A New Large Capitosaurid Temnospondyl Amphibian from the Early Triassic of Poland

The Early Triassic record of the large capitosaurid amphibian genus Parotosuchus is supplemented by new material from fluvial deposits of Wióry, southern Poland, corresponding in age to the Detfurth Formation (Spathian, Late Olenekian) of the Germanic Basin. The skull of the new capitosaurid shows an “intermediate” morphology between that of Parotosuchus helgolandicus from the Volpriehausen-Detfurth Formation (Smithian, Early Olenekian) of Germany and the slightly younger Parotosuchus orenburgensis from European Russia. These three species may represent an evolutionary lineage that underwent a progressive shifting of the jaw articulation anteriorly. The morphology of the Polish form is distinct enough from other species of Parotosuchus to warrant erection of a new species. The very large mandible of Parotosuchus ptaszynskii sp. nov. indicates that this was one of the largest tetrapod of the Early Triassic. Its prominent anatomical features include a triangular retro articular process and an elongated base of the hamate process.


Introduction
Tetrapod bones are rare in the Lower Triassic of Poland. An exception is the Czatkowice site in southern Poland, which has yielded one of the richest and most diverse tetrapod as− semblage of the Germanic Buntsandstein Basin (Borsuk− Białynicka et al. 1999;Borsuk−Białynicka and Evans 2003;Paszkowski 2009). Among the Early Triassic (Olenekian) vertebrate fossils from the fissure infillings of the Czatko− wice 1 locality, two taxa of temnospondyl amphibians have been recognized, the capitosaurid Parotosuchus speleus and the brachyopid Batrachosuchoides sp. (Shishkin and Sulej 2009). Both are represented almost entirely by remains of metamorphosed juveniles.
Isolated and poorly preserved vertebrate remains (mainly fragmented limb bones and ribs) have also been recognized from Buntsandstein strata on the northern margin of the Holy Cross Mountains (Senkowiczowa and Ślączka 1962;Senko− wiczowa 1970;Fuglewicz et al. 1981Fuglewicz et al. , 1990. Tetrapod re− mains, usually identified by geologists as "Labyrinthodontia indet.", were collected at a few localities from the four lithostratigraphical units in this region. Hitherto, only the finds from the Wióry locality were the subject of a short com− munication (Fuglewicz et al. 1981). Herein, we present a de− scription of a new species of large parotosuchid temno− spondyl, based on material collected at Wióry.
The objectives of this paper are to provide a description of the material of a new parotosuchid from the Late Olenekian of Poland, and a discussion of parotosuchid capitosaurid evolu− tion in Europe, based primarily on Olenekian specimens.

Geological background
The large outcrop at Wióry (Figs. 1, 2) resulted from the con− struction of a water barrage and reservoir on the Świślina River, from 1979 to 2005. The first vertebrate fossils from this site were discovered by Tadeusz Ptaszyński in autumn, 1980 (Niedźwiedzki and, and subsequently col− lected by Kazimierz Rdzanek, Mateusz Mielniczuk, Piotr Szrek, Paweł Król, and the authors (TS and GN). The largest collections (mainly tetrapod footprints) are deposited at the In− stitute of Paleobiology, Polish Academy of Sciences in War− saw and the Museum of Nature and Technology in Stara− chowice. Other collections also exist in other institutions (see Ptaszyński and Niedźwiedzki 2004). A number of specimens have also been gathered by amateur collectors.

