Thaumastosaurus sp.

Georgalis, Georgios L., Prendini, Elizabeth & Roček, Zbyněk, 2023, New information on the Eocene frog Thaumastosaurus (Anura, Pyxicephalidae) from the Phosphorites du ºuercy, France, Zoological Journal of the Linnean Society 199 (3), pp. 744-770 : 747-755

Thaumastosaurus sp.

Figs 1–4

Material

Unknown localities in the Phosphorites du Quercy: Two posterior parts of the skull ( NHMW 2019/0059/0005 and NHMW 2019/0059/0006) and four maxillae ( NHMW 2019/0059/0001– NHMW 2019/0059/0004); La Bouffie ( MP 17): eight maxillae ( UM BFI 3002– UM BFI 3009) and two squamosa ( UM BFI 3010 and UM BFI 3083); Sainte-Néboule ( MP 18): 38 maxillae ( UM SNB 5000– UM SNB 5024, UMN SNB 5035– UM SNB 5039, UM SNB 5044, UM SNB 5154, UM SNB 5155, UM SNB 5157– UM SNB 5160, and UM SNB 5183), four squamosa ( UM SNB 5025– UM SNB 5027 and UM SNB 5040), and 10 fragments of presumed squamosa ( UM SNB 5028– UM SNB 5034, UM SNB 5041– UM SNB 5043); Escamps 1 ( MP 19): one maxilla ( UU ESC1 7001); Escamps 2 ( MP 19): one squamosum ( UU ESC2 7001); Escamps 3 ( MP 19): one maxilla ( UU ESC3 7001); Escamps 4 ( MP 19): one squamosum ( UU ESC4 7001); Escamps indeterminate site(s) ( MP 19): two maxillae ( UU ESCun 7001 and UU ESCun 7002).

Description and taxonomic identification

Posterior parts of the skull

Both fragments of the skull (NHMW 2019/0059/0005; NHMW 2019/0059/0006) consist of the posterior part of the braincase with otic capsules (coalesced prootics and exoccipitals) ( Fig. 1 ). This endochondral portion is dorsally adjoined by the parietal portion of the frontoparietal, and ventrally by the posterior part of the parasphenoid, both firmly coalesced to the braincase. Moreover, one of these specimens (NHMW 2019/0059/0006) preserved the ramus paroticus of the squamosum adjoining the right otic capsule ( Fig. 1A right), but its lamella alaris is broken away.

The frontoparietal firmly coalesced to the braincase is a characteristic feature of fully grown Thaumastosaurus . On its dorsal surface, it bears sculpture which is basically the same in both specimens. It may be characterized as transitional between that consisting of more-or-less circular pits separated by constant ridges (e.g. Rage and Roček 2007: fig. 3B) and that consisting of tubercles interconnected by low, ossen indistinct ridges, or sometimes completely isolated (e.g. Rage and Roček 2007: fig. 5A). One is inclined to view the first type of ornamentation as if the primary surface would be at the level of ridges, only secondarily pierced by pits, and the second type as if the primary surface would be at the base of tubercles that were only secondarily interconnected by arising ridges. The tubercles can be well observed in anterior or posterior views ( Fig. 1B, C ). Two anteroposteriorly directed ridges protrude from the ventral surface of the frontoparietal (pars contacta sensu Roček and Lamaud 1995: fig. 2C) to firmly connect the frontoparietal to the lateral walls of the braincase ( Fig. 1C less). The lateral portion of the horizontal, sculptured part extending lateral to the pars contacta is called the tectum supraorbitale ( Fig. 1B, C right). Preservation of both specimens does not allow inspection of the ventral surface of the frontoparietal exposed inside the braincase, namely whether the frontoparietal incrassation is developed. It is probable that due to hyperostosis, the frontoparietal incrassation coalesced with the roof of the braincase, which may result in a compact and smooth dorsal surface of the braincase cavity. It is worth commenting here that when the braincase cavity is inspected by μCT-scanning, this can be erroneously interpreted as if the ventral surface of the frontoparietal is without any incrassation ( Lemierre and Blackburn 2022): given that the chondrocranial braincase, no maưer whether still at cartilaginous or already ossified stage, has its roof perforated by a large frontoparietal foramen, which is subdivided by cartilaginous or osseous tecta (depending on the degree of development, thus on the degree of ossification), and that these openings in the braincase roof are filled by incrassations (= convex thickenings) on the ventral surface of the frontoparietal, it is clear that in both non-hyperossified and hyperossified frogs the situation is the same. Differences are only in that in the first case (non-hyperossified frogs), the frontoparietal can be easily separated from the braincase, because they are not coalesced, whereas in hyperossified anurans the braincase (with its foramens filled with frontoparietal incrassations) they are firmly fused together. There is no anuran species, in which the roof of the braincase would not be perforated, i.e. would be uninterrupted. However, it is possible, that in early juvenile individuals, the incrassations (and ornamentation on the outer surface of frontoparietal) are not yet well developed.

