Introduction

Capitosaurs constituted one of the most abundant groups of Triassic temnospondyl amphibians. Despite their cosmopolitan distribution, fossil records in the Iberian Peninsula are scarce, with only three reported sites: Rocha da Pena, Portugal (Witzmann and Gassner 2008); and La Mora and Riera de Sant Jaume, Spain (Gaete et al. 1993; JF unpublished data).

The wide distribution of temnospondyls, especially capitosaurs, has been used in biostratigraphy (Cosgriff and Defauw 1987) to correlate Triassic tetrapod faunas (Lucas 1998). These faunas are well known in the Eastern European platform (e.g., Ochev and Shishkin 1989; Shishkin and Ochev 1994) and Beafourt Group of South Africa (Karoo Basin) (e.g., Hancox et al. 1995; Shishkin et al. 1995; Damiani 2004). However, the phylogenetic relationships of capitosaurs have remained controversial since the first discoveries, even with the more recent studies (e.g., Watson 1962; Welles and Crosgriff 1965; Ochev 1966; Schoch 2000; Schoch and Milner 2000; Damiani 2001; Steyer 2003; Schoch 2008; Maganuco et al. 2009).

The first revision of the group (Welles and Cosgriff 1965) focused on the evolution of the otic notch (open in primitive forms and closed in derived forms) in an attempt to establish the taxonomy of the “Capitosauridae”. The revision by Ochev (1966) was markedly different: a large number of genera and species were recognised by using the shape of the tabular horn as a criterion for determining taxonomic relationships. The most recent revisions (Schoch 2000; Damiani 2001; Schoch 2008; Maganuco et al. 2009) demonstrate that the evolution of the group involves more cranial characters than those regarded previously.

On the other hand, recent papers include new descriptions of old and new specimens recovered from the Central European Basin, providing crucial information to understand the evolution of the clade; especially, capitosaur remains have been described in detail (Maryańska and Shishkin 1996; Schoch 1997, 1999; Sulej and Majer 2005; Shishkin and Sulej 2009). The first capitosaur cranial remains recovered in Spain were assigned to Parotosuchus (Gaete et al. 1993, 1994, 1996). Here, we present a revised description of the original and new materials, enabling us to establish a new genus—Calmasuchus acri gen. et sp. nov. (Amphibia: Temnospondyli)—and providing new data to resolve the evolution of the group. In this regard, new data acquired by computed tomography, including complete skull reconstruction of this taxon, have been added to the previous information obtained by mechanical preparation of the matrix. Cladistic analysis including the new taxa performed by using an updated version of the previous matrix of Damiani (2001) for the group has enabled us to propose a new phylogeny.

Fig. 1.

Geographic and geologic location of the capitosaur Calmasuchus acri gen. et sp. nov. from the Anisian at the La Mora site, Spain, with a stratigraphic cross-section containing the vertebrate locality (arrow). See text for facies interpretation.

Institutional abbreviations.—IPS, Institut Català de Paleontologia, Sabadell, Spain; MB, Museum für Naturkunde, Berlin, Germany; MNHN, Muséum National d'Histoire Naturelle, Paris, France; PIN, Paleontological Institute of the Russian Academy of Sciences, Moscow, Russia.

Geological setting

The Triassic outcrops of the La Mora site (Catalonia, Spain, northeast of the Iberian Peninsula) belong to the Montseny-Llobregat domain (Calvet and Marzo 1994) of the Catalonian basin. This palaeogeographic unit has been identified as one of the eastern-most sub-basins of the Iberian plate. The Buntsandstein facies in this area (Fig. 1) is formed by continental deposits (Calvet and Marzo 1994). These materials are derived from the erosion of the Iberian Massif and they show thickness increment from northeast (145 m) to southwest (310 m).

The sedimentary deposits of this sub-basin are mainly composed of sandstone, mudstone, and red clay (Areniscas y Lutitas del Figaró unit); these materials are interpreted as fluvial deposits and distributed from northwest-northeast to southeast-southwest (Calvet and Marzo 1994).

