Free Dinosaurs Without Bones by Anthony J. Martin

which has tracks of about twenty large ornithopods heading in the same direction, and another from the Cretaceous of Canada, which had 10 to 12 ornithopods. A few ankylosaur tracksites have parallel trackways, suggesting that at least two ankylosaurs were traveling together at the same time. So far, stegosaur tracks are so rare we don’t know if these animals were social or not. Ceratopsian tracks are also uncommon enough to withhold judgment on that aspect of their lives too, although rocks bearing hundreds of bones of the same ceratopsian species tell us these dinosaurs were likely group-oriented also.
    Knowing that many mammalian herbivores today travel in sizeable groups, the preceding insights on the social lives of sauropods and ornithopods are probably not big surprises. But what about theropods? Do their tracks ever show that they hung out with one another, shared time in the same place, and hunted together like wolves or other social predators? Oh yes, and in some instances these trackways paint nightmarish scenarios for their intended prey.
    At one site in Middle Jurassic (about 165 mya ) rocks of Zimbabwe, trackways of at least five large theropods, with calculated hip heights of more than 2 m (6.6 ft), indicate they were traveling together. At this site, some of the theropods stepped on each others’ tracks, further suggesting they had some sort of pack arrangement with one or more theropods taking the lead in a loose formation. An Early Cretaceous (about 125 mya ) site in China also shows six theropod trackways, equally spaced and pointing in the same direction, all of their tracks about the same size, 24 to 28 cm (9–11in) long, and with only two toes on each foot. Yes, that’s right, these are dromaeosaurid tracks. The track sizes further indicate hip heights of about 1 to 1.1 m (about 3.5 ft), or slightly smaller than the fictional “ Velociraptors ” of the Jurassic Park movies. Yet these tracks reflect a chilling reality, one in which small or large prey would have been stalked and terrorized by sickle-clawed predators. Running dromaeosaur trackways—which I’ve seen at a spectacular tracksite in Utah—amplify this empathy, whether for the hunter or hunted.
    Dinosaurs Who Stalk and Feed
    Based on what you just learned about dinosaur pack-hunting behavior from tracks, along with other evidence, paleontologists have no doubt that some dinosaurs hunted other dinosaurs, birds, mammals, lizards, and additional animals. For example, gut contents in a few rare specimens tell us directly about a dinosaur’s last meal (which will be detailed in a later chapter). But what happened just before that meal was acquired? How did predatory dinosaurs hunt their prey? And how do tracks provide some insights on dinosaur hunting behaviors? All of these are good questions, and I’ll do my best to answer them through what dinosaur tracks tell us.
    Probably the most famous and longest-known example of a possible “stalking theropod” trackway comes from near Glen Rose, Texas. This trackway, discovered by paleontologist Roland Bird in 1938, was in a limestone bed cropping out in the Paluxy River. He noticed the trackway in direct association with a sauropod trackway, and was thrilled to see how the theropod tracks at first paralleled and then intersected those of the sauropod; at this point, the theropod tracks ceased. Bird surmised that this was where the theropod leaped onto the left side of the sauropod to bring it down, just like a lion would with its prey.
    “Wow, that sounds incredible!” you think. Yes, it does, which also means the story may not be so simple. For one thing, the sauropod tracks continue on past where the theropod tracks stopped, and show no alteration of gait or depth of tracks on the left side. One would think that the addition of a multi-ton predator on one side would cause some reaction, or at least a little bit ofimbalance. So now the more reasonable explanation is that, yes, the theropod