The posterior part of the parasphenoid with its two lateral processes is firmly co-ossified to the ventral surface of the braincase and of both otic capsules ( Fig. 1D ). A characteristic feature of this part of the parasphenoid is the elevated triangular field (ventrally projected in situ), which is delimited by a pronounced arched ridge on each of the lateral processes. These ridges run along each process from the anterolateral edge towards the posterior, converging posteromedially with their counterpart, and together extending posteriorly onto the posterior median process of the parasphenoid, where they form the tip of the rather narrow but prominent posterior median process. The processus cultriformis of the parasphenoid is broken off in both specimens at the level of anterior margins of both lateral processes, possibly suggesting that it was rather narrow at its base.

The ramus paroticus of the squamosum is preserved on the dorsal surface of the right otic capsule in NHMW 2019/0059/0006 ( Fig. 1A right), but not on the less side, and is absent also on both sides in NHMW 2019/0059/0005 (see triangular areas of aưachment, well seen in dorsal aspect; Fig. 1A less). This possibly suggests that the squamosum fused to the otic capsules later in development than the frontoparietal and parasphenoid.

The otic capsules and the braincase are monolithic, leaving no trace of sutures between the prootics and exoccipitals. In dorsal aspect, both otic capsules are tapered laterally where they are terminated by a horizontal lamina (termed the crista parotica), which is fully ossified. The dorsal surface of the crista parotica bears the above-mentioned triangular scar for the aưachment of the ramus paroticus squamosi ( Fig. 1A ). In the interior of this lateral portion of the otic capsule there is a horizontal, lateral semicircular duct. The vertical, posterior semicircular duct is prominent (both in dorsal and ventral aspects; Fig. 1A, D ) from the posterior wall of the otic capsules.

The walls of each otic capsule are pierced by several foramina. The largest, roofed by the crista parotica and facing laterally, is the foramen ovale ( Fig. 1B right, 1E right), which, in life, was covered by expanded portion of the columella (footplate). In anterior aspect, there is an oblong foramen, the foramen prooticum (or fontanella prootica) ( Fig. 1C ), which is in fact the connection between the braincase and orbit, through which the trigeminus and facialis nerves pass ( de Villiers 1934, Roček 1981, Roček et al. 2016). These nerves merge together to form a large ganglion before leaving the braincase (ganglion trigemino-geniculatum or ganglion prooticum commune) ( de Villiers 1934, Roček 1981, Roček et al. 2016). They can pass through the wall of the braincase via a single foramen or two separate foramina ( Gaupp 1899, de Villiers 1934, Roček 1981, Roček et al. 2016), the laưer seeming to be the case in NHMW 2019/0059/0005 ( Fig. 1C less). In such cases, the foramen prooticum is divided by a bony partition into a dorsal foramen for the trigeminal nerve, and a ventral foramen for the facial nerve; in the case of two separate foramina, the internal jugular vein passes together with the trigeminus nerve. Extending laterally from the foramen prooticum is a more or less distinct groove termed the sulcus venae jugularis, for the vena jugularis interna ( Fig. 1C ; see also Rage and Roček 2007: fig. 7A). The vena jugularis interna leaves the braincase through the foramen prooticum (if it is divided into separate trigeminal and facial foramina, it passes together with the trigeminus nerve), then it runs horizontally towards the lateral end of the prooticum as far as under the cartilaginous crista parotica, where it turns posteriorly through a notch that is clearly visible in the prootics that are disarticulated from the parotic ramus of the squamosum. In articulated skulls, the indentation on the prootic and a similar indentation on the prootic ramus of the squamosum form together a foramen (see Rage and Roček 2007: fig. 7A). The vein may run in a shallow horizontal groove on the anterior wall of the prootic, but may laterally merge deep into the bone. On the anterolateral surface of the otic capsule, there are distinct scars indicating areas of attachment of the medial ramus of the pterygoid ( Fig. 1C ). On the posterior surface of the otic capsules, partly hidden by the occipital condyle, lies the foramen jugulare ( Fig. 1B right, 1D right, 1E less) through which the glossopharyngeus and vagus nerves leave the braincase. In the lateral wall of the foramen jugulare is another foramen which represents a true connection into the otic capsule (foramen perilymphaticum). The partition between the foramen jugulare and foramen perilymphaticum is well seen in Figure 1D .