Material and methods
Although the new material is very fragmentary, it shows char− acters that distinguish it from the other Parotosuchus species. The skull (MPT.P 271) is represented by the posterior part of the left side of the palate, which is preserved in a block of sandstone and exposed in dorsal view. Complete extraction of this skull fragment from the rock would be very difficult be− cause the bone is extremely fragile. The preserved part of the skull consists of the bulk of the pterygoid, portions of the exoccipital, the ectopterygoid, the quadrate, the ventral pro− cesses of the tabular and postparietal, a fragment of the para− sphenoid, and the ventral edge of the quadratojugal and jugal. The length of the skull was approximately 43 cm (along the midline). The position of some bones suggests that the skull is slightly compressed dorsoventrally, with its roof displaced to− wards the right. This is inferred from the position of the occipi− tal condyle in relation to the tabular horn and from the strong rightwards inclination of the quadratojugal. The preserved part of the mandible (MPT.P 272) includes the middle and posterior portions of the left ramus, including the postglenoid region. Part of the lingual side of the postglenoid region and the hamate process are preserved as a thin remnant of the bone in the counterpart of the sandstone slab (Fig. 6). The length of the whole mandible was approximately 72 cm. A CT scan of the skull was made to study the ventral part of the palate, but the poor state of preservation means the scan is useful in gen− eral morphological description, but is not of high quality. Referred species.-Parotosuchus helgolandicus (Schroeder, 1913); P. orenburgensis (Konzhukova, 1965); P. orientalis (Ochev, 1966); P. panteleevi (Ochev, 1966) Sidor et al. 2007) are considered to be ge− nerically distinct based on hyperelongated and exception− ally broad snouts, tabular horns that are postero−laterally di− rected and recurved, and other characters described by Damiani (2001b) in the diagnosis of Cherninia.
The assignment of the Wióry capitosaurid to Paroto− suchus is based mainly on the structure of the mandible, which is preserved and well described only in P. oren− burgensis among Parotosuchus. In both P. orenburgensis and the new species the retroarticular process is shorter than the glenoid area (new character) and its dorsal surface is sloped horizontally (character 47 in Maryańska and Shishkin 1996). The crista articularis is straight and horizontal in lin− gual view. The Meckelian foramen has the length of a quarter or shorter of the adductor fossa length.  Ptaszyński and Niedźwiedzki 2006;Niedźwiedzki and Ptaszyński 2007;Becker et al. 2007). Diagnosis.-Parotosuchus with the following combination of character states: torus arcuatus has more vertical position than the common condition in other parotosuchids. The dor− sal surface of the retroarticular process is triangular, rather than roughly rectangular as in P. haughtoni and P. oren− burgensis. The base of the hamate process is longer antero− posteriorly than in P. haughtoni and P. orenburgensis. The quadrate ramus of the pterygoid is shorter in length (= jaw ar− ticulation positioned more anteriorly) than in P. helgolandi− cus, P. nasutus, P. haughtoni, and longer than in P. oren− burgensis. The lateral edge of the skull is more triangular in shape than in P. orientalis and P. nasutus.

Skull
The general skull morphology is similar to that of Paroto− suchus orenburgensis, especially the extremely strong curva− ture of the lateral edge of the interpterygoid fenestra. In all other Parotosuchus species this edge is much less concave, al− though the new material represents a larger skull than the holotype of P. orenburgensis (width of the skull PIN 951/42 is 315 mm while P. ptaszynskii is~400 mm). The whole fenestra is wide and rather short (the shape of the palatine edge).
Ectoterygoid.-Although the small fragment of the left most posterior part of this bone is preserved, the lateral edge of the element in this region is clearly visible. The fact that the lat− eral edge is very strongly curved is an evidence that the skull was narrowing anteriorly and was not elongated as in most parotosuchids (e.g., Parotosuchus nasutus, P. helgolandi− cus, P. orientalis).
Jugal.-The preserved part of processus alaris is massive and lay over the ectopterygoid.
Pterygoid.-The suture of the basipterygoid ramus with the parasphenoid is clearly visible in its anterior part. It seems that this ramus is relatively wide and results in a very blunt posterior end of the interpterygoid foramen. On its dorsal side there is a distinct pocket with vertical edge, which is di− rected antero−posteriorly. This appears to be the ventral edge of the recessus conoideus (Bystrov and Efremov 1940). The quadrate ramus is rather long with its posterior end covered by the quadrate. The lateral edge of the quadrate ramus is di− rected strongly posteriorly making the medial edge of the temporal foramen strongly blunt. The palatine ramus is nar− row and rather short, with a very distinct transverse flange. The medial edge of the palatine ramus is visible as an impres− sion in the sandstone. At the base of this ramus a thin shelf protrudes anteriorly, disturbing the shape of the curvature of this margin (posterior edge of the interpterygoid foramen). The sutures with the ectopterygoid are partly visible. Palatine.-The medial edge of the palatine is visible as an im− pression in the sandstone. It is rather strongly concave in ven− tral view, very similar to Parotosuchus orenburgensis (Fig. 4).
Quadrate.-The anterodorsal part of the quadrate is preserved lying over the quadrate ramus of the pterygoid. Its medial end forms a distinct edge with a vertical wall. This morphology was first described for Bentosuchus sushkini by Bystrov and Efremov (1940) as the incisura lateralis, but it is better illus− trated by Howie (1970). The same structure was observed in Metoposaurus diagnosticus krasiejowensis by Sulej (2007). Lateral to the incisura lateralis, on the anterior side of the quadrate, a sutural facet faces anterolaterally. According to Howie (1970) it articulates with the prearticular process of the mandible. Howie (1970) described it in Stenocephalosaurus pronus as present on the pterygoid but, in the new material de− scribed here, it occurs on the anterior edge of the quadrate.
Quadratojugal.-The ventral edge of the bone is straight. The anterodorsal process is directed medially and overlies the quadrate anterodorsally.
Exoccipital.-The suture of the exoccipital with the para− sphenoid is visible only in cross section (of the crista par− occipitalis of the parasphenoid and the dorsal part of the exoccipital). The whole occipital condyle is here visible in the CT scan (Fig. 3B, C). Its articular surface is directed posteroventrally and is approximately 15 mm wide medio− laterally.

