Sauroposeidon (/ˌsɔːroʊpoʊˈsaɪdən/SOR-o-po-SY-dən; meaning "lizardearthquakegod", after the Greek godPoseidon^[3][4]) is agenus ofsauropoddinosaur known from several incomplete specimens including a bone bed and fossilized trackways that have been found in the U.S. states ofOklahoma,Wyoming, andTexas.

Sauroposeidon Temporal range: Early Cretaceous (Aptian–Albian),118–110 Ma[1] PreꞒ Ꞓ O S D C P T J K Pg N
Skeletal reconstruction of the holotype ofS. proteles
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	Saurischia
Clade:	†Sauropodomorpha
Clade:	†Sauropoda
Clade:	†Macronaria
Clade:	†Somphospondyli
Genus:	†Sauroposeidon Wedel, Cifelli & Sanders, 2000
Species:	†S. proteles
Binomial name
†Sauroposeidon proteles Wedel, Cifelli & Sanders, 2000
Synonyms
Superposeidon Brochu, Long, McHenry, Scanlon, & Willis, 2002 (lapsus calami)[2] Paluxysaurus jonesi Rose, 2007

Thefossils were found in rocks dating from near the end of theEarly Cretaceous (Aptian–earlyAlbian), from about 113 to 110 million years ago, a time when sauropod diversity in North America had greatly diminished. It was the last known North American sauropod prior toan absence of the group on the continent of roughly 40 million years that ended with the appearance ofAlamosaurus during theMaastrichtian.

While the holotype remains were initially discovered in 1994, due to their unexpected age and unusual size they were initially misclassified as pieces ofpetrified 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.^[5]

Paleoecological analysis indicates thatSauroposeidon lived on the shores of theGulf of Mexico, in ariver delta. Extrapolations based on the more completely knownBrachiosaurus indicate that the head ofSauroposeidon could reach 16.5–18 m (54–59 ft) in height with its neck extended, which would make it one of the tallest known dinosaurs. With an estimated length of 27–34 m (89–112 ft) and a mass of 40–60 t (44–66 short tons), it also ranks among the longest and heaviest. However, this animal may not be as closely related toBrachiosaurus as previously thought, so these estimates may be inaccurate.

While initially described as abrachiosaurid closely related toBrachiosaurus andGiraffatitan, the discovery of additional remains in theCloverly Formation ofWyoming suggested that it was in fact more closely related to thetitanosaurs, in the groupSomphospondyli. Analysis of these remains and comparison with others fromTexas supported this conclusion, and demonstrated that the more completely known sauropods from theTwin Mountains Formation (including a partial skull and fossil trackways) previously namedPaluxysaurus jonesi also belonged toSauroposeidon.^[6] It is thestate dinosaur ofTexas.^[7]

The first fossils classified asSauroposeidon were four neck vertebrae discovered in ruralOklahoma, not far from theTexas border, in aclaystone outcrop that dates the fossils to about 110 million years ago (mya). This falls within the Early Cretaceous Period, specifically between theAptian andAlbian epochs. These vertebrae were discovered in May 1994 at theAntlers Formation inAtoka County, Oklahoma by dog trainer Bobby Cross and secured by Dr. Richard Cifelli and a team from theOklahoma Museum of Natural History in May 1994 and August 1994. 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 theJournal of Vertebrate Paleontology in March 2000. The new species was namedS. proteles, and theholotype is OMNH 53062. It garnered immediate media attention leading to some sources calling it inaccurately thelargest dinosaur ever.

The generic name comes fromsauros (Greek σαύρος for "lizard"), andPoseidon (Ποσειδών), theseagod inGreek mythology, who is also associated withearthquakes, that facet styled as Ennosigaios or Enosikhthōn, "Earthshaker". This is a reference to the notion that a sauropod's weight was so great that the ground shook as it walked.

Thespecific descriptorproteles also comes from the Ancient Greek πρωτέλης and means "perfect before the end", which refers toSauroposeidon's status as the last and most specialized giant sauropod known in North America, during the Early Cretaceous.

In 2012, numerous other sauropod remains that had been known for decades under various different names were also classified in the genusSauroposeidon.^[6] Sauropod bones andtrackways had long been known from thePaluxy River area of Texas, usually referred to the genusPleurocoelus, including partial skeletons (particularly from theGlen Rose Formation, above the Twin Mountains Formation). In the mid 1980s, students from theUniversity of Texas at Austin discovered a bonebed on a ranch in Hood County, but early work stopped in 1987. The quarry was reopened in 1993 and was subsequently worked by parties fromSouthern Methodist University, theFort Worth Museum of Science and History, andTarleton State University. All sauropod remains from this bonebed appear to come from the same genus of sauropod.Petrified logs are also known from the site. The site wasfluvial when its rocks were being deposited, with channel sands and muds, andconcretions ofcalcite-cementedsandstone containing fossils. Following excavation and preparation of the majority of the fossils from the site, its sauropod species was given the namePaluxysaurus jonesi.^[8]