At the La Mora site, the Buntsandstein facies deposits belong to the lower part of the Areniscas y Lutitas del Figaró unit. This unit is unconformable on Paleozoic metamorphic rocks. The section is 25 m thick and is composed of intercalations of red clay, mudstone, and sandstone in four sedimentary sequences with five different facies bound by calichetype palaeosols (Fig. 1). The materials are interpreted as infilling of a channel body with an erosional base and a topping plane. Facies A represents the first deposits that formed the base of the level and deposits B are enclosed by the margin of the channel. Both are interpreted as point bars. In relation to these point bars, the sandstone from facies C fills the central part of the channel and its equivalent to the lower part of the deposits of the point bar. Facies C yields the vertebrate locality. The clay and silt from facies D constitute the final infilling of the abandoned fluvial channel and extend beyond the boundary of the channel as flood-plain deposits. In facies E, the sediments show a concentration of calcium carbonate nodules.

Fig. 2.

Computed tomographic reconstruction of the capitosaur Calmasuchus acri gen. et sp. nov. from the Anisian at the La Mora site, Spain, in dorsal (A), ventral (B), lateral (C), and occipital (D) views.

The age of the Areniscas y Lutitas del Figaró unit remains uncertain. The first palynological work in this Buntsandstein facies (Solé de Porta et al. 1987) dated the unit as Anisian. A recent palaeomagnetostratigraphic study excludes the possibility of an Olenekian stage (Dinarès-Turell et al. 2005) and biostratigraphic analysis of the overlying lower Muschelkalk facies indicates an age of middle-to-upper Pelsonian to upper Illyrian (middle-to-upper Anisian), on the basis of the presence of the conodonts Paragondolella bulgarica, P. hanbulogi, P. bifurcata, Neogondolella constricta, N. cornuta, N. excentrica, and N. basisymetrica. In addition, the brachiopod Spiriferina (Mentzelia) mentzeli is recognised at the base of this facies and the ammonite Paraceratites fauna is located in the middle part of the lower Muschelkalk facies (see Mârquez-Aliaga et al. 2000; Dinarès-Turell et al. 2005 for further details). All these data restrict the La Mora site to an Aegean-to-middle Pelsonian age (early-to-middle Anisian).

Materials and methods

The La Mora site was discovered in 1989 by local hikers Emili Ramon and Pere Font. A year later, palaeontological fieldwork was undertaken by the Institut de Paleontologia de Sabadell (Spain), extracting hundreds of cranial and postcranial bones. Most of these bones were identified as belonging to capitosaurs. Other elements were postcranial elements of archosauromorphs and cranial remains of procolophonoids noted in previous studies and currently under study (Gaete et al. 1993, 1994, 1996; JF unpublished data). In addition, tetrapod ichnites were recovered close to the site, including the ichnogenera Rhynchosauroides, Chirotherium, and Synaptichnium (see Calzada 1987 for further details).

The hard matrix and high density of bones (often in contact) hindered their preparation for a long time and made description of the osteology of these materials and identification of diagnostic characters difficult (Gaete et al. 1994). Nevertheless, after several years of mechanical preparation, cranial remains were sufficiently prepared for description. Moreover, computed tomographic scans were performed to understand the morphology of some areas better, and as a useful tool to enable skull reconstruction by using cranial remains (Fig. 2). This reconstruction shows the mandible and the major part of the skull roof and palatal regions. All the cranial remains were scanned by multidetector computer tomography (Sensations 16; Siemens) at Hospital Universitari Mútua Terrassa (Barcelona, Spain). Each cranial specimen was scanned at 140 kV and 220 mA with an output of 512 × 512 pixels per slice, with an interslice space of 0.2 mm, and processed by using the Mimics software (Materialise, Leuven, Belgium), obtaining an almost complete skull reconstruction from the partial fossil material.

Systematic palaeontology

Fig. 3.

