Shringasaurus

Shringasaurus Temporal range: Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Composite skeleton from the fossils of multiple individuals
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Archosauromorpha
Clade:	Crocopoda
Clade:	†Allokotosauria
Family:	†Azendohsauridae
Genus:	†Shringasaurus Sengupta et al., 2017
Species:	†S. indicus
Binomial name
†Shringasaurus indicus Sengupta et al., 2017

Shringasaurus (meaning "horned lizard", from

Shringasaurus was a large-bodied quadruped, with an estimated body length of 3–4 metres (9.8–13.1 ft). It closely resembles the related Azendohsaurus, with its small, boxy head on a long neck and a large, barrel-shaped body with deep shoulders and ribs, sprawled to semi-sprawled limbs and a short tail. Aside from being notably larger than Azendohsaurus, Shringasaurus is most recognisable for its long curving brow horns, as well as for having a proportionately shorter and thicker neck than other azendohsaurids and much taller

The horns of Shringasaurus closely resemble those seen in ceratopsid dinosaurs, despite azendohsaurids and ceratopsids being totally unrelated to each other. The horns are attached to the frontal bones on the roof of the skull over the eyes, and sit across almost the entire breadth of the skull. They are pointed up and curve forwards from the skull, with slight variation in size and orientation existing among large individuals. Smaller and younger individuals had smaller, more gracile horns, indicating that the horns did not fully develop until the animals were mature. Intriguingly, at least one small specimen lacks horns entirely, whereas another similarly small specimen has small but well developed horns. It is suggested then that Shringasaurus was sexually dimorphic, and that possibly the females lacked horns.^[1]

The horns themselves have a rough, grooved texture that implies they were covered with a keratinous sheath of horn in life, also like ceratopsid horns, and so would have likely been longer than the bony cores indicate.^[4][5] The bones of the skull beneath the horns are unusually thick, and in the larger individuals the bones of roof of the skull (the nasal, prefrontal, frontal and postfrontal) are fused together on each side.^[1]

The teeth of Shringasaurus are low and leaf-shaped (lanceolate) with large

The

The shoulder and forelimb are broadly similar to those of Azendohsaurus, with a tall scapula that is concave along the front with an expanded tip, and an interclavicle with a long paddle-like process on the back and a short forward-pointing process (an unusual feature for archosauromorphs but also found in Azendohsaurus). The coracoid articulates with the scapula to form a glenoid (shoulder socket) that faces out to the sides and back. The humerus is likewise similar, with broad ends and a narrow midshaft, and a very well-developed deltopectoral crest half as long as the whole bone, indicating powerful forelimbs. The ulna, however, can be distinguished by a lower olecranon process below the elbow than in Azendohsaurus.^[1]

The hips and hind limbs are very similar to those of Azendohsaurus. The ilium has a prominent, semi-circular process at the front while the rear process is longer and thinner, and the acetabulum (hip socket) is also solid, unlike the perforated hip socket of dinosaurs. The femur is robust and slightly s-shaped, held out to the sides in a sprawl, with a robust tibia and a fibula only half as wide in the lower leg. The foot is typical for early archosauromorphs, including Azendohsaurus.^[1]

Discovery and naming

Shringasaurus is known from a single

The Shringasaurus bone bed consists of mostly disarticulated bones (although one partial skeleton was found in articulation) scattered within a 5 m X 5 m (25 square metres (270 sq ft)) area of red mudstone with fine, sandy laminations. The bonebed is monodominant, only containing fossils of Shringasaurus, and preserves eight individuals based on the minimum number of unique right femora, left humeri, skull roofs and horns discovered. The specimens also represent a variety of different ontogenetic stages of growth with a wide range of body sizes, from juveniles to adults. Of these individuals, only one or two lacked horns, and it's suggested that the bone bed was taphonomically biased towards the heavier, solidly built skulls of horned individuals while being transported and preserved.^[1][9][10]

However, the retention of bones rapidly lost in transport (such as ribs and limb bones), as well as minimal abrasion to many of the bones, indicates they were not transported a great distance after death. Although the bones were later disarticulated after transportation (apart from a single series of six dorsal vertebrae and ribs), they remained in closely associated clusters. They also show little weathering, indicating that most of the bones only remained exposed on the surface for perhaps only 1–3 years, with only a few exposed for longer (3–15 years). The articulated vertebrae, found lowest in the bonebed, was likely buried immediately, while the remaining bones higher in the bonebed were buried by subsequent floods. Similarly, the bones show now signs of trampling or marks from scavenging and plant growth, indicative of their short exposure before burial.^[9]

The fossils were excavated and prepared by Professor Saswati Bandyopadhyay, Dhurjati Sengupta and Shiladri Das of the

The results found by Sengupta and colleagues in 2017 is shown below as an excerpt of the full cladogram, simplified and focused on the relationships of Shringasaurus to other allokotosaurs:[1]

Crocopoda	To Archosauriformes Rhynchosauria Allokotosauria Trilophosauridae Teraterpeton hrynewichorum Trilophosaurus buettneri Spinosuchus caseanus ( = "Trilophosaurus" jacobsi) Azendohsauridae Pamelaria dolichotrachela Azendohsaurus laaroussii Azendohsaurus madagaskarensis Shringasaurus indicus

Shringasaurus and other azendohsaurids share several features, including confluent nares, leaf-shaped teeth and a long neck, as well as a few other minor details of the skeleton. It is particularly similar to Azendohsaurus in features of the parietals, the lower jaw, shoulder, hip, femur and vertebrae, but can be distinguished by teeth that are not expanded above the roots, the lack of a groove on the inside surface of the maxilla, tall neural spines, and of course the horns.^[1]

Palaeobiology

The Shringasaurus bonebed suggests that it was a

The horns of Shringasaurus are its most prominent feature, and so some focus was placed on their role and function in its initial description. Its describers considered its horns to be likely products of

One specimen of Shringasaurus is known to have had a pair of malformed vertebrae in its neck. The two cervicals are partially fused together, interpreted as either the result of a birth defect, spondyloarthropathy (a type of arthritis), or possibly a bacterial or fungal disc infection. The vertebrae belonged to a large adult animal, so it is unlikely that the quality of life for the individual was severely affected by the disorder, and it was probably not fatal to the animal. One of the vertebrae also preserves a healed fracture, although the cause for this injury is unknown.^[10]

Palaeoecology

In the upper Denwa Formation, Shringasaurus coexisted with the