Tuesday, August 22, 2017

[Paleontology • 2017] Shringasaurus indicus • A New Horned and Long-necked Herbivorous Stem-Archosaur from the Middle Triassic of India

Shringasaurus indicus 
Sengupta, Ezcurra & Bandyopadhyay, 2017

Illustration: Gabriel Lio

The early evolution of archosauromorphs (bird- and crocodile-line archosaurs and stem-archosaurs) represents an important case of adaptive radiation that occurred in the aftermath of the Permo-Triassic mass extinction. Here we enrich the early archosauromorph record with the description of a moderately large (3–4 m in total length), herbivorous new allokotosaurian, Shringasaurus indicus, from the early Middle Triassic of India. The most striking feature of Shringasaurus indicus is the presence of a pair of large supraorbital horns that resemble those of some ceratopsid dinosaurs. The presence of horns in the new species is dimorphic and, as occurs in horned extant bovid mammals, these structures were probably sexually selected and used as weapons in intraspecific combats. The relatively large size and unusual anatomy of Shringasaurus indicus broadens the morphological diversity of Early–Middle Triassic tetrapods and complements the understanding of the evolutionary mechanisms involved in the early archosauromorph diversification.

Figure 3: Skeletal anatomy of Shringasaurus indicus gen. et sp. nov. (a) Left premaxilla (ISIR 793) in lateral view. (b) Left maxilla (ISIR 795) in lateral view. (c) Left quadrate (ISIR 797) in lateral view. (d) Axis (ISIR 803) in left lateral view. (e) Posterior cervical vertebra (ISIR 820) in left lateral view. (f,g) Anterior dorsal vertebra (ISIR 825) in left lateral view in (f), and anterior view in (g). (h) Two anterior caudal vertebrae (ISIR 875) in right lateral view (mirrored). (i) Posterior caudal vertebra (ISIR 892) in left lateral view. (j) Right femur (ISIR 1016) in ventral view. (k) Left ilium (ISIR 991) in lateral view. (l), (m) Right astragalus and fused lateral centrale (ISIR 1059) in proximal view in (l), and dorsal view in (m). (n) Interclavicle (ISIR 950) in ventral view. (o) Left clavicle (ISIR 948) in medial view. (p) Left humerus (ISIR 951) in ventral view. (q) Left scapula (ISIR 929) and coracoid (ISIR 941) in lateral view. (r) Tooth crown (ISIR 801A) in labial view.

Scales = 1 cm for (a–c,i,m,l), 2 cm for (d–h,j,k,n–q), and 1 mm for (r), and skeleton = 25 cm. a. articulates with; ac, acetabulum; ain, axial intercentrum; ap, anterior process; ca, calcaneum; ce, lateral centrale; de, denticles; dpc, deltopectoral crest; fi, fibula; gf, glenoid fossa; gr, groove; hqh, hooked quadrate head; icl, interclavicle; itr, internal trochanter; la, lacrimal; lp, lateral process; mp, mammillary process; nag, non-articular gap; pcdl, posterior centrodiapophyseal lamina; pgp, postglenoid process; pnp, postnasal process; pof, popliteal fossa; pop, postacetabular process; pp, parapophysis; ppr, posterior process; ppdl, paradiapophyseal lamina; prdl, prezygodiapophyseal lamina; prp, preacetabular process; prz, prezygapophysis; qj, quadratojugal; sac, supraacetabular crest; sc, scapula; sgl, subglenoid lip; spdl, spinodiapophyseal lamina; sprdl, spinoprezygapophyseal lamina; ti, tibia.

Figure 2: Cranial anatomy of Shringasaurus indicus gen. et sp. nov. and comparison with the skull of a ceratopsid dinosaur that possesses convergent supraorbital horns. (a) Reconstruction of the skull of Shringasaurus indicus in left lateral view. (b) Drawing of the skull of Arrhinoceratops brachyops in left lateral view (based on ROM 79648). (c) Reconstruction of the skull of Shringasaurus indicus in dorsal view. (d–g) Partial skull tables of Shringasaurus indicus in dorsal views (ISIR 781, 780, 786, 789, 790 from left to right), one side has been digitally mirrored in (d–f). (h–k) Partial skull tables of Shringasaurus indicus in left lateral views (ISIR 781, 780, 786, 790 from left to right). Specimens (d–f) and (h–j) possesses horns and specimen/s (g) and (k) lacks horns.
Scales = 4 cm for (a) and ( c–k), and 20 cm for (b). en, external naris; ho, horn; or, orbit; stf, supratemporal fenestra.