Remains of the capitosaur Calmasuchus acri gen. et sp. nov. IPS-37401 (LM-83) from the Anisian at the La Mora site, Spain, in dorsal (A, B) and ventral (C, D) views. Photographs (A, C) and explanatory drawings (B, D).

Fig. 4.

Photographs and drawings of paratypes of the capitosaur Calmasuchus acri gen. et sp. nov. from the Anisian at the La Mora site, Spain. A. Cranial remains IPS-37401 (LM-63), in dorsal (A₁, A₂) and ventral (A₃, A₄) views. B. Palatal fragment IPS-37401 (LM-101), in dorsal (B₁, B₂) view. C. Posterior skull roof fragments of IPS-37401 (L and M1), in dorsal (C₁, C₂) view. Note that fragments L and Ml are in contact. Photographs (A₁, A₃, B₁, C₁) and explanatory drawings (A₂, A₄, B₂, C₂).

Fig. 5.

Photographs and drawings of lower jaws of the capitosaur Calmasuchus acri gen. et sp. nov. from the Anisian at the La Mora site, Spain; specimen IPS-42407 (LM-4). Photograph (A) and drawing (B) of the hemi-mandible in lingual view. Photograph (C) and drawing (D) of the hemi-mandible in labial view. E. Postglenoid area.

Fig. 6.

Cranial reconstruction in dorsal (A) and ventral (B) views of the capitosaur Calmasuchus acri gen. et sp. nov. from the Anisian at the La Mora site, Spain.

Phylogenetic analysis

In order to investigate the phylogenetic relationships of the new taxon, we incorporated its characters into a data matrix. We also scored Vladlenosaurus alexeyevi in a cladistic analysis, for the first time. This form was recovered from the late Vetlugian of Russia and confined to lacustrine habitats, and it shows an outline very similar to benthosuchids (Bystrow 1940; Getmanov 1989; Novikov 1990), although some cranial characters are similar to Wetlugasaurus (Morkovin and Novikov 2000; Shishkin et al. 2006). The data matrix was an updated version of Damiani (2001), with new characters and different coded taxa. Recent capitosaur findings (Morales and Shishkin 2002; Steyer 2003; Damiani 2008; Schoch 2008; Maganuco et al. 2009) provided new information on the cranial characters of the group; therefore, an upgrade of the Damiani (2001) matrix was required. From the original matrix, two characters were deleted because they were uninformative (characters 22 and 34; see Damiani 2001 for character details). In addition, eight characters were added to the matrix (see Appendix 1). These characters were previously used in cladistic analysis and provided informative data (Schoch 2000, 2008; Maganuco et al. 2009).

The analysis was performed by using PAUP 4.0 beta 1.0 for PC (Swofford 2001). The data matrix consisted of 53 characters and 26 terminal taxa, with three terminal taxa as an outgroup taxon (Rhineceps nyasaensis, Uranocentrodon senekalensis, and Lydekkerina huxleyi). The taxa analysed (see Appendix 2) are considered at the species level, except for Angusaurus, Eocyclotosaurus, and Watsonisuchus; for these taxa, we preferred to use the characters of the genus rather than those of the species, as exemplified by Damiani (2001), Damiani and Yates (2003), or Maganuco et al. (2009). Characters were scored by using information from the literature and JF personal observations (see Appendix 2). All characters were equally weighted and left unordered, except character 4 (tabular horn), because it forms a clear transformational series in which the otic notch is gradually closed posteriorly, as indicated by Damiani (2001). Delayed transformation (DELTRAN) and Accelerated transformation (ACCTRAN) were selected to optimize the character transformation. Taxa coded as having multiple states were treated as polymorphic. We used a heuristic search with simple addition sequence and only one tree at each step during stepwise addition and 10,000 replicates. Tree-Bisection-Reconnection branch swapping was performed and zero-length branches were collapsed to yield polytomies. See Appendix 3 for further details.

Fig. 7.

