Mariliabatrachus navai, Santos & Carvalho & Zaher, 2023

Santos, Rodolfo Otávio, Carvalho, Alberto B. & Zaher, Hussam, 2023, A new fossil frog (Lissamphibia: Anura) from the Late Cretaceous of Brazil and the early evolution of neobatrachians, Zoological Journal of the Linnean Society 202 (1), pp. 1-29 : 4-19

Mariliabatrachus navai gen. et sp. nov.

urn:lsid:zoobank.org:act:730D61E9-4502-4E7C-A07B-610BB48A637B

Etymology: ‘ navai ’, after the Brazilian palaeontologist William Roberto Nava, in recognition of his longstanding work discovering fossil vertebrates in the region of Marília municipality and vicinities.

Holotype: MZSP-PV 25 (a and b), housed at Museu de Zoologia da Universidade de São Paulo, represented by a nearly complete skeleton, comprising skull and postcranial remains, including vertebrae, scapular and pelvic girdles, and limb bones.

Referred material: MZSP-PV 26 (fragments of the skull, lower jaw, and postcranial remains, including pectoral girdle and the proximal portions of the forelimbs and anteromedial portions of vertebral column); MZSP-PV 27 (a fragmented braincase, including the otic capsules and parasphenoid); MZSP-PV 28 (an incomplete posterior portion of the skull, encompassing only the otic capsules); MZSP-PV 1326 (a partially preserved hindlimb, including tibiale, fibulare, tarsals, and the phalanges); MZSP-PV 1327 (partially preserved skull, including the left quadratojugal, and other indeterminate elements); MZSP-PV 1328 (elements of the pelvic girdle and distal part of the vertebral column); MZSP-PV 1329 (fragments of maxilla, scapula and sacral vertebra); MZSP-PV 1330 (an isolated fragment of a pterygoid); and MZSP-PV 1331 (isolated vertebrae).

Diagnosis: Mariliabatrachus navai gen. et sp. nov. is a small anuran species that differs from pipoids by having well-developed mentomeckelian bones and a T-shaped parasphenoid, and shares with neobatrachians features like the presence of a neopalatine, eightprocoelouspresacralvertebrae, roundedsacraldiapophyses, and the lack of free ribs. The new species can be distinguished from other fossil and living neobatrachians by the presence of the following combination of characteristics (autapomorphies marked with an asterisk): azygous frontoparietal bearing ornamentations in form of shallow grooves and two laterally projected and rounded supraorbital flanges*; tectal roofing of cavum cranii composed by taenia tecti transversalis and medialis; cultriform process without ventral medial ridge and almost reaching the level of the planum antorbitale anteriorly; laterally expanded crista parotica; vomer present and bearing a straight tooth row; undivided sphenethmoid exposed between nasals and frontoparietal; pars facialis of the maxilla smooth, decreasing in height in the orbital region, and lacking anterodorsal and anteroventral processes; articulation between lower jaw and skull located anteriorly in relation to the occiput but laterally to the otic capsules; atlas with widely separated cotyles; omosternum present and mineralized; fusion between clavicula, scapula and coracoid; forked cleithrum; humerus with well-developed crista ventralis and ulnar epicondyle; intercalary elements absent; straight urostyle, ilium lacking supraacetabular fossa but presenting a low dorsal prominence and an elongated dorsal protuberance; acetabular fossa roughly cordiform, with a well-marked acetabular rim, except for its dorsalmost portion; ilial shaft bearing a moderately high dorsal crest; pubic region ossified; and femur nearly equal to tibiofibula in length and bearing a well-developed crest.

Type locality and horizon: Outcrop located on the left margin of the Peixe river, known as Estrada Velha , municipality of Ocauçu, 18 km south-west of the municipality of Marília (49º56ʹ45ʹʹ W, 22º20ʹ32ʹʹ S). This deposit is traditionally assigned to the Coniacian-Maastrichtian ( Castro et al. 2018) Adamantina Formation, part of the Bauru Basin.

Description

The hypodigm of Mariliabatrachus navai comprises 10 three-dimensionally preserved specimens ( Fig. 2 ), encompassing almost all parts of the skeleton, except minor portions of the skull, forelimbs, and hindlimbs. The estimated snout–vent length of the holotype is 38.57 mm. The presence of carpal elements, along with the ossification of the epiphyses on the long bones, and a well-ossified mentomeckelian bone, indicate that the holotype MZSP-PV 25 ( Fig. 3 ) represents an adult individual.