The namePaluxysaurus wasbased on the specimen FWMSH 93B-10-18, a partial skull including an associated leftmaxilla,nasal, and teeth. Other bones from the quarry included a partial neck of sevenvertebrae, thirteen vertebrae from the back and 30 from the tail, and examples of all limb and girdle bones except some hand and foot bones. It wasdistinguished from all other sauropods by vertebral details, and has variousmorphological differences in other bones compared to other sauropods of the Early Cretaceous of North America. The genus was limited to the bonebed remains; for example, the partial skeleton fromWise County known asPleurocoelus sp. (SMU 61732) is not referred toPaluxysaurus; instead that specimen is the holotype ofAstrophocaudia slaughteri D'Emic 2012, another somphospondylan sauropod. There are differences in the remains ofP. sp. andPaluxysaurus, but they cannot be distinguished with confidence.^[8] In 2012, re-analysis of these specimens in light of additionalSauroposeidon remains led paleontologists D'Emic and Foreman to conclude thatPaluxysaurus was the same animal asSauroposeidon, and thus a junior synonym ofS. proteles.^[6]

The originalSauroposeidon find was composed of four articulated, mid-cervical vertebrae (numbers 5 to 8), with the cervicalribs^{[clarification needed]} 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.^[9] Examination of thebones revealed that they are honeycombed with tiny air cells, and are very thin, like the bones of achicken or anostrich, making the neck lighter and easier to lift.^[9] 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 forGiraffatitan, but exceeded in length by the cervical ribs ofMamenchisaurus.^[5]

Estimates ofSauroposeidon's size are based on a comparison between the fourSauroposeidon vertebrae and the vertebrae of the HM SII specimen ofGiraffatitan brancai, located in theBerlin's Natural History Museum. 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 relatives ofSauroposeidon are difficult due to limited remains.^[5]The neck length ofSauroposeidon is estimated at 11.25–12 m (37–39 ft), compared to a neck length of 9 m (30 ft) for the HM SIIGiraffatitan. This is based on the assumption that the rest of the neck has the same proportions asGiraffatitan, which is a reasonably good conjecture.^[5]

Sauroposeidon was probably able to raise its head 16.5–18 m (54–59 ft) above the ground, which is as high as a six-story building. In comparison,Giraffatitan could probably raise its head 13.5 m (44 ft) into the air.^[10][5][11]

Sauroposeidon's shoulder height has been estimated at 6–7 m (20–23 ft) based on an interpretation of the animal as abrachiosaurid. Estimates of its total possible length have ranged from 27 m (89 ft) to 34 m (112 ft).^{[3][5][12][13]}

The mass ofSauroposeidon is estimated at 40–60 t (44–66 short tons). While the vertebrae ofSauroposeidon are 25–33% longer thanGiraffatitan', they are only 10–15% larger in diameter. This means that whileSauroposeidon probably has a larger body thanGiraffatitan its body is smaller in comparison to the size of its neck, so it did not weigh as much as a scaled-upGiraffatitan. By comparison,Giraffatitan might have weighed 36–40 t (40–44 short tons). This estimate of theGiraffatitan is an average of several different methodologies.^[5][11][13]

However,Sauroposeidon has a gracile neck compared toGiraffatitan. 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 robustApatosaurus weighs far more than the longer but much slimmerDiplodocus. In addition, it is possible that sauropods may have had an air sac system, like those inbirds, 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.

— Matt Wedel,Sauroposeidon team leader^[14]

Sauropods, which include the largest terrestrial animals of all time, were a very wide-ranging and successful group. They first appeared in the EarlyJurassic and soon spread across the world. By the time of the late Jurassic, North America andAfrica 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 t (11–17 short tons), which makes the discovery of an extremely specialized super-giant likeSauroposeidon very unusual.

Sauroposeidon lived on the shores of theGulf of Mexico, which ran through Oklahoma at that time, in a vastriver delta similar to theMississippi delta today. This paleoenvironment, which has been preserved in theAntlers Formation, also stretches from southwest Arkansas through southeastern Oklahoma and into northeastern Texas. This geological formation has not been dated radiometrically. Scientists have used biostratigraphic data and the fact that it shares several of the same genera as the Trinity Group of Texas, to surmise that this formation was laid down during theAptian andAlbian stages of the Early Cretaceous Period, approximately 110 mya.^[15] The area preserved in this formation was a largefloodplain that drained into a shallow inland sea. Several million years later, this sea would expand to the north, becoming theWestern Interior Seaway and dividing North America in two for nearly the entireLate Cretaceous period. The paleoenvironment ofSauroposeidon consisted of tropical or sub-tropical forests,river deltas, coastal swamps, bayous and lagoons, probably similar to that of modern-dayLouisiana.^[16] There were few predators which could attempt to attack a full-grownSauroposeidon, but juveniles were likely to be preyed on by the contemporaryAcrocanthosaurus atokensis^[17] (acarnosaur slightly smaller than aTyrannosaurus), which likely were theapex predators in this region,^[18] and the smalldromaeosaurDeinonychus antirrhopus.Sauroposeidon also shared itspaleoenvironment with other dinosaurs, such as thesauropodAstrodon (Pleurocoelus)^[19] and the most common dinosaur in this region, theornithopodTenontosaurus. Other vertebrates present during this time included theamphibianAlbanerpeton arthridion, the reptilesAtokasaurus metarsiodon andPtilotodon wilsoni, thecartilaginous fishHybodus buderi andLissodus anitae, theray-finned fishGyronchus dumblei, thecrocodiliansGoniopholis,Bernissartia, andPaluxysuchus, and the turtlesGlyptops andNaomichelys.^[20][21] Possible indeterminate bird remains are also known from the Antlers Formation. The fossil evidence suggests that thegarLepisosteus was the most common vertebrate in this region. The early mammals known from this region includedAtokatherium boreni andParacimexomys crossi.^[22]

• A non-technicalarticle on Dino Land, with links to various news reports.