The posterior face of the braincase, presumably at the border between the exoccipitals and the frontoparietal (although the border cannot be recognized) is the foramen arteriae occipitalis ( Fig. 1B right). This is the entrance into a short canal that opens anteriorly below the tectum supraorbitale, above the dorsal surface of the capsula otica ( Fig. 1D ). Most probably, the canal follows the level where the frontoparietal and the roof of the otic capsule were originally in contact. Other openings in the walls of the otic capsules are crushed walls of the semicircular canals.

It is also worth noting that the horizontal distance between both condyli occipitales (coded traditionally from ventral view; Scoư 2005) is different in both individuals, being much greater in NHMW 2019/0059/0006 than in NHMW 2019/0059/0005 ( Fig. 1B ). In both specimens, these extend only around the lower half of the perimeter of the foramen magnum (thus, the condyles are slightly longer ovaloids in NHMW 2019/0059/0006). It is therefore necessary to assume that corresponding differences should be expected in the morphology of anterior cotyles of V

1.

Maxillae

The maxillae ( Figs 2–4 ) have the processus zygomatico-maxillaris consisting of two parallel ridges rimming a distinct groove, clearly visible both from the lateral and dorsal side ( Figs 2A–C , 4 A-3–A-6, B-3). This process is not a single prominence, but one prominence is formed by the external, ornamented layer and the second, arising from the inner surface of the bone, is markedly protruding beyond the dorsal margin of the bone ( Fig. 2 A-1–2C-1). The groove between both ridges abruptly becomes narrow towards the orbital margin, and obviously serves for extensive aưachment of the zygomatic process of the lamella alaris of the squamosum ( Laloy et al. 2013: figs 2A–B, 3A–C). The processus pterygoideus in dorsal aspect may be either only moderately prominent ( Fig. 2 A-2, B-2), or distinct ( Fig. 4 A-2), but in medial view it can be recognized by an abrupt termination of the lamina horizontalis ( Figs 2 A-3, B-3, 4A-5, A-6). The tooth row extends posteriorly beyond the level of the pterygoid process by five to ten tooth positions gradually decreasing in depth; this most posterior section of the tooth row is dorsally delimited by a low mound that ultimately terminates on the lower margin of the maxilla’s posterior process ( Fig. 2 A-3, 2B-3). At the level of the pterygoid process, there is a large pit facing posteriorly (marked by arrows in Fig. 2 A-2, A-3, B-3), pierced by several foramina with smooth margins, which enter into the intramaxillar vacuity. The largest may house the ramus maxillaris superior of the arteria temporalis and the ramus maxillaris superior of the nervus trigeminus [sensu Gaupp 1899; equivalent to the C.N.V 1 of Duellman and Trueb (1994) and Porro and Richards (2017)]. The subocular section of the palatoquadrate bar, much larger in cross section, lays on the dorsal surface of the lamina horizontalis ( Fig. 4D ). Further posteriorly on the inner surface of the posterior process, there is a large and well-delimited contact area for the quadratojugal ( Fig. 2 A-3).

