Etymology.

Areny is named after Arén (Areny in the Catalan language), the locality where ELI-1 was found, and souchus, Greek for crocodile, leading to Latin, suchus.

Type species.

Arenysuchus gascabadiolorum.

Diagnosis.

Arenysuchus is characterized by the following autapomorphies: infratemporal bar tabular and vertically oriented, with little dorsoventral thickness and extreme lateromedial compression; the dorsal portion of the anterior process of the frontal has a very elongated (≈60 percent of the total rostrocaudal length of the frontal) and lanceolate morphology; the anterior process of the frontal projects strongly beyond the main body of the frontal and extends between the nasals, ending in a sharp point beyond the anterior margin of the orbits and the prefrontal, at the height of the anterior end of the lacrimal. The lacrimal is very wide dorsally, only twice as long as wide (taking its maximum length and maximum width).

Differential diagnosis.

Arenysuchus can be differentiated from other crocodylians on the basis of the following unique combination of characters: Arenysuchus presents elevated dorsal rims of the orbits, like the derived crocodyloids, which distinguishes it from the rest of the basal crocodyloids to which it is closely related, such as Prodiplocynodon, Asiatosuchus, “Crocodylus” affinis, Brachyuranochampsa eversolei Zangerl 1944 and “Crocodylus” acer. The frontoparietal suture of Arenysuchus enters the supratemporal fenestra, preserving the plesiomorphic state for Crocodylia. The palatine process of Arenysuchus does not extend beyond the rostral end of the suborbital fenestra, as is also the case in other basal crocodyloids such as Prodiplocynodon langi, Asiatosuchus germanicus Berg 1966, “Crocodylus” affinis or “Crocodylus” acer, which present the same character. Arenysuchus has an occlusion pit between the seventh and eighth maxillary teeth, and all other dentary teeth occlude lingually, which distinguishes it from most crocodyloids, with some exceptions such as “Crocodylus” affinis, which presents the same character.

Distribution.

Late Maastrichtian, North Spain.

Arenysuchus gascabadiolorum sp. nov.

urn:lsid:zoobank.org:act:77F72F35-6DA9-47C5-9A3D-96FC7B290A20

Holotype.

MPZ ELI-1, partial skull (Figs. 3, 4). The specimen is housed in the Museo Paleontológico de la Universidad de Zaragoza (MPZ), Zaragoza, Aragón, Spain.

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Figure 3. Skull of Arenysuchus gascabadiolorum (ELI-1).

A–B, dorsal view. C–D, lateral view. Hatched grey pattern represents broken surfaces. Anatomical Abbreviations: ec, ectopterygoid; f, frontal; gef, groove for ear flap; itf, infratemporal fenestra; ju, jugal; l, lacrimal; ls, laterosphenoid; m, maxilla; mt10, maxillary tooth 10; mt11, maxillary tooth 11; n, nasal; na, naris; oa, otic aperture; or, orbit; p, parietal; pf, prefrontal; pm, premaxilla; pmn, premaxillomaxillary notch; pmt, premaxillary tooth; po, postorbital; pob, postorbital bar; pt, pterygoid; q, quadrate; qj, quadratojugal; sq, squamosal; stf, supratemporal fenestra.

https://doi.org/10.1371/journal.pone.0020011.g003

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Figure 4. Skull of Arenysuchus gascabadiolorum (ELI-1).

A–B, ventral view. C–D, posterior view. Hatched grey pattern represents broken surfaces. Anatomical Abbreviations: bo, basioccipital; bs, basisphenoid; cap, capitate process; ch, choana; ec, ectopterygoid; ex, exoccipital; f, frontal; fa, foramen aërum; fm, foramen magnum; fo, foramen ovale; if, incisive foramen; ju, jugal; ls, laterosphenoid; m, maxilla; mt10, maxillary tooth 10; mt11, maxillary tooth 11; n, nasal; op, 7^th–8^th occlusion pit; or, orbit; p, parietal; pl, palatine; pm, premaxilla; pmn, premaxillomaxillary notch; pmt, premaxillary tooth; po, postorbital; pt, pterygoid; q, quadrate; so, supraoccipital; sof, suborbital fenestra; sq, squamosal; stf, supratemporal fenestra; A and B, muscle scars on the quadrate.

https://doi.org/10.1371/journal.pone.0020011.g004

Referred material.

