Cranial morphology of a new phytosaur (Diapsida, Archosauria) from the Upper Triassic of India: implications for phytosaur phylogeny and biostratigraphy

Detailed description and phylogenetic assessment of a phytosaur skull collected from the Tiki Formation of the Rewa Gondwana Basin of India and earlier diagnosed as Parasuchus hislopi, show that it pertains to a new genus and species, Volcanosuchus statisticae. The new taxon is characterized by marginal overlapping of the nostrils by the antorbital fenestrae, external nares situated on a bulbous and raised dome, the lateral surface of the jugal ornamented by a prominent ridge defined by multiple tubercles and radiating thread‐like structures, and distinct ornamentation patterns on the rostrum and skull table. Phylogenetic analysis nests Volcanosuchus within Mystriosuchinae, where it forms a sister taxon to (Rutiodon + Leptosuchomorpha) and marks the transition between the basal Parasuchidae and more derived Mystriosuchinae phytosaurs. Evolution of the phytosaur skulls resulted in changes from non‐overlapping nostril and antorbital fenestra to an overlapping state, anteroposterior elongation of the exoccipital–supraoccipital shelf, appearance of a median ridge on the basioccipital, and reduction of the supratemporal fenestra. Considerable faunal overlap of the Tiki Formation is evident with the lower Maleri Formation, which is late Carnian based on the occurrence of Hyperodapedon, Parasuchus and Exaeretodon. The Tiki Formation correlates with the Ischigualasto Formation of Argentina, the upper part of the Santa Maria Formation, and the overlying lower Caturrita Formation of Brazil, the Isalo II Beds of Madagascar, Lossiemouth Sandstone of Scotland, and the lower Tecovas Formation of the Chinle Group of North America, and ranges from late Carnian to early/middle Norian.

Phytosaurs are known from several Upper Triassic horizons of the Pranhita-Godavari Basin, one of the major Gondwana basins of India (Fig. 1A, B). These include Parasuchus hislopi and an undescribed Rutiodon/ Angistorhinus-like form from the lower part of the Maleri Formation (Chatterjee 1978;Kutty et al. 2007;Bandyopadhyay 2011;Kammerer et al. 2016), two new taxa similar to Leptosuchus and Angistorhinus from the upper part of the Maleri Formation (Hungerb€ uhler et al. 2002, Fig. 1C) and an undescribed Nicrosaurus-like form from the lower Dharmaram Formation (Bandyopadhyay 2011;Novas et al. 2011). None of these phytosaurs was studied in detail except for Parasuchus hislopi.
Abbreviations used for measured parameters. When added to the anatomical abbreviations, the suffix L indicates length, and W and H indicate width and height, respectively. a, angle of the ascending maxillary process with vertical plane; b, angle of the descending maxillary process with vertical plane; h, symphyseal angle of the mandible; afnL, length of antorbital fenestra; afnW, width of antorbital fenestra; afoL, length of antorbital fossa measured along the dorsal margin of the antorbital fenestra; afoW, width of antorbital fossa measured along the posterior margin of the antorbital fenestra; chL, length of choana; chW, width of choana; enH, height of external naris measured along the posterior margin; enL, length of external naris; en-o, distance between external naris and orbit measured along dorsal midline; enW, width of external naris; ioW, width of interorbital area; itfH, height of infratemporal fenestra; itfL, length of infratemporal fenestra; jH, height of jugal; jL, length of jugal; msfW, median shaft width; mxL, maxillary length; nL, length of nasal measured along the dorsal midline; nW, width of the nasal measured along the posterior margins of the external nares; oL, length of orbit; oW, width of orbit; paL, length of palatine; paW, width of palatine; pmxL, length of premaxilla measured along dorsal midline; pmxfW, width of premaxillary fossa measured adjacent to the anterior border of the choanae; pmxW, width of premaxilla measured at posterior extremity; SH, skull height at the posterior end; SL, skull length measured along dorsal midline; sofL, length of suborbital fenestra; sofW, width of suborbital fenestra; subtfL, length of subtemporal fenestra; sub-tfW, width of subtemporal fenestra; SW, skull width at the quadrates; symH, symphyseal height; symW, symphysial width. Index is given in Figure 2. Derivation of name. Generic name, derived from the Latin word 'volcanus' referring to the raised dome-like narial prominence, which resembles a high volcanic crater in lateral view, and 'suchus' meaning crocodile-like.
Diagnosis. As for the type and only species.
Volcanosuchus statisticae sp. nov. Derivation of name. Specific name is after the Indian Statistical Institute, Kolkata, one of the first institutes in India to promote and establish a school of vertebrate palaeontology.
Holotype. ISIR 44, a partial skull with the anterior part of the rostrum and occipital region missing.
Differential diagnosis. The taxon differs from all other phytosaurs by a unique combination of the following features: external nares elevated on a bulbous and raised dome; marginal overlapping of external naris by antorbital fenestrae; thread-like ornamentation on premaxilla and maxilla; prominent ridge and radiating thread-like patterns on jugal; teardrop-shaped ornamentation on nasal, lacrimal, prefrontal and frontal. Autapomorphic characters of Volcanosuchus in relation to Mystriosuchinae include marginal overlapping (<50%) of the nares by antorbital fenestrae; thread-like ornamentation on premaxilla and maxilla; teardrop-shaped ornamentation on the nasal, lacrimal, prefrontal and frontal; prominent ridge and radiating thread-like patterns on jugal.
Remarks. The Tiki skull (ISIR 44) originally assigned to the genus Parasuchus hislopi shows significant morphological variations from the Maleri neotype specimens. These variations were attributed to ontogeny and sexual dimorphism (Chatterjee 1978, p. 92, text-fig. 4c State of fossil preservation. The skull (ISIR 44, is partially preserved with the anterior portion of the rostrum, part of the right skull table posterior to the orbits and the entire occiput missing. The entire right lateral surface posterior to the anteroventral corner of the infratemporal fenestra and the posterior portion of the right palate is also missing. The premaxillary rostrum contains two prongs held together by a metal rod placed between the latter (Fig. 3). The skull table is tilted ventrolaterally towards the right and, consequently, the righthand side of the skull table bears a dorsoventral compression. A portion of the internarial septum, the anterior half of the right antorbital fossa, the posterior extension of the left squamosal and a part of the quadrate ramus of the pterygoid have been reconstructed with plaster of Paris (calcium sulphate hemihydrates). In general, the specimen is well-preserved and bears c. 28 tooth alveoli on each side of the preserved upper jaw, all of which are devoid of teeth and matrix covered. The specimen is brownish in colour and recovered from a 'boulder of calcareous sandstone' of the Tiki Formation (Chatterjee 1978, p. 85), the latter being subsequently identified as a lenticular peloidal calcirudite unit. This fossil locality has also yielded a partial right mandibular ramus (IITKGPR803) containing a well-preserved and undistorted symphyseal plate.  . 3) is moderately thick (pmxW = 42 mm) with a convex dorsal surface, which bears thin thread-like, interconnecting ornamentation ( Fig. 4A, B). The premaxilla extends posteriorly and has sutural contact with the septomaxillanasal complex (Fig. 3). A long and deep, anteriorly extending furrow separates the two V-shaped prongs of the septomaxilla. Posteriorly the septomaxilla forms a major portion of the internarial septum with the septomaxilla-nasal suture located close to the posterior margin of the nostril. The septomaxilla forms the medial half of the anterior margin of the naris, the lateral half of which is formed by the nasal (Fig. 3). The dorsal surface of the septomaxilla bears rugosity (Fig. 3). The external nares (enL/enW = 3.1; Datta et al. 2019a, appendix S1) occur as a pair of anterodorsally oriented (in lateral view) teardrop-shaped/elliptical, non-emarginated openings separated by a prominent and robust internarial septum (Fig. 3), and posteriorly bear rugosity (Fig. 4C, D). The posterior margins of the nostrils do not converge at the mid-line, thereby forming a V-shaped furrow. Posterior to the nares, the nasal extends up to the frontal, forming a wide and horizontal platform in dorsal view, and borders the nares laterally (Fig. 4C, D). Coarse, teardrop-like ornamentation characterizes the nasal (Fig. 4C, D). Just anterior to the nasofrontal suture, the nasal tapers and is bounded on either side by the prefrontals (Fig. 4C, D). The nasofrontal suture is wavy and is located at a level just anterior to the posterior margin of the antorbital fenestra (Fig. 4C, D).

