Barosaurus Affinis

''Barosaurus'' ( ) is a genus of giant, long-tailed, long-necked, plant-eating sauropod dinosaur closely related to the more familiar ''Diplodocus''. Remains have been found in the Morrison Formation from the Upper Jurassic Period of Colorado, Utah, South Dakota, and eastern Wyoming at Como Bluff. It is present in stratigraphic zones 2–5.Foster, J. (2007). "Appendix." ''Jurassic West: The Dinosaurs of the Morrison Formation and Their World''. Indiana University Press. pp. 327-329.

The composite term ''Barosaurus'' comes from the Greek words ''barys'' (βαρυς) meaning "heavy" and ''sauros'' (σαυρος) meaning "lizard", thus "heavy lizard".

Description

''Barosaurus'' was an enormous animal, with some adults measuring about in length and weighing about 12–20 metric tons (13–22 short tons).Paul, G.S., 2016, ''The Princeton Field Guide to Dinosaurs 2nd edition'', Princeton University Press p. 213 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'', may actually belong to ''Barosaurus''. He suggested that, interpreted as belonging to ''Barosaurus'', the vertebra suggests an animal that was long and around in weight making it one of the largest known dinosaurs, with a neck length of at least . 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. Related diplodocids like ''Apatosaurus'' and ''Diplodocus'' had long, low skulls with peg-like teeth confined to the front of the jaws.

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.

The limb bones of ''Barosaurus'' were virtually indistinguishable from those of ''Diplodocus''. Both were quadrupedal, with columnar limbs adapted to support the enormous bulk of the animals. ''Barosaurus'' had proportionately longer forelimbs than other diplodocids, although they were still shorter than most other groups of sauropods. There was a single carpal bone in the wrist, and the metacarpals were more slender than those of ''Diplodocus''. ''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.

Below is a cladogram of Diplodocinae after Tschopp, Mateus, and Benson (2015).

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''. Another diplodocid genus, ''Seismosaurus'', is considered by many paleontologists to be a junior synonym of ''Diplodocus'' as a possible fourth species. ''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''. The other subfamily of diplodocids is Apatosaurinae, which includes ''Apatosaurus'' and ''Supersaurus''. The early genus ''Suuwassea'' is considered by some to be an apatosaurine, while others regard it as a basal member of the superfamily Diplodocoidea. 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.

Discovery, naming, and history

The first ''Barosaurus'' remains were discovered in the Morrison Formation of South Dakota by Ms. Isabella R. Ellerman, postmistress of Postville, and excavated by Othniel Charles Marsh and John Bell Hatcher of Yale University in 1889. Only six tail vertebrae were recovered at that time, forming the type specimen ( YPM 429) of a new species, which Marsh named ''Barosaurus lentus'', from the Classical Greek words ' (') ("heavy") and (') ("lizard"), and the Latin word ' ("slow"). 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. Meanwhile, the type specimen of ''Barosaurus'' had finally been prepared at Yale in the winter of 1917 and was fully described by Richard Swann Lull in 1919. Based on Lull's description, Holland referred the vertebrae ( CM 1198), along with a second partial skeleton found by Douglass in 1918 (CM 11984), to ''Barosaurus''. This second Carnegie specimen remains in the rock wall at Dinosaur National Monument and was not fully prepared until the 1980s.

The most complete specimen of ''Barosaurus lentus'' was excavated from the Carnegie Quarry in 1923 by Douglass, now working for the University of Utah after the death of U.S. Steel founder Andrew Carnegie, who had been financing Douglass' earlier work in Pittsburgh. Material from this specimen was originally spread across three institutions. Most of the back vertebrae, ribs, pelvis, hindlimb and most of the tail stayed at the University of Utah, while the neck vertebrae, some back vertebrae, the shoulder girdle and forelimb were shipped to the National Museum of Natural History in Washington D.C., and a small section of tail vertebrae ended up in the Carnegie Museum in Pittsburgh. However, in 1929 Barnum Brown arranged for all of the material to be shipped to the American Museum of Natural History in New York City, where it remains today. A cast of this specimen (AMNH 6341) was controversially mounted in the lobby of the American Museum, rearing up to defend its young (AMNH 7530, now classified as '' Kaatedocus siberi'') from an attacking ''Allosaurus fragilis''.

More recently, more vertebrae and a pelvis were recovered in South Dakota. This material (SDSM 25210 and 25331) is stored in the collection of the South Dakota School of Mines and Technology in Rapid City.

Darren Naish has noted a common error in books of the late 20th century to depict ''Barosaurus'' as a kind of brachiosaur-like short tailed sauropod with raphes on its neck and body, and often curving the upper half of its neck downwards into a U-shape, citing it as an example of a Palaeoart meme. 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.Royal Ontario Museum
ROM Channel: Constructing the Barosaurus. Added 2012-08-28. Accessed 2012-12-11.
/ref> The specimen is about 40% complete. As a skull of ''Barosaurus'' has never been found, the ROM specimen wears the head of a ''Diplodocus.''National Geographic, ''Museum Secrets, Episode 3: Royal Ontario Museum'', Segment "Lost Dinosaur"
. Broadcast December 10, 2012. 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.) In the rush to put the dinosaur on exhibit within ten weeks of its delivery to