a – angular; ar – articular; cl – clavicle; cop – coronoid process; d – dentary; ec – ectopterygoid; f – frontal; icl – interclavicle; ju – jugal; la – lacrimal; m – maxilla; n – nasal; na – naris; p – parietal; ptf – postfrontal; pgr – postglenoid region; pl – palatine; pm – premaxilla; po – postorbital; pp – postparietal; prf – prefrontal; ps – parasphenoid; psp – postsplenial; pt – pterygoid; q – quadrate; qj – quadratojugal; sa – surangular; sp – splenial; sq – squamosal; st – supratemporal; t – tabular; vo – vomer.

(1) Preorbital region 1.8–2.2 times as long as postorbital skull table, (2) tabular horn prominent, (3) postglenoid region posteriorly longer than the articular facet, (4) jugal narrower than greatest orbit width, and (5) interclavicle slender and at least twice as long as wide (modified from Schoch and Witzmann, 2009b).

Glanochthon latirostre (Jordan, 1849).

Glanochthon lellbachae (Krätschmer, 2006) comb. nov. (Figs. 2–5)

NHMM 2006/14, 102 mm SL, complete skeleton with skin impression (Fig. 2).

The Klauswald southwest of Odernheim am Glan, Rhineland-Palatinate, Germany (Fig. 1). M9 sequence, Klauswald facies, Odernheim Subformation, Meisenheim Formation, lower Rotliegend, Autunian, lowermost Permian.

Altogether, five additional specimens are referred to as Glanochthon lellbachae (see material section). There remains a substantial number of specimens in private collections.

Autapomorphies: (1) preorbital region in adults 1.8–2.0 times as long as postorbital skull table, (2) dermal ornament with continuous and relatively tall radial ridges in the snout, frontals and cheek (contrasting the more polygonal arrangement in S. nobilis), (3) prefrontal anterolaterally expanded to form a more equant pentagon, (4) squamosal posteriorly only half as wide as quadratojugal, (5) phalanges of manus and pes slightly longer and more gracile than in S. nobilis and (6) tail substantially longer than skull and trunk combined (shorter than that measurement in S. nobilis).

This taxon was originally erected as Cheliderpeton lellbachae by Krätschmer (2006), who made reference to its resemblance to Cheliderpeton latirostre as described and referred to by Boy (1993). Schoch and Witzmann (2009b) suggested the new genus name Glanochthon for Cheliderpeton latirostre after the type species Cheliderpeton vranyi had been redescribed by Werneburg and Steyer (2002) and was found not to be closely related to G. latirostre (Schoch and Witzmann, 2009b). Based on its below-demonstrated close relationship to G. latirostre, Cheliderpeton lellbachae is also referred to as Glanochthon as a new combination.

G. lellbachae co-occurs with Sclerocephalus nobilis in the same locality and horizon (Krätschmer and Resch, 2005; Schoch and Witzmann, 2009a). The combined list of autapomorphic characters 1–5 for the genus distinguish this taxon from S. nobilis and all other species of Sclerocephalus. Hypothetical larvae and small juveniles of G. lellbachae and S. nobilis may not be distinguished on the basis of the mentioned features, but S. nobilis generally has a wider jugal and more rounded orbit even at small stages. The presence of a third eryopiform temnospondyl at the Klauswald locality (suggested by Krätschmer, 2006) cannot be confirmed. With a maximum skull length of 17 cm (specimens in private collections), G. lellbachae appears to have been smaller than the more heavily ossified S. nobilis (24 cm), but admittedly the number of available specimens is very limited.

In the analysis reported below, S. nobilis and the Glanochthon clade are found to be sister taxa. This recognized topological pattern leads to the phylogenetically problematic situation that Sclerocephalus forms a grade towards Glanochthon, which under strict application of cladistic principles would prompt erection of new genera at each node. An alternative option would be to define Sclerocephalus more broadly, encompassing all of Sclerocephalidae including Glanochthon. At the present stage, I consider any such step premature as long as morphological effects of microevolution cannot be distinguished from other effects, especially plasticity (ecophenotypes), which is beyond the scope of the present study.

Based on the current phylogenetic findings, Glanochthon is referred to as the family Sclerocephalidae, which contains a monophyletic group including a long Sclerocephalus grade and a terminal Glanochthon clade. The former referral of Glanochthon (as Cheliderpeton latirostre) within the Intasuchidae (Schoch and Milner, 2000) was based on a suite of characters which appear to be convergent in the present light of evidence.

Although S. nobilis and G. lellbachae co-occur in the same locality and several successive horizons, they differ in sample size per horizon. Most notably, G. lellbachae is more common in the upper fish beds (Obere Fischschiefer, “kalkige Papierschiefer”, K5), whereas S. nobilis peaks in the lower fish beds (Untere Fischschiefer, K2) as defined by Krätschmer (2004). In the other beds (K3, 4), the two taxa co-occur, mostly represented by large juveniles.

