Hungarobatrachus szukacsi Szentesi & Venczel, 2010

Venczel, Márton, Szentesi, Zoltán & Gardner, James D., 2021, New material of the frog Hungarobatrachus szukacsi Szentesi & Venczel, 2010, from the Santonian of Hungary, supports its neobatrachian affinities and reveals a Gondwanan influence on the European Late Cretaceous anuran fauna, Geodiversitas 43 (7), pp. 187-207 : 190-198

Hungarobatrachus szukacsi Szentesi & Venczel, 2010 ( Figs 2-7 )

MATERIAL EXAMINED. — 31 isolated and mostly incomplete bones (see Table 1 ).

DISTRIBUTION. — Known exclusively from the SZÁL-6 site at the Iharkút vertebrate locality, Bakony Mountains, northwestern Hungary, in the Upper Cretaceous (Santonian) Csehbánya Formation.

EMENDED DIAGNOSIS (modified and expanded from Szentesi & Venczel 2010; Roček 2013). — Body size moderate (estimated 50-80 mm snout-vent length). Skull moderately hyperossified. Exostosis on external surfaces of frontoparietals, squamosals, and maxilla generally consists of pit-and-ridge ornament, with some

pif

weakly developed tuberculate ornament on lower portions of larger squamosals and adjacent portion of maxillae. Frontoparietals solidly fused along midline and no development of dorsal crests or ridges, at least posteriorly; posterolateral portion expanded laterally to form a large squamosal process that potentially contacts laterally with squamosal; ventral surface bears two unpaired frontoparietal incrassations, consisting of an evidently elongate anterior incrassation with a bi-lobed posterior margin and a subcircular posterior incrassation; and occipital canal completely enclosed within bone, with its foramen arteria temporalis opening ventrally between squamosal process and pars contacta. Squamosal having enlarged, ventroanteriorly directed processus zygomaticus and smaller, posteriorly directed processus posterodorsalis, both expanded to form broad lamella alaris that is tilted posteriorly, somewhat rhomboid in outline, with anterodorsal margin shallowly concave and fully enclosing posterior portion of orbit and with posteroventral margin more deeply concave; base of processus zygomaticus expanded anteroposteriorly and evidently abutted against complementary processus zygomatico-maxillaris on maxilla; anteroventral end of processus zygomaticus moderately elongate and tapered, with leading edge bearing tiny, knob-like projections. Maxilla moderately elongate, deep, and robust; preorbital region deepest, orbital region indented by moderately elongate and concave margo orbitalis, and postorbital region moderately deep, elongate, and tapered posteriorly; lamina horizontalis deep and lingually narrow, ending posteriorly in an evidently well developed processus pterygoideus; processus posterior lingually bears sutural surface for quadratojugal articulation, indicating maxillary arcade was closed posteriorly forming a bony ‘cheek’; and maxilla dentate, bearing numerous small and closely spaced teeth. Angulosplenial having processus coronoideus bearing single low, broadly convex dorsal tubercle. Ilium heavily built; dorsal crest high (about 2.5 times higher than ilial shaft) and sail-like in lateral outline, and mediolaterally thick; lateral surface of dorsal crest and adjacent dorsolateral surface of shaft prominently ornamented with anteroposteriorly elongate grooves and posteriorly anastomosing ridges, with ornamented surface demarcated ventrally by a convex ridge extending anteroposteriorly along lateral surface of ilial shaft; dorsal protuberance developed as a medially thickened, low, and laterally projecting flange, with undivided and roughened surface; interiliac tubercle greatly enlarged to cover entire medial portion of ilial body including preacetabular region and with its medial surface flattened and variably roughened for strong sutural contact with opposite ilium.

DESCRIPTION OF NEWLY REFERRED MATERIAL

General remarks

The seven ilia and five tibio-fibulae originally reported for Hungarobatrachus szukacsi were thoroughly documented in English by Szentesi & Venczel (2010) in the type description and later in Hungarian by the same authors ( Szentesi & Venczel 2012a). No additional tibio-fibulae are known, but another two ilia are now available. Our descriptions and remarks below focus on the new ilial specimens and on newly recognized skull bones (incomplete frontoparietals, squamosals, maxillae, and angulosplenials). Most new examples of those elements are depicted in Figs 3-6 and our tentative reconstruction for the skull of Hungarobatrachus is presented in Figure 7 . On the basis of ilia and tibio-fibulae then available, Szentesi & Venczel (2010) estimated a body size of 50-60 mm for Hungarobatrachus . The largest of the newly recognized squamosals and maxillae suggest a higher upper size range, of about 80 mm.

