Calmasuchus acri, Fortuny & Galobart & Santisteban, 2011

Calmasuchus acri sp. nov.

Figs. 2–6 View Fig View Fig View Fig View Fig View Fig .

1993 Parotosuchus sp. ; Gaete et al. 1993.

Etymology: From the Latin acre, defined as hard or strong and referring to the hardness of the matrix that surrounds the fossils and makes preparation of the material difficult.

Type material: Holotype: IPS−37401 (LM−83) has a partial skull roof and palate ( Fig. 3 View Fig ). Paratypes: IPS−37401 (LM−63, LM−101, L, and M1) consists of skull fragments and IPS−42407 (LM−4) is a complete hemimandible ( Figs. 4 View Fig , 5 View Fig ).

Type locality: All the specimens were collected from the La Mora site of the Catalonian basin, Barcelona, Spain. All were collected by Àngel Galobart, Rodrigo Gaete, and Xavier Ros in 1990 .

Type horizon: Catalonian basin, Catalan Coastal Ranges, Buntsandstein facies from the Montseny−Llobregat Domain , included in the Areniscas y Lutitas del Figaro unit, and dated as early−to−middle Anisian (Middle Triassic) .

Diagnosis.—Distinguished from all other capitosaurs by a combination of the following characters: posterolaterally directed tabular horns, orbital margins flush with the plane of the skull, the postorbital and prefrontal near each other by thin projections, paired anterior palatal vacuity, long choanal outline, the frontal enters the medial border of the orbit, presence of a transversely oriented transvomerine tooth row, cultriform process of the parasphenoid extends beyond the anterior border of the interpterygoid vacuities, absence of the denticle field in the pterygoid and parasphenoid, elongated and well developed postglenoid area.

Preservation.—Fossil bone remains from the La Mora site are well preserved despite the hard matrix that wraps parts of the bones and the action of sedimentary compaction and tectonic stress that slightly crushed some anatomical structures, making assessment of some cranial characters difficult. To resolve this problem, other cranial fragments are described when the characters are poorly or not preserved in the holotype. Here, we focus on the study of some incomplete skulls recovered from the La Mora site. All the cranial remains display well−fused sutures, indicating that they belong to adult animals. The partial cranial fragments recovered and the computed tomographic reconstruction allowed description of the skull.

Description

Skull roof.—The skull roof is nearly complete in IPS−37401 (LM−83) ( Fig. 3 View Fig ). The length of the skull roof, as preserved, is 30.9 cm from the posterior margin of the skull to the external nares (anterior margin). The tip of the snout anterior to the external nares is not preserved in the dorsal view. The posterolateral region of the skull roof is incomplete in IPS−37401 (LM−83), but it is well preserved in IPS−37401 (LM−63, L, and M1) ( Figs. 4 View Fig , 6 View Fig ). The sutures of the skull elements in IPS−37401 (LM−83) are firmly fused and discernible. The bone ornamentation is well developed and corresponds to the typical temnospondyl pitted sculpture pattern. In the dorsal view, the overall shape of the skull roof displays a convex snout. The tabular sutures the squamosal at the level of the anterior margin of the otic notch. The tabular horns are posterolaterally directed where the apex of the horn is in close proximity to the squamosal posteriorly, without suturing it posteriorly. The posterior tip of the tabular is nearly equally expanded mediolaterally but only slightly expanded anterodistally. The tabular horns are complete and well preserved in IPS−37401 (L and M1). IPS−37401 (LM−63) preserves the tabular–squamosal and tabular–supratemporal sutures. In this fragment, the tabular horns are not completely preserved, preventing description of its postparietal–tabular margin, which shows an unpreserved suture. On the other hand, Calmasuchus acri lacks the long processus lateralis present in the tabular of some capitosaurs. The posterior margin of the squamosal is slightly convex dorsally, with a narrow falciform crest.

The parietal is longer than the supratemporal, which is slightly longer than the postparietal. The supratemporal is excluded from the otic notch. The frontal enters the medial border of orbit. The morphology of the orbit is slightly subcircular, and in IPS−37401 (LM−63), it is 35 mm in length and 30.3 mm in width. The orbital margin lies in the same plane of the skull roof. Apart from this, the interorbital area is flattened and moderately broad ( 55.2 mm in width) in comparison with other capitosaurs (e.g., Stanocephalosaurus pro−

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nus) with narrow interorbital distance. The postorbital is moderately expanded anterolaterally because it occupies less than half of the orbital border. The postorbital and prefrontal are not in contact. A thin projection of the jugal reaches the orbital margin. The external nares are not completely preserved; therefore, the morphology of this structure is uncertain.

Sensory sulci.—The lateral line sensory canals are discontinuous. The supraorbital sensory canal passes across the posterior section of the suture between the lacrimal and the nasal. It follows the nasal anteriorly, similar to that in some specimens of Eryosuchus garjainovi or Cyclotosaurus robustus as observed by Schoch (2008). On the other hand, the lacrimal flexure of the infraorbital sensory canal is partially preserved, preventing observation of any Z−shaped morphology. The occipital sensory canal is absent.

Palate.—The palate is partially preserved in IPS−37401 (LM−83), enabling the various palatal vacuities to be outlined ( Figs. 3 View Fig , 6 View Fig ). The vomerine plate is elongated. The transvomerine tooth is oriented transversely. The choanal outline is long but its preservation prevents discrimination between narrow choanae as in Parotosuchus orenburgensis or ovalshaped choanae as in Wetlugasaurus angustifrons . Nevertheless, the circular−subcircular outline of the choanae is rejected. Paired anterior palatal vacuities are present.