DESCRIPTION
Above the posterodorsal margin of the antorbital fossa rests a small, triangular prefrontal (Fig. 4C, D). As on the nasal, the prefrontal bears teardrop-shaped ornamentation on its dorsal surface (Fig. 4C, D). The prefrontal extends posteriorly along the lateral margin of the frontal and forms the anterodorsal margin of the orbit. Only a small portion of the frontal is preserved and it shares a straight anteroposteriorly oriented suture with the prefrontal. Similar to the nasal and the prefrontal, the frontal bears teardrop-shaped ornamentation (Figs 3, 4C, D).
Lateral elements of the skull. The most prominent feature in lateral view is a swollen, elevated dome on which rest the external nares (enH = 73 mm; Datta et al. 2019a, F I G . 2 . Index to the measured parameters as shown on the schematic representation of a phytosaur skull and mandible. A-C, skull: A, dorsal; B, ventral; C, lateral view. D-E, mandible: D, dorsal; E, lateral view. Abbreviations: a, angle of the ascending maxillary process with vertical plane; b, angle of the descending maxillary process with vertical plane; h, symphyseal angle of the mandible; afnL, length of antorbital fenestra; afnW, width of antorbital fenestra; afoL, length of antorbital fossa measured along the dorsal margin of the antorbital fenestra; afoW, width of antorbital fossa measured along the posterior margin of the antorbital fenestra; chL, length of choana; chW, width of choana; enH, height of external naris measured along the posterior margin; enL, length of external naris; en-o, distance between external naris and orbit measured along dorsal midline; enW, width of external naris; ioW, width of interorbital area; itfH, height of infratemporal fenestra; itfL, length of infratemporal fenestra; jH, height of jugal; jL, length of jugal; msfW, median shaft width; mxL, maxillary length; nL, length of nasal measured along the dorsal midline; nW, width of the nasal measured along the posterior margins of the external nares; oL, length of orbit; oW, width of orbit; paL, length of palatine; paW, width of palatine; pmxfW, width of premaxillary fossa measured adjacent to the anterior border of the choanae; pmxL, length of premaxilla measured along dorsal midline; pmxW, width of premaxilla measured at posterior extremity; SH, skull height at the posterior end; SL, skull length measured along dorsal midline; sofL, length of suborbital fenestra; sofW, width of suborbital fenestra; subtfL, length of subtemporal fenestra; subtfW, width of subtemporal fenestra; SW, skull width at the quadrates; symH, symphyseal height; symW, symphyseal width. appendix S1; Figs 5, 6A-D). The narial prominence is similar to that of Angistorhinus grandis (Mehl 1915, p. 134, fig. 3), although it is below the level of the skull table (Fig. 5). The internarial septum lies at the level of the lateral margins of the external nares for most of its length (Fig. 5A, B). Only the anterior part of the internarial septum rests above the lateral margins of the nares, given that the latter are oriented anteroventrally. The zigzag premaxilla-maxilla suture occurs just anterior to the external naris (Figs 5,6A,B), as seen in all other phytosaurs (Kammerer et al. 2016). A sliver of the maxilla slides beneath the premaxilla in this region. The lateral surface of the maxilla, anterior to the antorbital fenestra, bears small, interconnecting thread-like ornamentation ( Fig. 6A-D). Anterior to the antorbital fenestra, the maxilla bifurcates into two processes. These are: (1) the ascending maxillary process (sensu Butler et al. 2014), which partly forms the dorsal margin of the antorbital fenestra and is bordered by the nasal anterodorsally and the lacrimal posterodorsally (Fig. 5); and (2) the main body of the maxilla, which is bordered by the jugal posteriorly, and forms the ventral margin of the antorbital fenestra ( Fig. 5A, B). At the anterior end of the antorbital fenestra, the main maxillary body is not perpendicular to the vertical plane but makes an angle to it, and is termed here as the descending maxillary process (Fig. 2C). The ascending maxillary process is inclined at an acute angle to the vertical plane (a = 73°) whereas the descending process makes an angle (b) of 101°(Datta et al. 2019a, appendix S1).
In lateral view, the ventral margin of the orbit rests above the dorsal margin of the antorbital fenestra (Fig. 5). The circumorbital ridge is thin, weakly elevated, rugose (Fig. 5A, B), and most prominent along the anterodorsal orbital margin. The antorbital fenestra (afnL/afnW = 3.1; Datta et al. 2019a, appendix S1) is large, oval and partially surrounded by a deep antorbital fossa (Figs 5, 6E-H). The fossa is present only along the posterior and dorsal fenestral margins. The dorsal margin is formed by the ascending maxillary process and the lacrimal; the latter continuing as the posterior margin of the fossa (Fig. 6E-H). A sliver of the lacrimal borders the prefrontal laterally as a thin, anteriorly convex element. Teardrop-shaped ornamentation is found only on the dorsal surface of the lacrimal (Fig. 4C, D). The jugal forms the posteroventral margin of the antorbital fossa (Fig. 5). Laterally, the antorbital fenestra is depressed into the skull and the nasal forms a prominent overhanging shelf above it. The ventral margin of the antorbital fenestra is formed by the maxilla anteriorly and jugal posteriorly (Figs 5, 6E, F). The maxilla-jugal suture is located at the mid-length of the ventral margin of the antorbital fenestra (Fig. 6E, F).
