In 1913, after 3 years of laboratory work in the Carnegie Museum the big Apatosaurus was on its feet in the Hall of Vertebrate Paleontology—1 of the 4 mounted specimens of this genus in the country and the most perfect of all. Prepared and erected by Arthur S. Coggeshall and his associates, it measures 71½ feet long and stands 15 feet tall at the arch of the back.
As the excavating progressed it was not long before the diggings became what is known to the profession as a “general quarry.” Dinosaurs of “all kinds and sizes” were showing up. Other quarries of this type had been developed in previous years in the Morrison formation at Como Bluff, Wyo., and Canon City, Colo., but they contained nothing like the variety of forms found here. Moreover, these at the monument were better preserved and the skeletons more intact.
The remains most frequently encountered in the diggings were those of sauropods—the huge plant-feeding dinosaurs with long tapering extremities that lumbered about on four pillar-like legs. Camarasaurus and the larger Apatosaurus were typical members of this group, and their numerous bones show them as being common animals of their time.
More common were the Diplodoci, of the exaggerated neck and even longer whiplash tail. This genus distinguished itself by producing not only the largest amount of skeletal material from the quarry, but also the largest number of skulls—those rarest of fossils. One skull was found in exact position with the neck bones, which settled all doubts as to the details of this animal’s head piece. The longest Diplodocus to come from the monument extended 75½ feet.
Contrast this with the diminutive Laosaurus, a 2½-foot biped which ranks as the smallest dinosaur yet taken from the deposit. This tiny creature had hollow limb bones and was one of the agile, quick-running types. Only one was found. When discovered, Douglass thought it a “baby” dinosaur, but study proved it to be a full-grown specimen. The condition of the skeleton reflected considerable agitation before and after burial. It lay on its back, the limbs distended. The tail was gone and the skull crushed.
In many respects, the most interesting dinosaur found was the sauropod, Barosaurus. It was an extremely long-necked form, some of the individual cervical vertebrae measuring 3 feet in length. Two specimens were excavated.
The flesh-eaters, as might be expected from their scarcity in other localities, made but a small showing. Two specimens of Antrodemus were unearthed. Thirty feet long, this animal was the ranking predator of its day, although hardly comparable to the towering Tyrannosaurus that entered upon the earthly scene at a later age.
Stegosaurus remains—so abundant that Douglass grew tired of them—added a bizarre note. An armored form, it was equipped with a frill of bony plates that extended the length of the back and terminated in a pair of sharp spines. Its chief claim to fame rests in its supposed two sets of “brains,” one a motor-control center situated in the hip region, and the other in the usual place.
Everywhere they dug, the excavators found fresh material—a vast jumble of bones so concentrated and intermingled as to make it difficult to distinguish one specimen from another. Douglass was amazed. Obviously, it was not with animals of a single area that he was dealing, but of an entire region. He was dealing with a dinosaur fauna. He was also perplexed. How did so many different types happen to occur in one small locality?
Slowly, as Douglass’s acquaintance with the deposit grew, the answer came. It was, he reasoned, the work of a river. The sandstones were ancient sediments. In their structure and composition lay the story of swift swirling currents. The coarse granular texture told of fast water; the crossbedding, of shifting channels; the grouping of the bones into clusters, of eddies.