Ilium ( Fig. 2 )

Consistent with the seven ilia previously reported for Hungarobatrachus szukacsi (e.g., Szentesi & Venczel 2010: figs 2, 3A-E, 4A), both of the newly referred ilia preserve much of the ilial body (= acetabular region) and the posterior portion of the ilial shaft. The more nearly complete of the two new ilia, MTM VER 2015.145.1 ( Fig. 2 A-D), is comparable in size to the holotype ilium (cf., Szentesi & Venczel 2010: fig. 2; this study: Fig. 2E, F ), although the former preserves less of its supra- and subacetabular regions and dorsal crest. The other newly referred example, MTM VER 2015.145.2 (not figured), is less intact. Our abbreviated description below focuses on the better preserved and figured specimen, MTM VER 2015.145.1.

The ilium is heavily built and robust. In lateral view, the ilial body is triangular in outline; the acetabular fossa is fully enclosed within the ilial body, shallowly concave in medial depth, sub-circular in outline, and bordered anteroventrally by a low acetabular rim; the dorsal acetabular expansion is moderately tall and lacks a supraacetabular fossa; the ventral acetabular expansion is relatively shallower; and the preacetabular zone is moderately expanded anteroventrally in the form of an asymmetrically convex bulge that is confluent medially with the enlarged interiliac tubercle. In medial view, the interiliac tubercle covers the entire medial face of the ilial body and even expands anteriorly across the preacetabular region to connect with the posteriormost portion of the ilial shaft. The enlarged interiliac tubercle is triangular in dorsal or ventral view, being medially thickest

anteriorly and narrowing posteriorly, and its medial face is broad, flattened, and covered by a roughened surface that we call the “interiliac scar” (sensu Gómez & Turazzini 2016). The preacetabular angle (i.e., angle between anterior margin of ventral acetabular expansion and ventral surface of ilial shaft, measured in lateral aspect) is slightly more than 90°. The ilial shaft is cylindrical in cross section and, extending along its dorsolateral surface, bears a prominent dorsal crest. The crest is both tall (about 2.5 times taller than ilial shaft and with dorsal edge of crest lying well above level of dorsal surface of acetabular dorsal expansion) and mediolaterally thickened. The posterior end of the dorsal crest is approximately in line with the anterior portion of the acetabular rim and lies well behind the anterior limit of the anteriorly expanded interiliac tubercle. The dorsal crest projects dorsally and slightly medially; its medial face is flattened and smooth, whereas its lateral face is shallowly convex. Prominent ridge-and-groove ornament is developed across the lateral surfaces of the dorsal crest and the dorsal three-quarters of the underlying ilial shaft. The lowermost boundary of that ornamented area is sharply defined by a narrow, but prominent ridge extending along the ventrolateral surface of the ilial shaft; that ridge is in approximately the same position as the calamita ridge reported in some bufonids (seeGómez & Turazzini 2016: 8), but is not clearly homologous with the latter structure. Along the shaft and onto the lower two-thirds of the dorsal crest, the lateral ornament on MTM VER 2015.145.1 consists of anteroposteriorly elongate grooves and posteriorly anastomosing ridges, whereas across the upper one-third of the crest the ridges are shorter and oriented more vertically. Along its posterior edge, the dorsal crest bears a dorsal protuberance in the form of a low and moderately thickened flange that projects laterodorsally and has a slightly roughened surface.

In their preserved features, both newly referred ilia are virtually identical to those previously reported for Hungarobatrachus szukacsi , especially in exhibiting the seemingly unique combination of an enlarged interiliac tubercle and a prominent dorsal crest ornamented laterally with pronounced ridges and grooves. Several features known for the originally described ilia are not preserved in either of the new specimens. These include: 1) orientation and posterior extent of the dorsal acetabular expansion, which in the holotype is oriented dorsoposteriorly at a shallow angle and was inferred not to have borne a posteriorly tapered ischiadic process that projected beyond the posterior limit of the acetabular fossa ( Fig. 2E ); 2) medial outline of the interiliac tubercle, which in the holotype resembles a bell tilted onto its side ( Szentesi & Venczel 2010: fig. 2C); 3) form of ilioischiadic juncture, which in the holotype is mediolaterally thin and its posterior face is smooth and shallowly concave from sideto-side ( Fig. 2F ); and 4) lateral outline of the dorsal edge of the dorsal crest, which on two of the previously referred ilia is seen to be broadly arcuate and dipping anteriorly ( Szentesi & Venczel 2010: figs 3A, D). The newly referred and figured ilium (MTM VER 2015.145.1) corroborates earlier reports that the interiliac scar, which is broadly developed across the medial surface of the interiliac tubercle, may be either roughened (e.g., MTM VER 2015.145.1: Fig. 2D ; previously referred MTM V 2008.15.1: Szentesi & Venczel 2010: fig. 3C) or nearly smooth (e.g., holotype MTM V 2008.16.1: Szentesi & Venczel 2010: fig. 2C). Those differences in surface texture imply corresponding differences in the relative strength of the interiliac joint. Intriguingly, those textural differences do not appear to be size-related. Finally, MTM VER 2015.145.1 exhibits a slightly different pattern of lateral ornament on the dorsal crest, with ridges across the upper one-third of its crest being short and extending more vertically, rather than being oriented more horizontally as in the holotype (cf., Fig. 2A, B versus Fig. 2E ). We do not regard that minor variant in lateral ornament as being taxonomically significant.