Four teeth from Blasi 2 (MPZ2010/948, MPZ2010/949, MPZ2010/950, MPZ2010/951) (Appendix S3). This material is housed in the Museo Paleontológico de la Universidad de Zaragoza (MPZ), Zaragoza, Aragón, Spain.

Etymology.

The specific epithet of “gascabadiolorum” is dedicated to the researchers José Manuel Gasca and Ainara Badiola, who discovered the holotype.

Locality and Age.

ELI-1 was gathered from a level of sandstones at the Elías site in Unit 2 of the Tremp Formation (late Maastrichtian) (Fig. 2), approximately equivalent to the Conques Formation. The Blasi sites are situated in the low part of the Tremp Formation (late Maastrichtian). These sites are located in Arén (Huesca), North Spain (Fig. 1A).

Distribution.

As for genus.

Description.

ELI-1 is a fairly complete and well-preserved cranium (Figs. 3, 4, measurements in Appendix S5). The mandible, the right half of the maxillary rostrum, most of the teeth, a large part of the palate, and the posterior part of the braincase are absent or incomplete. No associated postcranial material has been found. Internally, the cranium presents small circular depressions produced by the pressure of the detritic clasts of the rock.

The dorsal surface of the cranium displays well-developed ornamentation, comprising pits and grooves. These grooves are more abundant and deeper on the anterior margin of the orbits and on the posterior end of the squamosals. The orbits are large, slightly elongated anteroposteriorly, and display an ovoidal morphology similar to other plesiomorphic crocodylians such as Prodiplocynodon and Leidyosuchus canadensis Lambe 1907 [43]. The anterior and medial rim of the orbits is upturned. There is an arc-shaped ridge offset by a groove or “spectacle” between the anterior axes of the orbits that is very similar to the one presented by eusuchians such as Allodaposuchus precedens Nopcsa 1928 [16], many alligatoroids such as Leidyosuchus canadensis [43], and several basal crocodyloids such as Prodiplocynodon. The suborbital fenestrae are large and elongated, with straight lateral and medial margins. The supratemporal fenestrae are smaller than the orbits and subrounded. These fenestrae present almost the same lateromedial as anteroposterior width, unlike in other basal crocodyloids such as Prodiplocynodon and Asiatosuchus, where the openings are somewhat narrower anteroposteriorly. The infratemporal fenestrae are triangular and have a somewhat greater anteroposterior width than the supratemporal fenestrae, very similar to that of the orbits, though their lateromedial width is much less than either.

The premaxillae present an undivided naris. The naris occupies roughly 30 percent of the area of maximum premaxillary width. The naris is longer than it is wide, with the posterior part slightly wider than the anterior part and projecting dorsally. The naris is almost completely enclosed by the premaxillae, and the naris may contact to the nasal, although the right half of the maxillary rostrum is missing and the anterior extent of the nasal cannot be determined with certainty. The narial margin is somewhat inflated, rather than depressed. The dorsal posterior process of the premaxilla is short and wide, and extends to a point level with the third maxillary alveolus, as in nearly all non-longirostrine crocodylians and close relatives with a few exceptions (Brachyuranochampsa, some globidontans) [44]. The palatal portion of the premaxillae is not well preserved, but presents a small subcircular incisive foramen close to the first premaxillary alveoli. There is a notch between the premaxillomaxillary suture (Fig. 3A) for the reception of the third and/or fourth tooth of the dentary. At least two alveoli are preserved in the premaxilla, the bigger of which contains a premaxillary tooth, although two or three more alveoli may also have occurred. The preserved premaxillary tooth is conical, and its apex is slightly curved in the distolingual direction. The tooth has a circular cross-section, and a series of very fine basiapically aligned striations ornament the surface. No crests or carinae are preserved, probably due to the poor state of preservation of the surface. We found isolated teeth of similar morphology and with mesial and distal carinae at Blasi 2 [24] (Appendix S3, A).