Another diagnostic feature is the marginal overlap of the anterior end of the antorbital fenestra and the posterior end of the external naris (Figs 5, 6A-D). The lacrimal-jugal suture is located beneath the ventral margin of the orbit along the posteroventral margin of the antorbital fenestra ( Fig. 6E-H). The lacrimal-jugal suture beneath the orbit has a dorsally directed concave flexure, which is most prominent on the left lateral surface of the skull (Fig. 5A, B). The jugal is elongate (jL/jH = 1.2) and bears thread-like, radiating ornamentation just posterior the antorbital fossa in left lateral view (Fig. 6E, F). However, the right jugal does not exhibit such thread-like ridges because of poor preservation, although a weakly raised, anteroposteriorly oriented ridge ornamented with small tubercles is evident (Fig. 6G, H). The left jugal has a faint impression of such a ridge, given that most of that area is missing and reconstructed with plaster of Paris.
The jugal-quadratojugal suture is zigzag in nature and located posterior to the infratemporal fenestra (Fig. 5A, B). The jugal extends posteriorly beneath the ventral margin of the quadratojugal and forms a short protuberance (Fig. 5A, B). The partially preserved posterodorsal process of the jugal is more prominent on the right side. It extends dorsally to the anteroventral corner of the infratemporal fenestra (Figs 5C, D, 6G, H). Only the left infratemporal fenestra (itfL/itfW = 1.1) is preserved, which is trapezoid in shape and extends beneath the orbit posteriorly, covering almost half of its length (Fig. 5A, B). On the anteroventral margin of the left infratemporal fenestra, the fossa is poorly developed (Fig. 5A, B). The jugal forms the anteroventral and the entire ventral margin of the infratemporal fenestra, whereas the posterior margin is formed largely by the squamosal (Fig. 5A, B). The latter ventrally borders the quadratojugal at the posteroventral corner of the infratemporal fenestra in lateral view. Beneath the ventral margin of the infratemporal fenestra, the subtemporal fenestra is partially visible (Fig. 5A, B). The quadratojugal is bordered posteriorly by the quadrate (Fig. 5A, B).
Quadrate-quadratojugal complex. The quadrate-quadratojugal complex bears two well-developed condyles, with a broader lateral condyle and a smaller medial condyle (Fig. 7). The quadrate-quadratojugal suture extends dorsomedially from the lateral half of the lateral condyle past the quadrate foramen. The quadrate foramen is large, crescent shaped and posterolaterally oriented (Fig. 7). The quadratojugal and quadrate form its anterior margin, whereas the ventral margin is largely formed by the quadrate, with a small part formed by the quadratojugal. The lateral and medial margins of the quadrate foramen are formed by the quadratojugal and quadrate, respectively.
Palate. Ventrally, the premaxillary rostrum bears a series of elliptical and/or circular alveoli, which increase in size posteriorly (Fig. 8A, B). These alveoli are closely packed; inter-alveolar septa are poorly developed, and bound medially by pairs of thin and sharp alveolar ridges. These The inserted metal rod, matrix-covered and reconstructed areas are marked by cross-hatching. Abbreviations: afn, antorbital fenestra; afo, antorbital fossa; en, external naris; f, frontal; ins, internarial septum; j, jugal; l, lacrimal; mx, maxilla; n, nasal; pmx, premaxilla; prf, prefrontal; qj, quadratojugal; sm, septomaxilla. Scale bar represents 50 mm. are most prominent near the rostral mid-length (alveoli 11-15), and tend to be flush with the surface posteriorly ( Fig. 8A, B). The alveolar ridges are separated by a welldeveloped, concave premaxillary fossa (pmxfW = 37.9 mm; Datta et al. 2019a, appendix S1; Fig. 8A, B). The alveoli on the maxilla are larger than the premaxillary alveoli (Fig. 8). The premaxilla-maxilla suture is located at the rostral mid-length, near alveolus 14 (Fig. 8C, D). Posteriorly the premaxilla extends up to the anterior border of the choana, where it meets the palatine laterally and the vomer posteriorly (Fig. 8C, D). The maxillary alveoli increase in size posteriorly, with the largest one lateral to the choana (Fig. 8C, D). The alveolar rim lateral to the choana is swollen. The choana is elliptical (chL/chW = c.7; Datta et al. 2019a, appendix S1), and separated by the vomers, which occur as a thick median ridge. The premaxilla forms the anterior choanal margin, whereas the palatine forms the anterolateral and lateral margins (Fig. 8). The posterior margin of the choana is formed by the pterygoid and vomer (Fig. 8). Posterior to the premaxilla, the maxilla constitutes the lateral margin of the palate, which extends beyond the posterior margin of the choana (Fig. 8).
Only the left subtemporal fenestra is preserved, which occurs as a large, sub-rectangular opening (subtfL/sub-tfW = c.2; Fig. 8A, B) posterior to the suborbital fenestra. The anterior margin of the subtemporal fenestra is formed by the pterygoid and the ectopterygoid while the posteromedial margin is formed by the quadrate (Fig. 8A, B). A weakly developed pterygoid flange extends laterally into the subtemporal fenestra ( Fig. 8A, B). Laterally, the subtemporal fenestra is bordered by the jugal, whereas the quadratojugal-quadrate complex forms the posterolateral and posterior margins (Fig. 8A, B). The left pterygoid is partially preserved, and its anterior half is bordered laterally and medially by the palatine and vomer, respectively. Posteriorly, it bears a weakly developed pterygoid flange, medial to which is a deep concavity for the basipterygoid process of the basisphenoid (Fig. 8A, B). The quadrate ramus of the pterygoid is robust but the position of the pterygoid-quadrate suture along this ramus cannot be determined. The rest of the palate and braincase is not preserved.

