Here we describe new cranial material referable to R. sakalavae and consisting of an almost complete right premaxilla, the rostral half of a left dentary, a maxillary fragment with diagnostic teeth, and a very large isolated tooth crown. In addition, we tentatively refer to the same taxon five cranial fragments that were likely collected at the same locality. This new material greatly improves our knowledge on the cranial anatomy of this species, permitting us to: (1) clarify some previously uncertain features of the holotype due to its fragmentary nature; (2) make more in-depth anatomical comparisons with members of Crocodylomorpha and Theropoda, definitely ruling out it pertaining to the latter group; (3) test the phylogenetic relationships of the species and shed light on the evolutionary history and paleobiogeography of Notosuchia; (4) attempt a cranial reconstruction; and (5) confirm previous remarks on its paleobiology.

A decade ago, Maganuco, Dal Sasso & Pasini (2006) described the fragmentary remains of a very large predatory archosaur from the Middle Jurassic (Bathonian) of the Mahajanga Basin, Madagascar. The material included a fragmentary right maxilla bearing three teeth, and seven peculiar isolated teeth clearly belonging to the same taxon. In spite of the scanty remains, the presence of a unique combination of features, which included a well-developed bony palate on the maxilla, mesial and lateral teeth respectively U-shaped and sub-oval in cross-section, and very large tooth denticles (1 per mm) on the carinae, allowed the authors to erect the new taxon Razanandrongobe sakalavae Maganuco, Dal Sasso & Pasini, 2006 . However, the systematic position of the new species remained uncertain: indeed, besides the autapomorphic denticle size, R. sakalavae shared a mix of potential autapomorphic, synapomorphic, and homoplasic features with crocodylomorphs and theropods. Therefore, the species was referred to Archosauria incertae sedis .

Remarks — R. sakalavae differs from other known crocodyliforms in the following combination of characters: large predatory mesoeucrocodylian with oreinirostral snout; premaxillae taller than long, bearing five teeth and having aperturae nasi osseae facing rostrally, confluent medially, and bordered by smooth perinarial fossae; lateral edge of aperturae nasi osseae without notch on the premaxilla; very large incisive foramen, with length slightly more than half the greatest width of the premaxilla; premaxillary bony palate ( sensu Kley et al., 2010 ) with subcircular paramedian depressions, located rostrally on the premaxilla; paradental shelf of the premaxilla and maxilla with a surface texture consisting of marked ridges and furrows, in the maxilla extending for a short distance also above the medial neurovascular groove; deep robust maxilla, bearing at least ten teeth and a stout maxillary bony palate ( sensu Kley et al., 2010 ) located well above the level of the alveolar row; deep robust dentary, bearing at least eight teeth, the largest of which are the first three (fourth hypertrophied caniniform tooth absent); preserved part of the dentary with a convexity followed by a concavity along the dorsal edge; splenial contributing to the mandibular symphysis for at least 20% of the whole symphyseal length; dental implantation in separate alveoli; alveolar channels nearly straight in the sagittal plane; alveoli subrectangular to subcircular in occlusal view, with the former located on the paradental wall of the maxilla and on the rostralmost portion of the dentary; dentition heterodont and pachydont ( sensu Hendrickx, Mateus & Araújo, 2015 ); lateral teeth ( sensu Farlow et al., 1991 ) stout, suboval to salinon-shaped in cross-section; mid-lateral tooth crowns not compressed, subcircular in cross section; smallest lateral teeth globe-shaped.

Emended diagnosis — The following characters are synapomorphic to R. sakalavae : tip of dentary edentulous, for a length surpassing the diameter of the first alveolus; alveoli with labiolingual diameter larger than mesiodistal diameter; mesial teeth incisiform, U-shaped in cross-section, with both carinae facing the lingual side; denticles present on both carinae in all teeth, homogeneous, symmetrically convex, and very large (0.8–1.4 per mm).

Identical counterlateral copies, 3-D printed from CT data, of the left dentary (MHNT.PAL.2012.6.1) and right premaxilla (MHNT.PAL.2012.6.2) herein described, rearticulated with the original specimens. The perfect occlusion of the two bones, in medial (A) as well as in ventral (B) views, unequivocally demonstrates that MHNT.PAL.2012.6.1 and MHNT.PAL.2012.6.2 pertain to the same individual. Scale bar = 5 cm. Abbreviations: see text.

