Barosaurus ( ) is an extinct genus of giant, long-tailed, long-necked, plant-eating sauropod dinosaur closely related to the more familiar Diplodocus. Definitive remains have been found in the Morrison Formation from the Upper Jurassic Period of South Dakota, Utah and Montana, with other possible remains also found in Colorado, eastern Wyoming and Oklahoma. The generic name, Barosaurus, comes from the Greek words barys (βαρυς) meaning "heavy" and sauros (σαυρος) meaning "lizard", and thus meaning "heavy lizard".
Description
thumb|left|Life reconstruction of an individual rearing up to defend itself against a pair of [[Allosaurus]]
Barosaurus was an enormous animal, with some adults measuring about in length and weighing about 12–20 metric tons (13–22 short tons). The estimated tail length of Barosaurus makes up about half the total body length. According to Mike Taylor, the long vertebra BYU 9024, previously identified as part of the type individual of Supersaurus vivianae, In 2020 Molina-Perez and Larramendi estimated it to be slightly smaller at and . However, research presented by Brian Curtice at the Society of Vertebrate Paleontology conference has supported the previous interpretation of BYU 9024 as a Supersaurus vertebra. Despite this, there are other specimens that provide evidence of gigantic Barosaurus individuals which may have been among the longest dinosaurs. One of these is a series of three cervical vertebrae (BYU 3GR/BYU 20815) and the third vertebra is 1110 mm to 1220 mm in length. Dr Mike Taylor and Dr Matt Wedel compared the size of this bone to the same bone in smaller Barosaurus specimens, such as AMNH 6341, and estimated the neck length of the BYU 3GR/20815 Barosaurus at , which would make it one of the longest necks of any dinosaur and indicate a total body length of around . Barosaurus was differently proportioned than its close relative Diplodocus, with a longer neck and shorter tail, but was about the same length overall. It was longer than Apatosaurus, but its skeleton was less robust.
Sauropod skulls are rarely preserved, and scientists have yet to discover a Barosaurus skull.<!--(Although a jaw is being studied, that may belong to a Barosaurus.)--> Related diplodocids like Apatosaurus and Diplodocus had long, low skulls with peg-like teeth confined to the front of the jaws.
thumb|right|Size comparison
Most of the distinguishing skeletal features of Barosaurus were in the vertebrae, although a complete vertebral column has never been found. Diplodocus and Apatosaurus both had 15 cervical (neck) and 10 dorsal (trunk) vertebrae, while Barosaurus had only 9 dorsals. A dorsal may have been converted into a cervical vertebra, for a total of 16 vertebrae in the neck. Barosaurus cervicals were similar to those of Diplodocus, but some were up to 50% longer. The neural spines protruding from the top of the vertebrae were neither as tall or as complex in Barosaurus as they were in Diplodocus. In contrast to its neck vertebrae, Barosaurus had shorter caudal (tail) vertebrae than Diplodocus, resulting in a shorter tail. The chevron bones lining the underside of the tail were forked and had a prominent forward spike, much like the closely related Diplodocus. The tail probably ended in a long whiplash, much like Apatosaurus, Diplodocus and other diplodocids, some of which had up to 80 tail vertebrae. Barosaurus feet have never been discovered, but like other sauropods, it would have been digitigrade, with all four feet each bearing five small toes. A large claw adorned the inside digit on the manus (forefoot) while smaller claws tipped the inside three digits of the pes (hindfoot).
Classification and systematics
Barosaurus is a member of the sauropod family Diplodocidae, and sometimes placed with Diplodocus in the subfamily Diplodocinae. Diplodocids are characterized by long tails with over 70 vertebrae, shorter forelimbs than other sauropods, and numerous features of the skull. Diplodocines like Barosaurus and Diplodocus have slenderer builds and longer necks and tails than apatosaurines, the other subfamily of diplodocids.
upright|thumb|[[Royal Ontario Museum|ROM 3670 (nicknamed Gordo), Royal Ontario Museum skeleton, Toronto]]
The systematics (evolutionary relationships) of Diplodocidae are becoming better established. Diplodocus has long been regarded as the closest relative of Barosaurus. Barosaurus is monospecific, containing only the type species, B. lentus, while at least three species belong to the genus Diplodocus. Tornieria (formerly "Barosaurus" africanus) and Australodocus from the famous Tendaguru Beds of Tanzania in eastern Africa have also been classified as diplodocines. With its elongated neck vertebrae, Tornieria may have been particularly closely related to Barosaurus. Diplodocid fossils are found in North America, Europe, and Africa. More distantly related within Diplodocoidea are the families Dicraeosauridae and Rebbachisauridae, found only on the southern continents. The rest of the type specimen was left in the ground under the protection of the landowner, Ms Rachel Hatch, until it was collected nine years later, in 1898, by Marsh's assistant, George Reber Wieland. These new remains consisted of vertebrae, ribs, and limb bones. In 1896 Marsh had placed Barosaurus in the Atlantosauridae; in 1898 it was classified by him as a diplodocid for the first time. In his last published paper before his death, Marsh named two smaller metatarsals found by Wieland as a second species, Barosaurus affinis, but this has long been considered a junior synonym of B. lentus.