Mandible
The partial right mandibular ramus (IITKGPR803, Figs 9, 10) is mediolaterally compressed, robust and high (symH/ symW = 1.4). In dorsal view, the mandibular width increases posteriorly across the symphyseal region coupled with a progressive decrease in the width of the median shaft. The latter is raised with respect to the alveoli and borders them medially (Fig. 9A, B). Posterior to the symphysis the ramus diverges away from the horizontal at an angle of 18°. A total of 21 alveoli are preserved, all of which are devoid of teeth. The alveoli progressively increase in size posteriorly and are circular in outline. The posterior-most alveoli (19-21) are elongate with their long axes nearly parallel to that of the mandibular ramus ( Fig. 9A, B). The alveoli are restricted to the dentary, with the latter forming the entire dorsal surface of the preserved length of the mandibular ramus and the anterior portion of the ramus in ventral view (Fig. 9C, D).  The dentary-splenial zigzag suture rests posterior to the symphyseal region and continues posteriorly and ventrolaterally ( Fig. 10A, B).
shortly after entering the symphyseal plate in the form of a Meckelian fossa.

Reconstruction of the skull and mandible
The missing elements of the snout, including the extent of the premaxilla, and skull roof have been reconstructed based on other Mystriosuchinae genera such as Brachysuchus (Case 1929, fig. 3), Angistorhinus grandis (Mehl 1915, p. 134, fig. 3) and Rutiodon (Colbert 1947, p. 83, fig. 7). Volcanosuchus (ISIR 44) is phylogenetically bracketed by these forms and shows overall similarity, including overlapping of the nostrils by the antorbital fenestra, elevated circumnarial morphology and robusticity of the skull table. The width of the premaxillary rostrum of ISIR 44 appears wider due to the insertion of a metal rod between its two halves ( Fig. 3A) because of which, only the widths of the two rostral halves were considered during reconstruction (Fig. 11A). The orbital region bears a slight dorsolateral inclination towards the right. Consequently, the right side of the skull shows dorsoventral compression with the ventral margin of the orbit descending below the dorsal margin of the antorbital fenestra, unlike the left side. For restoration, both sides of the skull were brought to the same level, and the ventral margin of the right orbit was raised above the dorsal margin of the antorbital fenestra. The rest of the reconstruction involved making mirror images of the preserved portions of the cranium and juxtaposing them with the latter. The occiput was not restored because most of it was not preserved.
The reconstructed skull of Volcanosuchus is robust and comprises a posteriorly expanding triangular skull with a long premaxillary rostrum (SL/SW = 2.5). The nostrils are teardrop shaped (L/W = c. 3), orbits are small and oval (oL/oW = 1.1), weakly emarginated and dorsolaterally oriented, whereas the supratemporal fenestrae were equally small and elliptical (Fig. 11A). In comparison, the antorbital fenestra is large, elongated and broadly triangular (afnL/afnW = c. 3) in dorsal view. The anterior end of the maxilla and most of the skull roof including the nasals, frontals, prefrontals and lacrimals is characterized by a dense pattern of small, teardrop-shaped ornamentation whereas the rostrum, composed essentially of the premaxillae, contains long, thread-like ornamentation (Fig. 11A, C).
In ventral view (Fig. 11B), the choanae are large, elliptical (chL/chW = c.7), bifurcated by a robust vomer, and bordered anterolaterally and posteriorly by the palatines and pterygoid, respectively. The suborbital fenestra is distinct and boomerang shaped. Numerous alveoli border the premaxilla and maxilla; the alveoli are closely spaced and increase in size posteriorly. In lateral view, several features such as the nares placed on a dome-shaped prominence (enH/SL = 0.13), marginal overlapping of the nares and antorbital fenestra, high skull roof (SH/ SL = 0.22), laterodorsally placed orbits, an elliptical antorbital fenestra bordered by a distinct fossa, jugal ornamented by a ridge and radiating fine thread-like patterns, and a trapezoid infratemporal fenestra (Fig. 11C), characterize Volcanosuchus.
Given that the partial right mandibular ramus (IITKGPR803) is without any distortion, the symphyseal region of the mandible was reconstructed by simply mirror imaging the left portion. The restored mandible is robust and wide posterior to the symphysis, with a symphyseal angle (h) of 36° (Fig. 11D). The median shaft narrows at the posterior symphyseal end and occupies 40% of the mandibular width (Fig. 11D). to Parasuchus hislopi, a non-Mystriosuchinae member of Parasuchidae. However, the non-Mystriosuchinae phytosaurs, including the genera Wannia (Fig. 12A), Parasuchus (P. bransoni, P. hislopi and P. angustifrons; Fig. 12B-D) and Ebrachosuchus (Fig. 12E), are characterized by non-overlapping of the nostrils by the antorbital fenestrae (Stocker & Butler 2013), which is in contrast to that seen in ISIR 44 ( Fig. 11A-C). Hence, comparison with several non-Mystriosuchinae and Mystriosuchinae phytosaurs based on skull proportions and various other cranial features indicates that ISIR 44 is a new taxon within the subfamily Mystriosuchinae. However, characteristic features of the leptosuchomorphs such as the rostral crest, dorsoventrally taller than wide premaxilla, depression of the parieto-squamosal bars below the level of the skull roof, and a long posterior process of the squamosal (Stocker & Butler 2013) are either absent or not preserved in ISIR 44.

Septomaxilla
In Volcanosuchus, the septomaxilla forms the internarial septum and the anteromedial narial margins. In Diandongosuchus the septomaxilla is absent, whereas in Wannia the septomaxilla forms the entire anterior margin of the nares but is excluded from the internarial septum The nares of Volcanosuchus are elevated on a bulbous dome-like structure, and the nasals surrounding the nostrils laterally are swollen (Fig. 11C). This dome-like structure is relatively much higher than the dorsal prominence of Wannia. The latter flares posteriorly in dorsal view and is further enhanced by a mediolateral constriction of the skull ventral to the nares (Stocker 2012b). Such a lateral constriction is not seen in Volcanosuchus. In P. hislopi and P. angustifrons, the nares are weakly elevated and well emarginated with a rugose posterior margin ( Although the narial morphology of Angistorhinus grandis (Mehl 1915) and Rutiodon (Colbert 1947) is similar to that of Volcanosuchus, with the nares elevated on a dorsal prominence, there are distinct differences between the taxa. In Angistorhinus grandis the external nares are situated above the level of the skull roof and the dorsal prominence is restricted only to the posterior narial ends (Mehl 1915). As in Volcanosuchus, the nares of Rutiodon remain at the level of the skull roof (Colbert 1947). The ornamentation on the narial prominence also differs from Volcanosuchus, given that irregular pits and rugosity are present in Angistorhinus grandis and Brachysuchus, respectively (Mehl 1915;Case 1929). In contrast, the external nares of Protome differ from Volcanosuchus in being elliptical and elevated on a crest, which is slightly elevated above the skull roof (Stocker 2012a).

Internarial septum
The internarial septum is level with the lateral narial margins in Volcanosuchus, whereas in Wannia the lateral narial margins are high and dorsal to the internarial septum (Stocker 2012b, p. 254, fig. 3). The internarial septum rests above the level of the external nares in P. hislopi, P. angustifrons and Ebrachosuchus, with the septum well arched in P. hislopi (Butler et al. 2014;Kammerer et al. 2016). The nares of Angistorhinus grandis consist of a slender internarial septum, with the latter remaining below the level of the lateral and posterior border of the nares, giving the appearance of a single narial opening (Mehl 1915), which contrasts with the two distinct nostrils of other phytosaur genera examined, including Volcanosuchus.

Nasal
Volcanosuchus is characterized by prominent, teardropshaped ornamentation on the nasals, whereas in Diandongosuchus and Wannia, the nasals bear dorsoventrally oriented faint grooves and ridges (Stocker 2012b;Stocker et al. 2017). Coarse ridges and furrows characterize the surface of the nasals in P. hislopi (ISIR 43), whereas in P. bransoni small tubercles and irregular pits and elevations are present (Lees 1907). In P. angustifrons, in contrast, the nasals are devoid of any ornamentation except for the rugose lateral margins above the antorbital fossa The nasal of Protome is non-inflated, unornamented and bears a fossa along the posteromedial margin of the nostril (Stocker 2012a). The portion of the nasals surrounding the circumnarial region in Angistorhinus grandis and Brachysuchus is characterized by irregular pits and rugosity, respectively (Mehl 1915;Case 1929).