The orbital section of the maxilla is rather thin ( Fig. 2 D-1), apparently because it was reinforced by the zygomatic process of the lamella alaris of the squamosum. The processus frontalis is the highest point by which the orbital margin of the maxilla is anteriorly terminated, and from which the dorsal margin of the bone slants down towards the anterior end of the bone ( Fig. 2 D-3). It should be emphasized that this margin is formed by a groove between the outer, sculptured level of the bone and inner, smooth layer ( Fig. 2 D-1), the same as was described above in case of the zygomatico-maxillar process. The orbital margin may be either ornamented (e.g. Roček and Lamaud 1995: fig. 4A–B), which suggests that the maxilla was joined by the processus zygomaticus of the squamosum, or rounded and smooth ( Figs 2D , 3N, P , 4A, B ), which suggests that the processus zygomaticus was short and did not extend anteriorly alongside the maxilla. In this anterior section of the bone, the lamina horizontalis becomes a thin ledge, rather deflected dorsally and terminating abruptly in a spine, from which another ridge splits towards the processus frontalis, thus approximately following the orbital margin. Between both ridges, there is a deep triangular area termed the fossa maxillaris ( Fig. 2 D-1).

Whereas the above maxillar characteristics are present in all specimens, regardless of their degree of preservation, they substantially differ in the type of ornamentation. In NHMW 2019 /0059/0002, the sculpturing paưern may be characterized as ‘pit-and-ridge’ type ( Fig. 2 A-1), whereas that of NHMW 2019 /0059/0004 is reticular and distinctly pustulous ( Fig. 2 D-2). The sculpturing paưerns in the remaining two maxillae are transitional between them.

Maxillae and squamosa ffom La Bouffie, Sainte-Néboule, and Escamps

Besides the two posterior parts of the skull and the four maxillae from the NHMW collection, we were able to study numerous fragmentary, but surprisingly variable, materials from the localities La Bouffie, Sainte-Néboule, and Escamps, deposited in the collections of UM and UU. Fragmentary maxillae from La Bouffie are rather large ( Fig. 3A–D ), corresponding by their size to the reconstructed maxillae of Thaumastosaurus bottii (c. 20 mm; see Roček and Lamaud 1995: fig. 4C), the neotype of which was previously designated from the same locality ( Roček and Lamaud 1995). The ornamentation corresponds to the ‘pit-and-ridge’ type, which extends up to the lower margin of the bone. Along the lower margin of the bone, there is a narrow zone where its outer surface is moderately inclined inwards (marked by arrow in Fig. 3B ). On the inner surface, there is a robust and rounded lamina horizontalis whose depth approximately corresponds to that of the crista dentalis ( Fig. 3 D-2). From the lamina horizontalis, a subtle, straight ledge runs antero-dorsally at ~65° to the dorsal margin of the bone, thus delimiting a triangular fossa maxillaris. The anterior end of the bone is widely rounded. The lamella alaris of the squamosum ( Fig. 3E ) is regularly rounded on its posterior end, with the same type of ornamentation as that on the maxillae, but only with remnants of the ramus paroticus and processus posterolateralis on its inner surface. By its shape, ornamentation and size, it recalls the squamosum of T. bottii ( Roček and Lamaud 1995: fig. 5). It should be noted that even if its alary lamella is incomplete, it may be inferred from more complete maxillar fragments described by Roček and Lamaud (1995) that the alar lamella of T. bottii extended anteriorly up to the postnasal wall, as is the case with the material that was assigned to Thaumastosaurus gezei ( Fig. 5A ; Rage and Roček 2007: fig. 1C).