Frontoparietal ( Fig. 3 )

The only available specimen, MTM VER 2016.2546, represents the posteromedian and adjacent left posterolateral portion of an azygous (i.e., fused) pair of frontoparietals. The specimen is a small (maximum width = 7.5 mm and maximum anteroposterior length = 6.9 mm) and relatively flat piece of bone, with a somewhat pentagonal dorsal or ventral outline ( Fig. 3A, B, D ). Most of the margins are broken surfaces; the only intact margins are an anteroposteriorly short portion along the left posterolateral edge ( Fig. 3 D-F) and a moderately broad portion across the middle of the occipital (posterior) surface ( Fig. 3G, H ). Due to breakage, the overall size, proportions, and shape of the azygous frontoparietals are largely unknown. Nevertheless, enough of the posterolateral portion is preserved on the left side to show that region is moderately expanded both laterally and anteroposteriorly (see below). Additionally, the specimen is traversed by several major cracks and, along its sagittal midline, is indented by a small, sub-circular divot ( Fig. 3B, C ) that may represent a bite or puncture mark.

Although MTM VER 2016.2546 is incomplete and broken asymmetrically, its sagittal midline ( Fig. 3G, H ) can be recognized using two sets of landmarks along the occipital surface: 1) a dorsally placed processus posterior superior and a ventrally placed processus posterior inferior that both project a short distance posteriorly from the posterior midline; and 2) an equal distance from, and to either side of, the posterior midline, the occipital face of the specimen is perforated by an intact (left) and incomplete (right) opening for the foramen arteriae occipitalis. The dorsal and ventral surfaces of MTM VER 2016.2546 lack a suture or a line of fusion demarcating the sagittal midline. Instead, the bone is solid and continuous throughout that region. This indicates that the left and right frontoparietals were solidly fused, at least along the posterior portions of their medial edges. Based on comparisons with other anurans having solidly fused frontoparietals, we predict that the left and right frontoparietals were solidly fused together along their entire lengths in Hungarobatrachus .

The facies dorsalis or roofing portion of MTM VER 2016.2546 is moderately thick, becoming slightly thicker

posteriorly, and is essentially horizontal. In anterior (not shown) and posterior ( Fig. 3G, H ) views, the median portion of the facies dorsalis is shallowly depressed along the sagittal midline, similar to the extant calyptocephalellid Calyptocephalella gayi ( Lynch 1971: fig. 20B, depicted as Caudiverbera caudiverbera ) and the Eocene ranoid Thaumastosaurus De Stefano, 1903 ( Roček & Lamaud 1995: fig. 2B; Rage & Roček 2007: fig. 1D; Laloy et al. 2013: fig. 3D). On the left side, enough of the posterolateral portion is preserved to show that the processus lateralis superior is expanded both laterally and anteroposteriorly to form a broad flange that we call the “squamosal process”. This process projects laterally in a shallowly convex arc ( Fig. 3G ) and, in life, would have overhung the prootic region and at least partially enclosed the posterior margin of the orbital opening ( Fig. 7 ). Best seen in oblique ventral and left lateral view ( Fig. 3E, F ), the posterior portion of the lateral surface of the squamosal process is intact and roughened. We provisionally interpret this anteroposteriorly roughened surface as a sutural surface for contact laterally with the squamosal. We are forced to qualify that statement, because none of the six available squamosals (see next section) preserves evidence of a complementary contact surface along their dorsal margin. AsLynch (1971: 46-47) noted, many anuran genera have frontoparietals with a posterolaterally expanded portion that approaches, but fails to directly contact with the dorsal rim of the squamosals—that potentially could be the pattern in Hungarobatrachus . Regardless of whether the frontoparietal laterally contacted the squamosal, it is evident that the posterolateral portion of the frontoparietal was broader relative to the more anterior portion of the bone. In dorsal or ventral outline, the intact frontoparietals would have resembled an inverted ‘T’ ( Fig. 7 ).