Skull

Components of the skull are present in nearly all analysed specimens (holotype and the paratypes MZSP-PV 26 , MZSP-PV 27 , MZSP-PV 28 , MZSP-PV 1327 , MZSP-PV 1329 , and MZSP-PV 1330 ), but are better preserved in the holotype. The skull of the holotype ( Fig. 4 ) is small and has approximately equal width and length. In dorsal view, it shows a roughly triangular outline (maximum width of 13.46 mm, measured at the level of the lower jaw articulation; median length of 13.15 mm, measured from the anterior margin of the premaxilla to the posterior margin of the occipital condyles).

Eoocranium Both nasals are present in the holotype and arranged obliquely in relation to the sagittal plane of the skull. There is no medial contact between them, and they are positioned at the same level in relation to the anterior tip of the maxilla, but both conditions could not reflect the exact morphology of the fossil, as they could be also related to shifts that occurred during the fossilization process. Due to their damaged condition at the lateral margins, the exact morphology of this portion is uncertain. Their dorsal surface is smooth, without ornamentations. The nasals also bear pointed maxillary processes that project laterally, and the posterior margins of such processes contribute to the anterior margin of the orbits. The posterior portion of the nasal maxillary process abuts the maxilla, near the region in which the maxilla and the palatine articulate. There is no evidence of the contact among nasals with premaxilla, squamosal, or frontoparietal.

The frontoparietals are fused into a single bone and lack a conspicuous suture line medially positioned. In dorsal view, the surface of this bone bears numerous irregular ornamentations, in the form of small and shallow grooves, more pronounced at its posteromedial portion. The frontoparietal covers anteriorly the posterior margins of the sphenethmoid. The fontanelle is absent, whereas short and posterolaterally directed supraorbital flanges are present on each lateral side of the frontoparietal. The lamina perpendicularis is present, being more pronounced at the posterior portion of the frontoparietal and narrowing anteriorly. As the posterolateral portions of the sphenethmoid were not preserved, it is not possible to determine if the lamina perpendicularis is fused to them or not. The posterior region of the frontoparietal is clearly fused to the otic capsules and the exoccipitals. The dorsal surface of the endocranium left an imprint on the ventral part of the frontoparietal (i.e. incrassatio frontoparietalis), comprising two faint but still noticeable fenestrae parietales (Supporting Information, Fig. S5 ).

In the holotype, only the right premaxilla (Supporting Information, Fig. S2A, B ) was preserved. This bone (2.11 mm in length) is almost complete, lacking only the alary process and a portion of its lateral end. The pars facialis is smooth, without ornamentations. As only the base of the alary process was preserved, its size, orientation, and shape are uncertain. The pars palatina has a short and lingually projected palatine process, but due to its fragmentary condition, the configuration of its lateral end is uncertain. As the premaxilla is slightly shifted from its original position, the kind of contact with the maxilla is uncertain. The presence of teeth in the premaxilla could be inferred due to the presence of numerous pedicels, but the crowns were not preserved.

Only the left maxilla (total length of 8.04 mm) was preserved in the holotype (Supporting Information, Fig. S2G, H ). Its pars facialis has a wide orbital portion but narrows gradually posteriorly, and there are no ornamentations on its surface. In the anterior margin of the maxilla, the anterodorsal process is absent, whereas the anteroventral process, despite being present, is limited to a short projection. The kind of contact between the maxilla and quadratojugal (Supporting Information, Fig. S3E, F ) is uncertain since the latter was preserved disarticulated from the rest of the skull. The pars dentalis bear pedicels along almost its entire length, being absent only at the last 3 mm of its posterior portion. However, no complete teeth were preserved. Near the region of the maxillary preorbital process, the anterior branch of the pterygoid and the nasopalatine lateral tip are articulated, as well as the maxillary process of the nasals.

The triradiate squamosal is represented partially by the left element in the holotype and complete in MZSP-PV 1327 (Supporting Information, Fig. S3C, D ), presenting a slender ‘T’-shape, without ornamentations on its dorsal surface. The squamosal is also slightly shifted from its original position but, based on its general shape, there is no contact between this bone and the azygous frontoparietal. The zygomatic ramus is short and narrow, and does not reach the maxilla. The otic ramus is short and narrow, slightly overlapping only the lateral portions of the crista parotica, whereas the ventral ramus is long, narrow, and straight.

In the holotype, both palatines [neopalatine of Trueb (1993)] were preserved (Supporting Information, Fig. S2E, F ), being visible in both dorsal and ventral views. This bone is thin and positioned anterolaterally in relation to the sagittal line of the skull. Despite the lack of odontoids in the ventral surface of this bone, a short ventral ridge is present. The palatine is also partially covered by the sphenethmoid lateral process and by the maxillary process of the nasal. On its lateral margin, there is a contact with the pars palatina of the maxilla, near the preorbital process.