The maxilla is slightly arched in lateral view, presenting its maximum concavity at the height of the eighth maxillary alveolus. Towards the anterior part, the maxilla has a convex profile with its maximum thickness at the height of the fifth maxillary alveolus; this area also has the maximum width in dorsal view. Posterior to the sixth maxillary alveolus the left and right margins of the maxilla are more parallel to each other in dorsal view. The dorsal surface of the maxilla has a slight circular protuberance posterodorsal to the fifth alveolus. In palatal view, between the tooth row and the suborbital fenestra, the maxilla presents an area of width very similar to the tooth row. This area tends to be much wider in alligatoroids, with the exception of Diplocynodon styriacus, where this area is narrower [45]–[48]. The maxilla has at least 15 alveoli, the eleventh and twelfth of which still include the tooth. Given that the part corresponding to the eighth maxillary tooth is broken, and the posterior end of the tooth row is not very well preserved, we infer a total of 16 or 17 maxillary alveoli. The biggest maxillary alveolus is the fifth. There seem to be no depressed areas in the maxilla corresponding to occlusion grooves for accommodating the teeth of the lower mandible, indicating an overbite occlusal pattern, with the exception of the lateral notch between the premaxilla and the maxilla and an occlusion pit between the seventh and eighth maxillary teeth. The preserved maxillary teeth are low, small in size, slightly flattened labiolingually, wider mesiodistally, and with smooth enamel. The eleventh tooth narrows slightly at its base, giving it a somewhat lanceolate morphology. Isolated teeth of similar morphology have also been found at Blasi 2 [24] (Appendix S3, B).

The left nasal is mediolaterally narrow, with an elongated morphology (10 times longer rostrocaudally than it is wide), with a contour similar to that in Bernissartia fagesii Dollo 1883 and Allodaposuchus precedens [16], [49]. The anterior end of the nasal is not well preserved, so it is difficult to determine the participation in the naris (Fig. 3A), although the nasal is dorsally constricted between the premaxillae and it is possible that the nasal could reach the naris. Posteriorly, the nasals widen abruptly as far as the vertex of the posterior process of the premaxilla, from which point they continue to widen slightly until they reach their maximum width at the point of contact with the lacrimals. From a point level with the eighth maxillary tooth, the nasals are split by the anterior process of the frontal.

The anterior ramus of the jugal is not preserved in the preorbital region, although the bone's morphology can be discerned given that the maxilla and the lacrimal are almost complete in this area. From the anterior ramus, the jugal widens posteriorly, reaching its maximum dorsoventral width at the lateral orbital margin, at which point the posterior ramus becomes narrower again until it reaches the quadratojugal. The jugal forms most of the infratemporal bar, although it is impossible to tell whether the posterior angle of the infratemporal fenestra is formed by the jugal or the quadratojugal, because this region has not been preserved. The jugal forms a large part of the postorbital bar, with an ascending process that starts from the medial surface of the jugal and rises posteromedially until it contacts the ventral part of the postorbital. Two small medial foramina pierce the area anterior and posterior to the postorbital bar. The jugal is raised above the base of the postorbital bar, forming an elevated margin. The shape of the infratemporal bar is very tabular, elongated and lateromedially narrow, similar to Allodaposuchus precedens. In lateral view, the infratemporal bar has very little dorsoventral thickness (average thickness of 6 mm) (Fig. 3B), and in dorsal view it presents an extreme lateromedial compression (average width of 3 mm) (Fig. 3A).

The lacrimal is very wide dorsally, lateromedially and anteroposteriorly wider than the prefrontal. The posterior margin of the lacrimal in contact with the orbit is upturned with respect to the dorsal surface of the rostrum and has marked ornamentation on its dorsal surface. The anterior contact between the lacrimal and the maxilla is very sinusoidal, forming two undulations, and the contact with the nasal is broad. A small, dorsoventrally flattened foramen is visible in the anterior wall of the orbital portion of the lacrimal. This may correspond to the lacrimal duct.

The prefrontal has a subtriangular anterior process, with its apex situated between the lacrimal and the nasal. The prefrontals are separated by the frontal and the nasals and do not meet along the midline. The posterolateral end of the prefrontal participates in the anteromedial margin of the orbit and is upturned, like the lacrimal. On its posterior margin, the prefrontal expands medially, causing a narrowing at the beginning of the anterior process of the frontal and giving the frontal a lanceolate shape. The ventral surface of the prefrontal contributes to the anterior portion of the orbit. The entire dorsal surface of the prefrontal is ornamented with subcircular grooves. The prefrontal pillar is longitudinally expanded dorsally, but is more columnar ventrally, as in most crocodylians with the exception of gavialoids. Dorsally, the prefrontal has a fine lateral lamina on the orbital margin beneath the lacrimal and the prefrontal, forming the concavity in which the olfactory bulbs are housed [12] (Fig. 4). The medial process of the prefrontal pillar is not preserved.

