Sauroposeidon (pronounced SAWR-o-po-SIE-don, meaning "earthquake-lizard god") is a genus of sauropod dinosaur known from four neck vertebrae that were found in the southwestern portion of the US state of Oklahoma. The fossils were found in rocks dating to the Early Cretaceous, a period when the sauropods of North America had diminished in both size and numbers, making it the last known giant dinosaur on the continent. While the fossils were discovered in 1994, due to their unexpected age and unusual size they were initially misclassified as pieces of petrified wood. A more detailed analysis in 1999 revealed their true nature which resulted in a minor media frenzy, and formal publication of the find the following year.
Paleoecological analysis indicates it lived on the shores of the Gulf of Mexico, in a river delta. Like other brachiosaurids, Sauroposeidon was a quadrupedal herbivore with longer forelimbs than hindlimbs, a similar body design to the modern giraffe. Extrapolations based on its more completely known relative Brachiosaurus indicate that the head of Sauroposeidon could reach 17 m (56 ft) in height with its neck extended, making it the tallest known dinosaur. With an estimated length of 30 m (98 ft) and a mass of 36–40 MT (40–44 short tons) it also ranks among the longest and heaviest.
The vertebrae were discovered in rural Oklahoma, 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 Period, 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. Initially the fossils were believed to be simply too large to be the remains of an animal, and due to the state of preservation, believed to be tree trunks. In fact, they are the longest such bones known in dinosaurs.
Thus, the vertebrae were stored until 1999, when Dr. Cifelli gave them to a graduate student, Matt Wedel, to analyze as part of a project. Upon their realization of the find's significance, they issued a press release in October 1999, followed by official publication of their findings in the Journal of Vertebrate Paleontology in March 2000. The new species was dubbed S. proteles, and the holotype is OMNH 53062.
Size comparison of Sauroposeidon to a human. (*)
The generic name comes from sauros (Greek for "lizard"), and Poseidon, a sea-god in Greek mythology, who is also associated with earthquakes, that facet styled as Ennosigaios or Enisokhthōn, "Earthshaker". This is a reference to the notion that a sauropod's weight was so great that the ground shook as it walked.
The specific descriptor proteles also comes from the Ancient Greek and means "perfect before the end", which refers to Sauroposeidon's status as the last and most specialized giant sauropod known in North America, during the Early Cretaceous.
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 Sauroposeidon is probably the tallest known dinosaur, it is neither the longest nor the most massive. Argentinosaurus is a better candidate 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 having an overall length of 1.4 m (4.6 ft), making it the longest sauropod neck vertebra 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. The cervical ribs were remarkably long as well, with the longest measurable rib (on vertebra 6) measuring 3.42 m (11.2 ft) – about 18% longer than the longest rib reported for Brachiosaurus, but exceeded in length by the cervical ribs of Mamenchisaurus.
Estimates of Sauroposeidon's 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 relatives of Sauroposeidon are difficult due to limited remains.
The neck length of Sauroposeidon is estimated at 11.25–12 m (37–39 ft), compared to a neck length of 9 m (30 ft) for the HM SII Brachiosaurus. This is based on the assumption that the rest of the neck has the same proportions as Brachiosaurus, which is a reasonably good conjecture.
Sauroposeidon was probably able to raise its head 17 m (56 ft) 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, Brachiosaurus could probably raise its head 13.5 m (44 ft) into the air.
Sauroposeidon's shoulder height was probably 6–7 m (20–23 ft) and its estimated length is just under 30 m (98 ft).
The mass of Sauroposeidon is estimated at 50–60 MT (55–66 short tons). While the vertebrae of Sauroposeidon are 25–33% longer than Brachiosaurus', they are only 10–15% larger in diameter. This means that while Sauroposeidon probably has a larger body than Brachiosaurus its body is smaller in comparison to the size of its neck, so it did not weigh as much as a scaled-up Brachiosaurus. By comparison, Brachiosaurus might have weighed 36–40 MT (40–44 short tons). This estimate of the Brachiosaurus is an average of several different methodologies.
However, Sauroposeidon has a relatively gracile neck compared to 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 robust Apatosaurus weighs far more than the longer but much slimmer Diplodocus. In addition, it is possible that sauropods may have had an air sac system, like those in birds, which could reduce all sauropod mass estimates by 20% or more.
Sauroposeidon was an unexpected discovery, because it was a huge, gas-guzzling barge of an animal in an age of subcompact sauropods.
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 (though only in the southern hemisphere). Between these periods, in the Early Cretaceous, the fossil record is sparse. Few specimens have been found in North America 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 15 m (49 ft) in length, and maybe 10–15 MT (11–17 short tons), which makes the discovery of an extremely specialized super-giant like Sauroposeidon very unusual.
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 Acrocanthosaurus (a carnosaur a little smaller than a T. rex) and to 'packs' of Deinonychus.
A giant brachiosaurid, similar to Sauroposeidon, was described in 2004 by Darren Naish and colleagues and is from the Early Cretaceous period 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.
1. ^ a b Wedel, Mathew J.; Cifelli, Richard L. (Summer 2005). "Sauroposeidon: Oklahoma's Native Giant" (PDF). Oklahoma Geology Notes 65 (2): 40–57, http://sauroposeidon.net/Wedel-Cifelli_2005_native-giant.pdf.