Vomers (Supporting Information, Fig. S2C, D ) are present and bear teeth, which are positioned anteriorly in relation to the planum antorbitale. The tooth row is straight, but as both vomers are shifted from their original positions, it is difficult to determine if the vomerine tooth rows were arranged angled or perpendicular to the skull midline. An anterior process is present, but as both vomers and maxilla were shifted in the fossilization process, the contact between these elements is uncertain. The prechoanal process is elongated, whereas the postchoanal one, despite being broken, appears to be distinct but short.

In the holotype, the parasphenoid is partially preserved and exhibits a ‘T’-shape (i.e. the parasphenoid alae are perpendicular to the cultriform process), and it is not fused to other skull elements, as seen in the paratype MZSP-PV 1327 (Supporting Information, Fig. S1D, F, G ). The parasphenoid alae reach the otic capsules and their lateral margins are transverse and convergent medially. Poorly developed ventral crests are present on its ventral surface. The arrow-shaped and long cultriform process has parallel lateral margins and gradually narrows anteriorly. In its anteriormost portion, the cultriform process reaches the region of the planum antorbitale. There is no evidence of a longitudinal ridge on its ventral surface.

Both pterygoids were preserved in the holotype, but the right one is slightly shifted from its original position. The anterior ramus of the pterygoid (Supporting Information, Fig. S3A, B ) is long, contacting medially the anteromedial portion of the pars palatina of the maxilla, but does not reach the planum antorbitale. There is no ventral flange on the anterior process, but the dorsal one is present, despite being weakly developed. The medial ramus is moderately developed and contacts the anterior face of the otic capsule. The posterior ramus is almost complete, lacking only its distal end. This process is short, not reaching the posterior limits of the skull.

Endocranium and stapes The sphenethmoid is a single bone dorsally, with no evidence of ornamentations on its surface. In dorsal view, its posterior margins are partially covered by the frontoparietal. The anterior portion abuts the posterior margin of the nasals, but these margins do not overlap the sphenethmoid, which is exposed dorsally. Anteriorly, there is no bone extension of the sphenethmoid between the nasals. Laterally, the sphenethmoid bears an expansion that partially overlaps the palatine and forms part of the anterior margin of the orbits. The sphenethmoid is ossified only up to half of the planum antorbitale region, and the orbitonasal foramen is completely bound by bone (Supporting Information, Fig. S1C ). In ventral view, this bone also forms a single element, bearing a smooth surface without conspicuous ornamentations. The lateral walls of the sphenethmoid, at the level of the optic foramen, are completely cartilaginous. The septum nasi is narrow and partially ossified, and the nasal capsules are medially close.

The prootics and the exoccipitals are fused into a single element, the otoccipital, which forms the otic capsule and the posteriorportionoftheskull.The cristaparotica isossifiedandhas a distal expansion. The deep scar located on the distal terminus of the crista parotica indicates the presence of a surface for articulation with the otic ramus of the squamosal. The exoccipitals are fused ventral and dorsally, surrounding completely the foramen magnum. The epiotic eminences are high, protrude posterolaterally, and are not covered by the frontoparietal. The occipital artery runs in an open groove located in the otoccipital. The occipital condyles are distinct and well separated from each other, with no confluence between them.

The stapes are well preserved in the paratype MZSP-PV 27 and located beneath the otic capsules (Supporting Information, Fig. S1E–G ). The preservation of a distinct stapes and the shape of the squamosal indicate the presence of a tympanic annulus.

Lower jaw

Elements of the lower jaw ( Fig. 5 ) are better represented in the holotype (11.38 mm total length), but some bone fragments were also preserved in MZSP-PV 26 . The lower jaw of Mariliabatrachus navai is composed of well-ossified and edentate mentomeckelian bone, dentaries, and angulosplenials. In the holotype, only the mentomeckelians, right dentary, and both angulosplenials were preserved, whereas in MZSP-PV 26 only a fragmentary portion of the left angulosplenial is present.