Ciadogram of the capitosaurs analysed in the data matrix. A. One of the two most parsimonious trees. B. Consensus trees (strict and majority rule show identical topology) of the two most parsimonious trees.

Our phylogenetic analysis resulted in two most parsimonious trees of 141 steps each (CI = 0.41, RI = 0.70, RC = 0.29). As reported by Damiani (2001) and Maganuco et al. (2009), a high amount of homoplasy was suspected in the evolution of the group, resulting in a low CI value. The strict and majority-rule consensus trees of the two most parsimonious trees were identical (Fig. 7) and showed one unresolved polytomy at the level of the clade composed of Cyclotosaurus robustus, Tatrasuchus wildi, Mastodonsaurus giganteus, and Eryosuchus garjainovi.

The support for the single nodes and their robustness according to bootstrap were low. Only seven nodes reached bootstrap values higher than 50% (1, 100%; 2, 93%; 4, 71%; 5, 94%; 9, 69%; 16, 77%; 18, 94%). In brief, this indicated that, apart from the Capitosauria and Trematosauria, only the trematosaurs and few capitosaur clades are well supported. The clade notation used in the paper (taxon X + taxon Y) refers to the least inclusive clade in the resolved cladogram comprising the two given taxa and does not imply that these taxa share a direct sister-taxon relationship. Node numbers are indicated in Fig. 7. The phylogenetic discussion is based on most parsimonious tree number 1, whose topology is congruent to that of the consensus trees. See Appendix 4 for the apomorphy list and more details about the character evolution.

Discussion

Previous morphological studies.—Previous studies on some of the already described material suggest close affinities to Parotosuchus sp. (Gaete et al. 1993, 1994, 1996). These authors published a preliminary reconstruction of the material and referred it to the genus Parotosuchus, reporting the presence of paired anterior palatal vacuities as a rather distinctive morphology from this genus. However, this is not the only difference between Parotosuchus sp. and Calmasuchus acri: the tabular morphology differs, being posteriorly directed in all the specimens of Parotosuchus and posterolaterally directed in those of Calmasuchus acri. The relative orbital size of Parotosuchus sp. and Calmasuchus acri is similar, but they differ in their orbital margins, which are elevated in Parotosuchus specimens and flushed in the same plane in Calmasuchus acri. Differences are also present in the mandibles, especially in the postglenoid area. Parotosuchus orenburgensis resembles type III of Maryańska and Shishkin (1996) whereas Calmasuchus acri belongs to type IV.

More recently, some authors, based on the descriptions and drawings supplied from the first papers, suggested that the La Mora specimens could be referred to as a stenotosaurid indet. (Shishkin 2000) or Eryosuchus sp. (Damiani 2001). However, the material described here cannot be attributed to stenotosaurids because it does not display the prefrontal—postorbital contact, typical of stenotosaurids (and heylerosaurids). Its supraorbital sensory canal is slightly displaced laterally in Calmasuchus acri and contacts the lacrimal—nasal suture, as in some specimens of Cyclotosaurus robustus and other capitosaurs such as Eryosuchus garjainovi; its interpterygoid vacuities are equally wide along their extension, as in Stanocephalosaurus pronus (Howie 1970) but unlike those of stenotosaurids, where the interpterygoid vacuities are tapered posteriorly. In addition, the otic notch and tabular horns appear to be more primitive in Calmasuchus than in stenotosaurids and related forms, where the squamosal usually contacts the tabular to create an embayment that is not found in Calmasuchus.