Lacrimal, prefrontal and frontal
The lacrimal of Volcanosuchus bears teardrop-shaped ornamentation (Figs 4D, 11A), in contrast to the unornamented lacrimal of P. hislopi and P. angustifrons and the rugose lacrimal in Diandongosuchus and Ebrachosuchus The ornamentation pattern on the prefrontal and frontal in Angistorhinus grandis differs from those in Volcanosuchus, given that the former contains irregular pitting (Mehl 1915). The prefrontal in Angistorhinus grandis is quadrangular in (Mehl 1915). When the dorsal view of the skulls of these two taxa is brought to the same length, the frontal in Angistorhinus grandis extends much closer to the external nares (Mehl 1915) compared with Volcanosuchus. The nasofrontal suture in Angistorhinus grandis is concave, whereas that in Volcanosuchus is wavy.
Protome differs from Volcanosuchus in having multiple ridges ornamenting the prefrontal and frontal (Stocker 2012a). The prefrontal is irregular in outline in Protome (Stocker 2012a).

Orbit
Contrary to the 'Parasuchus-grade' phytosaurs (Butler et al. 2014;Kammerer et al. 2016), the orbit of Volcanosuchus is weakly emarginated, with its ventral margin placed dorsal to the dorsal margin of the antorbital fenestra. These features are also not seen in Ebrachosuchus, in which the orbital ridges are strongly thickened and anteriorly have a preorbital depression (Butler et al. 2014). Similar to Volcanosuchus, Diandongosuchus has a weakly developed orbital ridge, but the ventral margin of the orbit in the latter rests ventral to the dorsal margin of the antorbital fenestra. A well-developed orbital ridge is seen in Protome (Stocker 2012b), which continues on to the prefrontal. However, the orbit of Protome is similar to that of Volcanosuchus in being dorsolaterally oriented with the ventral margin remaining dorsal to the dorsal margin of the antorbital fenestra.

Jugal
As mentioned earlier, a distinct ridge is present along the lateral surface of the jugal in Volcanosuchus, similar to Diandongosuchus, Wannia and P. angustifrons. A similar ridge is also present in Ebrachosuchus. However, this ridge is unornamented and posterodorsal in orientation in Wannia (Stocker 2012b) and Ebrachosuchus (Butler et al. Reexamination of both of these specimens shows that the lateral surface of the jugal beneath the orbit does not preserve any nodes. Rather, the surface of the right jugal in ISIR 42 bears multiple fractures, which, when restored by plaster of Paris, gave rise to the appearance of a series of small weakly elevated regions (Datta et al. 2019a, appendix S2).
The jugal forms the posteroventral and a part of the ventral margin of the antorbital fenestra in Volcanosuchus, and the maxillojugal suture is anterior to the posterior margin of the fenestra. Wannia does not exhibit this condition, given that the jugal does not border the antorbital fenestra and the maxillojugal suture rests posteriorly (Stocker 2012b). In P. angustifrons, P. bransoni and Ebrachosuchus, the maxillojugal suture is located posterior to the antorbital fenestra (Lees 1907; Butler et al. 2014). However, in P. hislopi and Volcanosuchus, the maxillojugal suture is placed anteriorly and shows similarity with that of Angistorhinus grandis and Brachysuchus. In these taxa, the jugal forms the posterior half of the ventral margin and a part of the posterior margin of the antorbital fenestra. Unlike Angistorhinus grandis, however, Volcanosuchus contains a ridge on the jugal, the latter forming the entire ventral margin of the infratemporal fenestra.
The antorbital fossa is reduced in Volcanosuchus, and present only along the dorsal and posterior margins of the antorbital fenestra. This contrasts with that of

Infratemporal fenestra
The infratemporal fenestra in Volcanosuchus extends anteriorly almost up to the mid-length of the orbit, and its ventral margin is formed by the jugal. In P. bransoni the jugal also forms the entire ventral margin of the infratemporal fenestra (Lees 1907 The infratemporal fenestra extends anteriorly well beyond the mid-point of the orbit in Angistorhinus grandis, Brachysuchus and Rutiodon (Mehl 1915;Case 1929;Colbert 1947). Similar to Volcanosuchus, the jugal forms the entire ventral margin of the infratemporal fenestra in Brachysuchus, and the squamosal forms the majority of the posterior margin of the infratemporal fenestra in both Angistorhinus grandis and Brachysuchus (Mehl 1915;Case 1929). Angistorhinus grandis differs from Volcanosuchus, in that the jugal-quadratojugal suture is located at the mid-length of the ventral margin of the infratemporal fenestra.

Premaxillary-maxillary alveoli
The alveoli of Volcanosuchus show a progressive increase in size from the premaxilla to the maxilla. The maxillary alveoli are closely spaced, mostly circular in outline, and those lateral to the choanae have thick swollen margins. In contrast, the anterior maxillary alveoli of Wannia are smaller than the posterior maxillary alveoli as well as the premaxillary alveoli (Stocker 2012b). Although the maxillary alveoli are closely spaced as in Volcanosuchus, those lateral to the choanae do not bear swollen margins. The alveoli in Ebrachosuchus are subcircular and widely spaced, separated by well-developed interalveolar septa (Butler et al. 2014). Other features distinguishing Ebrachosuchus from Volcanosuchus include high tooth/alveolus count on either side (c. 50), and similar sized alveoli in the former. In Volcanosuchus, the estimated number of alveoli on either side is c. 28, and the alveoli show a progressive increase in size posteriorly. In contrast, the premaxillary-maxillary alveoli are of equal size, bordered by rounded alveolar ridges and separated by well-developed interalveolar septa in Angistorhinus grandis (Mehl 1915). In Brachysuchus the premaxillary alveoli are similar sized, succeeded by smaller anterior maxillary alveoli (Case 1929). The maxillary alveoli progressively increase in size posteriorly (Case 1929).

Alveolar ridge
In Volcanosuchus the alveolar ridges are thin, sharp and widely spaced, which contrasts with the rounded and thick alveolar ridges observed in all Parasuchus species. Similar to Volcanosuchus, the alveolar ridges are widely spaced in P. angustifrons (Butler et al. 2014), whereas in P. hislopi these ridges are closely spaced. In Ebrachosuchus, however, the alveolar ridges are weakly developed and present only on some areas of the premaxilla (Butler et al. 2014).

Choanae
The choanae of Volcanosuchus are elliptical in outline and bordered by the premaxilla anteriorly and palatine laterally, and by the pterygoid posteriorly. The maxilla is excluded from bordering the choana, a feature shared by P. bransoni (Stocker 2012b). In contrast, the maxilla forms the anterolateral border of the choana in Wannia, P. hislopi, P. angustifrons and Ebrachosuchus, thereby excluding the premaxilla from the choana (Stocker 2012b;Butler et al. 2014;Kammerer et al. 2016).
The shape of the choana in P. hislopi, P. bransoni and Ebrachosuchus (Lees 1907;Butler et al. 2014;Kammerer et al. 2016) is elliptical, whereas in P. angustifrons it is slit-like (Butler et al. 2014). The choana is roughly triangular in Angistorhinus grandis, which is similar to that of Volcanosuchus. It differs from the latter in having the premaxilla excluded from the choana (Mehl 1915). The choana of Volcanosuchus (ISIR 44; chL/chW = c.7) is slender and more elongated than that of Angistorhinus grandis (FMNH UC631; chL/chW = 3.4), whereas that of Brachysuchus (UMMP 10336; chL/chW = 8.7) is slit-like and more elongated than that of Volcanosuchus.