More abundant material is available from Sainte-Néboule. Only the maxillary fragment UM SNB 5000 ( Fig. 3F ) is of a size comparable with that of T. bottii described by Roček and Lamaud (1995), but it differs in type of ornamentation, which consists of deep pits separated by thin partitions, which at points where they meet protrude in small pustules. The anterior end of the bone is robust and bifurcated in accordance with a vertically bifurcated lamina horizontalis. Its dorsal branch turns outwards toward the vertical wall of the bone, thus closing the fossa maxillaris anteriorly. Its ventral branch, obviously exceeding the dorsal one, bears teeth, but the tooth row ends in a short distance ( Fig. 3 F-1). The lamina horizontalis is deeper than the crista dentalis, the teeth are closely packed to each other (five tooth positions on 2 mm). The specimen UM SNB 5004 ( Fig. 3H ) is similar in the shape of the bifurcated anterior end of the lamina horizontalis, but differs by its reticular ornamentation which, nevertheless, also tends to protrude in pustules. The third maxillary fragment ( UM SNB 5011 ; Fig. 3K ) is rather worn out, but judging by its ornamentation, it could belong to those illustrated in Figure 3F, H . These three maxillae may be associated, based on a similar degree of reticulo-pustular ornamentation, with the fragmentary squamosum ( Fig. 3G ). The original shape of the lamella alaris is difficult to reconstruct, but judging by its thin posterior end, which seems to be only slightly damaged, it did not extend far posteriorly. It preserves the proximal portion of the processus posterolateralis, which laterally enveloped the palatoquadrate (see arrow in Fig. 3 G-2) .

The remaining maxillae from Sainte-Néboule are much smaller. Specimen UM SNB 5013 ( Fig. 3I ) is represented by about the posterior half of its original length, which presumably did not extend over 15 mm. As in Thaumastosaurus bottii , this small frog had nearly no processus zygomatico-maxillaris, and the ornamentation also covered the dorsal (orbital) margin of the maxilla ( Fig. 3 I-2). The posterior process of the maxilla was very short, only exceeding the posterior end of the tooth row by a small amount. The processus pterygoideus was rounded, only slightly prominent medially. The ornamentation recalls honeycomb cells, which may be arranged in rows. Teeth are small, closely packed to each other, eight to nine on 2 mm ( Fig. 3 I-1).

UM SNB 5015 ( Fig. 3J ) and perhaps also UM SNB 5005 ( Fig. 3L ) are of similar size, but they differ in dentition (teeth are fang like, their roots are separated by thick partitions which do not extend much beyond the level of the margin of the crista dentalis and may enclose the bases of the crowns lingually, and the crowns are cone shaped). Maximum number of tooth positions is six on 2 mm. The teeth exceed beyond the margin of the crista dentalis, thus they are visible also in outer aspect ( Fig. 3 L-2). Ornamentation is very irregular, on a single bone consisting of pits of various depth interchanged by large portions completely smooth ( Fig. 3 L-2).

Among these middle-sized maxillae (estimated length 12–15 mm) from Sainte-Néboule there are the posterior parts of maxillae UM SNB 5009 ( Fig. 3M ) and UM SNB 5023 ( Fig. 3O ). They differ from one another by shape of the processus zygomatico-maxillaris, type of ornamentation, size of processus posterior, presence or absence of ornamented dorsal margin of the bone, vertical diameter of the lamina horizontalis, posterior extent of the tooth row, and type of dentition (seven tooth positions in 2 mm below the processus pterygoideus in the former, 10 in the laưer). UM SNB 5023 ( Fig. 3O ) is in many respects similar to UM SNB 5024 ( Fig. 3N ) which is, however, slightly smaller.

The two maxillary fragments UM SNB 5024 and UM SNB 5044 ( Fig. 3N, Y ) correspond to each other by their size, type of ornamentation, and tiny, dense dentition. A highly important feature is that they have, like the slightly larger UM SNB 5023 ( Fig. 3O ), a smooth orbital margin, which indicates that they had their squamosum not extended anteriorly .

Other maxillary fragments from Sainte-Néboule include three specimens with tiny and dense dentition ( UM SNB 5037 , Fig. 3P ; UM SNB 5017 , Fig. 3R ; UM SNB 5036 , Fig. 3S ), and two with relatively robust dentition observable from the labial side ( UM SNB 5039 , Fig. 3 º; UM SNB 5022 , Fig. 3T ) .

None of these small maxillae ( Fig. 3I–T ) have their processus zygomatico-maxillaris groove-like depressed as those in Figure 2 A-2–C-2; this process is a simple vertical wall and their margo orbitalis is, where intact, smooth without any ornamentation. Moreover, there is no large pit on the posterior surface.