Regarding the affinities of the material described here with Eryosuchus, as suggested by Damiani (2001), we compared Calmasuchus acri with the eryosuchids sensu Schoch and Milner (2000) from the Eastern European platform. In the case of the capitosaur described here, the tip of the tabular is relatively wide throughout its length, with a slight anterodistally expansion. This morphology differs from Eryosuchus garjainovi, because the anterodistal expansion is well developed in the latter taxon. In Calmasuchus, the orbital size is reduced compared with that of Eryosuchus and resembles the medium-sized orbits of Parotosuchus or Tatrasuchus wildi. The outline of the orbits in Eryosuchus garjainovi is slightly more elongated and suboval than in Calmasuchus acri. The proportional interorbital distance is smaller in Calmasuchus acri than in Eryosuchus garjainovi; the position of the orbits in the skull roof in both genera is similar. Damiani (2001) used the position of the occipital condyles in relation to the quadrate condyles as one of the characters to group the Russian Eryosuchus species with the Gondwanian ones: in Eryosuchus, the occipital condyles are slightly anterior to the quadrate condyles. This is also the case in Calmasuchus acri, whereas some Gondwanian species such as Stanocephalosaurus pronus and Xenotosuchus africanus differ, with the occipital condyles at the same level (or posterior) as the quadrate condyles.

In the lower jaw, the postglenoid form of Calmasuchus acri is well extended and slightly concave without a medial ridge aligned sagitally as it is possible to observe in Eryosuchus. On the other hand, the morphology of the posterior Meckelian foramen is short, differing from the elongated morphology found in Eryosuchus species.

Comparisons with other taxa.—Posterolaterally directed tabular horns are considered by Schoch and Milner (2000) and Damiani (2001) as a derived character for the following capitosaurs: Cherninia denwai, Eryosuchus, Xenotosuchus africanus, Mastodonsaurus giganteus, Stanocephalosaurus pronus, Paracyclotosaurus crookshanki, and Tatrasuchus wildi. The tabular horns in Calmasuchus acri are slightly anterodistally broadened, and this expansion is more distinct in Eryosuchus. Further, Calmasuchus acri lacks a long processus lateralis in the tabular horns (present in Tatrasuchus wildi and Stanocephalosaurus pronus). Altogether, these are indications of a more derived condition in the horn morphology of Eryosuchus, Tatrasuchus, and Stanocephalosaurus pronus than of Calmasuchus.

The orbital size, in proportion to the skull, is smaller than that of Mastodonsaurus giganteus and similar to those of Parotosuchus orenburgensis and Tatrasuchus kulczyckii. The relative position between the postorbital and the prefrontal varies in capitosaurs. This character is also considered derived when these bones are near each other by thin projections (Schoch 2008). This is the case of Calmasuchus acri and differs from other advanced capitosaurs, where the bones are widely separated, such as in Eryosuchus, Tatrasuchus, or Xenotosuchus, and resemble the condition found in Paracyclotosaurus and Stanocephalosaurus.

In the palatal view, the region between the anterior palatal vacuity and the anterior border of the interpterygoid vacuities (occupied by the two vomerine plates) is elongated as in Parotosuchus orenburgensis and Stanocephalosaurus pronus, and considered a derived character (Damiani 2001; Schoch 2008). The same authors considered oval or narrow slit-like choanae as plesiomorphic (e.g., Calmasuchus acri or Benthosuchus sushkini) and subcircular or circular choanae as apomorphic (Liu and Wang 2005; e.g., Yuanansuchus laticeps or Mastodonsaurus giganteus). In Tatrasuchus wildi, the snout is very short and broad with foreshortened vomerine plates and subcircular choanae. Calmasuchus acri lacks a ventral exoccipital—pterygoid contact, a character also present in Tatrasuchus wildi and Xenotosuchus africanus, differing from Eryosuchus garjainovi and Tatrasuchus wildi.

Although the presence of unpaired or paired anterior palatal vacuities is often considered a diagnostic character in trematosaurs (Welles and Cosgriff 1965; Damiani 2001), this character is also phylogenetically informative in capitosaurs. Calmasuchus acri has a paired anterior palatal vacuity, as does Mastodonsaurus giganteus. In most specimens of Eryosuchus, this character represents the primitive condition, but it was referred by Schoch and Milner (2000) from a gigantic undescribed specimen.