Pterygoid, quadrate-quadratojugal complex
A striking difference between Volcanosuchus and Wannia is the presence of a dorsoventrally deep pterygoid-quadrate wing in the latter, with the posteroventral margin of the pterygoid bearing a sharp shelf (Stocker 2012b). In Volcanosuchus the pterygoid-quadrate wing is relatively slender, dorsoventrally compressed and devoid of a shelf. In Volcanosuchus, the quadrate foramen is crescentic and posterolaterally oriented. P. bransoni has a similar orientation of the quadrate foramen (Lees 1907). In all other Parasuchus-grade phytosaurs and Ebrachosuchus, the quadrate foramen faces posteriorly. The quadrate foramen is oval in P. hislopi and Ebrachosuchus whereas in P. angustifrons it is elliptical (Butler et al. 2014). Both Angistorhinus grandis and Brachysuchus differ from Volcanosuchus in having small and circular quadrate foramen facing posteriorly (Mehl 1915).
From the foregoing discussion, it is evident that marginal overlapping of the nostril by the antorbital fenestra characterizes the Tiki specimen (ISIR 44), suggesting that it belongs to the more derived subfamily Mystriosuchinae and is not restricted to the basal family Parasuchidae as previously thought. In addition, ISIR 44 exhibits several characteristic features involving skull proportions, patterns of ornamentation on different bones, sutural patterns and fenestral morphology to suggest that it pertains to a new Mystriosuchinae taxon Volcanosuchus statisticae. Although the partial mandibular ramus (IITKGPR803) was not associated with ISIR 44, it may be assigned to Volcanosuchus because it was collected from the same fossil locality and markedly differs from that of Parasuchus hislopi based on symphyseal robustness and angle, and dentary-splenial arrangement.  (2018). Several of these characters were either modified or combined. Twenty-eight new characters have been added, which includes five narial characters, two characters describing antorbital fenestra, one orbital character, two characters based on the infratemporal fenestra, two characters describing the quadrate foramen, and the suborbital and subtemporal foramen each described by a single character. Six and three characters define the pre-narial and circumnarial regions, respectively. The new characters include those describing the skull roof and three characters describing lateral elements of the skull.

Results
The phylogenetic analysis was performed on a data matrix comprising 21 taxa and 86 characters (Datta et al. 2019a, appendix S4) in TNT version 1.1 (Goloboff et al. 2008), using New Technology Search with default settings for sectorial searching, ratchet, tree drift and tree fusing. The constraint for the number of times the minimum tree length is to be found was set at 50. Symmetric resampling was carried out with 10 000 replicates and a change probability of 33 for obtaining group present/contradicted  (2018), although there are a few major differences. The strict consensus tree (Fig. 13A) is poorly resolved although there is a clear distinction between the basal non-Mystriosuchinae and the more derived Mystriosuchinae phytosaurs (sensu Kammerer et al. 2016). Parasuchus hislopi and Parasuchus angustifrons are recovered as sister taxa. Ebrachosuchus neukami is the most derived non-Mystriosuchinae taxon. Within the clade Mystriosuchinae, Angistorhinus grandis and Brachysuchus are resolved as sister taxa, whereas Volcanosuchus forms a polytomy with Rutiodon and the more derived leptosuchomorph forms. The Mystriosuchini taxa, Machaeroprosopus mccauleyi, and Machaeroprosopus lottorum, and Mystriosuchus planirostris and Mystriosuchus westphali are recovered as sister taxa, respectively.
The 50% majority-rule tree shows a comparatively higher resolution (Fig. 13B). Diandongosuchus and Wannia are the least derived and form a polytomy at the base of Phytosauria. Similar to the results of the strict consensus, Parasuchus hislopi and Parasuchus angustifrons are resolved as sister taxa and Ebrachosuchus is the most derived among non-Mystriosuchinae forms. Angistorhinus grandis and Brachysuchus are resolved as sister taxa, whereas Volcanosuchus forms a polytomy with the derived forms such as Rutiodon, Protome, and Machaeroprosopus jablonskiae, and is more derived in comparison to Angistorhinus grandis and Brachysuchus.
The resolution of the resampled tree (Fig. 13C) is perceptibly greater compared with the former two. Diandongosuchus is the least derived taxon, at the base of Phytosauria, which is conformable with that of Jones & Butler (2018). Nine unambiguous synapomorphies (Table 1) support clade A (Phytosauria). These are: moderately elongated snout (1); trapezoidal skull with width across squamosals less than width across the quadrates (2); transverse rostral width between the antorbital fenestrae ≥1.5-fold the interorbital width in dorsal view (3); non-terminal nares placed anterior to antorbital fenestra (11); presence of orbital ridges (18); foramina or sculptures present on the lateral surface of the maxilla (41); ornamentation in the form of ridges, grooves and pits present on the nasals (52); ornamentation in the form of rugosity and pits present on the dorsal surface of the frontals (54); and quadratojugal subtriangular in outline (77).
Clade B (Parasuchidae) is well resolved by five synapomorphies such as dorsally oriented nares (4); non-terminal nostrils placed posteriorly on the snout (12); reduced antorbital fossa with maxilla and lacrimal/jugal fossa either in contact dorsally or not in contact (15); moderately reduced suborbital fenestra (29); and angle of ascending maxillary process (a) ≥ 55°(44). Within Parasuchidae, Parasuchus hislopi + Parasuchus angustifrons (clade C) are recovered as sister taxa based on the angle of descending maxillary process (b) ranging between 115 and 100°(45). In clade D, Ebrachosuchus is the closest non-Mystriosuchinae taxa to the subfamily Mystriosuchinae, and is supported by the infratemporal fenestra extending beneath the middle or anterior half of the orbit (23).
Volcanosuchus is placed within Mystriosuchinae (clade E), as a sister taxon to (Rutiodon + Leptosuchomorpha). Clade E is well resolved and supported by four synapomorphies. These are: elevation of the nostrils on a dorsal prominence present along both the anterior and posterior margin of the nares (5); non-terminal nares with its posterior margin behind the anterior rim of the antorbital fenestrae (11); ≥ 50% of the external nares overlapped by the antorbital fenestrae (13); and palatine extending anteriorly beyond the anterior rim of the choana (86). Within Mystriosuchinae, Angistorhinus grandis and Brachysuchus are recovered as sister taxa in clade F. The latter is supported by the three synapomorphies: dorsoventral expansion of the posterior process of squamosal in lateral view (61); curved parietal-squamosal bar that is medially convex and wide (69); and approximately of the same mediolateral width as the postorbital-squamosal bar (70).
Within clade G Rutiodon is the most derived of the Mystriosuchinae taxa closest to Leptosuchomorpha based on: parietal process of the squamosal beneath the skull roof and a partially depressed supratemporal fenestra (21); greatly expanded posterior process of the squamosal, which are rounded posteriorly (61); and gently sloping dorsal edge of parieto-squamosal bar (67). Leptosuchomorpha (clade H) is poorly resolved, with Leptosuchus crosbiensis being the least derived taxon within this clade. The latter is supported by two synapomorphies: the long posterior squamosal process extending beyond the opisthotic process of the squamosal (60); and medially expanded dorsal edge of the squamosal (62).
The most derived Mystriosuchini (clade I) is well resolved, with Machaeroprosopus jablonskiae being the least derived taxon within this clade. The latter is supported by fully depressed supratemporal fenestra, with the posterior process of the parietal and the entire parietalsquamosal bar below the level of the skull roof (21). The most derived clade, clade J, comprises (Machaeroprosopus lottorum + Machaeroprosopus mccauleyi) and (Mystriosuchus westphali + Mystriosuchus planirostris), and is supported by characters such as: narrow slit-like interpremaxillary fossa (37); approximately transverse sutural articulation between the postorbital and squamosal in dorsal view (56); and exoccipital-supraoccipital shelf broad and overhanging over the foramen magnum and occipital condyle (80).