The skull is slender with nearly straight lateral margins. Almost all skull-roofing elements are somewhat narrower than in S. nobilis. This is most conspicuous in the case of the squamosal, quadratojugal and jugal. The orbits also differ, being sagittally oval in G. lellbachae and almost perfectly round in S. nobilis. In G. lellbachae, the prefrontal and jugal form a markedly angled anterolateral region of the orbit.

The adult dermal ornament consists of elongated radial ridges, especially on the nasal, frontal, prefrontal, jugal and the anterior part of the parietal. Compared with S. nobilis, the ridges are taller and more continuous, and the polygons on the posterior skull table and cheek are larger. In the largest specimens, the ridges are tallest. Like in S. nobilis and G. angusta and in contrast to G. latirostre, lateral line sulci are entirely absent.

The tip of the snout is blunt as in S. haeuseri and in contrast to the more rounded outline in S. nobilis. The region anterior to the naris is not longer than in S. nobilis but shorter than in G. angusta. The slightly more elongated preorbital region compared to S. nobilis is dominated by a more slender and relatively longer nasal. The lacrimal is often obscured by displaced neighboring elements, especially the maxilla; it does not appear to be substantially smaller than in S. nobilis. The prefrontal is markedly distinct from that of S. nobilis; its posterior region is narrower, the anterior one is wider than in the sister taxon, and the lateral margin is nearly straight and sagittally aligned in some specimens.

In G. lellbachae, the orbits are elongate oval rather than round, and the interorbital distance (0.15–0.17) is slightly smaller than in S. nobilis (0.19–0.24), resulting from narrower postfrontals and frontals. The prefrontal–postfrontal contact is nevertheless well established. The posterior skull table is consistent with S. nobilis in the proportions and suture patterns, especially the shape of the posterior (occipital) margin of postparietals and tabulars, as well as the elongate shape of the supratemporal, which is more consistent with other Glanochthon species than Sclerocephalus species.

The cheek differs most conspicuously in some specimens with the more slender squamosal and quadratojugal bones. In G. lellbachae, the squamosal is substantially narrower than the quadratojugal, which inverses the condition in all Sclerocephalus species. The jugal is clearly narrower in the type of G. lellbachae compared with most S. nobilis specimens, but there are a range of specimens with intermediate conditions which otherwise group with either G. lellbachae or S. nobilis.

The ventral side of the skull is exposed only in SMNS 90507 (Fig. 4a, b). The palate has little to distinguish it from that of S. nobilis or any species of that genus. The vomer is wider than in other Glanochthon species, but the tusk pair is relatively larger than in S. haeuseri, which is in turn more consistent with Glanochthon. The palatine is about twice as wide anteriorly than along its posterior part and bears two large tusks aligned at the lateral margin, and there are at least two smaller teeth posterior to these. The ectopterygoid meets the palatine in an S-shaped suture, and it bears 5–6 large teeth arranged in a straight row. The palatine ramus of the pterygoid is slender and anteromedially stepped, whereas the lateral wing of the pterygoid is laterally expanded much like in Sclerocephalus species.

In the parasphenoid, the base of the cultriform process is twice as wide as the anterior two-thirds, and it bears an elongate triangular denticle field that is posteriorly continuous with that of the basal plate. The plate is wider than in G. angusta, which is more consistent with that of G. latirostre (Schoch and Witzmann, 2009b). On the basal plate, the denticle field is wedge-shaped, which is most similar to that of G. angusta. Laterally, an offset triangular region bears a marked groove, but a foramen is not preserved. Consistent with Glanochthon, and in contrast to the situation of S. haeuseri, muscular pockets along the posterolateral margin of the basal plate are not present.

The marginal teeth are straight conical and not recurved. Their bases are striated, indicating labyrinthodont infolding of enamel and dentine. The teeth of the premaxilla and maxilla are generally smaller than those of the dentary. In the maxilla, tooth size decreases continuously towards the posterior end. The tooth count of the premaxilla is 11, that of the maxilla is unknown, and the dentary bears 21 teeth (with many irregular distances between) in UGKU POL-F 1997/1.

There are no elements of the braincase exposed, and in the single specimen exposed in ventral view, the absence of braincase ossifications indicates that the neurocranium remained cartilaginous at least up to that stage. This is consistent with most Sclerocephalus and Glanochthon species (Boy, 1988).

The mandible has little to distinguish it from S. haeuseri and S. nobilis, with the exception of the features described as follows. The coronoid process is somewhat more raised than in S. haeuseri. The postglenoid region is well established with a rounded posterior end and posteroventrally sloping dorsal margin. The dorsal surface is triangular and markedly concave. The postglenoid region is distinctly longer and more robust than in S. haeuseri, and its lateral side is more robustly ornamented than in other taxa.

Only the distal, undiagnosed end of the stapes is exposed in UGKU POL-F 1997/1 (Fig. 3b). It is slender, apparently without quadrate process and with expanded distal end. No hyobranchial ossification has been identified.