Pronounced sculpturing in the palatine region of the pterygoid is present mainly in trematosaurs, but this character is variable in capitosaurs. Basal and “advanced” forms such as Wetlugasaurus angustifrons, Tatrasuchus wildi, Cyclotosaurus robustus, Eocyclotosaurus lehmani, and the capitosaur described herein show ornamentation, whereas other forms such as Cherninia denwai, Eryosuchus garjainovi, Mastodonsaurus giganteus, Paracyclotosaurus crookshanki, and Stanocephalosaurus pronus display the ventrally smoothed palatine without any sign of ornamentation.

Maryańska and Shishkin (1996) recognised four patterns in the postglenoid area of capitosaurs. They referred to the plesiomorphic condition in Wetlugasaurus angustifrons. The postglenoid area of eryosuchids, mastodonsaurids, and tatrasuchinids was considered as the most derived one, with the retroarticular process markedly elongated and depressed in the dorsal surface (Maryanska and Shishkin 1996). This morphology is also recognised in Calmasuchus acri, being more derived than the morphology present in Xenotosuchus africanus.

The morphology of the posterior Meckelian foramen in Calmasuchus acri represents the primitive condition (Schoch 2000; Damiani 2001), differing from the derived condition found in Eryosuchus garjainovi and Mastodonsaurus giganteus. Moreover, the type mandible of Tatrasuchus kulczyckii is incomplete, but it is inferred that its posterior Meckelian foramen is elongated (Maryańska and Shishkin 1996). This is not the case of Xenotosuchus africanus, which displays a short posterior Meckelian foramen.

The length of the adductor fossa is short in Calmasuchus acri and, when compared with the total length of the mandible, similar to that of Mastodonsaurus giganteus and Eryosuchus garjainovi. On the other hand, the outline morphology of Calmasuchus acri resembles the Tatrasuchinae. This group combines parotosuchid-like features with other features usually found in cyclotosaurs (Schoch and Milner 2000). Calmasuchus acri differs from the tatrasuchinids in several characters, as already discussed: less separated postorbital and prefrontal, supraorbital sensory canal traversing the nasal and lacrimal, more elongated prefenestral division of the palate, narrower choanae, divided anterior palatal vacuity (it is undivided in the two species of Tatrasuchus), equally wide interpterygoid vacuities anteriorly and posteriorly (they are tapered posteriorly in Tatrasuchus wildi and unpreserved in T. kulczyckii), no sculptured ventral surface of the parasphenoid basal plate, shorter posterior Meckelian foramen, and postglenoid area longer than the glenoid facet.

The inclusion of Calmasuchus acri in any of the capitosaur families recognised in the literature (see Schoch and Milner 2000 for further details) is controversial because the combination of characters present in this new genus is not in agreement with the synapomorphies used to define the different families (sensu stricto Schoch and Milner 2000). Therefore, a re-definition of some capitosaur families (i.e., Parotosuchidae, Tatrasuchidae, Eryosuchidae) will be necessary. Nevertheless, as some aspects of Calmasuchus acri remain undiscovered, we prefer to be conservative, discarding its inclusion in any capitosaur family or even creating a new one, until additional material allows accurate assessment of the characters that remain unclear.

Phylogenetic remarks

The dichotomy between the Trematosauria and the Capitosauria was recognised in previous studies (Yates and Warren 2000; Damiani 2001; Steyer 2002; Damiani and Yates 2003; Schoch et al. 2007; Schoch 2008; Maganuco et al. 2009). Herein, the capitosaur clade is also recognised and well supported by seven unambiguous synapomorphies.

Benthosuchus sushkini was previously included in the capitosaur clade (Yates and Warren 2000; Damiani 2001; Steyer 2003). However, Damiani and Yates (2003) indicated that three characters (the lacrimal flexure of the infraorbital sensory canal, morphology of the marginal teeth, and oblique ridge of the pterygoid) were incorrectly coded in the revision by Damiani (2001). This problem is resolved here and confirms the basal position of Benthosuchus sushkini in the trematosaurian clade.