Discussion
The phytosaur interrelationships obtained from the present phylogenetic analysis are largely comparable with that of previous studies (Stocker 2012b; Kammerer et al. The recovery of Volcanosuchus (ISIR 44) as a Mystriosuchinae taxon is based on the overlapping of the nostrils by the antorbital fenestrae (11), and extension of the palatine beyond the anterior margin of the choana (86). Hence, ISIR 44 was more derived than previously F I G . 1 3 . Cladogram showing phytosaur interrelationships. A, strict consensus. B, 50% majority-rule tree. C, resampled tree with group present/contradicted (GC) values indicated by numbers above the nodes. suggested by Chatterjee (1978), and by Kammerer et al. (2016). The basal position of Volcanosuchus in the subfamily Mystriosuchinae can be explained by marginal overlapping (<50%) of the nares by the antorbital fenestrae (13) compared with other Mystriosuchinae taxa, which show a strong (≥50%) overlapping of the nares by the antorbital fenestrae. Volcanosuchus is defined by the autapomorphic characters such as thread-like ornamentation on the premaxilla and maxilla (36, 41), teardropshaped ornamentation on the nasal and frontal (52, 54) and lateral surface of the jugal ornamented by a ridge bearing tubercles, and radiating thread-like fine structures.
Contra Kammerer et al. (2016), Angistorhinus and Brachysuchus are resolved as sister taxa based on curved parieto-squamosal bars (69), dorsoventrally expanded posterior process of the squamosal (61) and parieto-squamosal bars having the same mediolateral width as the postorbital-squamosal bar (70). Moreover, Rutiodon was the most derived non-leptosuchomorph taxon in the current work, which contradicts Jones & Butler (2018). This is based on the character states such as the partially depressed supratemporal fenestra and the parietal process of the squamosal depressed beneath the skull roof (21), rounded posterior process of the squamosal, which is greatly expanded dorsoventrally (61), and gently sloping parieto-squamosal bar (67). However, the placement of Protome with other leptosuchomorph taxa is in accordance with Jones & Butler (2018). Machaeroprosopus jabolonskiae is the least derived taxon within Mystriosuchini while Mystriosuchus westphali and Mystriosuchus planirostris are recovered as sister taxa (Jones & Butler 2018). Machaeroprosopus mccauleyi and Machaeroprosopus lottorum show a sister-taxa relationship based on the presence of slit-like supratemporal fenestra due to strongly developed medial lamella of the postorbito-squamosal bar (58).
Node A: Order Phytosauria (1,2,3,11,18,41,52,54,77) Moderate snout length, trapezoidal occiput with width across squamosal less than width across the ventral edge of quadrate, transverse rostral width between the antorbital fenestrae in dorsal view ≥1.5-fold the width of the interorbital area, nonterminal nares placed completely anterior to the antorbital fenestra and snout, presence of orbital ridges, ornamentation on the lateral surface of the maxilla in the form of sculpture or foramina; ridges, grooves and pits present on the nasals, ornamented dorsal surface of the frontal, subtriangular-shaped quadratojugal Node B: Family Parasuchidae (4,12,15,29,44) Dorsally directed narial openings, non-terminal nares placed posteriorly on the snout, reduced antorbital fossa with lacrimal/ jugal and maxillary fossae either in contact dorsally or not in contact with one another, suborbital fenestra moderately reduced, angle of ascending maxillary process with the vertical plane (a) ≥ 55N ode C: Parasuchus angustifrons + Parasuchus hislopi (45) Angle of descending maxillary process with the vertical plane range: 115˚> b ≥ 100N ode D: Ebrachosuchus+ all taxa above (23) Infratemporal fenestra extended anteriorly below the middle or anterior half of the orbit Node E: Mystriosuchinae (5,11,13,86) Nares elevated on a dorsal prominence present along both the anterior and posterior margin of the nares, non-terminal nares with its posterior margin behind anterior margin of antorbital fenestra, ≥50% of the external naris overlapped by the antorbital fenestra, palatine extends anteriorly beyond the anterior rim of choana Node F: Angistorhinus + Brachysuchus (61,69,70) Posterior process of squamosal is dorsoventrally expanded in lateral view, parietal-squamosal bar is curved and medially convex, parietal-squamosal bar is wide and approximately of the same mediolateral width as the postorbital-squamosal bar Node G: Rutiodon + all above taxa (21,61,67) Parietal process of squamosal depressed below the skull roof and partially depressed supratemporal fenestra, posterior process of squamosal rounded and greatly expanded, dorsal edge of parieto-squamosal bar is gently sloping Node H: Leptosuchomorpha (60,62) Long posterior process of squamosal extending posteriorly far beyond the opisthotic process of the squamosal, medially expanded dorsal edge of the squamosal Node I: Mystriosuchini (21) Supratemporal fenestra fully depressed with the entire parietal-squamosal bar and the posterior process of parietal below level of skull roof Node J: Mystriosuchus planirostris + all taxa above (37,56,80) Inter-premaxillary fossa present as a narrow slit, approximately transverse sutural articulation of squamosal with postorbital in dorsal view, exoccipital-supraoccipital shelf broad and overhangs foramen magnum and occipital condyle The number of each character in the data matrix is given in parentheses.
2002) as shown by PAUP* 4.0b10 (Swofford 2000) and define the evolution of the phytosaur cranium. There are several ancestral phytosaurian conditions, which included the non-terminal nostrils, a slender parietosquamosal bar that trends straight posteriorly to articulate with the squamosal, and a sloping or vertical medial edge of the palatine below the posterior part of the palatal vault. The non-Mystriosuchinae phytosaurs are characterized by the nostrils positioned anterior to the anterior border of the antorbital fenestrae. The quadrate foramen is roughly circular and the suborbital fenestra is moderately reduced. In the basal non-mystriosuchid forms such as Wannia, the maxilla-jugal suture is located posterior to the antorbital fenestrae. However, in more derived non-mystriosuchid taxa, such as Parasuchus hislopi and Ebrachosuchus, the maxilla-jugal suture rests ventral to the antorbital fenestra. A low and dorsoventrally compressed cross-section of the posterior half of the postorbito-squamosal bar and a narrow medial lamella of the postorbito-squamosal bar is observed in the non-mystriosuchid phytosaurs. Non-Mystriosuchinae phytosaurs are typified by parietal-squamosal bars extending straight posteriorly, and narrower or of the same mediolateral width as the parieto-squamosal bar.
In the basal forms, the exoccipital-supraoccipital shelf is anteroposteriorly short and the basioccipital between the tubera comprises a concave depression. Furthermore, within Parasuchidae (outside Mystriosuchinae) the lateral extent of the basitubera is equal to that of the basipterygoid processes in basal forms such as Wannia scurriensis. However, in the more derived forms such as Parasuchus angustifrons and Ebrachosuchus, the lateral extent of the basitubera exceeds that of the basipterygoid processes. The more derived Mystriosuchinae phytosaurs (sensu Kammerer et al. 2016) are characterized by overlapping of the nostrils by the antorbital fenestrae. The degree of overlap increases from a partial overlap (<50%) in Volcanosuchus to a greater degree of overlap (>50%), as is observed in the Mystriosuchinae taxa Rutiodon and the leptosuchomorph phytosaurs. Volcanosuchus, therefore, marks the intermediate stage/transition from the non-Mystriosuchinae to the Mystriosuchinae phytosaurs. The quadrate foramen changes from circular in the basal forms to crescentic as seen in Volcanosuchus. Mystriosuchinae phytosaurs, however, exhibit several basal features such as a moderately reduced suborbital fenestra, maxilla-jugal suture ventral to the antorbital fenestra, a narrow medial lamella of the postorbito-squamosal bar, low and dorsoventrally compressed cross-section of the posterior half of the postorbito-squamosal bar, short exoccipital-supraoccipital shelf, the basioccipital between the tubera comprising a concave depression and the lateral extent of the basitubera at par with the lateral extent of the basipterygoid process.
In the subfamily Leptosuchomorpha (sensu Stocker 2010), the suborbital fenestra becomes greatly reduced and the morphology of the basioccipital between the tubera changes from being depressed to bearing an anteroposteriorly oriented ridge. Leptosuchomorph phytosaurs, however, retained some basal characters such as maxilla-jugal suture located ventral to the antorbital fenestra, a narrow medial lamella of the postorbito-squamosal bar, and lateral extent of the basitubera equal to that of the basipterygoid process. In the most derived clade, Mystriosuchini (Kammerer et al. 2016), the medial lamella of the postorbito-squamosal bar is moderate to strongly developed. Consequently, in these forms, the supratemporal fenestra is either half of its original width or abridged to a slit. However, the medial lamella continues to be narrow in the genus Mystriosuchus. In this genus only, the cross-section of the posterior half of the postorbito-squamosal bar becomes high and triangular. The exoccipital-supraoccipital shelf expands from being anteroposteriorly short in basal forms to a broad shelf overhanging the foramen magnum and occipital condyle.