Computed tomography (CT) of the two most important referred specimens was performed at the Radiology Department, Spedali Civili di Brescia, Italy, with a Siemens Dual Source Scanner SOMATOM Definition Flash CT. Analysis and post-processing were performed at Siemens Milano, Italy, with a SyngoVia post-processing system using the Region Growing Algorithm to segment volumes and visualize internal anatomical structures. The CT data of the right premaxilla and left dentary were also used to print life-size identical counterlateral bones in 3-D, permitting us to rearticulate them and verify their juxtaposition at jaws closed ( Fig. 2 ). This revealed that the labial margin of the dentary perfectly fits the rim of the medial neurovascular groove of the premaxilla, and that the rostral tip of the dentary symphysis fits the descending margin of the interpremaxillary suture. Moreover, the premaxilla has a bony palate overhanging the edentulous tip of the dentary, leaving no space for any teeth, and two large notches just in front of the first and second dentary alveolus, which accommodated enormous teeth erupting from the dentary. In ventral view, the curvature of the labial sides of the two bones are identical. Moreover, the sutures of the counterlateral bones are correctly aligned along the medial sagittal plane. The perfect occlusion of the two bones demonstrates unequivocally that MHNT.PAL.2012.6.1 and MHNT.PAL.2012.6.2 pertain to the same individual.

The matrix encrusting the nasal attachment of the premaxilla was removed, analyzed, and compared to the matrix of the holotype maxilla. They were found to be similar in aspect and mineralogical composition, supporting the hypothesis that the three specimens came from the same geological age [i.e., Middle Jurassic, Bathonian,167.7–164.7 MA ( Cohen et al., 2013 )] and stratigraphic horizon [Sakaraha Formation sensu Geiger, Clark & Mette (2004) , formerly mentioned in the literature as the Isalo IIIb subunit,‘Faciès Mixte Dinosauriens’ ( Besairie, 1972 )].

The very large isolated tooth crown (catalogue n. MSNM V7144) is part of the fossil vertebrate collection at the Museo di Storia Naturale di Milano. This specimen was collected several years ago in the Mahajanga Basin by G Cortenova, an Italian agronomist living in Madagascar. Before his death, Cortenova gave it to G Colombo, an amateur entomologist, who eventually donated the specimen to the museum.

Map depicting the Triassic and Jurassic outcrops of the Mahajanga Basin (black areas on the left), and geological map of the surroundings of Ambondromamy, highlighting the Sakaraha Fm. (light blue). Part of the material described herein (the premaxilla and the dentary) comes from the area marked by the blue asterisk. Based on Besairie (1968–1969)

The most relevant material described here consists of an almost complete right premaxilla, the rostral half of a left dentary, and a very large isolated tooth crown. The first two specimens belong to the same individual (see below) and are deposited at the Muséum d’Histoire Naturelle de Toulouse under catalogue numbers MHNT.PAL.2012.6.1 (dentary) and MHNT.PAL.2012.6.2 (premaxilla). They were collected by the assistant director of technical services of Société Sucrière de la Mahavavy (D Descouens, pers. comm., 2012) between 1972 and 1974 in the surroundings of Ambondromamy ( Fig. 1 ), the same locality of the Mahajanga Basin that yielded the holotype of R. sakalavae ( Maganuco, Dal Sasso & Pasini, 2006 ) and the sauropod Archaeodontosaurus ( Buffetaut, 2005 ). The specimens were exported from Madagascar under authorization No. 1702 and 2547 of the Mines and Energy Directorate, Ministry of Economy and Finance. Recent careful preparation allowed the specimens to be recognized as belonging to the enigmatic species Razanandrongobe sakalavae . In April 2012, they were acquired by the Muséum d’Histoire Naturelle de Toulouse from the private collection of D Descouens, together with six other cranial fragments anatomically reminiscent of R. sakalavae (catalogued as MHNT.PAL.2012.6.3 to 8) that were collected from an indeterminate Malagasy locality. Of the latter, the largest bone pieces are spongier and more friable, with residual patches of smoothed matrix (possibly due to recent chemical preparation); the smallest pieces are proportionally heavier, denser, whitish, and polished (which suggests prolonged exposure to air and sunlight).