Two additional maxillar fragments provide information not only about their external morphology, but also on their internal structure. UM SNB 5158 ( Fig. 4A ) belongs to a small maxilla (estimated maximum length 15 mm); it bears a characteristic honeycomb ornamentation directed posteriorly, where it becomes irregularly pit-like, with pits and grooves below the orbit separated by thin partitions. The posterior process is broken off, and the orbital margin is smooth. The horizontal lamina is deep and rounded, posteromedially extending in a pointed and dorsoventrally compressed pterygoid process. Slightly above the posterior termination of the horizontal lamina is a posterior orifice of a larger canal accompanied by several small foramina ( Fig. 4 A-3, A-4), which communicate with intraosseous vacuities and could house the maxillary branches of the trigeminus nerve and temporal artery. The posterior orifice is dorsomedially covered by a rather rectangular margin ( Fig. 4 A-5, A-6) which may be an articular margin of the ramus maxillaris of the pterygoid (see Fig. 4D ). Teeth are tiny, close to each other, and their crowns obviously did not exceed the vertical diameter of the horizontal lamina. This maxilla corresponds by its size to UM SNB 5023 ( Fig. 3O ) and UM SNB 5024 ( Fig. 3N ).

UM SNB 5157 ( Fig. 4B ) is moderately larger and more robust, with its posterior process preserved. The posterior opening is similar as in UM SNB 5158 ( Fig. 4A ), but the bone differs by its weakly developed piưed ornamentation, thin and dorsoventrally compressed horizontal lamina, and irregular, coneshaped teeth, separated from each other by thick bony partitions.

Both these maxillary fragments, UM SNB 5157 and UM SNB 5158, have a smooth orbital margin and a distinct articular facet for the processus zygomaticus of the squamosum ( Fig. 4A, B ).

Besides all these maxillae, in the Sainte-Néboule sample, there are also certain squamosal fragments. One of them ( UM SNB 5040 , Fig. 3U ) falls by its size within the category of the small maxillae, whereas the other two ( UM SNB 5025 , Fig. 3G ; UM SNB 5026 , Fig. 3V ) are similar in their ornamentation to the large maxilla UM SNB 5000 ( Fig. 3F ). The former squamosum ( UM SNB 5040 , Fig. 3U ) is represented by the lamella alaris with preserved part of the ramus prooticus and the base of the processus posterolateralis (both marked by arrows in Fig. 3 U-1). The anterior portion of the lamella is broken, thus its anterior extent cannot be reconstructed. The squamosum UM SNB 5026 ( Fig. 3V ) is represented by the elongated anterior end of the lamella alaris that extends between the processus frontalis of the maxilla and the nasale, and forms the anterolateral part of the orbital margin (cf. Fig. 5 A-2). A fragment of maxilla with the same type of ornamentation is illustrated in Figure 3W (specimen UM SNB 5021 ). Other dermal bones from Sainte-Néboule are too fragmentary ( UM SNB 5028 – UM SNB 5034 and UM SNB 5041 – UM SNB 5043 ), though some of them probably represent squamosa .

The sample from Escamps is represented by a few maxillae and squamosa originating from different (but coeval) sites of the locality. Among them, of particular importance is one peculiar less squamosum (UU ESC4 7001; Fig. 3X ) from Escamps 4, with a partly preserved ramus paroticus and processus posterolateralis. Its narrow lamella alaris is slightly damaged on its posterior end, and it appears that its anterior end is complete (also judging by gradually lowering ornamentation on its outer surface), and has the articular facet for the processus zygomatico-maxillaris of the maxilla. Another, but fragmentary, squamosum is from Escamps 2 (UU ESC2 7001) and possesses a distinctly different ornamentation paưern than the squamosum from Escamps 4 (UU ESC4 7001), being distinctly pustular and with some pustules fusing and forming continuous ridges.

There are only four maxillae from Escamps but nevertheless, these still possess different kinds of ornamentation, with some bearing a reticulated paưern (e.g. UU ESC1 7001) and others bearing a honeycomb paưern (e.g. UU ESC3 7001). The maxillae with the reticulated paưern may be thus associated with the squamosum UU ESC2 7001, whereas those with the honeycomb paưern may be associated with the squamosum UU ESC4 7001, although it has to be noted that there were no maxillae recovered from the two sites that yielded squamosa (Escamps 2 and 4).