The anterior process of the frontal has a smooth, flat dorsal surface, without ornamentation, that is elongated (≈60 percent of the total rostrocaudal length of the frontal), narrow (nine times longer rostrocaudally than it is wide) and lanceolate, showing the plesiomorphic state for Crocodylia. This process is somewhat similar to but longer than that in other eusuchians such as Allodaposuchus [12], [16] and Crocodylus niloticus. This anterior process is separated from the main body of the frontal and terminates in a sharp point beyond the anterior margin of the orbits and the prefrontal, at the height of the anterior end of the lacrimal (Fig. 3A). The suture with the prefrontals and nasals is smooth, without serrations, and the suture with the prefrontal forms a right angle. The margin of the prefrontal and the frontal between the orbits is elevated in relation to the rostrum, as in derived crocodylids such as Crocodylus or Tomistoma. The dorsal surface of the frontal between the orbits is markedly ornamented and is practically flat, even though the margin of the orbits is slightly elevated. Posteriorly, the frontal narrows between the supratemporal fenestrae and contacts the parietal at the start of the frontoparietal bar, forming a slightly convex suture. The frontoparietal suture enters the supratemporal fenestra, preventing broad contact between the postorbital and the parietal, as in basal gavialoids and alligatoroids, certain pristichampsines and Borealosuchus sternbergii Gilmore 1910, which is plesiomorphic for Crocodylia.

The postorbital is crescentic in dorsal view and forms the dorsal part of the postorbital bar. The postorbital extends somewhat more dorsolaterally than ventromedially on the postorbital bar and is superimposed upon the ascending process of the jugal, the two processes coinciding at roughly the halfway point of the postorbital bar. As occurs in many crocodylians, a slight dorsal swelling on the postorbital bar occurs in the area of contact between the jugal and the postorbital. There is no descending process of the postorbital, a character present in many alligatorids [44], [50], although this area is not very well preserved. As in most basal crocodylians, the postorbital contacts the quadrate medially in the dorsal region of the infratemporal fenestra (Fig. 4A); the postorbital may also contact the quadratojugal, although this area is incomplete and difficult to interpret.

The squamosal constitutes almost a quarter of the boundary of the supratemporal fenestra, corresponding to the posterolateral margin. The squamosal has a fairly horizontal dorsal surface, with ornamentation consisting of deep subcircular grooves, particularly at the posterior end. At this end the squamosal has a horn-shaped posterior projection, although in ELI-1 it is impossible to establish its extent due to incomplete preservation. The squamosal has an elongated and lobular anterior process which extends ventrally to the posterodorsal end of the postorbital (Fig. 3B). The squamosal forms the upper part of the otic opening, and in lateral view it presents the groove for the external ear valve musculature, the rims of which are parallel. This groove traverses the squamosal from the posterior region to roughly the point of contact with the postorbital. The area of contact between the squamosal, the exoccipital, and the posterior region of the quadrate is not well preserved.

The parietal is completely fused, and its most posterior end is missing. The anterolateral margin of the parietal is depressed at the edge of the supratemporal fenestra. The frontoparietal suture enters the supratemporal fenestra (Fig. 3A), and the parietal becomes narrower anteriorly along the anteromedial wall of the supratemporal fenestra, until a point where the parietal wedges out between the frontal and the laterosphenoid, ending in contact with the suture of the postorbital and the frontal. The parietal and the squamosal contact in the most dorsal part of the posterior wall of the supratemporal fossa, but an ascending process from the quadrate prevents contact further ventrally. In dorsal view, the parietal expands very slightly laterally in the area anterior to and between the supratemporal fenestrae, forming the anterior sector of the frontoparietal bar.

The quadratojugal is incomplete, and consequently the development of the quadratojugal spine and the degree of quadratojugal participation in the infratemporal bar cannot be determined. The extension of the quadratojugal to the superior angle of the infratemporal fenestra prevents the quadrate from participating in this fenestra. The preserved part lacks ornamentation.