The trunk is consistent in the number of vertebrae (24) with the conditions in S. nobilis and other species of Sclerocephalus and Glanochthon. However, the proportionate length of the trunk with respect to the skull is somewhat greater than in S. nobilis and about equal to that of S. haeuseri from both Jeckenbach (M6) and Pfarrwald (M9P). Furthermore, the tail (= preserved skin outline) of G. lellbachae is substantially longer than in all Sclerocephalus species, reaching the length of skull and trunk combined. The caudal skeleton ossified slowly and in adults reached only 50 % the length of the tail, as revealed by the preserved tail skin. The vertebral centra are consistent in morphology and extent of ossification with those of S. nobilis. The first four (cervical) neural arches have the same proportions and relative differences in height as in classical S. haeuseri (Boy, 1988). The anterior trunk ribs are long, and at least 6–7 of them have large blade-like uncinate processes which have blunt ends and bear large foramina presumably for blood vessels, a feature also described in large adults of S. haeuseri (Schoch and Witzmann, 2009a).

The dermal pectoral girdle differs in G. lellbachae in having a more slender interclavicle that is twice as long as wide. In S. nobilis, the interclavicle width usually reaches two-thirds the length, which is similar to stratigraphically older Sclerocephalus samples (Schoch and Witzmann, 2009a). In large S. nobilis and S. haeuseri, the interclavicle and clavicle are proportionately larger, and the interclavicle is even wider than in juveniles (Boy, 1988). The interclavicle has a well offset ornamented region on the ventral side with ridges most pronounced in the anterior half and a serrated anterior margin which has only half the greatest width of the element. The scapulocoracoid is larger in S. nobilis compared to G. lellbachae of similar size. This was probably simply a function of ossification, which was slightly higher in S. nobilis of the same size as G. lellbachae and much higher in adult S. nobilis, in which it reached levels nearing those of Onchiodon and Eryops (Werneburg, 2008).

There is no consistent difference in the shape and relative size of the ilium between the two taxa, although the largest adult of G. lellbachae has a markedly downcurved anteroventral margin in the acetabular region. The long axis always measures twice the length of the ventral margin, and the shaft is posterodorsally angled in adults of both taxa. The pubis remained unossified throughout life in G. lellbachae, whereas in the large adult of S. nobilis, the pubis and ischium formed a vast co-ossified plate.

The limbs are well ossified in adults (10–17 cm skull length), but even the largest specimens lack carpal ossifications. The tarsus contains three small polygonal bones arranged in an oblique row running from the fibula to the first toe (SMNS 90507). Manus and pes are slightly longer relative to skull length than they are in S. nobilis of similar size. In addition, the phalanges are markedly more slender with less broadened ends in G. lellbachae. The humerus is well differentiated with fully ossified distal condyles but no supinator. Throughout ontogeny, the humerus is substantially shorter relative to the skull (0.28–0.3 in G. lellbachae, 0.33–0.56 in S. nobilis).

The scalation of the ventral and lateral regions in the trunk is consistent with that of Sclerocephalus as described by Boy (1988) and Witzmann (2007).

The original data matrix contained 54 characters (Schoch and Witzmann, 2009b) to which 10 new characters were added (see Appendix A). Six taxa were added: S. sp. Concordia (from Lake Concordia deposit, St. Wendel, Quirnbach Formation; Schoch and Sobral, 2021), S. bavaricus (Boy, 1988), S. jogischneideri (Werneburg, 1992), S. nobilis (Schoch and Witzmann, 2009a), G. lellbachae and Sclerocephalus stambergi (Klembara and Steyer, 2012).

The analysis of 64 characters and 24 taxa found a single most parsimonious tree requiring 121 steps (CI = 0.57, RI = 0.814). The analysis was conducted in the ACCTRAN mode under the New Technology search option. Bremer support values were calculated, revealing some robust support for the Glanochthon clade and the more inclusive sister group G. latirostre + G. angusta (three steps), as well as Eryopiformes in general (each three steps), a slightly lower support for Sclerocephalidae and Eryopidae (each two steps), but low support for the single nodes of the Sclerocephalus grade, as well as the relationship between archegosaurids (each just one step).

In the obtained topology (Fig. 6), the general branching pattern differs from that of Schoch and Witzmann (2009b) in two major aspects: (1) Sclerocephalus forms a grade towards Glanochthon and (2) Cheliderpeton vranyi, Melosaurus and Intasuchus form successive sister taxa of the archegosaurids Archegosaurus, Platyoposaurus and Australerpeton. This is the first analysis to obtain Sclerocephalus and Glanochthon as part of the same clade rather than a grade towards stereospondyls. However, Boy (1987) was already tempted to consider Glanochthon (then only known by its stratigraphically youngest species G. latirostre) as a close relative of Sclerocephalus. The Sclerocephalidae (Sclerocephalus + Glanochthon) is thus recognized as a relatively speciose basal clade of the Stereospondylomorpha.

The paraphyletic taxon Sclerocephalus was found to be a grade with respect to the genus Glanochthon, in which S. stambergi, S. bavaricus, S. jogischneideri, S. sp. Concordia + S. haeuseri and S. nobilis form successive sister taxa to Glanochthon. In the present analysis, S. haeuseri was confined to Boy's subspecies S. haeuseri haeuseri.