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Shringasaurus
Temporal range: Anisian
Shringasaurus indicus.png
Restoration with various fossil bones
Scientific classification
Type species
Shringasaurus indicus
Sengupta et al., 2017

Shringasaurus (meaning "horned lizard", from Sanskrit शृङ्ग (śṛṅga), "horn", and Ancient Greek σαῦρος (sauros), "lizard") is a genus of allokotosaurian archosauromorph from the Middle Triassic (Anisian) of India. It is known from one species, S.indicus. The specimen comes from the Denwa Formation in the state of Madhya Pradesh. It is a sister taxon of Azendohsaurus. Like the ceratopsids, Shringasaurus had two frontal horns which it may have used to display.[1]

Shringasaurus indicus

Reconstruction of the skeleton

Description

Shringasaurus skull

Reconstruction of the skull compared to that of Arrhinoceratops

Shringasaurus was 3 to 4 meters long.[1]

The skull of Shringasaurus was rectangular with two large but short horns. These horns had a conical shape. It was a quadruped animal of a massive aspect. Its shoulder girdle is very massive and, like Azendohsaurus, its teeth are in the form of leaves. Shringasaurus possesses a series of characters that differ from other stem Archosauromorpha in the following combination of character states: confluent external nares; Pair of anterodorsally oriented supraorbital horns; Marginal teeth and palatins of similar size and shape with large denticles; Cervical mid-posterior, dorsal and at least the first two caudal vertebrae with mammalian processes on the neural spines; Cervical, dorsal and sacral middle-posterior vertebrae with hyposphene-hypantrum accessory joints; Cervical vertebrae 2-5 with epipophysis (unknown in Cv6); Dorsal vertebra with leaves of spinoprezygapophyseal and spinopostzygapophyseal; Dorsal vertebrae 1-12 with spinodiapophyseal blades; Anterior dorsal vertebrae with neural spines twice as large as their respective central centers. Shringasaurus indicus has a proportionally small skull with a short, rounded muzzle and confluent outer nares. The premaxilla has no prior process and the postnarial process is plate-shaped and has an anteroventral lateral groove at its base, as occurs in Azendohsaurus madagaskarensis 20. Premaxilla has four dental positions. The nasal has a long previous ventricular ventricular process.[1]

The marginal crowns of the tooth are weak, with a slightly bulbous base and numerous denticles on both margins, resembling those of Pamelaria dolichotrachela. The prefrontal and postfrontal are thick and almost exclude the front of the orbit boundary. The prefrontal, nasal, frontal and postfrontal on each side of the skull are fused to each other in large individuals (ie, the bones remain unmelted with their counterpart on the sagittal line). The roof of the skull has a curved anterior conical bone horn, almost equal in height to the rest of the skull in large individuals. Fragments of shells show that the base of the horn occupies the frontal width and the largest of the transverse width of the pachyostotic cream roof. The surface of the horn is decorated with tangential roughnesses and grooves, characteristics which have been identified as osteological correlations of cornified sheaths. 21 The parietal has a very narrow supratemporelle fossa which is separated from its counterpart by a broad flat surface, devoid of a sagittal crest. The quadrate has a dorsal end in the form of a hook, as occurs in other allokotosaurians. The crowns of the Vomerine are more lanceolate than those of the marginal dentition. The parabasphenoid has a main axis oblique, anteroventrural.[1]

Shringasaurus indicus reconstruction

Restoration

The anterior-middle cervical centra of Shringasaurus is approximately 1.5 times longer than high, indicating a relatively long neck, but proportionally shorter than in A. madagascariensis and Pamelaria dolichotrachela. In addition, cervical neural spines are proportionally larger than in the latter two species. The first to the twelfth dorsal vertebra has well-developed paradiapophyseal, centrodiapophyseal, prezygodiapophyseal, spinodiapophyseal and spinoprezygapophyseal blades that connect deep pits similar to those of the basal sauropods. Epipophyses are present in the anterior cervical vertebrae and are absent in the seventh to The ninth cervical vertebra. The mammillary processes (a pair of transverse expansions on the distal part of the vertebral column which is not confluent with the vertebral column, see reference are weak, laterally protruding and displaced prior to the mean antero- Posterior of the distal End of the vertebral column in at least the fifth to the ninth cervical, all the dorsal vertebrae recovered and the first two caudal vertebrae. The first sacral vertebra is slightly longer than the second and both have ribs of similar size. An intercentrum is conserved between two anterior caudal vertebrae.[1]

The clavicle is constricted near its ventral end and the interclavicular is T-shaped with a short anterior process and a long pallet-like posterior process similar to A. madagaskarensis. The scapular blade has a distinctly concave anterior margin, as in A. madagaskarensis, but unlike the sub-rectangular blade of P. dolichotrachela. The scapular blade is moderately expanded antero-posteriorly to its distal end. The coracoid is part of a post-eastern glenoid fossa and has a short post-glenoid process. The humerus is strongly constricted at mid-length and the delusional crest occupies half the length of the bone. The ulnar has a weak olecranon process.[1]

Ilium has a well developed semi-circular pre-metabolic process and a longer, dorsoventrally shallow postacetabular process. The acetabulum is entirely closed and anterodynamically delimited by a low and thick supra-acetabular ridge. The pubis has a transversely broad apron that contacts its counterpart and, proximally, extensive contact with ischium. The femur is sigmoid with a prominent internal trochanter that does not converge with the femoral head as in A. madagaskarensis and Trilophosaurus buettneri. The distal end of the femur is transversely wider than the proximal end and the fibular condyle is slightly more Distally extended than the tibial condyle.[1]

Discovery and naming

Shringasaurus occurrence

Maps showing geographical and geological occurrence of Shringasaurus

The fossil bones of Shringasaurus were recovered from a red mudstone in the upper part of the Denwa Formation. At least seven individuals of different ontogenetic stages were dug in an area of 25 square metres (270 sq ft). Most of them were disarticulated, except for a partially articulated skeleton. The holotype consists of a partial skull roof (prefrontal, frontal, postfrontal and parietal) with a pair of large supra-orbital horns.[1]

Classification

According to Sengupta and colleagues, Shringasaurus is a member of the Azendohsauridae within Allokotosauria. This is a basal family in Archosauromorpha.[1]

Paleoecology

Shringasaurus occurs in the Denwa Formation along with the dipnoan Ceratodus sp., the capitosaurid Paracyclotosaurus crookshanki, the mastodonsaurid Cherninia denwai, a lonchorhynchine trematosaurid, undescribed rhynchosaurs and brachyopoids, and small to large-sized dicynodonts. The red mudstone in which Shringasaurus has been found may indicate a bushy floodplain.[1]

References

  1. 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 (2017) "A new horned and long-necked herbivorous stem-archosaur from the Middle Triassic of India". 'Scientific Reports' 7: 8366. DOI:10.1038/s41598-017-08658-8. 
Template:Archosauromorpha
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