The entire dorsal surface of MTM VER 2016.2546 exhibits modest exostosis, in the form of pit-and-ridge style ornament ( Fig. 3 A-C). The pits are of varying diameters and outlines, ranging from small to moderate and oval, sub-circular, or polygonal, but are consistently shallowly concave and their floors are perforated by one or several tiny holes. The pits are bordered by low, narrow ridges that coalesce to form a loosely reticulate arrangement. Although variation is evident in the size and outlines of the pits and ridge, there is no obvious change in ornament across the preserved posterior portion of the frontoparietals. A similar pit-and-ridge ornament occurs on the external surfaces of the squamosals and maxillae. Aside from its dorsal ornamentation and the previously mentioned, possible bite mark, the dorsal surface of MTM VER 2016.2546 lacks other prominent surface features such as crests or ridges. There is no dorsal exposure of the canal for the arteria occipitalis (see below), which indicates that at least along its posterior portion that canal is fully enclosed within the frontoparietal.

Returning to its ventral surface, MTM VER 2016.2546 exhibits several notable features ( Fig. 3 D-F). Midway across the specimen, the posterior portion of the pars contacta is preserved as a moderately deep and ventrally projecting flange that traces a sinuous anteroposterior path. Along its preserved anterior portion, the pars contacta is anteroposteriorly straight in ventral view. In this region, the pars contacta laterally bears a weak bony pillar that extends dorsally and then curves laterally onto the underside of the facies dorsalis to demarcate the shallowly concave, posteromedial wall of the orbit. Lateral to the preserved anterior portion of the pars contacta, enough of the laterally expanded portion of the facies dorsalis remains in front of the bony pillar and squamosal process to show that the tectum supraorbitale (= alae supraorbitale) overhung the orbital region, although how far it projected laterally is unknown because the margo orbitalis is not intact. Midway along its length, the pars contacta thickens and flares laterally and, in this region, its ventromedial and ventral surfaces are roughened for sutural contact with the underlying (and not preserved) endocranium. Posteriorly the pars contacta grades into the ventral surface of the pars facialis, but here the bone is broken away where the processus paraoccipitalis would have projected posteriorly. Best seen in oblique ventral and left lateral view ( Fig. 3E, F ), a moderately large foramen opens midway along the lateral base of the pars contacta. We interpret this opening as the foramen arteria temporalis, for exit of one of the branches of the arteria occipitalis. Extending from that foramen is a shallow groove for the canalis arteria temporalis, which traces the anterolateral path of the arteria temporalis between the ventral surface of the squamosal process and the underlying temporal musculature ( Roček 1981). Anterior to the foramen arteria temporalis, a smaller foramen of uncertain identity also opens laterally in the base of the pars contacta. Medial to the pars contacta, the ventral midline of the fused frontoparietals bears slightly thickened bony imprints or patches that represent the incompletely preserved incrassatio frontoparietalis ( Fig. 3D ). Anteriorly is the posterior portion of what appears to be an unpaired anterior incrassatio frontoparietalis (= facies cerebralis anterior) having a bilobed posterior margin with the indentation at the midline, whereas more posteriorly is a broader, sub-circular, and unpaired posterior incrassatio frontoparietalis (= facies cerebralis posterioris).

Squamosal ( Fig. 4 )

Six incomplete squamosals are available. Specimens range in size, with the largest (MTM VER 2016.695: Fig. 4G ) being about 20 mm in its maximum preserved dimension and, when complete, would have been about twice as large as the smallest example (MTM VER 2016.701.2: Fig. 4E, F ). Although no specimen is intact, collectively these demonstrate that the squamosal retained the tri-radiate structure typical for anurans. For Hungarobatrachus , its tri-radiate squamosal consists of a prominent and anteroventrally projecting processus zygomaticus (= anterior or zygomatic ramus), a less prominent and posteriorly directed processus posterodorsalis (= posterior or otic process/ramus), and a processus posterolateralis (= squamosal shaft or ventral ramus) of uncertain form and, presumably, directed ventroposteriorly.

The main portion of the squamosal in Hungarobatrachus is formed by the processus zygomaticus, portions of which are preserved in all six specimens ( Fig. 4 ), and by the smaller

