Sauroposeidon proteles (SAWR-o-po-SYE-don pro-TEL-ees) is a one-of-a-kind dinosaur. In 1994, vertebrate paleontologist Richard Cifelli and his team from the Sam Noble Oklahoma Museum of Natural History at the University of Oklahoma found four vertebrae of one of these dinosaurs in southeastern Oklahoma. Each vertebra measures four feet or more in length. The bones were so enormous that Cifelli himself was unsure what he had uncovered at first.

"I thought we had a petrified tree trunk," Cifelli said. "I just could not get my mind around the size of these bones."

Once a closer look had confirmed that the find was, indeed, fossilized bones, Cifelli knew he had something special. No neck bones of this size had ever been found.

In the lab, the bones revealed more surprises. One of Cifelli's graduate students named Matt Wedel, now a paleontologist at the University of California at Merced, ran one of the vertebra through a CT scanner—a high-tech x-ray machine that creates a three-dimensional image of the inside of an object. The scans showed him that, despite their size, the fossils are extremely delicate. The vertebrae are full of air pockets surrounded by thin membranes of bone—in some place the bone is no thicker than a fingernail. These holey bones are very similar to those of modern birds. The air pockets make the bones lighter, without making them any less strong.

Cifelli and Wedel named the new dinosaur Sauroposeidon proteles. Poseidon was the Greek god of earthquakes, and certainly the earth must have quaked under the feet of this mighty beast. "Proteles" means "perfected before the end," because this enormous dinosaur was one of the last and most specialized of its kind. It lived during the Cretaceous Period, around 110 million years ago. Though there were many long-necked dinosaurs in North America during the earlier Jurassic Period, there were fewer and fewer in the Cretaceous, and they finally disappeared around 100 million years ago. Sauroposeidon was among the last and mightiest of a dying breed.

Sauroposeidon seems to be a relative of Brachiosaurus, and like Brachiosaurus, probably held its neck upright like a giraffe, rather than out in front of it like the Apatosaurus. Sauroposeidon would have been much larger than Brachiosaurus, however. Cifelli and Wedel believe Sauroposeidon would have been nearly 100 feet long and stood some 60 feet tall. It could have stood flat-footed and looked into a sixth story window. Sauroposeidon is recognized by the Guinness Book of World Records as the world's tallest dinosaur.

Despite several return trips to the site of the initial find to search, no additional fossils of Sauroposeidon have been uncovered.

"The chances of finding more are remote," admitted Cifelli. Compared to the light-weight neck bones, most of the dinosaur's other bones would have been very large and heavy. If the skeleton had still been all together when it was fossilized, the team would have found other bones nearby. It is likely that the neck bones were moved—by water or predators, for example—away from the rest of the dinosaur's body. There is no way of knowing where to look.

Nevertheless, visitors to the Sam Noble Oklahoma Museum of Natural History need now look no further than the museum's Great Hall to get a glimpse of this record-setting dinosaur. A reconstruction of the forty-foot neck and head of Sauroposeidon can be seen peeking out into the Great Hall from the museum's new Orientation Gallery, which will open March 29, 2009.