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Omeisaurus junghsiensis

Reptilia - Mamenchisauridae

Taxonomy
Omeisaurus junghsiensis was named by Young (1939). Its type specimen is IVPP, a partial skeleton, and it is a 3D body fossil. Its type locality is Hsikuashan, Junghsien, which is in a Jurassic fluvial-lacustrine sandstone in the Xiashaximiao Formation of China.

Synonymy list
YearName and author
1939Omeisaurus junghsiensis Young pp. 280-281 figs. 1-20
1943Omeisaurus junghsienensis Young et al. p. 18
1958Omeisaurus junghsiensis Young pp. 20-21
1964Omeisaurus junghsiensis Tatarinov p. 549
1970Omeisaurus junghsiensis Steel p. 71
1977Omeisaurus junghsiensis Rozhdestvensky p. 112
1978Omeisaurus junghsiensis Dong et al.
1983Omeisaurus junghsiensis Dong et al. p. 27 figs. 13-35
1984Omeisaurus junghsiensis He p. 56
1988Omeisaurus junghsiensis He et al. p. 128
1990Omeisaurus junghsiensis McIntosh p. 380
1992Omeisaurus junghsiensis Dong p. 75
1996Omeisaurus junghsiensis Zhang and Chen
1998Omeisaurus junghsiensis Dong p. 81
1998Omeisaurus junghsiensis Wilson and Sereno p. 15
1999Omeisaurus junghsiensis Martin-Rolland p. 294 figs. 6-7
2004Omeisaurus junghsiensis Upchurch et al. p. 262
2011Omeisaurus junghsiensis Jiang et al. p. 190
2011Omeisaurus junghsiensis Saegusa and Tomida p. 253
2013Omeisaurus junghsiensis Tschopp and Mateus p. 324

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RankNameAuthor
kingdomAnimalia()
Triploblastica
Nephrozoa
Deuterostomia
phylumChordataHaeckel 1847
subphylumVertebrata
superclassGnathostomata
Osteichthyes()
Sarcopterygii
subclassDipnotetrapodomorpha(Nelson 2006)
subclassTetrapodomorpha()
Tetrapoda()
Reptiliomorpha
Anthracosauria
Batrachosauria()
Cotylosauria()
Amniota
Sauropsida
classReptilia
subclassEureptilia()
Romeriida
Diapsida()
Eosuchia()
RankNameAuthor
Neodiapsida
SauriaGauthier 1984
Archosauromorpha(Huene 1946)
Crocopoda
ArchosauriformesGauthier 1986
Eucrocopoda
Archosauria()
informalAvemetatarsalia
Ornithodira
Dinosauromorpha
Dinosauriformes
Dinosauria()
Saurischia()
Eusaurischia
Sauropodomorpha(Huene 1932)
Massopoda
Sauropodiformes
Sauropoda()
Eusauropoda
familyMamenchisauridae
genusOmeisaurus
speciesjunghsiensis

If no rank is listed, the taxon is considered an unranked clade in modern classifications. Ranks may be repeated or presented in the wrong order because authors working on different parts of the classification may disagree about how to rank taxa.

