Sauroposeidon

''Sauroposeidon'' ( ; meaning "lizard earthquake god", after the Greek god Poseidon) is a genus of sauropod dinosaur known from several incomplete specimens including a bone bed and fossilized trackways that have been found in the U.S. states of Oklahoma, Wyoming, and Texas.

The fossils were found in rocks dating from near the end of the Early Cretaceous (Aptian–early Albian), 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 to an absence of the group on the continent of roughly 40 million years that ended with the appearance of ''Alamosaurus'' during the Maastrichtian.

While the holotype remains were initially 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 that ''Sauroposeidon'' lived on the shores of the Gulf of Mexico, in a river delta. Extrapolations based on the more completely known ''Brachiosaurus'' indicate that the head of ''Sauroposeidon'' could reach in height with its neck extended, which would make it one of the tallest known dinosaurs. With an estimated length of and a mass of , it also ranks among the longest and heaviest. However, this animal may not be as closely related to ''Brachiosaurus'' as previously thought, so these estimates may be inaccurate.

While initially described as a brachiosaurid closely related to ''Brachiosaurus'' and ''Giraffatitan'', the discovery of additional remains in the Cloverly Formation of Wyoming suggested that it was in fact more closely related to the titanosaurs, in the group Somphospondyli. Analysis of these remains and comparison with others from Texas supported this conclusion, and demonstrated that the more completely known sauropods from the Twin Mountains Formation (including a partial skull and fossil trackways) previously named ''Paluxysaurus jonesi'' also belonged to ''Sauroposeidon''. It is the state dinosaur of Texas.

Discovery

The first fossils classified as ''Sauroposeidon'' were four neck vertebrae 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, specifically between the Aptian and Albian epochs. These vertebrae were discovered in May 1994 at the Antlers Formation in Atoka County, Oklahoma by dog trainer Bobby Cross and secured by Dr. Richard Cifelli and a team from the Oklahoma 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 the ''Journal of Vertebrate Paleontology'' in March 2000. The new species was named ''S. proteles'', and the holotype is OMNH 53062. It garnered immediate media attention leading to some sources calling it inaccurately the largest dinosaur ever.

The generic name comes from ''sauros'' (Greek σαύρος for "lizard"), and ''Poseidon'' (Ποσειδών), the sea god in Greek mythology, who is also associated with earthquakes, 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.

The specific descriptor ''proteles'' also comes from the Ancient Greek πρωτέλης 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.
In 2012, numerous other sauropod remains that had been known for decades under various different names were also classified in the genus ''Sauroposeidon''. Sauropod bones and trackways had long been known from the Paluxy River area of Texas, usually referred to the genus ''Pleurocoelus'', including partial skeletons (particularly from the Glen Rose Formation, above the Twin Mountains Formation). In the mid 1980s, students from the University 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 from Southern Methodist University, the Fort Worth Museum of Science and History, and Tarleton 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 was fluvial when its rocks were being deposited, with channel sands and muds, and concretions of calcite-cemented sandstone containing fossils. Following excavation and preparation of the majority of the fossils from the site, its sauropod species was given the name ''Paluxysaurus jonesi''.

The name ''Paluxysaurus'' was based on the specimen FWMSH 93B-10-18, a partial skull including an associated left maxilla, nasal, and teeth. Other bones from the quarry included a partial neck of seven vertebrae, 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 was distinguished from all other sauropods by vertebral details, and has various morphological 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 from Wise County known as ''Pleurocoelus'' sp. ( SMU 61732) is not referred to ''Paluxysaurus''; instead that specimen is the holotype of '' Astrophocaudia slaughteri'' D'Emic 2012, another somphospondylan sauropod. There are differences in the remains of ''P.'' sp. and ''Paluxysaurus'', but they cannot be distinguished with confidence. In 2012, re-analysis of these specimens in light of additional ''Sauroposeidon'' remains led paleontologists D'Emic and Foreman to conclude that ''Paluxysaurus'' was the same animal as ''Sauroposeidon'', and thus a junior synonym of ''S. proteles''.