The Trematosauroidea (node 4) were defined as the last common ancestor of Thoosuchus yakovlevi and Trematosaurus brauni and all its descendants (Yates and Warren 2000). This was confirmed by Damiani and Yates (2003), Maganuco et al. (2009), and the present study. Trematosaurus brauni is included in the trematosaurian clade as the sister taxon of Angusaurus, yet considered a more primitive form (Damiani and Yates 2003).

The more recent update of the Capitosauria (node 6) (Damiani and Yates 2003) defined the group as stereopondyls that share a more recent common ancestor with Parotosuchus than with Trematosaurus. Wetlugasaurus was included in the trematosaurian group (Schoch 2000; Schoch and Milner 2000), although other authors consider it as a basal capitosaur or sister group to them (Ochev 1966; Kamphausen 1989; Maryańska and Shishkin 1996; Damiani 2001; Damiani and Yates 2003). A recent analysis (Schoch 2008; Maganuco et al. 2009) indicated Wetlugasaurus as a member of the Capitosauria. In the present study, Wetlugasaurus appears as the most basal member of the Capitosauria. Therefore, we define the Capitosauria as stereopondyls that share a more recent common ancestor with Wetlugasaurus than with Trematosaurus.

The position of Vladlenosaurus alexeyevi within the Capitosauria is controversial. This taxon was suggested to be a species of Wetlugasaurus (Shishkin et al. 2006) or closely related to this genus (Morkovin and Novikov 2000). In the present analysis, Vladlenosaurus alexeyevi and the enigmatic Odenwaldia heidelbergensis resulted as sister taxa.

On the other hand, the Watsonisuchus—Edingerella clade appears as the sister group of the huge clade of Gondwanian forms, plus heylerosaurids and stenotosaurids, being the more primitive forms of the clade. The position of Edingerella madagascariensis is controversial. It was initially described as a species of Benthosuchus (Lehman 1961) and later to the genus Parotosuchus, and then assigned to the capitosaur group (Schoch 2000) and surprisingly to the lydekkerinid group (Damiani 2001). Finally, the genus Edingerella was established for the species E. madagascariensis (Schoch and Milner 2000), defined as a stem capitosaur. Recently, a new description of Lehman's (1961) specimens and new exceptionally well-preserved specimens (Steyer 2003; Maganuco et al. 2009) indicated the basal position of this genus within the capitosaur group and its close relationship with Watsonisuchus, although in a recent revision of the group, Schoch (2008) included Edingerella madagascariensis within the trematosaurs. In the case of Watsonisuchus, these taxa are studied here at the genus level. Four species (Watsonisuchus aliciae, W. gunganj, W. magnus, and W. rewanensis) have been described from the Early Triassic of Australia and South Africa; they are considered as one of the most basal genera within the Capitosauria (Damiani 2001). However, W. gunjanj and W. aliciae were transferred to the genus Rewanobatrachus (Schoch and Milner 2000), another stem-capitosaur. Watsonisuchus aliciae remains the best known species documented by ontogenetical information (Warren 1980; Warren and Schroeder 1995). Damiani (2001) retained W. aliciae within the genus with caution. Recently, the genus Warrenisuchus (Maganuco et al. 2009) was established for W. aliciae (Warren and Hutchinson 1988). This genus is considered basal to Watsonisuchus. In the present study, we followed Damiani (2001), retaining W. gunganj, W. magnus, W. rewanensis, and W. aliciae with caution in the genus Watsonisuchus. Moreover, the analysis reflects the close, sister-taxon relationships between Edingerella and Watsonisuchus.

Xenotosuchus africanus, Cherninia denwai, and Paracyclotosaurus crookshanki form successive sister taxa to the remaining stenotosaurids and heylerosaurids plus Stanocephalosaurus. Regarding Stanocephalosaurus, we consider S. birdi as the senior synonym of P. peabodyi and separated it from Wellesaurus. On the other hand, the South African capitosaur S. pronus was included as an Eryosuchus member (Damiani 2001). This suggestion was not followed here. In the present analysis, S. birdi and S. pronus are sister taxa, with two unambiguous synapomorphies, demonstrating that this genus had widespread distribution, being present in South Africa and North America.

