After more than three years of battling the elements of an Arizona Desert that can broil a careless lizard or frostbite fingers, a team comprised mostly of dedicated field and lab volunteers led by this writer, the excavation of Pima County's grand dinosaur has come to a close. After moving more than 100 tons of rock, it is likely that few if any important bones remain in the mountainside excavation. This dinosaur, a 55 foot long, 25 foot tall, longneck monster apparently unique to southern Arizona has formally been described by myself in the Journal of the Arizona-Nevada Academy of Science and named Sonorasaurus thompsoni ratkevich. Everything about this animal is so new that leading dinosaur specialists agree to its uniqueness. Sonorasaurus belongs to a group of long-neck giants called brachiosaurs, the largest animals ever to walk the earth.
Sonorasaurus: Dinosaur of the Desert is a small book I wrote as Paleontologist for the Arizona-Sonora Desert Museum. It's a nice story of the discovery and work on this Arizona Dinosaur. A box of them just surfaced and I'd be happy to pass one along to you for $3.50 plus $2 shipping etc. Send me an email to and I'll see you get a copy.
Sonorasaurus was probably the last living Brachs
Sonorasurus likely weighed as much as an entire herd of elephants, and lived entirely on dry land, rarely if ever venturing into the water as was once thought.
From tooth gouges found on it's bones it is likely that this individual was killed and eaten by one of the large tyrannosaur-like monsters of the time. The single blade-like tooth of a huge meat eater called Acrocanthosaurus was found near the bones and suggests that this was the predator that killed Sonorasaurus. The fact that many of the bones are missing from the skeleton is no surprise since one bite from Acrocanthosaurus could have ripped off more than 400 pounds of meat and bone, and since we know that these predators hunted in packs, that's a lot of flesh and bones that were swallowed and carried away.
Sonorasurus, meaning dinosaur found in the Sonoran Desert, was discovered in 1994 in a remote southern Arizona canyon in the South East part of Pima County. It's bones were discovered by a University of Arizona student Richard Thompson. The dinosaur's full scientific name Sonorasaurus thompsoni honors the discoverer Rich Thompson. Very few people have ever found a dinosaur, especially in Arizona, and this specimen is proving to be one of the most important ever found, for not only were the bones found, but a great deal of fossilized tissue was uncovered. The bones remain and are being prepared by experienced volunteers.
In the photo at right, the remains of Sonorasaurus are exhibited in a fairly faithful reconstruction of the of the Sonorasaurus site showing a composite of how many of the bones were seen in place.
I often stood looking at the original bone bed in the Turney Ranch Formation and imagined the carcass of this brachiosaur being ripped apart by a hunting pack of acrocanthosaurs, much like a whale today is dismembered by schools of hungry sharks.
A number of gastroliths, or stomach stones were found with the dinosaur. Since Sonorasaurus had no grinding teeth, these fist-size rocks were swallowed by the dinosaur and made their way into the animal's gizzard where they aided in digestion by grinding tough plant material into pulp that was mixed with digestive fluids. The rough rocks were eventually rounded and by rubbing together for a long time in the gizzard they took on a high polish, much like what happens in a rock tumbler. Some modern birds will swallow stones, which then reside in their gizzards and aid in digestion of food by helping to grind tough food material.
We found lots of gastroliths within the body cavity
Because birds do not have teeth, they need their gizzards to grind their food, which helps to increase the surface area of the food for easier digestibility. Stones used to help in the mechanical breakdown of food within a digestive tract are called gastroliths ("gastro" = "stomach" and "lith" = "stone") and a colloquial term for gastroliths is "gizzard stones." Apparently dinosaurs also swallowed stones for the same reason as birds; numerous polished stones are associated with some dinosaur remains and are especially convincing when found within the thoracic regions of a skeleton. These stones are typically smooth, polished, and oblate to semispherical.
Geological studies of the rocks, told me much about the dinosaur's habitat. So far, we know the animal lived in a pine covered upland region, not far from a shallow sea. A great deal of petrified wood can be found at the Sonorasaurus site, and it belongs to a form of conifer called Brachioxylon. I believes that the kinds of rock found in the dinosaur's gizzard, tells us that Sonorasaurus traveled as far as the distance from the Whetstone Mountains to Roosevelt lake in Central Arizona, likely on a yearly migration.
Originally plans were to reconstruct the entire 55 foot long skeleton, the exhibit was scaled down to become an in situ exhibit, outside Desert Museum's Earth History Gallery, showing the bones as we uncovered them, and a restored front limb of the animal. Perhaps in the future a more complete exhibit of a reconstructed skeleton will come to be. Even though not a skeleton, the exhibit is impressive and will tell the story of Pima County's grand dinosaur, its place in the Mid Cretaceous habitats of what was to become southeastern Arizona, and Sonorasaurus' place in the evolution of sauropod dinosaurs.
At 55 feet in length, Sonorasaurs was small for a brachosaur. A juvenile? Female? Or was it just a small species?
Like an elephant, Sonorsaurs walked on its toes.