processus posterodorsalis, portions of which are preserved in the first five of the illustrated specimens ( Fig. 4 A-I). Both processes are conjoined and expanded into a broad plate, the lamella alaris. In lateral and medial views ( Fig. 4 ), the lamella alaris is tilted posteriorly, with its long axis extending ventroanteriorly-dorsoposteriorly, and is somewhat rhomboid in outline, with its anterodorsal margin (margo orbitalis) shallowly concave and its posteroventral margin deeply concave. In anterior and posterior views (not shown), the lamella alaris is moderately thick and bent, with about its lower twothirds oriented essentially vertically and its upper one-third tilted mediodorsally. The processus posterodorsalis portion of the lamella alaris is moderately deep and projects a short distance posteriorly. The available size range of specimens indicates that the processus posterodorsalis becomes deeper and its posterior end becomes more broadly rounded with increased size (cf., Fig 4E vs. G). The lower margin of the processus posterodorsalis and the posteroventral margin of the processus zygomaticus together form a concave margin that becomes relatively deeper with increased size and, in life, may have bordered the anterior margin of the cartilaginous tympanic annulus ( Fig. 7 ). The dorsal margin of the lamella alaris is formed posteriorly by the processus posterodorsalis and anteriorly by the processus zygomaticus; it is broadly convex in lateral outline and, as noted in the frontoparietal account above, its dorsal and dorsomedial surfaces lack clear evidence of sutural contact with the frontoparietal. The remaining margins of the lamella alaris are formed exclusively by the processus zygomaticus. The margo orbitalis is long, shallowly concave, and faces anterodorsally to completely enclose the posterior and posteroventral margins of the orbital opening ( Fig. 7 ). The ventral edge of the processus zygomaticus is nearly straight or shallowly concave in lateral or dorsal outline and lateromedially thin. The relatively smooth ventral surface of the processus zygomaticus suggests it abutted against the complementary processus zygomatico-maxillaris on the maxilla (see next account). Preserved for two squamosal specimens (MTM VER 2016.695 and 2016.3575: Fig. 4G and Fig. 4 J-L, respectively), the anteroventral end of the processus zygomaticus is notable for being moderately elongate and tapered anteriorly, and, in MTM VER 2016.3575 ( Fig. 4 J-L), its leading edge bears tiny, knob-like projections. This anterior projection is reminiscent of some anurans, such as Thaumastosaurus ( Rage & Roček 2007: fig. 1A, C; Laloy et al. 2013: fig. 3A, C) in which the anteroventral end of the squamosal extends anteriorly along the dorsal edge of the maxilla and contacts the posteriorly expanded nasal, thereby excluding the maxilla from the orbital margin. Although we lack any articulated specimens that unequivocally demonstrate the pattern of squamosal-maxilla contact in Hungarobatrachus , the form of the anteroventral end of the isolated squamosals is potentially suggestive of that contact pattern ( Fig. 7 ). If squamosal-nasal contact existed, that may have been strengthened by the tiny, knob-like projections on the leading end of the anterior projection of the squamosal.

The external surface of the lamella alaris is variably ornamented. The available size series indicates that with increased squamosal size, ornament becomes both more pronounced and its coverage increases. In smaller specimens about the posterior one-third of the lamella alaris is unornamented and smooth, whereas in larger specimens the ornamented area covers the entire lamella alaris (cf., Fig. 4A, C vs Fig. 4G, J ). Ornament patterns also vary dorsoventrally across the squamosal. The upper, medially tilted portion of the lamella alaris bears pit-and-ridge style ornament similar to that on the frontoparietals. That gives way to a more loosely reticulate and somewhat tuberculate pattern across the middle and onto the ventral portions of the lamella alaris. In medial view, three specimens preserving the dorsal portion retain the broken, cup-shaped base of the medially directed ramus paroticus ( Fig. 4D, F, I ); those bases are too incomplete to establish

cd

the form of the ramus paroticus and its pattern of contact with the complementary crista parotica on the braincase. At least two of those same specimens ( Fig. 4D, I ) also preserve the broken base of the processus posterolateralis. Considering that the processus posterolateralis is universally present in anurans as a ventroposteriorly projecting strut that invests the palatoquadrate and helps brace the jaws against the braincase (e.g., Trueb 1973, 1993), we assume a similar form and function for Hungarobatrachus .

Maxilla ( Fig. 5 )

Eight maxillae are available. Most are fragmentary, but one (MTM VER 2016.690: Fig. 5 A-C) is nearly complete and, except where indicated otherwise, forms the basis for our maxillary description. MTM VER 2016.690 is a right maxilla preserving most of the bone. It is missing its anteriormost end, the anterodorsal portion of its processus frontalis, and much of its processus pterygoideus. Additionally, the ventral edge of the maxilla is damaged along much of the tooth row and no teeth are preserved. Finally, several vertical cracks extending through the maxilla have caused minor labiolin-

gual displacement of adjacent portions. As preserved, MTM VER 2016.690 is about 22 mm long and, when complete, the maxilla was probably about 25 mm long. The long axis of the maxilla curves anteriorly in an extremely shallow arc ( Fig. 5C ). In cross section, the interior of the bone is perforated by small canals and its labial surface is labially convex ( Fig. 5M ). The maxilla is relatively robust in its construction.