Figure 4: Phylogenetic relationships of Shringasaurus indicus gen. et sp. nov. and evolution of body size among early archosauromorphs. (a) Time calibrated strict consensus tree found in the data set analysed here (Supplementary Information). Diapsids more basal than Protorosaurus are not shown and all clades except Allokotosauria have been collapsed for clarity. Numbers at the nodes are Bremer support values higher than 1. (b) Evolution of femoral length (as proxy of body size) optimized as a continuous character using maximum parsimony among non-archosauriform archosauromorphs (Supplementary Information). The horizontal axis represents phylogenetic distance. Green circles represent non-allokotosaurian species, red circles represent allokotosaurians, light blue circles represent non-allokotosaurian ancestral femoral lengths, and violet circles represent allokotosaurian ancestral femoral lengths. The dotted line represents a branch not included in the phylogenetic analysis of this study and the horizontal bar with dotted vertical lines on the right side of the graphic represents the median and standard deviation of Permian to Middle Triassic non-allokotosaurian, non-archosauriform archosauromorph femoral length. a, Crocopoda; b, Allokotosauria; c, Trilophosauridae; d, Azendohsauridae; e, Azendohsaurus.

Systematic Palaeontology

Diapsida Osborn, 1903
Archosauromorpha Huene, 1946 sensu Dilkes19

Allokotosauria Nesbitt et al., 2015
Azendohsauridae Nesbitt et al., 2015

Shringasaurus indicus gen. et sp. nov.

Etymology: Śṛṅga’ (Shringa), horn (ancient Sanskrit), and ‘sauros’ (σαῦρος), lizard (ancient Greek), referring to the horned skull; ‘indicus’, Indian (Latin English), refers to the country where such species was discovered.

Holotype: ISIR (Indian Statistical Institute, Reptile, India) 780: partial skull roof (prefrontal, frontal, postfrontal, and parietal) with a pair of large supraorbital horns (Fig. 2e,i).

Locality and horizon: Near Tekapar village, Hoshangabad district, Madhya Pradesh, India (Fig. 1); Denwa Formation, Anisian, early Middle Triassic18, Satpura Gondwana Basin.

Diagnosis: Relatively large (3–4 m total body length; Fig. S1) allokotosaurian archosauromorph that differs from other stem-archosaurs in the following combination of character-states: confluent external nares; pair of anterodorsally oriented supraorbital horns; similar sized and leaf-shaped marginal and palatal teeth with large denticles; middle-posterior cervical, dorsal, and at least the first two caudal vertebrae with mammillary processes on the neural spines; middle-posterior cervical, dorsal, and sacral vertebrae with hyposphene-hypantrum accessory articulations; cervical vertebrae 2–5 with epipophyses (unknown in Cv6); dorsal vertebrae with spinoprezygapophyseal and spinopostzygapophyseal laminae; dorsal vertebrae 1–12 with spinodiapophyseal laminae; anterior dorsal vertebrae with neural spines two times taller than its respective centrum (see Supplementary Information for differential diagnosis).

Shringasaurus indicus Sengupta, Ezcurra & Bandyopadhyay, 2017
Illustration: Gabriel Lio 

Saradee Sengupta, Martín D. Ezcurra and Saswati Bandyopadhyay. 2017. A New Horned and Long-necked Herbivorous Stem-Archosaur from the Middle Triassic of India.  Scientific Reports. 7, Article number: 8366.  DOI:  10.1038/s41598-017-08658-8

 Cómo era el mundo cuando vivía el Shringasaurus indicus 
lanacion.com.ar/2055099 via @LANACION
Encuentran en India un reptil con cuernos de 240 millones de años  conicet.gov.ar/encuentran-en-india-un-reptil-con-cuernos-de-240-millones-de-anos/

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