The close relationship between the poorly known stenotosaurids (Paton 1974; e.g., Procyclotosaurus stantonensis) and heylerosaurids (e.g., Eocyclotosaurus and Quasicyclotosaurus) was indicated by Schoch and Milner (2000). Here, stenotosaurids appear as a sister taxon of heylerosaurids, the latter forms being more advanced. On the other hand, the present analysis seems to partially corroborate the hypothesis of the diphyli between Eocyclotosaurus and Cyclotosaurus (Damiani 2001), which are not closely related forms. Otherwise, the Eocyclotosaurus—Odenwaldia relationship is not supported here.

The cosmopolitan genus Parotosuchus is known to be from the Early Triassic. Recent published papers clarified the valid species of this genus (e.g., Schoch and Milner 2000; Damiani 2001; Morales and Shishkin 2002; Shishkin and Sulej 2009 and references therein). To date, at least eight species are considered valid: Parotosuchus orenburgensis, P. nasutus, P.helgolandicus, P. orientalis, P. komiensis, P. bogdoanus, P. panteleevi, and P. speleus. In the present analysis, P. orenburgensis is the sister taxon of Calmasuchus acri and their descendants, supported by two unambiguous synapomorphies. The new capitosaur described here, Calmasuchus acri, appears as a more derived form than Parotosuchus orenburgensis and the sister taxon of the Cyclotosaurus—Tatrasuchus and Eryosuchus—Mastodonsaurus clades, revealing a more basal position than the tatrasuchines.

Finally, we report a dichotomy between cyclotosaurs and related forms (e.g., Tatrasuchus) and the Eryosuchus—Mastodonsaurus clade. On one hand, Cyclotosaurus robustus and Tatrasuchus wildi were found to be sister taxa in previous works (Maryańska and Shishkin 1996; Schoch and Milner 2000; Damiani 2001; Maganuco et al. 2009; present study). On the other hand, the cladistic analysis indicated phylogenetic affinities between mastodonsaurids and eryosuchids as previously reported by other authors (Maganuco et al. 2009). Further research is needed on related taxa, such as the Anisian Heptasaurus, Komatosuchus, and the gigantic undescribed skull from Ladinian of Russia referred by Schoch and Milner (2000) to Eryosuchus sp., to clarify the relationships within this clade.

Conclusions

The capitosaur remains recovered from the La Mora site (Eastern Iberian Peninsula) allowed us to describe a new form of capitosaur, Calmasuchus acri. The remains date to the early-to-middle Anisian (Middle Triassic). Its cranial reconstruction suggests that this capitosaur does not belong to Parotosuchus, Eryosuchus, or a stenotosaurid indet., as previously suggested (Gaete et al. 1993, 1994, 1996; Shishkin 2000; Damiani 2001). The new capitosaur is characterised by a combination of parotosuchid characters and others such as posterolaterally directed tabular horns, paired anterior palatal vacuities, and unique morphological characters in its lower jaw. The outline of the skull resembles that of tatrasuchines, but several different character polarities demonstrate the basal position of the new form ahead of the tatrasuchines. The phylogenetic analysis suggests that Parotosuchus orenburgensis and Calmasuchus acri are the sister taxa of the Cyclotosaurus—Tatrasuchus and Eryosuchus—Mastodonsaurus clades. Calmasuchus acri is more derived than Parotosuchus sp. As a group, the Capitosauria are supported by seven synapomorphies. Wetlugasaurus is the most basal member of the capitosaur clade. We scored the Russian genus Vladlenosaurus for the first time. This genus is the sister taxon of Odenwaldia heidelbergensis, occupying a basal position in the capitosaur clade, although it is more derived than Wetlugasaurus. This latter genus is the most basal member of the Capitosauria. The Madagascarian Edingerella is the sister taxon of Watsonisuchus.