Diagnosis
ReferenceDiagnosis
Z. Dong et al. 1983(Original) A moderate to large sauropod with a relatively high skull, short rostrum, maxillary foramina are absent, and an anteroventral process is present on the anterior maxilla dorsal to the dentition which contacts the premaxilla. The maxilla contains 12-14 teeth and is relatively thin with a laterally compressed trilaminar ascending process. The antorbital fenestra is large, the prefrontal is a principal component of the orbit, the postfrontal is particularly thickened and may attain 18 mm, and the supratemporal fenestra is elliptical. The mandible contains 15-17 teeth with a relatively thin ramus that is higher anteriorly, has a posteriorly oblique anterior end, and a rostrum that projects ventrally at its anterior end. Its lateral surface is coarsely textured with nutrient foramina present. Medially it is flat and smooth, the ventral margin is very slightly crescentic, and there is a groove upon it that extends to the symphyseal region. Dentition is spoon-shaped and slightly posteriorly oblique. Premaxillary teeth are largest with long acute crowns and denticles present laterally with small tuberosities at both sides of the apex. Both maxillary and dentary dentition are labially convex and lingually concave which becomes more pronounced posteriorly. A lingual medial ridge is conspicuous, and anterior and posterior margins are symmetrical with denticles anteriorly. Base of the crown is lingually constricted and is then inflated as a root with a medial longitudinal groove. Dentition gradually diminishes in size posteriorly. Vertebral column is composed of 17 cervical, 12-13 dorsal, and four sacral vertebrae. Posterior centra are opisthocoelous, relatively short, and have well developed pleurocoels. Anterior cervical neural spines are low, and laminar structure is well developed. Posterior cervicals have relatively low spines and possess a well developed pseudospinous process, posterior cervical and anterior dorsal spines are bifid, the anterior process on cervical ribs is asymmetrical, and caudal centra are relatively long and laterally compressed. The first several anterior caudals are procoelous with fan-shaped caudal ribs. The diapophyses on the first caudal attach to the first caudal rib to compose a thin flat element. The scapula is broad with an expansive depressed surface and a terminus that differs from the distinctly expanded morphology of typical sauropods. The perforated coracoid is short, elliptical, and fuses with the scapula with a straight suture line. Breadth at the proximal end is equivalent to or exceeds its length. The sternum is elliptical. The ilium is generally short and high with a medially but slightly anteriorly positioned pubic peduncle. The pubis is broad with expanded anterior and posterior termini and a spaciously open obturator foramen. A horizontal notch lies on the ventral surface of the pubic symphysis. The proximal ischium is thick and expanded, whereas its shaft is flattened, and the distal end is not expanded. The four limbs of Omeisaurus are relatively long. Both ends of the humerus are of equivalent breadth, and are triangular in morphology with the proximomedial angle occasionally projected as a palm shaped expansion. The femoral shaft is elliptical in cross-section with the fourth trochanter lying dorsal to the midpoint of the shaft, and the femoral head is distinctly separate. The tibia is equivalent to or longer than three-fifths the length of the femur, and fibula is slightly shorter than the tibia.
(Supplemental) The skull is high, rostrum short, maxilla robust, occipital broad, and supraoccipital is large and laminar-shaped. Mandible is thick with a conspicuous mandibular angle with a relatively small dentition. Dental formula: Premaxilla-4, maxilla-12-13, dentary 14. This is a moderate-sized sauropod approximately 10-15 m in length, being a member of the high-skulled forms with a short rostrum and greatest breadth of skull is posterior to the orbit. Medial nasal ridge is not projected, and bifurcates the large nares which are situated laterally and anterior to the antorbital fenestra. Supratemporal fenestra are large and dorsally situated, and orbits are large, triangular, and laterally situated. Quadrate is straight and teeth are spoon-shaped. Premaxillary teeth differ in morphology from maxillary dentition. There are 14-17 cervicals, 12-13 dorsals, and four fused sacrals with the anterior three fusing their spines. Presacral vertebrae have honeycombed structure but caudals do not. Ventral axis is keeled. Cervical centra are opisthocoelous with well developed pneumatocoels, a flat ventral surface, but with a longitudinal ridge on each side providing the centrum with a rectangular morphology in ventral perspective. Neural spines are low, not conspicuously bifurcated, but may be said to have a plate-shaped pseudospinous process. Posterior cervicals are weakly bifid and cervical centra are two and a half times the length of the dorsals. Thirteen opisthocoelous dorsal vertebrae are recognized with generally well-developed anterior condyles and pleurocoels located anterodorsally. Neural arches are high, diapophyses and neural spines form a right angle to each other, dorsal spines on the anterior sequence are elongated, posterior dorsal spines have elongated apices, prezygapophyseal articular facets are convex and postzygapophyseal facets are concave. Membranes facilitating musculature attachment on the spine were well developed. Four sacral vertebrae are present but are not completely fused, although the three anterior sacral dorsal spines are completely fused to compose a uniform longitudinal plate, and the sacral ribs and diapophyses are fused into yoke-shaped plates, but the dorsal spines may be separated at their apices. The spine on S4 is completely isolated and rod-shaped, approaching the morphology of the anterior caudals. The precise count of the caudals is unclear but is generally 35 (_5). The first caudal is amphiplatyan with slightly concave ends. Caudal ribs are fused to diapophyses and are flattened. Caudals 2-7 are procoelous, medial caudals 8-21 are amphicoelous, and terminal caudals are amphiplatyan. Forelimbs are four-fifths the length of the hindlimbs. Scapula is straight with a large elliptical corocoid. A long, flat, and relatively straight blade-shaped clavicle is present with a lanceolate distal end and two small condyles on the proximal ends, and sternal plates are round and thin. Radius and ulna are four-fifths the length of the humerus. The ilium is high with a weak postacetabular process and a slightly stronger preacetabular process, the pubic peduncle is a large club-shaped process, distal pubis is boot-shaped, proximal pubis is thick and large, and ischium is straight, and relatively flat, with ligament attachments distally. The femur is straight with a relatively elliptical shaft and a large but undefined head. The fourth trochanter is situated posteromedially at a point one-third down the shaft, and two well developed condyles lie distally with the medial condyle larger than the lateral condyle. The tibia is robust with a distal astragalar process. The astragalus is large and flatly elongate with a simple morphology. Five robust digits are present with digit V reduced.