In labial or lingual outline, MTM VER 2016.690 ( Fig. 5A, B ) is elongate and moderately deep. Although broken anteriorly, it is clear that the preorbital region was the deepest portion of the maxilla. Judging by its preserved portion, the processus frontalis was a moderately deep flange, as is typical for many anurans. By comparison, the postorbital region is slightly lower, much more elongate, and tapers posteriorly. This region consists anteriorly of a processus zygomatico-maxillaris that is deepest anteriorly. Behind its weakly triangular apex, the dorsal edge of the processus zygomatico-maxillaris is shallowly concave and descends at a shallow angle posteriorly to a point about three-fifths of the distance along the postorbital region; at that point, the dorsal edge of the bone descends at a steeper angle and terminates posteriorly in a low and blunt processus posterior. Separating the pre- and postorbital regions, the orbital region is moderately elongate and its margo orbitalis is shallowly concave.

MTM VER 2016.690 and more fragmentary specimens show that much of the labial surface of maxilla is ornamented, except for a shallow strip along the ventralmost portion corresponding to the crista dentalis (= pars dentalis) ( Fig. 5A, D, H, K ). The ornament pattern varies across the labial surface of the maxilla. On both MTM VER 2016.690 and 2016.700.2 ( Fig. 5A and D, E , respectively), about the upper one-half of the processus zygomatico-maxillaris and adjacent portion of the orbital region are ornamented with small tubercles that may be isolated, but more typically are aligned and joined into short, broken ridges; this resembles the labial ornament on the adjacent, lower portion of the squamosals. The remainder of the labial surface of the maxilla bears irregular pit-and-ridge ornament.

A substantial portion of the lingual surface of the maxilla is preserved on MTM VER 2016.690 ( Fig. 5A ). Best developed along the suborbital region, the lamina horizontalis (= pars palatinus) is a moderately deep (i.e., accounts for about onethird of the suborbital depth) and lingually narrow ledge, with a shallowly convex labial face and a broad groove along its dorsal surface. Anteriorly, the lamina horizontalis shallows and its anteriormost end is broken away. More posteriorly, the lamina horizontalis deepens and expands lingually as it grades into the broken base of the processus pterygoideus.

Although no maxillary specimen preserves more than the broken base of that process ( Fig. 5B, F, G ), those remnants indicate that the processus pterygoideus would have been relatively well developed (although its shape and lingual extent are uncertain) and, as in most anurans, would have articulated with the pterygoid. In life, the pars palatina palatoquadrati would have fit into the deep dorsal groove that extends anteriorly from the processus pterygoideus onto the dorsal surface of the lamina horizontalis ( Fig. 5C, F ). Because the anterior and anterodorsal portions of the maxilla are missing, patterns of contact with the premaxilla anteriorly and the nasal anterodorsally cannot be determined ( Fig. 7 ). Along its preserved lingual surface, the processus frontalis bears the anterodorsally directed, broken base of the processus palatinus. The ductus nasolacrimalis is enclosed by bone along the upper part of the suborbital region and opens posteriorly as a foramen above the base of the processus pterygoideus. A second, unidentified foramen opens more posteriorly, behind the base of the processus pterygoideus. As noted in the squamosal description above, the dorsal and dorsoventral surfaces of the processus zygomatico-maxillaris lack obvious sutural surfaces for contacting the squamosal; instead, those two bones probably simply abutted against one another. Along its dorsolingual surface, the processus posterior bears a shallow, triangular facet for contact with the quadratojugal. This indicates the maxillary arcade was closed posteriorly, forming a bony ‘cheek’ braced against the

fp

suspensorium. Although none of the available maxillae preserves an intact crista dentalis or any teeth, it is evident that the crista dentalis was shallow. Several specimens ( Fig. 5B, F, G, I, L ) preserve faint tooth slots along the lingual surface of the crista dentalis that indicate teeth were present, small, closely spaced, and numerous, and that the tooth row terminated posteriorly approximately in line with the base of the processus pterygoideus.

Angulosplenial ( Fig. 6 )

The posterior portions of two left angulosplenials are available. The less nearly complete specimen, MTM VER 2015.153 ( Fig. 6 A-C), lacks the posterior end of the extremitas spatulata (= pars spatulaeformis prearticularis), but the preserved bone is uncrushed and has pristine surfaces. Breakage through the posterior portion of the extremitas spatulata in MTM VER 2015.153 reveals small canals extending anteroposteriorly through that portion of the bone ( Fig. 6C ). The more nearly complete specimen, MTM VER 2016.1948 ( Fig. 6 D-F) preserves the entire processus coronoideus (= coronoid process) and extremitas spatulata, but exhibits some crushing, the latter being especially evident in the partial closure of the sulcus pro cartilage Meckeli (= Meckelian groove).