Mandible
The specimen belongs to a larger individual (about 72 cm skull length) than that represented by the above described skull fragment (skull approximately 43 cm long). The oval Meckelian foramen is small and very short, and the torus arcuatus of the surangular has a very steep dorsal edge (Fig. 5).
The base of the hamate process is longer in lateral view in Parotosuchus ptaszynskii than in the holotype of P. orenbur− gensis. As preserved, the postglenoid area of P. ptaszynskii ap− pears to be more deformed than that of P. orenburgensis. The retroarticular process is shorter than the glenoid area and its dorsal surface is sloped horizontally (character 47 in Mary− ańska and . The crista articularis is straight and horizontal in lingual view (Fig. 6). The crista supraangularis which borders it labially is not so strongly convex in dorsal view as in P. orenburgensis (Maryanska and Shishkin 1996: fig. 22) and P. haughtoni (Damiani 2002: fig. 7 = Kestro− saurus dreyeri Shishkin et al. 2004: fig. 5), but this difference may result from the state of preservation of the Polish speci− men. The chorda tympani foramen is not visible. The crista articularis is distinct as in P. orenburgensis (Maryańska and Shishkin 1996: fig. 22), but begins at the posterior part of the glenoid area as in P. haughtoni (= Kestrosaurus dreyeri; Damiani 2002: fig 6). In P. orenburgensis it begins much more anteriorly (TS personal observation).