Figures

Figure 1. Thaumastosaurussp. from the Phosphorites du ºuercy. Posterior part of braincase with otic capsules and fragment of squamosum. NHMW 2019/0059/0005 (less column), NHMW 2019/0059/0006 (right column). A—dorsal view; B—posterior view; C—anterior view; D—ventral view; E—lateral view.E in right column is reversed to facilitate comparisons. All specimens are at the same scale.

Figure 2. Thaumastosaurus sp. from the Phosphorites du ºuercy. Maxillae.A, Posterior part of right maxilla (NHMW 2019/0059/0002) in lateral (A-1), dorsal (A-2) and medial (A-3) views. B, Posterior part of right maxilla without tip of processus posterior (NHMW 2019/0059/0001) in lateral (B-1), dorsal (B-2), and medial (B-3) views.C, Fragment of less maxilla involving processus zygomatico-maxillaris (NHMW 2019/0059/0003, reversed for comparisons) in lateral (C-1), dorsal (C-2), and medial (C-3) views.D, Anterior half of less maxilla (NHMW 2019/0059/0004, reversed for comparisons) in medial (D-1), dorsal (D-2), and lateral (D-3) views.Arrows in A, B, and C point to a large pit facing posteriorly.All specimens are at the same scale.

Figure 3. Thaumastosaurus sp.maxillae and squamosa from the localities La Bouffie,Sainte-Néboule, and Escamps.A, Fragmentary maxilla (UM BFI 3002) in lateral view.B, Fragmentary maxilla(UM BFI 3004) in lateral view.Arrow marks inclined strip-like zone of external surface of the bone. C, Fragmentary maxilla (UM BFI 3005) in lateral view.D, Anterior part of right maxilla (UM BFI 3008) in lateral (D-1) and medial (D-2)

Figure 4. Thaumastosaurus sp. tiny maxillae with smooth orbital margin from Sainte-Néboule. A, Posterior part of less maxilla with posterior process broken off (UM SNB 5158) in lateral (A-1), dorsal (A-2), posterior (A-3), postero-medial (A-4), medial (A-5), and dorso-medial (A-6) views. B, Posterior part of less maxilla with posterior process preserved (UM SNB 5157) in lateral (B-1), dorsal (B-2), antero-dorsal (B-3), and medial (B-4) views.Unlabelled arrows mark entrance into intramaxillar vacuity for the ramus maxillaris superior of nerve V and its orifice on the broken surface below the orbit.Labelled arrows mark groove-lake articular facet for processus zygomaticus of the squamosum. Red doưed lines mark course of the subocular palatoquadrate bar.C, Less maxilla (UM SNB 5183) in medial (C-1), dorsal (C-2), and lateral (C3) aspects.Anterior and posterior parts of bone are broken away.D, Transverse section through a less maxilla of a recent Pelobates fuscus in posterior view at the level of posterior end of lamina horizontalis where the ramus maxillaris of the pterygoid meets the most posterior end of the nasale. Note the spacious inner vacuity through which the nerve and vessels pass through the bone, and position of the subocular palatoquadrate bar on the dorsal surface of the lamina horizontalis. All specimens (except D) are at the same scale.

Figure 5. Individual variation.Nearly complete articulated skull of Thaumastosaurus gezei (holotype, MNHN.F.ºU17376; see also Rage and Roček 2007), considered as a synonym of Thaumastosaurus servatus by Lemierre et al. (2021), in dorsal (A-1) and less lateral (A-2) views, compared with μCT reconstructions of two different skulls of Pyxicephalus angusticeps male individuals. B, Pyxicephalus angusticeps, male (CAS 164712). B-1, Skull in dorsal view.B-2, Magnified frontoparietal in dorsal view.B-3, Skull in less lateral view. B-4, Magnified squamosum and posterior part of maxilla. C, Pyxicephalus angusticeps, male (CAS 164708). C-1, Skull in dorsal view.C-2, Magnified frontoparietal in dorsal view. C-3, Skull in less lateral view.C-4, Magnified squamosum and posterior part of maxilla. Contact between osseous lamella produced by dorsal edge of maxilla and anterior end of lamella alaris is marked by arrows.