The preserved portions of the angulosplenials are typical for anurans in the following features: bone is elongate and sinuosus in dorsal or ventral outline; consisting anteriorly of a rod-like extremitas cultellata (for which only the posteriormost portion is preserved in MTM VER 2016.1948) and posteriorly of an extremitas spatulata, the latter being expanded into a scoop-like structure with its basin opening dorsolabially; the dorsal portion of extremitas spatulata is expanded into an elongate bony flange called the processus coronoideus; the dorsal surface of the processus coronoideus bears a low and broadly convex dorsal tubercle (marked by arrow in Fig. 6A ); a low bony ridge called the crista paracoronoidea extends along the dorsolabial surface of the processus coronoideus; and a trough-like sulcus pro cartilage Meckeli extends posteriorly along the labial surface of the extremitas cultellata, widens and ascends dorsally along the processus coronoideus, and ultimately opens into the basin of the extremitas spatulata. The anterior and posterior portions of the processus coronoideus are developed as dorsally convex mounds. Although these mounds are reminiscent of the double coronoid processes in the Oligocene-Recent alytid Latonia von Meyer, 1843 (e.g., Roček 1994: fig. 12 and references therein; Biton et al. 2013: fig. 3a; Syromyatnikova & Roček 2018: fig. 3), we do not regard them as being homologous, because the mounds in Hungarobatrachus are part of an anteroposteriorly elongate and broad, ridge-like processus coronoideus and both are labiolingually broad, relatively low, and subequal in height (versus double coronoid processes in Latonia are separate, labiolingually narrow, and relatively taller, with the more posterior process typically being substantially taller and having a more triangular or recurved outline). The lingual surface of the extremitas spatulata in MTM VER 2015.153 is faintly ornamented with tiny pits and low, narrow, anteroposteriorly elongate ridges.

Figures

FIG. 2. — Incomplete ilia of Hungarobatrachus szukacsi Szentesi & Venczel, 2010 from the Santonian of Iharkút, Hungary: A-D, MTM VER 2015.145.1, newly referred, right ilium in lateral (A, B), dorsal (C), and medial (D) views; E, MTM V 2008.16.1, holotype right ilium in lateral view;F, Reconstruction of acetabular region in Hungarobatrachus szukacsi in posterior view (right ilium is holotype, left ilium is mirror image of holotype). All images are photographs. Specimen in B dusted with ammonium chloride to enhance surface details; remaining images are of undusted specimens. Arrows (B, E) indicate calamita ridge-like rim demarcating lower boundary of ornamented area. Abbreviations: acf, acetabular fossa; acr, acetabular rim; dae, dorsal acetabular expansion; dc, dorsal crest; dpt, dorsal protuberance; iis, interiliac scar; ij, ilioischiatic juncture; ish, ilial shaft; it, interiliac tubercle; lo, lateral ornament; pz, preacetabular zone; vae, ventral acetabular expansion. All images at same magnification. Scale bar: 5 mm.

FIG. 3. — Newly referred, incomplete and fused frontoparietals of Hungarobatrachus szukacsi Szentesi & Venczel, 2010 from the Santonian of Iharkút, Hungary: A-H, MTM VER 2016.2546, posteromedian and left posterolateral portions of a fused pair of frontoparietals, entire specimen in dorsal (A, B) views, enlargement of dorsal surface with putative bite mark circled (C), entire specimen in ventral view (D), entire specimen in oblique ventral and slightly left lateral view as both a photograph (E) and interpretive image (F), and entire specimen in posterior view (G, H). Photographs in B, D, E, and H dusted with ammonium chloride to enhance surface details; remaining images are of undusted specimens. Abbreviations: aif, anterior incrassiato frontoparietalis; bm, putative bite mark; bp, bony pillar extending dorsally along lateral surface of pars contacta onto underside of squamosal process; gcat, groove for canalis arteria temporalis; fao, intact left foramen arteriae occipitalis; (fao), preserved medial rim of right foramen arteriae occipitalis; fcat, foramen canalis arteria temporalis; moc, intact medial portion of margo occipitalis; pc, pars contacta; pif, posterior incrassatio frontoparietalis; pmd, posteromedian depression; ppi, processus posterior inferior; (ppo), broken base of processus paraoccipitalis; pps, processus posterior superior; spps, surface of postorbital parasagittal suture; sqp, squamosal process; ts, tectum supraorbitale; uf, unidentified foramen. Images at different magnifications. Scale bar: A, B, D-H, 5 mm; C, 1 mm.