Discussion
The skull fragment and the mandible were found at the same locality, where large bone fragments are very rare. Their size differences indicate that they belonged to two different indi− viduals. Without comparison to other better preserved fossils, showing that they represent the same species is impossible. The skull is identified as Parotosuchus based on its similarity to Parotosuchus orenburgensis. The holotype of P. oren− burgensis (PIN 951/42) and the skull fragment from Wióry share the following characters: (i) a strongly concave lateral edge of the interpterygoid fenestra, (ii) skull that strongly nar− rows anteriorly, (iii) the parotic process of the tabular is di− rected at 45°to the long axis of the skull. This combination of characters is known only in these two species. The identifica− tion of the skull fragment is strengthened by the similarity of ® the mandible fragment from Wióry to the holotype of the Parotosuchus orenburgensis (PIN 951/42). They share the following characters: (i) a very short Meckelian foramen, (ii) a strongly convex ventral edge of the mandible in lateral view, (iii) the retroarticular process is shorter than the glenoid area and its dorsal surface is sloped horizontally (character 47 in Maryańska and Shishkin 1996), (iv) the crista articularis is straight and horizontal in lingual view, (v) a very steep dorsal edge of the torus arcuatus of the surangular. The capitosaurids appear in the Induan to Early Olene− kian (Early Triassic), and include taxa such as Wetluga− saurus, Rewanobatrachus, Edingerella, and Deltacephalus (Schoch 2008). In Late Olenekian deposits, capitosauroids are represented by Parotosuchus, Kestrosaurus, Cherninia, Odenwaldia, Stanocephalosaurus, and the aberrant Sclero− thorax Damiani 1999Damiani , 2001aDamiani -c, 2002Damiani , 2008Schoch 2000a, b;Schoch and Milner 2000;Damiani and Hancox 2003;Damiani and Rubidge 2003).
From the Olenekian, many species of large Parotosuchus species have been described from both northern and southern Pangea (Sidor et al. 2007). All of them display very elongate, slit−like choanae, and open otic notches (showing no clear trend to closure), and elongated, posterolaterally directed tabular horns. Some of these species are represented only by incomplete fossils, and therefore apomorphies are unknown. However most of them share the following characters: (i) retroarticular process of the mandible is shorter than glenoid area Shishkin 1996, Damiani 2001a), with the dorsal margin of this process sloping horizontally (Mary− ańska and Shishkin 1996), and (ii) a crista articularis that is straight and horizontal in lingual view (new character). Damiani (2001a) recognized two variable states of the length of the Meckelian foramen, long or short. According to him, the short Meckelian foramen is common among Triassic temnospondyls. Comparison of forms with this state of char− acter described by Damiani (2001a) shows that only Paroto− suchus orenburgensis, P. haughtoni, P. ptaszynskii, and Rewanobatrachus aliciae (sensu Damiani 2001a, different from all Parotosuchus in having an oval choana and V−shaped transvomerine tooth row), have the Meckelian foramen that is a quarter of the length of the adductor fossa or shorter. Other species analyzed by Damiani (2001a), including Xenotosu− chus africanus, Benthosuchus sushkini, all Eryosuchus spp., Lydekkerina, andWellesaurus peabodyi (sensu Damiani 2001a), have a Meckelian foramen that is approximately one third of the length of the adductor fossa or longer. Addition− ally, all forms which are represented by mandibular fossils (P. orenburgensis, P. haughtoni, and P. ptaszynskii) have a man− dible with a strongly convex ventral margin in lateral view.
During the Olenekian, two distinct Parotosuchus species are known from the Germanic basin, P. helgolandicus (Early-early Late Olenekian) and the younger P. nasutus (Late Olenekian) (Bachmann and Kozur 2005). Numerous species were also described from the Late Olenekian (Shish− kin et al. 2000) of the European part of Russia and Kazakh− stan. They are as follows: P. orenburgensis (Konzhukova, 1965), P. panteleevi (Otschev, 1966), P. orientalis (Otschev, 1966), P. sequester (Lozovsky and Shishkin, 1974) miensis (Novikov, 1986), and P. bogdoanus (Woodward, 1932). Only the first is known from a complete skull and mandible. Recently, P. speleus was described on the basis of disarticulated skull bones of a juvenile (Shishkin and Sulej 2009). Furthermore, well preserved but still undescribed ma− terial of other Parotosuchus species has been reported from the Moenkopi Formation of North America (Schoch and Milner 2000;Lucas and Schoch 2002). The form from the lower subzone of the Cynognathus Zone identified by Damiani (2002) as P. haughtoni (Broili and Schroder, 1937) is known from the most complete cra− nial material of any Parotosuchus species, which includes well−preserved palatal morphology.
Parotosuchus helgolandicus (Schroeder, 1913) from the lower part of the Middle Buntsandstein, Volpriehausen For− mation or Detfurth Formation, Smithian-lower Spathian, Germany (after Bachman and Kozur 2005), seems to be one of the closest in age to the new Polish species. Although in the original description of this German taxon Schroeder (1913) did not mention the exact locality and horizon of dis− covery, this species is from Helgoland Island where only sediments of the Volpriehausen and Detfurth Formations oc− cur (Bachman and Kozur 2005). It differs from P. ptaszynskii in the following characters: (i) the skull is elongated (al− though it is narrower-skull width is 364 mm, contrary tõ 400 mm for P. ptaszynskii); (ii) the interpterygoid and subtemporal fenestrae are elongated.
Younger than P. helgolandicus is P. nasutus, also from Germany. It originates from the lower Solling Formation (Rainer Schoch, personal communication 2009) (Spathian). It is similar to the previous form in that the interpterygoid and subtemporal fenestrae are elongated and the quadrate ramus of the pterygoid is long. All these characters distinguish it from P. ptaszynskii.
In the Cis−Urals of Russia, Parotosuchus orientalis Ochev, 1966 is known from the lower part of the Petropavlovskaya Formation, belonging to the Yarenskian Stage, Spathian, and Parotosuchus orenburgensis Konzhukova, 1965 from the same formation (Shishkin et al. 2000). Both species are closest in age to the new taxon. The subtemporal fossa in P. ptaszyn− skii is almost identical in proportions to that in P. orientalis (skull width is~380 mm). The shape of the interpterygoid fenestra is unknown but the position of the maxilla shows that the whole skull was rather elongated as in P. helgolandicus and P. nasutus.
Information from the age and skull morphology of the European Parotosuchus species known from the skull sug− gests some aspects of the evolution of this genus. The ratio of length to width of the temporal fenestra is: P. helgolandicus, 1.76; P. ptaszynskii, 1.62; P. orenburgensis, 1.54 (Fig. 8). It seems that P. ptaszynskii is intermediate in age and morphol− ogy between P. helgolandicus and P. orenburgensis. The re− lationships of P. nasutus are unknown.

Conclusions
The new material of Parotosuchus from the early Spathian of Poland represents a new species morphologically intermedi− ate between congeneric finds in Germany and Russia. This suggests a lineage persisting in Europe through the Late Olenekian, with changes occurring mainly in the shape of the skull and interpterygoid and subtemporal fenestrae.
At the end of the Early Triassic (Late Olenekian), impor− tant enviromental changes took place in the marginal parts of the Germanic Basin. Rivers became larger and developed from small local gullies over braided river systems into  (Schroeder, 1913) and Parotosuchus nasutus (Meyer, 1858) (based on Welles and Cosgriff 1965), Parotosuchus orenburgensis (Kon− zhukova, 1965) (based on Konzhukova 1965). fast−changing, larger meandering rivers covering larger areas (Mader 1981;Mader and Rdzanek 1985;Fuglewicz et al. 1990). Such large rivers and small lakes from alluvial plains created niches for large aquatic temnospondyls. Large−bodied predatory temnospondyls (Parotosuchus, Trematosaurus, Sclerothorax, Odenwaldia, Meyerosuchus) are widely known from the Upper Olenekian deposits of the Germanic Basin (Schoch 2011). It is possible that these environmental changes may have stimulated the origin and early evolution of the large capitosaurids.