Camarasaurus Grandis

''Camarasaurus grandis'' is an extinct species of sauropod dinosaur in the genus that lived during the Jurassic in what is now the western United States. It is the geologically oldest of the four species of the genus ''Camarasaurus''.

Taxonomy

''Camarasaurus grandis'' was named by Othniel Charles Marsh in 1877. It is one of four valid species of ''Camarasaurus'', alongside ''Camarasaurus lentus'', '' Camarasaurus lewisi'', and '' Camarasaurus supremus''. The type specimen of ''Camarasaurus grandis'' is the holotype YPM 1901, a partial skeleton of an immature individual from Como Bluff, Wyoming.

''Camarasaurus grandis'' is regarded as having three junior synonyms: ''Morosaurus impar'', ''Morosaurus robustus'', and ''Pleurocoelus montanus''. One of these junior synonyms, ''M. impar'', is the type species of ''Morosaurus'', the genus to which ''C. grandis'' and ''C. lentus'' were assigned until it was synonymized with ''Camarasaurus''. ''Amphicoelias latus'', which is conventionally regarded as a synonym of ''C. supremus'', may also be synonymous with ''C. grandis'', based on where its type specimen was found. ''C. grandiss contemporary, ''C. lewisi'', may also be synonymous with ''Camarasaurus grandis''. The holotype of ''C. lentus'' may be a specimen of ''C. grandis'', rather than the species conventionally known as ''C. lentus''.

There are numerous specimens of ''Camarasaurus grandis'', and the majority of the skeleton is known.

Description

''Camarasaurus grandis'' was a moderately-sized member of its genus, similar in size to ''C. lentus'' but smaller than ''C. supremus''. Gregory S. Paul estimated its length as and mass as 13 tonnes, whereas John Foster estimated its length as and mass as 12.6 tonnes for an average-sized individual, with large individuals reaching over 16.5 tonnes.

The anterior dorsal vertebrae of ''Camarasaurus grandis'' are one of the most distinctive parts of the skeleton. The vertebrae are much taller than in ''C. lentus'' and ''C. supremus''. The vertebrae are also unusual in the position of the connections between the neural arch and centrum, known as the neurocentral synostoses. In most reptiles, including ''Camarasaurus lentus'', the neurocentral synostoses lie at the level of the ventral margin of the neural arch. In contrast, in ''C. grandis'', the neurocentral synostoses are elevated above the level of the neural canal, with raised pedicels on the centrum separating the neural arch from the articular faces of the centrum. The centrum can completely surround the canal, resulting in a neural arch that does not actually form an arch over the neural canal. This characteristic is only visible in juveniles.

''C. grandis'' differs from ''C. lentus'' in having T-shaped expansions of its anterior caudal neural spines.

History of study

In 1877 during the Yale Peabody Museum’s expedition to Como Bluff, William Harlow Reed and several other field workers for Othniel Charles Marsh collected a basioccipital and partial postcranial skeleton. ''Camarasaurus grandis'' was named by Marsh in 1877 on the specimen (YPM 1901). He initially considered it a species of ''Apatosaurus''. The next year, Marsh named another new species, ''Morosaurus impar'', and shortly thereafter reclassified ''Apatosaurus grandis'' as ''Morosaurus grandis'' and named a third species, ''Morosaurus robustus''. The type specimens of ''M. impar'' and ''M. robustus'' could be from the same individual as YPM 1901. Additional material of ''C. lentus'' would be collected between 1877 and 1879 by YPM crews, including some skull material. In 1896, Marsh named another species of Sauropod from Como Bluff, ''Pleurocoelus montanus'', based on a fragmentary postcranial skeleton of a juvenile from. The species was later synonymized with ''C. grandis.'' All of the material found at Como Bluff came from the Kimmeridgian of the Morrison Formation.

During the Second Dinosaur Rush in 1900, crews of the Field Museum of Natural History collected several appendicular and axial elements, including a nearly complete forelimb, near Fruita, Colorado. The ''C. grandis'' material from Fruita led to new reconstructions of Sauropod manus and pes structure. In 1898, Samuel Wendell Williston regarded ''M. impar'' as synonymous with ''M. grandis''. In 1901, Elmer Riggs recognized that ''Morosaurus'' was a junior synonym of ''Camarasaurus''. ''C. robustus'' was suggested to be synonymous with ''C. grandis'' in 1930 by Richard S. Lull. In 1958, Theodore E. White synonymized ''C. grandis'' with ''C. supremus''. This proposed synonymy has not been upheld by subsequent study.

A specimen of ''Camarasaurus grandis'' was excavated in New Mexico in 1978, and was one of the first partial skeletons from the Morrison Formation to be excavated in the state. It was initially reported as a specimen of ''C.'' cf. ''supremus'' in 1982, but reinterpreted as ''C. grandis'' in 2005.

A relatively complete skeleton of ''Camarasaurus grandis'', GMNH-PV 101, was described in 1996. However, an unpublished study by Emanuel Tschopp and colleagues presented at the 2014 meeting of the Society of Vertebrate Paleontology suggested that this specimen may have closer affinities to ''Camarasaurus lewisi'', which they argued represented a distinct genus, ''Cathetosaurus''.

Paleoecology

''Camarasaurus grandis'' lived during the Kimmeridgian age of the Jurassic in what is now Wyoming, Colorado, and New Mexico. It is one of the more common species of ''Camarasaurus'', with 9.1% of known ''Camarasaurus'' specimens identified as ''C. grandis'' (the majority of specimens cannot be identified as belonging to any particular species).

A specimen of ''C. grandis'' from New Mexico showed signs of having been fed on by ''Allosaurus''.

''Camarasaurus grandis'' is the geologically oldest species of ''Camarasaurus'', and may be ancestral to the later species of the genus.

References

{{Taxonbar, from=Q56377349

Macronaria
Dinosaur species
Kimmeridgian dinosaurs
Tithonian dinosaurs
Morrison Formation
Dinosaurs of the United States
Fossil taxa described in 1877
Taxa named by Othniel Charles Marsh