The palatines are elongate (12–13 times longer rostrocaudally than they are wide), straight and narrow. They are slightly wider at their anterior ends than at their posterior ends, and they expand laterally at the height of the posterior margin of the suborbital fenestra. The anterior end of the palatine and a large part of the maxilla in ventral view have not been well preserved, so the contact between these elements is difficult to resolve. In spite of this, it seems that the anterior end of the preserved palatine coincided with the area of the suture with the maxilla (Fig. 4A). It can thus be deduced that the palatine does not extend beyond the anterior margin of the suborbital fenestra and has a rounded shape similar to other basal crocodyloids such as Prodiplocynodon, “Crocodylus” affinis and Brachyuranochampsa [51]. A straight midline suture joins the two palatines; they do not reach the posterior end of the suborbital fenestra due to the intrusion of the pterygoid. The prefrontal pillar contacts the dorsal surface of the palatine, roughly in the area where the palatine begins its anterolateral expansion.

The maxillary ramus of the ectopterygoid is adjacent to the tooth row, almost contacting the final four or five maxillary alveoli (Fig. 4A) and possibly even forming the medial wall of the final two alveoli. The anterior part of the maxillary ramus ends in a point. The posterolateral process of the ectopterygoid contacts the lateroventral surface of the pterygoid, although the process does not reach as far as the posterior margin of the pterygoid. The ectopterygoid extends partially along the postorbital bar.

The pterygoids contact the palatines by means of a “zig-zag” suture on the posterolateral margin of the suborbital fenestra, but not in its most posterior angle. As in all eusuchians, the secondary choana is completely included within the pterygoids. The choana is located close to the posterior margin. The pterygoid is not depressed at the margins of the choana, and this does not form a neck. No septum divides the choanal opening. The pterygoid wings are dorsoventrally slender and are expanded posteriorly on the lateral margin where this articulates with the ectopterygoid. The posterior axis of the pterygoid is strongly curved, and a concave edge is formed in the posterior area of contact between the two pterygoids. The posteromedial process of the pterygoid is prominent and projects ventrally (Fig. 4B), displaying the plesiomorphic condition seen in other basal crocodyloids such as Brachyuranochampsa eversolei, “Crocodylus” acer, “Crocodylus” affinis, Asiatosuchus germanicus and Prodiplocynodon langi [51], [52]. In lateral view, sutures between the pterygoid, quadrate, and laterosphenoid are difficult to make out due to poor preservation, but a significant ventral process of the quadrate on the lateral braincase wall, together with the laterosphenoid, prevents the pterygoid from participating in the opening of the foramen ovale (Figs. 3B, 4A).

As in most crocodylians, with the exception of most alligatorids, the quadrate forms the anterior, ventral and posterior margin of the otic opening, and the squamosal forms the dorsal margin; in other words, the quadratosquamosal suture extends dorsally along the posterior margin of the opening. The dorsal surface of the quadrate lacks ornamentation. A gentle medial depression on the quadrate could correspond to the foramen aërum. The medial hemicondyle has not been preserved. Ventrally the quadrate is crossed by a crest associated with depressed areas, muscular insertion crest “B”, and though less marked, crest “A” also seems to be preserved (sensu [53]). The quadrate forms the posterolateral margin of the foramen ovale, which is surrounded by two longitudinal grooves, one aligned lateromedially and the other anteroposteriorly (Fig. 4A).

The neurocranium is the worst-preserved part of ELI-1. All that remains are the laterosphenoid, part of the basioccipital and part of the basisphenoid. The basisphenoid is very incomplete, but forms a thin sheet ventral to the basioccipital (Fig. 4). The right half of the basioccipital bone below the foramen magnum has been preserved (the occipital condyle is not preserved). This portion of the basioccipital is semicircular in posterior view, with ventral curvature, and it projects perpendicular to the occipital plane (Fig. 4B). The suture with the exoccipital is located just below the foramen magnum, slightly above where the quadrate begins. The foramen magnum is not well preserved. The laterosphenoid is Y-shaped, with three diverging rami, one projecting anteriorly and the other two posteriorly (Fig. 4A). These posterior rami participate in the anterolateral and anteromedial margin of the foramen ovale, where it makes contact with the quadrate. These rami of the laterosphenoid participate slightly in the posteromedial region of the posterior wall of the supratemporal fenestra, until the rami meet the ascending process of the quadrate, which occupies most of the posterior wall. The anterolateral ramus forms the base of the medial wall of the supratemporal fenestra, and wedges the parietal laterally. The capitate process of the laterosphenoid is oriented anteroposteriorly toward the midline.