FIG. 4. — Newly referred,incomplete squamosals of Hungarobatrachus szukacsi Szentesi & Venczel,2010 from the Santonian of Iharkút,Hungary:A, B, MTM VER 2016.701.1, right squamosal in lateral (A) and medial (B) views; C, D, MTM VER 2016.697.1, left squamosal in lateral (C) and medial (D) views; E, F, MTM VER 2016.701.2, left squamosal in lateral (E) and medial (F) views; G, MTM VER 2016.695, left squamosal in lateral view; H, I, MTM VER 2016.702, left squamosal in lateral (H) and medial (I) views; J-L, MTM VER 2016.3575, right squamosal, entire specimen in lateral (J) and medial (K) views and detail (L) of anterior margin of processus zygomaticus in medial view.All images are photographs. Specimen in G dusted with ammonium chloride to enhance surface details; all other images are of undusted specimens Abbreviations:kp, tiny knob-like projections on anteroventral end of processus zygomaticus;mo, margo orbitalis;ppd, processus posterodorsalis; (ppl), broken base of processus posterolateralis;pz, processus zygomaticus;(rp), broken base of ramus paroticus. Scale bars:A-K, 5 mm; L, 2 mm.

FIG. 5. — Newly referred, incomplete maxillae of Hungarobatrachus szukacsi Szentesi & Venczel, 2010 from the Santonian of Iharkút, Hungary: A-C, MTM VER 2016.690, nearly complete right maxilla in labial (A), lingual (B), and oblique dorsal and slightly lingual (C) views; D-F, MTM VER 2016.700.2, fragmentary right maxilla preserving region bearing processes pterygoideus (broken) in labial (D), oblique labial and slightly dorsal (E), and lingual (F) views;G, MTM VER 2016.700.1, fragmentary right maxilla preserving less of region bearing processus pterygoideus (broken) in lingual view; H-J MTM VER 2015.141.2, fragmentary right maxilla preserving posterior portion of suborbital region in labial (H), lingual (I), and dorsal (J) views; K-M MTM VER 2015.141.3, fragmentary right maxilla preserving posterior portion of tooth row in labial (K), lingual (L), and posterior (M) views. Images in A-G are photographs of specimens dusted with ammonium chloride to enhance surface details; images in H-M are scanning electron micrographs. Abbreviations: cd, crista dentalis; dnl, ductus nasolacrimalis; gpq, groove for pars palatina palatoquadrati; iqj, imprint marking contact area for quadratojugal; lh, lamina horizontalis; (pp), broken base of processus palatinus; (ppt), broken base of processus pterygoideus; pzm, processus zygomatico-maxillaris; uf, unnamed foramen. Arrow (D) points to unornamented area along ventrolabial surface of maxilla. All images at same magnification. Scale bar: 5 mm.

FIG. 6. — Newly referred, incomplete angulosplenials of Hungarobatrachus szukacsi Szentesi & Venczel, 2010 from the Santonian of Iharkút, Hungary:A-C, MTM VER 2015.153, left angulosplenial in dorsal (A), lingual (B), and posterior (C) views; D-F, MTM VER 2016.1948, left angulosplenial in lingual (D) and dorsal (E, F) views. All images are photographs. Specimen in F dusted with ammonium chloride to enhance surface details; remaining images are of undusted specimens. Abbreviations: (ec), broken posterior part of extremitas cultellata; es, extremitas spatulata; pc, processus coronoideus; spcM, sulcus pro cartilage Meckeli. Arrows point to coronoid tubercle. All images at same magnification. Scale bar: 2 mm.

FIG. 7. — Tentative skull reconstruction, in dorsal view, for Hungarobatrachus szukacsi Szentesi & Venczel, 2010. Photographs of the fused and anteriorly incomplete frontoparietals (MTM VER 2016.2546), the largest and one of the most nearly complete squamosals (MTM VER 2016.695, left squamosal), and the most nearly complete maxilla (MTM VER 2016.690, right maxilla) are overlain onto skull image of the Eocene anuran Thaumastosaurus gezei (modified from Laloy et al. 2013: fig. 3A). To improve symmetry, for the frontoparietals the intact portion from its left side was mirrored onto the right side and the left squamosal and right maxilla were mirrored onto the opposite sides of the skull. Dotted lines denote skull outline,inferred natural margins along broken surfaces for bones, and inferred contacts among bones. Although the posterior end of the maxilla is depicted as free, a shallow facet preserved on the dorsolingual surface of MTM VER 2016.690 indicates the maxilla posteriorly contacted the quadratojugal to form a closed ‘cheek’. All fossil bones are depicted at their actual sizes relative to one another (i.e., they have not been arbitrarily re-sized in an attempt to improve proportions and contacts).Thaumastosaurus De Stefano, 1903 was chosen as the basis for our reconstruction, not because it is closely related (see our phylogenetic analysis and Fig. 8), but because its shape and proportions are a good fit for the available fossil bones of Hungarobatrachus. Abbreviations: fp, frontoparietals; max, maxilla; sq, squamosal.