Description

Premaxilla, MHNT.PAL.2012.6.2 (Fig. 3 and Table 1). The almost complete right premaxilla is taller than long (16 vs 13.5 cm), with the premaxillary symphysis straight in rostral and ventral views. This indicates that the rostrum was rostrocaudally short, dorsoventrally deep, mediolaterally wide, and not pointed. The premaxilla bears five teeth that are sub-vertical and only slightly curved lingually.

Specimen TCH labial margin FABL BW FABL /BW FABL/TCH serr. per 5 mm mesial carina serr. per 5mm distal carina DSDI PAL.2012.6.2 pm1 (repl. tooth) – – – – – 5 5 1.00 PAL.2012.6.2 pm2 (41) (24) (24) (1.00) (0.58) – 4.5 – PAL.2012.6.2 pm3 (59) 31 29 1.07 (0.52) – – – PAL.2012.6.2 pm4 (56) 31 27 1.15 (0.55) 4 4 1.00 PAL.2012.6.2 pm5 (51) (30) 28 (1.07) (0.59) 4 – – PAL.2012.6.2 pm5 (repl. tooth) – – – – – 4 – – PAL.2012.6.1 d1 – – – – – – – – PAL.2012.6.1 d2 – [28] [27] [1.04] – – – – PAL.2012.6.1 d3 (48) 27 28 0.96 (0.56) 5 4.5 1.11 PAL.2012.6.1 d4 (23) (27) (26) (1.04) (1.17) – – – PAL.2012.6.1 d5 16 (20) (21) (0.95) (1.25) 6 5.5 1.09 PAL.2012.6.1 d6 (repl. tooth) – – – – – 5 5 1.00 PAL.2012.6.1 d7 (23) 18 16 1.12 (0.78) – – – PAL.2012.6.1 d8 – [19] [19] [1.00] – – – – MSNM V7144 Isolated ?m tooth (67) 35 31 1.13 (0.52) – – – DOI: 10.7717/peerj.3481/table-1

In medial and ventral views, two subcircular paramedian depressions are visible, corresponding to the tip of the mesialmost dentary tooth crowns at jaws closed. The bone wall at one depression is damaged, revealing a well-developed replacement tooth. Dorsal to these depressions is the surface for contact with the palatal portion of the maxilla, namely the rostral portion of the maxillary bony palate. Rostrally, this palatal shelf did not reach the symphysis between the two premaxillae, but instead left an open space in the palate (the incisive foramen) bordered rostrally and laterally by the premaxillae. A subtriangular notch for the premaxillary peg of the maxilla is visible dorsal to the depression hosting the dentary teeth. The rest of the premaxillomaxillary suture is almost flat. There is no lateral groove in the premaxilla for reception of a hypertrophied lower caniniform tooth.

The apertura nasi ossea (often improperly called the external naris, which instead refers to the fleshy nostril) is bordered caudolaterally and ventrally by the premaxilla, and dorsally—in all likelihood—by the nasal, whereas rostromedially it clearly lacks any trace of a dorsally directed nasal process along the medial sagittal plane. Therefore, the left and right aperturae nasi osseae did not only face rostrally, but were also confluent medially.

The surface of the perinarial fossa is smooth and lateromedially wide, and extends from the caudoventral margin of the apertura nasi ossea to the alveolar margins of premaxillary teeth 1–3 ventrally, and to the ornamented facial portion of the premaxilla caudally. The premaxilla is also dorsolaterally rough and ornamented with small crests, pits, and fine grooves. Near the alveolar margin, the ornamented palatal surface, visible in medial view, is pitted by small neurovascular foramina, which are more abundant in a groove delimiting the dorsal end of the paradental shelf. Dorsally, the walls of the premaxilla taper up to form an extended (80 mm long) attachment area for the nasal.

