposed only during low tide (and considerably farther north of where they were originally made, thanks to the gradual migration of Earth’s tectonic plates), the fossilized tracks are the first ever found made by these creatures in Scotland. The site provides new information about the region’s sauropods, which were previously known only from fragments of a tail bone, a leg bone, and a few bits of teeth—scraps so small that researchers couldn’t assign the fossils to a particular species or even estimate its size. With the new tracks, however, Scotland’s sauropods are beginning to come into focus. Impressions left by a large claw on the innermost toe on the dinosaur’s front foot (the analog of the human thumb) indicate that the still-unknown species was located near the base of the sauropod family tree, and the sizes of the footprints—in some cases 70 centimeters across—suggest that the behemoths grew to reach 15 meters in length and weighed up to 10 metric tons, the researchers report online today in the Scottish Journal of Geology. (That’s small for sauropods; in later eras, some dinosaurs in the group stretched almost twice as long and weighed six times as much.) The footprints were apparently made in water deep enough to have remained submerged even at low tide, which raises the question of what the dinosaurs were doing in waters that deep. Although the Jurassic beasts could have been foraging for shallow-water vegetation, they may have been avoiding predators or maybe even cooling their bodies with a dip in the surf.