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The tallest dinosaur known, at 60 feet, Sauroposeidon (meaning "earthquake lizard-god") is an Early Cretaceous sauropod related to the Brachiosaurus. The only specimen to date is represented by four neck vertebrae.

Discovery

The vertebrae were discovered, not far from the Texas border, in a claystone outcrop that dates the fossils to about 110 million years ago (mya). This falls within the Early Cretaceous, specificially between the Aptian and Albian epochs.

The four neck vertebrae were discovered in 1994 at the Antlers Formation in Atoka County, Oklahoma by Dr. Richard Cifelli and a team from the Oklahoma Museum of Natural History.

While discovered in 1994, the vertebrae were stored until three years later, when Dr. Cifelli gave them to a graduate student, Matt Wedel, to analyze as part of a project. After realizing the significance of the find, a press release was made in October of 1999, followed by official publication in the Journal of Vertebrate Paleontology in March of 2000. The new species was dubbed S. proteles, and the holotype is OMNH 53062.

Etymology

The genus name comes from sauros (Greek for "lizard"), and Poseidon, a sea-god in Greek mythology, who is also associated with earthquakes. The species name proteles also comes from the Greek, and means "perfect before the end" — which refers to the Sauroposeidon's status as the last, and most specialized giant sauropod known in North America during the Early Cretaceous.

Who's the biggest?

"It's truly astonishing. It's arguably the largest creature ever to walk the earth."

— Richard Cifelli, discoverer of Sauroposeidon

The press release in 1999 immediately garnered international media attention, which led to many (inaccurate) news reports of "the largest dinosaur ever!". While it is true that the Sauroposeidon is probably the tallest known dinosaur, it is neither the longest nor the most massive. The Supersaurus and the Argentinosaurus are better candidates for the title "World's Largest Dinosaur", though weak fossil evidence makes an exact ranking impossible.

The Sauroposeidon find was composed of four articulated, mid-cervical vertebrae (numbers 5 to 8), with the cervical ribs in place. The vertebrae are extremely elongated, with the largest one about 1.2 meters (4 feet) long, which makes it the longest on record. Examination of the bones revealed that they are honeycombed with tiny air cells, and are very thin, like the bones of a chicken or an ostrich, making the neck lighter and easier to lift.

Estimates of size are based on a comparison between the four Sauroposeidon vertebrae and the vertebrae of the HM SII specimen of Brachiosaurus brancai, located in the Humboldt Museum in Berlin. The HM SII is the most complete brachiosaur known, though since it is composed of pieces from different individuals its proportions may not be totally accurate. Comparisons to the other brachiosaurid cousins of the Sauroposeidon would be difficult due to limited remains.

The neck length of the Sauroposeidon is estimated at 37 to 39.5 feet (11.25 to 12 meters), compared to a neck length of 30 feet (9 meters) for the HM SII Brachiosaurus. This is based on the assumption that the rest of the neck has the same proportions at the Brachiosaurus, which is a reasonably good conjecture.

The Sauroposeidon was probably able to raise its head 60 feet (18 meters) above the ground, which is as high as a six-story building. The long neck and the high brachiosaurid shoulders are what makes it the tallest known dinosaur. In some ways, its build is similar to the modern giraffe, with a short body and an extremely long neck. In comparison, the brachiosaur could probably raise its head 45 feet (13.5 meters) into the air, and the previous record holder, the Diplodocus, might have been able to raise its head 50 feet (15 meters).

The Sauroposeidon's shoulders were probably 22 to 24 feet (7 meters) off the ground. Its estimated length is just under 100 feet (30 meters).

The mass of the Sauroposeidon is estimated at 50 to 60 metric tonnes (55 to 65 tons). While the vertebrae of the Sauroposeidon are 25–33% longer than the brachiosaur's, they are only 10–15% larger in diameter. This means that while the Sauroposeidon probably has a larger body than the Brachiosaurus its body is smaller in comparison to the size of its neck, so it did not weigh as much as a scaled-up brachiosaur. By comparison, the brachiosaur might have weighed 36 to 40 tonnes (40 to 44 tons). This estimate of the brachiosaur is an average of several different methodologies.

However, Sauroposeidon has a relatively gracile neck compared to the Brachiosaurus. If the rest of the body turns out to be similarly slender, the mass estimate may be too high. This could be similar to the way the relatively chunky Apatosaurus weighs far more than the longer but much slimmer Diplodocus. In addition, it is possible that sauropods may have an air sac system, like those in birds, which could reduce all sauropod mass estimates by 20% or more.

Environment

"Sauroposeidon was an unexpected discovery, because it was a huge, gas-guzzling barge of an animal in an age of subcompact sauropods."

—Matt Wedel, Sauroposeidon team leader

The Sauroposeidon may be the last of the giant North American sauropods. Sauropods, which include the largest terrestrial animals of all time, were a very wide ranging and successful group. They first appeared in the Early Jurassic, and it wasn't long before they spread across the world. By the time of the late Jurassic, North America and Africa were dominated by the diplodocids and brachiosaurids, and by the end of the Late Cretaceous, titanosaurids were widespread. But in the middle, in the Early Cretaceous, the fossil record is sparse. Most of the other sauropods at the time were dying out, and as a result few specimens have been found in North American from that time, and those specimens that do exist are often fragmentary or represent juvenile members of their species. Most of the surviving sauropods at the time were also shrinking in size (to a mere 50 feet, or 15 meters, in length, and maybe 10 to 15 tons or tonnes), which makes the discovery of an extremely specialized super-giant like the Sauroposeidon very unusual.

The Sauroposeidon lived on the shores of the Gulf of Mexico, which ran through Oklahoma at that time, in a vast river delta, similar to the Mississippi delta today. There were probably no predators who could take down a full-grown Sauroposeidon, but juveniles were likely prey to the Acrocanthosaurus (a carnosaur a little smaller than a T. rex), and packs of Deinonychus.

A giant brachiosaurid similar to Sauroposeidon was described in 2004 by Darren Naish and colleagues, and is from the Early Cretaceous of England. Known only from two neck vertebrae, it was apparently similar in some details to Sauroposeidon and perhaps similar in size. Its discovery highlights the similarity seen between Early Cretaceous North American and European dinosaurs.

References

• "Sauroposeidon proteles, a new sauropod from the Early Cretaceous of Oklahoma", by Mathew J. Wedel, Richard L. Cifelli, and R. Kent Sanders (Journal of Vertebrate Paleontology 29(1), pages 109–114, March 2000).
• "Osteology, paleobiology, and relationships of the sauropod dinosaur Sauroposeidon", by Mathew J. Wedel, Richard L. Cifelli, and R. Kent Sanders (Acta Palaeontologica Polonica 45, pages 343–388, 2000).

External links

• Sauroposeidon's listing in the Guinness Book of World Records.
• A non-technical article on Dino Land, with links to various news reports.
• An interview on Dino Land with Matt Wedel, lead researcher on the Sauroposeidon team at the University of Oklahoma.
• The classification of the Sauroposeidon, at the Dinosauricon.
• Publications of the Sam Noble Oklahoma Museum of Natural History, including the two technical papers listed under References.

• Sauropods