After the turn of the 20th century, Pittsburgh's Carnegie Museum of Natural History sent fossil hunter Earl Douglass to Utah to excavate the Carnegie Quarry in the area now known as Dinosaur National Monument. Four neck vertebrae, each 1 meter (3 feet) long, were collected in 1912 near a specimen of Diplodocus, but a few years later, William Jacob Holland realized they belonged to a different species. This originated with a drawing by Robert Bakker in a 1968 article, in which two Barosaurus appeared to have short tails due to a mix of foreshortening and one obscuring the other.
In 2007, paleontologist David Evans was flying to the U.S. Badlands when he discovered reference to a Barosaurus skeleton (ROM 3670) in the collection of the Royal Ontario Museum in Toronto, where he had recently become a curator. Earl Douglass had excavated this specimen at the Carnegie Quarry in the early 20th century; the ROM acquired it in a 1962 trade with the Carnegie Museum. The specimen was never exhibited and remained in storage until its rediscovery by David Evans 45 years later. He returned to Toronto and searched the storage areas and found many fragments, large and small, of the skeleton. It is now a centrepiece of the ROM's dinosaur exhibit, in the James and Louise Temerty Galleries of the Age of Dinosaurs. At almost 27.5 meters (90 feet) long, the specimen is the largest dinosaur ever to be mounted in Canada. The specimen is about 40% complete. As a skull of Barosaurus has never been found, the ROM specimen wears the head of a Diplodocus. Each bone is mounted on a separate armature so that it can be removed from the skeleton for study and then replaced without disturbing the rest of the skeleton. (See video "Dino Workshop" at reference.) The ROM specimen is nicknamed "Gordo" after Gordon Edmunds, the museum curator who arranged for the skeleton to be brought to the ROM, and who had hoped to display it fully but was unable to. John McIntosh believes that the ROM's skeleton is the same individual represented by four neck vertebrae labeled "CM 1198" in the collection of the Carnegie Museum. However, this genus name had already been given to the fragmentary remains of a sauropod from England. Both species were moved to a new genus, Tornieria, in 1911. Upon further study of these remains and many other sauropod fossils from the hugely productive Tendaguru Beds, Werner Janensch moved the species once again, this time to the North American genus Barosaurus. In 1991, "Gigantosaurus" robustus was recognized as a titanosaur and placed in a new genus, Janenschia, as J. robusta. Meanwhile, many paleontologists suspected "Barosaurus" africanus was also distinct from the North American genus, However, this material is poorly preserved and fragmentary and was not adequately diagnosed as such, and so its referral to Barosaurus is doubtful. It may represent Tornieria.
Paleobiology
Feeding
thumb|Skull cast, [[Natural History Museum of Utah]]
The structure of the cervical vertebrae of Barosaurus allowed for a significant degree of lateral flexibility in the neck, but restricted vertical flexibility. This suggests a different feeding style for this genus when compared to other diplodocids. Barosaurus swept its neck in long arcs at ground level when feeding, which resembled the strategy that was first proposed by John Martin in 1987. The restriction in vertical flexibility suggests that Barosaurus did not primarily feed on vegetation that was high off the ground.
Paleoecology
Barosaurus remains are limited to the Morrison Formation, which is widespread in the western United States between the Great Plains and Rocky Mountains. or approximately 155 to 148 million years ago. Barosaurus fossils are found in late Kimmeridgian to early Tithonian sediments, A more recent study suggested even higher CO<sub>2</sub> concentrations of up to 3180 parts per million. Warm temperatures that led to significant evaporation year-round, along with possible rain shadow effect from the mountains to the west, led to a semi-arid climate with only seasonal rainfall. This formation is similar in age to the Solnhofen limestone Formation in Germany and the Tendaguru Formation in Tanzania. In 1877 this formation became the center of the Bone Wars, a fossil-collecting rivalry between early paleontologists Othniel Charles Marsh and Edward Drinker Cope.
The Morrison Formation records an environment and time dominated by gigantic sauropod dinosaurs such as Camarasaurus, Diplodocus, Apatosaurus and Brachiosaurus. Dinosaurs that lived alongside Barosaurus included the herbivorous ornithischians Camptosaurus, Dryosaurus, Stegosaurus and Othnielosaurus, and predators in this paleoenvironment included the theropods Saurophaganax, Allosaurus, Torvosaurus, Ceratosaurus, Marshosaurus, Stokesosaurus and Ornitholestes. Allosaurus accounted for 70 to 75% of theropod specimens and was almost at the top trophic level of the Morrison food web. Other vertebrates that shared this paleoenvironment included ray-finned fishes, frogs, salamanders, turtles, sphenodonts, lizards, terrestrial and aquatic crocodylomorphs, and several species of pterosaur. Early mammals were present such as docodonts, multituberculates, symmetrodonts, and triconodonts. The flora of the period has been revealed by fossils of green algae, fungi, mosses, horsetails, cycads, ginkgoes, and several families of conifers. Vegetation varied from river-lining forests of tree ferns, and ferns (gallery forests), to fern savannas with occasional trees such as the Araucaria-like conifer Brachyphyllum.
Assistant Curator David Evans mounted the ROM specimen conservatively, with a relatively low head to give the dinosaur moderate blood pressure.