The premaxilla bears four erupted teeth implanted in alveolar positions 2–5. The tooth replacement process is described in detail for the holotype maxilla in Maganuco, Dal Sasso & Pasini (2006). However, CT of the new specimen has provided the following additional information on this process. Resorption of the roots is apparent at positions 2 and 5, in correspondence with the growing replacement teeth, but the roots are still firmly developed and the replacement teeth are growing mostly medial/mesiomedial to the roots. The tips of the replacement teeth are 36 mm from the ventral surface of the premaxilla. At position 3, resorption of the root is more advanced: the tip of the replacement tooth is 22 mm away from the ventral surface of the premaxilla, and is aligned with the erupted tooth. The first alveolus is occupied by a large unerupted replacement tooth. The limited depth of the tooth-bearing portion of the premaxilla in correspondence with the first alveolus (i.e., below the apertura nasi ossea) and the diameter of the alveolus itself indicate that the first premaxillary tooth, even when completely grown, was less than 80% the height of the other premaxillary teeth. Moreover, CT scanning revealed that the roots are straighter mesially than distally when seen in lateral view.

Dentary, MHNT.PAL.2012.6.1 (Fig. 4 and Table 1). The left dentary is incomplete caudally. In lateral view, its maximum dorsoventral depth/height (13 cm) is at the level of alveolus 3. The bone then tapers caudally up to the level of alveolus 6, where the dorsal and ventral margins become almost parallel. There is no constriction at or near the mandibular symphysis along the lateral margin. The rostral edge of the symphysis forms an angle of about 50° with the ventral margin of the dentary. The preserved portion of the dentary bears eight large mandibular teeth; however, none can be considered a hypertrophied caniniform tooth. The size of the alveoli varies along the tooth row. Based on alveolar diameter, the mesial teeth are the largest, numbers 4 and 5 slightly decreasing in size; from 6 onward, their size is constantly half the diameter of alveoli 2 and 3. The position of the first alveolus indicates that the tip of the lower jaw is edentulous. Of the eight tooth positions, number 1 is represented by an empty alveolus, number 6 by a replacement tooth erupting from its alveolus, number 7 by a longitudinally broken and empty crown, numbers 2, 4, and 6 by broken crowns without apex, and only numbers 3 and 5 by almost complete crowns.

The mandibular symphysis with the counterlateral element is 16 cm long and extends caudally to the level of the third tooth, but considering also the estimated contribution of the splenial, it probably extended posteriorly to the level of the fourth tooth. The splenial itself is not preserved, and is represented by a scar; its apex terminated rostrally in a squared peg at the level of the third tooth, as indicated by rostrocaudally elongate sutural marks on the dentary; it contributed to at least 20% of the length of the mandibular symphysis. Caudal to the symphysis, the splenial formed the medioventral portion of the mandibular ramus, resulting visible also in lateral view. The Meckelian groove is exposed in medial view: rostrally, it reaches the mandibular symphysis; caudally, it fades into the contact surface for the splenial.

The lateral surface of the dentary is as well-ornamented as the lateral surface of the premaxilla, and is densely sulcated by rostrocaudally oriented zigzagging vascular canals. Dorsomedially, the bone bears one row of neurovascular foramina parallel to the alveolar margins; internal nutritive foramina bordering alveoli 1–3; and foramina caudal to alveolus 3 aligned in a grooved row closely flanking the lingual margin of the remaining alveoli.

Maxillary fragment, MHNT.PAL.2012.6.3 (Figs. 5A–5D). This incomplete maxillary ramus has six incomplete, straight to slightly curved alveoli, as well as two tooth roots and at least one unerupted tooth. The curvature of the bone, the shape of the roots in lateral and medial views, and the position of the replacement tooth with respect to the alveoli indicate that this specimen is part of the right side of the skull. Moreover, the increasing curvature of the rostral portion of the specimen is suggestive of close proximity to the premaxillary contact, permitting us to designate the alveoli as belonging to teeth 1–6 or 2–7. Of note, the interior of the mesialmost tooth has been replaced by a cast made from a coarse-grained, pale-brownish calcite nodule of alabastrine appearance (F Pezzotta, pers. comm., 2016). Position 4 (or 5) still houses the fossilized root dentine of a slightly larger tooth and, mesiomedially, the tip of a replacement tooth protruding vertically down and exposing the large denticles that are diagnostic of R. sakalavae. A small portion of the lateral (external) maxillary wall is preserved caudodorsally to this tooth position, showing the rugose texture seen in the caudal portion of the premaxilla MHNT.PAL.2012.6.2. In rostral view, a triradiate-shaped broken section of the bone marks the remains of the maxillary bony palate, at mid-height of the preserved alveolar height. Dorsal to the shelf, the medial (internal) wall of the maxilla shows a wide concave surface, relatively smooth where the bone is not broken; ventral to the shelf, the bone of the palate is even smoother, with larger nutritive foramina, but is much more concave (this is the transition point from the palate to the dentigerous margin).

