Period: Late Jurassic
Order, Suborder, Family: Saurischia, Sauropodomorpha, Brachiosauridae
Location: North America (United States)
Length: 90 feet (27 meters)
Ultrasaurus was enormous, which is how it got its name, "ultra reptile." It could be the largest dinosaur known. Ultrasaurus could have peered into fifth and sixth story windows. Walking in a line, only two or three could have fit in a city block, and they were so large that they would have had difficulty turning around except in an intersection.
Like Supersaurus, which also came from the Dry Mesa Quarry in southern Colorado, Ultrasaurus is known only from one bone, a vertebra from the rib region of the body. Other bones from the quarry may also belong to Ultrasaurus, but scientists are not yet positive. The other bones include a shoulder bone (the scapulacoracoid), a vertebra from the neck, and several vertebrae from the tail.
The scapulacoracoid is about nine feet long and is slightly larger than the scapula-coracoids of Supersaurus. It is much more like the shoulder bones of the brachiosaurs. Also, the vertebra from the rib region looks like those of Brachiosaurus, although it may be somewhat larger. Ultrasaurus belongs in the same family as Brachiosaurus, and its body shape resembles that of the brachiosaurs more than other sauropods.
The tall front legs of Ultrasaurus reached a height at the shoulder of perhaps 25 feet, and the long, massive neck could have reached nearly 60 feet above the ground. It had proportions like a giraffe; the front legs were taller than the rear legs and the greatest mass of the body was in the front. The tail was small and short compared to the tails of the diplodocids. The length of Ultrasaurus was probably close to 90 feet, nearly as long as Supersaurus. However, because it was a heavy-bodied brachiosaur, Ultrasaurus was twice as heavy as the other giant sauropods.
Ultrasaurus was a plant-eater, like all sauropods. It ate leaves and needles of conifers and tree ferns and any other plant it could reach. With such a large body, weighing more than 80 tons, Ultrasaurus fed almost constantly, probably always moving to search for food. Herds of Ultrasaurus must have devastated every forest they entered.
The main enemy of Ultrasaurus was the two-ton predator Allosaurus and its relatives such as Ceratosaurus, which were no match for these 80-ton giants. However, packs of Allosaurus could have followed the herds, bothering single animals or babies, or waiting for a sick animal to fall. Like elephants today, though, a healthy adult Ultrasaurus was seldom bothered by predators.
Until more bones from the Dry Mesa Quarry are excavated and identified positively as Ultrasaurus, this poorly known sauropod will be a puzzle for scientists.