Description

The press release in 1999 immediately garnered international media attention, which led to many (inaccurate) news reports of "the largest dinosaur ever!". While ''Sauroposeidon'' likely represents the tallest known dinosaur taxon, it does not hold records for either the longest or most massive. '' Maraapunisaurus'' or '' Argentinosaurus'' make better candidates for the title "World's Largest Dinosaur" , though incomplete fossil evidence (and in the case of ''Maraapunisaurus'', lost) makes exact rankings impossible.

The original ''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 , 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 – about 18% longer than the longest rib reported for ''Giraffatitan'', but exceeded in length by the cervical ribs of ''Mamenchisaurus''.

Estimates of ''Sauroposeidons size are based on a comparison between the four ''Sauroposeidon'' vertebrae and the vertebrae of the HM SII specimen of ''Giraffatitan brancai'', located in the Berlin'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 of ''Sauroposeidon'' are difficult due to limited remains.
The neck length of ''Sauroposeidon'' is estimated at , compared to a neck length of for the HM SII ''Giraffatitan''. This is based on the assumption that the rest of the neck has the same proportions as ''Giraffatitan'', which is a reasonably good conjecture.

''Sauroposeidon'' was probably able to raise its head above the ground, which is as high as a six-story building. In comparison, ''Giraffatitan'' could probably raise its head into the air.

''Sauroposeidon's'' shoulder height has been estimated at based on an interpretation of the animal as a brachiosaurid. Estimates of its total possible length have ranged from to .
/ref>Paul, G.S., 2016, ''The Princeton Field Guide to Dinosaurs 2nd edition'', Princeton University Press p. 230

The mass of ''Sauroposeidon'' is estimated at . While the vertebrae of ''Sauroposeidon'' are 25–33% longer than ''Giraffatitan, they are only 10–15% larger in diameter. This means that while ''Sauroposeidon'' probably has a larger body than ''Giraffatitan'' its body is smaller in comparison to the size of its neck, so it did not weigh as much as a scaled-up ''Giraffatitan''. By comparison, ''Giraffatitan'' might have weighed . This estimate of the ''Giraffatitan'' is an average of several different methodologies.

However, ''Sauroposeidon'' has a gracile neck compared to ''Giraffatitan''. 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.

Paleoecology

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 soon 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 in length, and maybe , 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. This paleoenvironment, which has been preserved in the Antlers 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 the Aptian and Albian stages of the Early Cretaceous Period, approximately 110 mya. The area preserved in this formation was a large floodplain that drained into a shallow inland sea. Several million years later, this sea would expand to the north, becoming the Western Interior Seaway and dividing North America in two for nearly the entire Late Cretaceous period. The paleoenvironment of ''Sauroposeidon'' consisted of tropical or sub-tropical forests, river deltas, coastal swamps, bayous and lagoons, probably similar to that of modern-day Louisiana. There were few predators which could attempt to attack a full-grown ''Sauroposeidon'', but juveniles were likely to be preyed on by the contemporary ''Acrocanthosaurus atokensis'' (a carnosaur slightly smaller than a ''Tyrannosaurus''), which likely were the apex predators in this region, and the small dromaeosaur ''Deinonychus antirrhopus''. ''Sauroposeidon'' also shared its paleoenvironment with other dinosaurs, such as the sauropod ''Astrodon'' (Pleurocoelus) and the most common dinosaur in this region, the ornithopod '' Tenontosaurus''. Other vertebrates present during this time included the amphibian ''Albanerpeton arthridion'', the reptiles ''Atokasaurus metarsiodon'' and ''Ptilotodon wilsoni'', the cartilaginous fish '' Hybodus buderi'' and ''Lissodus anitae'', the ray-finned fish '' Gyronchus dumblei'', the crocodilians ''Goniopholis'', ''Bernissartia'', and '' Paluxysuchus'', and the turtles ''Glyptops'' and ''Naomichelys''. Possible indeterminate bird remains are also known from the Antlers Formation. The fossil evidence suggests that the gar '' Lepisosteus'' was the most common vertebrate in this region. The early mammals known from this region included ''Atokatherium boreni'' and '' Paracimexomys crossi''.

References

External links

* A non-technica

on Dino Land, with links to various news reports.

{{Taxonbar, from=Q131693

Early Cretaceous dinosaurs of North America
Fossil taxa described in 2000
Macronarians
Taxa named by Matt J. Wedel
Cloverly fauna
Paleontology in Oklahoma
Paleontology in Wyoming
Paleontology in Texas