The palatal fragment in IPS−37401 (LM−101) ( Fig. 4 View Fig ) shows both the major part of the vomer and the maximal outline of the choanae, although as in the case of IPS−37401 (LM−83) its preservation prevents discernment of the narrow or oval choanal morphology. Postfenestral teeth can be clearly outlined and placed. The distance between the postfenestral teeth and the posterior part of the anterior palatal vacuity is 5 mm. IPS−37401 (LM−101) also shows the anterior process of the palatal vacuity. Although not well preserved, the presence of an anterior process closing the vacuity on the right side of the palatal view allows us to reject an unpaired vacuity or a medially subdivided one, as is the case in Benthosuchus shushkini . The ectopterygoid does not contact the interpterygoid vacuities. The interpterygoid vacuities are equally wide along their extension.

The cultriform process of the parasphenoid is preserved in IPS−37401 (LM−83). It extends beyond the anterior border of the interpterygoid vacuities to the level of the choanae. In contrast, in the posterior region of the cultriform process, there is no evidence of a deltoid base. The participation of the palatine at the margin of the interpterygoid vacuities prevents the palatine ramus of the pterygoid from contacting the vomer. The pterygoid is slender. The posterior half of the palatine ramus curves medially, where it forms the corpus of the pterygoid; then, this corpus curves laterally, forming the quadrate ramus. The pterygoid displays a pronounced sculpture in the palatine region and corpus. The palatine ramus and most of the corpus

http://dx.doi.org/10.4202/app.2010.0025

of the pterygoid are present in IPS−37401 (LM−83), but the quadrate ramus of the pterygoid is damaged and badly preserved. This region is well preserved in IPS−37401 (LM−63), displaying a parasagittally oriented quadrate ramus and preserved quadrate–pterygoid suture. The suture between the pterygoid and the parasphenoid is anteroposteriorly short. The parasphenoid prevents the exoccipital from contacting the pterygoid ventrally. As revealed in IPS−37401 (LM−83), the parasphenoid plate, with a rectangular shape, is flattened without any depression or sculpturing. The crista muscularis of the parasphenoid is poorly preserved and can be discerned only at the level of the pterygoid–parasphenoid suture. The occipital condyles are located slightly anterior to the quadrate condyles.

Occiput.—Most of the occiput is not preserved and only a few characters are available for description, because of the use of computed tomographic scans ( Fig. 2 View Fig ). Structures of the occiput are recognisable only in IPS−37401 (LM−63). Matrix deletion and virtual repositioning of the cranial structures allowed us to confirm that the quadratojugal contributes to the upper jaw condyle, whereas the post−temporal fenestra displays a triangular morphology, as is the case of almost all capitosaurs and trematosaurs.

Mandible.—At least seven well−preserved hemi−mandibles were recovered in the type locality. The general description is based on IPS−42407 (LM−4) ( Fig. 5 View Fig ), which is complete and well preserved, at a total length of 39.5 cm. The hemimandible is low except for its posterior area, which is dorsally straight along the posterior two−thirds and slightly curved in the anterior part. In the labial view, the angular shows well−defined ornamentation that becomes less evident in the postsplenial. In the posterior part of the hemi−mandible, a weakly developed mandibular sulcus is present. The dentary shows two anterior tusks and 47 teeth with moderately compressed bases. Both the dentary and the splenial form part of the symphyseal region, as is typical in temnospondyls. The postglenoid area is elongated and contains the articular and surangular, without any sign of the prearticular. The angular lies ventrally to the articular. The foramen chorda tympani lies in the posterior region of the glenoid fossa, separating the articular and prearticular.

Although Jupp and Warren (1986) discuss the lower jaw anatomy of temnospondyls, the morphology of the postglenoid area cannot be clearly placed in any of the two types described by these authors. It shares with type I the following features: the prearticular does not extend into the postglenoid area, the articular is the major component of the postglenoid area, the angular lies ventral to the articular, and the foramen chorda tympani separates the articular and prearticular. On the other hand, as in type II, the angular lies labial to the articular and the postglenoid area is elongated.

Moreover, the prearticular does not suture the splenial because it is separated by the coronoid. Although the mandibular sutures are not clearly discernable because of taphonomic reasons, the major part of the middle coronoid probably does not reach the prearticular or the posterior Meckelian foramen. The posterior Meckelian foramen is short, being less than half the size of the adductor fossa ( Damiani 2001) and less than 25% of the total length of the mandible (Schoch 2000).The anterior Meckelian foramen is poorly preserved, but it is situated slightly in an anterior position in comparison with that in other capitosaurs.

The prearticular shows a well−developed, high, and massive hamate process. The quadrate trochlea is shorter than the hamate process. Comparisons of the postglenoid area with that of other capitosaurs allowed us to classify the mandible of Calmasuchus acri as type IV of Maryańska and Shishkin (1996), with an elongated postglenoid area and a depressed dorsal surface. The crista articularis is poorly preserved but is displaced and continuous with the crista medialis. The glenoid fossa lies above the dorsal surface of the dentary. The adductor fossa is short. As in most capitosaurs, the labial wall of the adductor fossa is straight and horizontal.