BIOSTRATIGRAPHIC IMPLICATIONS
Recent calibration of the geological time scale places the Carnian-Norian boundary at c. 228 Ma, and the Norian stage lasted c. 20 myr (Gradstein et al. 2012;Ogg et al. 2016). This is based on radioisotopic and magnetostratigraphic data from marine strata (Irmis et al. 2010(Irmis et al. , 2011Olsen et al. 2011). Intense debate exists regarding the Late Triassic vertebrate biochronology, especially on the North American biostratigraphic correlations. One school proposed correspondence between the Adamanian/Revueltian and Carnian/Norian boundaries, and considered Otischalkian and Adamanian to be Carnian faunachrons (Lucas 1998(Lucas , 2018. Others have argued for an entirely post-Carnian age for the Chinle Formation in Arizona andNew Mexico (Irmis et al. 2010, 2011;Olsen et al. 2011;Martz et al. 2013), and the Otischalkian and Adamanian to be early Lacian (early early Norian) and late Lacian (late early Norian), respectively (Martz & Parker 2017). This has resulted in considerable confusion in terms of global correlation, especially for the Gondwana faunas of different stratigraphic horizons where radioisotopic data are absent (Abdala & Ribeiro 2010). The conventional method based on vertebrate faunal similarity correlated the major vertebrate-bearing Upper Triassic horizons around the world with those from India (Fig. 14), based on the lowest and highest occurrences of multiple index taxa. These included the multi-specific rhynchosaur Hyperodapedon Of the three Upper Triassic vertebrate fossil-bearing horizons in India, the Maleri Formation of the Pranhita-Godavari Basin straddles the Carnian-Norian boundary (Fig. 1B). This is evident from the two distinct non-overlapping vertebrate faunas of this formation (Kutty & Sengupta 1989). The lower Maleri fauna has yielded two phytosaurs (

CONCLUSIONS
1. In the current work, an isolated and partial phytosaur skull, from the Late Triassic Tiki Formation of the Rewa Gondwana Basin of India and previously identified as Parasuchus hislopi, is described in detail, compared with other phytosaur genera and assigned to a new genus and species Volcanosuchus statisticae. 2. Volcanosuchus is characterized by marginal overlapping of the nostrils by the antorbital fenestrae, lateral surface of the jugal ornamented by a prominent ridge defined by multiple tubercles and radiating threadlike structures, external nares situated on a bulbous and raised dome, thread-like ornamentation on the premaxilla and maxilla, and teardrop-shaped ornamentation on the skull table. 3. Phylogenetic analysis places Volcanosuchus within the derived phytosaur subfamily Mystriosuchinae, where it is recovered as a sister taxon to (Rutiodon + Leptosuchomorpha) based on overlapping of the nostrils by the antorbital fenestrae and extension of palatine beyond the anterior margin of the choana. The genus marked the transition from the basal non-Mystriosuchinae to the more derived Mystriosuchinae phytosaurs based on marginal overlapping (<50%) of the nares by the antorbital fenestrae. Angistorhinus and Brachysuchus are resolved as sister taxa, whereas Rutiodon was the most derived non-leptosuchomorph taxon. 4. Characteristic phytosaurian conditions include nonterminal nostrils and a narrow parieto-squamosal bar extending straight posteriorly to articulate with the squamosal. The evolution from the basal non-Mystriosuchinae to the derived Mystriosuchinae phytosaurs was marked by changes from non-overlapping to overlapping nostril with respect to the antorbital fenestra, and circular to crescentic quadrate foramen.
In the more derived leptosuchomorphs changes are related to the appearance of a median ridge on the basioccipital between the basitubera and highly reduced suborbital fenestra. In the most derived Mystriosuchini, cranial evolution included a reduced supratemporal fenestra due to broadening of the medial lamella of the postorbito-squamosal bar and overhanging of the exoccipital-supraoccipital shelf over the foramen magnum and occipital condyle.