What Dinosaurs Walked Here?

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Long before the dinosaurs were scientifically described in the early 19th century, their tracks were known. The strange footprints inspired Native American legends and were said to be “turkey tracks” by some European settlers. The first scientific studies of the tracks concluded that they had been made by ancient birds. Single footprints were impressive, but even more astounding were large slabs that recorded that the hoary birds had flocked together. As the science of paleontology developed, however, scientists realized that these tracks were made by dinosaurs, not birds, and people starting finding more tracks all over the world.

One of the most intriguing recent finds, described in the latest issue of the journal PALAIOS, is what has been informally called a “dinosaur dance floor.” It is doubtful that these animals were rocking out to Was (Not Was), but the 190 million year old Jurassic sandstone nestled in the Arizona-Utah border represents a piece of highly trafficked ground, with tracks laid on top of other tracks. Measuring 100 meters long and 30 meters wide, the trackway has about 12 footprints per square meter, and the photographs from the site show a piece of land pockmarked with holes.

The majority of the identifiable tracks were made by theropod dinosaurs and carry the names Grallator, Anchisauripus, and Eubrontes. If the names sound unfamiliar, it is because footprints are named differently than skeletons are. Unless a dinosaur dies in its tracks and it preserved, it can’t be certain what genus of dinosaur which made each type of track, so tracks are identified based upon tell-tale characteristics and given their own names. Prints left by a sauropod-relative (a sauropodomorph) were also found at the site.

Of particular interest was a tail-drag mark. During most of the 20th century dinosaurs were depicted as animals that dragged their tails on the ground behind them, but the majority of evidence (from skeletons to trackways) showed that dinosaurs held their tails off the ground. The tail-drag mark does not overturn what has been learned about dinosaur posture, but it does indicate that a dinosaur that walked on four feet and had a long, sinuous tail briefly dragged it on the ground.

Why did so many dinosaurs congregate in this one area? The high amount of tracks is certainly unusual, but the answer may have to do with a shortage of water. Around the track site were huge sand dunes that were part of an immense desert, but the tracks themselves were made on a damp surface near an ancient water source. This site may represent a prehistoric watering hole in which many different kinds of dinosaur came to drink (and perhaps some even preyed on the animals that came to quench their thirst).

There is a lot more work to be done at the site, particularly because the paleontologists found a new kind of track they had never seen before. Could this site preserve traces of a dinosaur otherwise unknown to scientists?

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