ALLOSAURUS — FOOTPRINTS IN DEEP TIME Because New Mexico contains a well-exposed, nearly complete record of the geologic formations through time (stretching back over 500 million years of the a roadrunner, and considerably faster than an Paleozoic, Mesozoic, and Cenozoic Eras), the state average human. Allosaurus was capable of kill- has a phenomenally rich fossil record. The many ing healthy, medium-sized sauropods (long- local discoveries of dinosaurs, prehistoric reptiles, necked herbivores), and they may have and extinct mammals include one of the earliest hunted in packs. dinosaurs, many of the planet’s fiercest preda- Allosaurus was among the earli- tors, some of the largest animals to ever walk, est dinosaur discoveries, and its fossils and bizarre giant reptiles and birds. Due to its are abundant. It was first unearthed in outstanding exposures of Mesozoic rocks that Colorado in 1877, and named by Yale paleontolo- represent ancient river systems where creatures gist Othniel Charles Marsh. The name Allosaurus would congregate for food and water, the Rio Chama is derived from the Greek “allos" (different) and watershed is a hub of dinosaur discovery. “sauros” (lizard), so-named because its vertebrae At the top of the Jurassic food chain was the differed from other known dinosaurs. Although theropod dinosaur Allosaurus, the largest land-based Marsh’s specimen consisted of only a few fragments of predator of the time. Allosaurus reigned supreme for the dinosaur, many more were later collected, and in 5 million years, from 155.7 to 150.8 million years ago. 1991, a Wyoming team unearthed "Big Al” which was Although smaller than T. rex (the top Cretaceous pred- 95 percent complete. ator) it was an imposing creature, Although no skeletons have been growing over 30 feet long, 16 feet reported along the river, a fantas- tall, and weighing over 3,300 tic Allosaurus fossil trackway pounds. The largest living the- exists in a nearby side ropod is the common ostrich, canyon. Most Allosaurus fossils which grows to 9 feet tall are from the Morrison and can weigh 320 pounds. Allosaurus had a short neck and a huge, elongated skull. The mouth contained dozens of sharp, serrated Formation; teeth, which were commonly this trackway is lost during feeding, but rapidly in the Summerville regrown. The teeth were thinner Formation. Paleontolo- and sharper than T. rex, adapted to gists measure tracks to deduce cut meat rather than crush bones. walking and running speeds, and Despite its large skull, Allosaurus social behavior, such as herding had a bite that was likely weaker and pack hunting. Fossil foot- than alligators, lions, or leopards. prints are a rare, nonrenewable Allosaurus had short, strong resource. If you are lucky enough front limbs armored with three, to find trackways, please preserve hook-shaped claws. The massive body and protect them. was supported by two powerful hind legs and a large tail. Each foot had three weight-bearing toes and an inner dewclaw. Models suggest Allosaurus could run up to 21 mph, about equal to the top speeds of a grizzly bear or