Premaxillary fragment, MHNT.PAL.2012.6.4 (Figs. 5I–5J). This is a small fragment of bone with three half-sections of alveoli, the middle one still housing a tooth root, broken longitudinally and with the pulp cavity exposed. Orienting the alveoli vertically, the external wall can be seen divided into a rugose dorsal portion and a smoother ventral portion; the latter continues caudodorsally, curving inward into a concave area. By comparison with specimen MHNT.PAL.2012.6.3, we interpret this concave area as a caudolateral tract of the apertura nasi ossea, and the smooth ventral portion as part of the perinarial fossa. Therefore, this bone fragment likely comes from a left premaxilla.

Maxillary fragment, MHNT.PAL.2012.6.5 (Figs. 5E–5H). This is a trapezoidal fragment of ornamented bone. The internal wall is traversed by a large, smooth, concave groove. Parallel to one margin of the groove is a long, exposed longitudinal suture. We tentatively refer this fragment to a mediodorsal portion of the ?left maxilla likely contacting the nasal via the aforementioned suture. If the fragment has been correctly placed, the ornamentationwould represent transverse ridges and the groove might be part of a pneumatic space of the maxilla, parallel to the internal choanae, which in mesoeucrocodylians run more medially, below the nasals (e.g., Alligator, Brochu, 1999).

Indeterminate fragments, MHNT.PAL.2012.6.6–8. These three specimens are so fragmentary that it is impossible to determine their anatomical positions. However, we tentatively propose cranial or mandibular origins for MHNT.PAL.2012.6.6 and MHNT.PAL.2012.6.8, for the former because of the presence of a heavily rugose and sulcate ?external surface that fades to a smooth texture ?internally via a convex, U-shaped margin, and for the latter because it has a zigzagging suture mark and a possible internal concavity somewhat reminiscent of a cranial opening. MHNT.PAL.2012.6.7 remains totally indeterminate, and is mentioned here only because it is associated with the other fragments.

New remarks on the holotype maxilla, MSNM V5770 (Maganuco, Dal Sasso & Pasini, 2006: figs. 3–7). The holotypic cranial fragment of R. sakalavae consists of a portion of right maxilla bearing a markedly rugose paradental shelf, a robust sub-horizontal maxillary bony palate positioned definitely higher (dorsal) to the row of alveoli, five large subvertical alveoli, and three unerupted teeth that illuminate the process of tooth replacement (see Maganuco, Dal Sasso & Pasini, 2006 for details). Thanks to the new material described here, the phylogenetic affinities of R. sakalavae have become clearer. Moreover, they have shed light on some previously uncertain features of the holotype maxilla, such as its position in the skull, some doubtful attachment areas (palatine or ectopterygoid; jugal or lacrimal), the presence/absence of the antorbital fenestra, and the margin of the suborbital fenestra. MSNM V5770 bears the caudal portion of the maxillary tooth row, as indicated by the tapering of the paradental shelf, the ending of the maxillary bony palate, and by the scar on the medial surface of the caudalmost portion of the bone that represents the attachment area for the ectopterygoid. Therefore, the rostralmost portion of the ectopterygoid is rostral to the distal alveoli. The thickest part of the maxillary bony palate is confirmed to be the attachment area for the palatine (Kley et al., 2010: figs. 7D, 7E), as previously suggested by Maganuco, Dal Sasso & Pasini (2006), and participates to the rostral margin of the suborbital fenestra. These features render the palate of Razanandrongobe sakalavae quite basal-ziphosuchian-like [e.g., Araripesuchus (Pol & Apesteguía, 2005)], and not at all baurusuchian-like [e.g., Pissarrachampsa (Montefeltro, Larsson & Langer, 2011)] or peirosaurid-like [e.g., Hamadasuchus (Larsson & Sues, 2007)]. It is impossible to estimate how long the missing rostral portion of the maxilla was, but we have at least some indication of the minimum length thanks to the new specimens (see, Cranial reconstruction and size). The caudolateral surface visible in dorsal view most likely represents the remaining portion of the attachment area for the jugal (e.g., Larsson & Sues, 2007: fig. 2) rather than the pavement of the antorbital fenestra.