Free Dinosaurs Without Bones by Anthony J. Martin Page B

selection of what I think are provocative perspectives on dinosaurs bestowed by their tracks, and that we might not have ever figured out from bones alone.
    Imagine you are a small theropod dinosaur, out on a walkabout one fine Jurassic day, on the prowl for food or mates, and not necessarily in that order. As you stride over some slightly bumpy terrain,you smell something interesting in a meter-wide mud-filled pit. As soon as you jump into the pit to investigate, your feet start sinking into the saturated mud and you suddenly realize you’re stuck. Even worse, as you struggle to free yourself, you’ve further liquefied the mud and caused it to envelop you even more. At some point you just stop flailing because you can’t move. You’ve just been buried alive.
    During the next few days, several others of your species make the same mistake. A few make it out, but most others, including additional species of dinosaurs, likewise become stuck and die. Meanwhile, the sauropods that unwittingly made these traps are already miles away, having no idea that they contributed to the asphyxiation and fossilization of these small theropods. Their deep tracks, pushing down into the moist substrate, had created new hazards for smaller animals, which fell in and became mired in the squishy track interiors.
    Oddly enough, the preceding scenario is exactly what three paleontologists proposed to explain how some exquisitely preserved small theropods in Middle Jurassic rocks of western China were unwillingly ushered into the fossil record. In a 2009 journal article with the beguiling title of “Dinosaur Death Pits from the Jurassic of China,” the researchers—David Eberth, Xu Xing, and Julia Clark—proposed that specimens of the small theropod Guanlong wucaii had fallen into 1 to 2 m (3.3–6.6 ft) deep mud-filled pits made by large sauropods similar to the Late Jurassic Mamenchisaurus . Guan-long wasn’t the only animal to suffer such a fate at the feet of these sauropods, either, as the theropod Limusaurus and about twenty other species were entombed in these tracks. What all of these dinosaurs had in common was that they were small and bipedal, meaning they lacked sufficient limb strength to yank themselves out of their morasses. More than 160 million years later, those dinosaurs’ misfortunes became paleontologists’ treasures, as this unusual mode of death and fossilization resulted in beautifully complete skeletons of scientifically significant species. All thanks to the sauropod tracks.
    But let’s say your timing was even worse, and you just happened to be in the same place where a dinosaur foot—with the rest of aliving dinosaur attached to it—happened to land. If the dinosaur was Microraptor or some other similarly puny feathery theropod, then no big deal, unless you were a small insect. But if the foot belonged to a tyrannosaur, ceratopsian, ankylosaur, stegosaur, or sauropod, then that was a problem for any animal smaller than that foot. Sure enough, a few fossils, such as snails and clams, found in dinosaur tracks were crushed underfoot, although we can’t tell for sure whether they were alive or already dead when stomped.
    Dinosaur tracks can also sometimes tell us if a given dinosaur had any health problems. We know a fair number of dinosaur bones show evidence of having been broken and later healed, but it’s difficult to say whether these had an effect on an animal getting around, either while healing or afterwards. Fortunately, dinosaur trackways are abundant enough that some with asymmetrical gait patterns pop out. In these trackways, one side of the body stepped less distance than the other, resulting in noticeably unequal strides. The easiest explanation for these imbalanced patterns is that these dinosaurs were compensating for a weak leg, such as one injured from an accident or combat.
    One theropod trackway in a Late Jurassic stratum in Utah leaves no doubt that its maker had a tough time walking, showing