The mentomeckelian bones are well ossified and fused to the dentaries ( Fig. 5D, E ), despite the left one being broken and separated from the left dentary, which was not preserved. They are also slightly shifted from the region of the mandibular symphysis. There is no evidence of the presence of a lateral process on them. The right dentary of the holotype is slender, extending for approximately 66% of the total length of the lower jaw and forming most of the anterior portion of the lower jaw. Ornamentations are absent on its labial surface. There is no evidence of teeth or pedicels. The dentaryoverlapslaterallytheanteriorportionoftheangulosplenial, covering part of the Meckel’s canal. The angulosplenial is represented on both sides of the holotype, but the left element is better preserved. It is an elongated and arched bone, presenting a pronounced sulcus on its lateral face for the passage of the Meckel’s cartilage. The coronoid process is discrete and forms a relatively elongate, dorsomedially projected, and rounded lamina of bone in the posterior portion of the angulosplenial ( Fig. 5C ). There is a lateral expansion of the angulosplenial at its posterior portion, whose dorsal face articulates with the jaw suspensorium. The articulation between the lower jaw and the skull is positioned anteriorly in relation to the occiput and laterally to the otic capsule.

Postcranium

The postcranial bones of Mariliabatrachus navai are represented in the holotype and also in the paratypes ( MZSP-PV 26 , MZSP-PV 1326 , MZSP-PV 1328 , MZSP-PV 1329 , and MZSP-PV 1331 ), encompassing the vertebrae, pectoral and pelvic girdles, fore and hindlimbs. The only missing elements are the cartilaginous parts of the pectoral girdle and some phalanges.

Vertebral column Despite its fragmentary condition, the vertebral column ( Fig. 6A–C ) is complete (presacral vertebrae I to VIII, sacrum and urostyle) in the holotype, and represented by partially articulated presacral vertebrae ( III to VII) in the paratype MZSP-PV 26 . In total, Mariliabatrachus navai presents eight presacral vertebrae, all of them procoelous, a condition observed mainly in the ventral view of the specimen MZSP-PV 26 . These vertebrae present neural arches not imbricated, with a short portion of the spinal canal exposed dorsally, and there is no evidence of the presence of a dorsal shield.

The first presacral vertebra (atlas) bears two well-defined and widely separated cotyles, which are positioned ventrolaterally in relation to the neural canal [type I of Lynch (1971)]. The atlas is articulated but not fused to the presacral II and does not exhibit a transverse process. The neural arch of the atlas has a low neural spine, whereas the postzygapophyses are limited to a short extension posteriorly directed. The presacral II is articulated to the atlas and exhibits elongated transverse processes projecting anterolaterally. The presacral III is articulated to the second presacral and also bears long transverse processes anterolaterally directed and distally expanded but lacking an uncinate process. The presacral IV is damaged in the holotype, and thus only disarticulated and indistinct portions of the neural arch and transverse processes were preserved. However, in MZSP-PV 26 the presacral IV is partially preserved, and the transverse processes are long and laterally directed. The presacral V is represented partially in the holotype and almost complete in MZSP-PV 26 , bearing transverse processes laterally directed. The presacral VI was preserved in the holotype and MZSP-PV 26 , despite being highly damaged in the paratype. This vertebra presents slender and long transverse processes laterally projected. The presacral VII, present in the holotype and MZSP-PV 26 , also bears transverse processes laterally projected, but they are considerably shorter than those of presacral VI. The following vertebra (presacral VIII) was preserved only in the holotype and exhibits short transverse processes (clearly shorter than the diapophyses of the sacral vertebra), which are projected slightly anterolaterally. The transverse processes of the vertebrae are unequal in length, according to the following sequence: III > II > IV ≅ V ≅ VI > VIII > VII. Neural spines are low in all presacral vertebrae. There is no evidence of the presence of free ribs associated with the transverse process of presacral vertebrae.

The sacral vertebra is almost entirely preserved in the holotype except for the distal ends of the diapophyses (total sacral length of ~ 6.59 mm) ( Fig. 6D–G ). However, in the specimen MZSP-PV 1328 (Supporting Information, Fig. S4 ), the lateral margin of the sacral diapophysis is well preserved (1.16 mm in length, 0.58 mm in width). Two distinctive prezygapophyses are present and articulate the sacral vertebra with the postzygapophyses of the last presacral vertebra. This vertebra also exhibits two cylindrical but slightly flattened (ratio between height and length nearly equal to 0.5) sacral diapophyses posterolaterally directed, which are only slightly distally expanded. The articulation between this vertebra and the urostyle is bicondylar. The sacral diapophyses are oriented almost horizontally in relation to the horizontal plane in a posterior view. In MZSP-PV 1328 , an oval sesamoid is present on the distal margin of the sacral diapophysis.

The long urostyle of the holotype ( Fig. 6H–J ) is entirely preserved and is straight in lateral view, presenting a total length of 9.78 mm. Next to the anterior margin, there is a foramen for the passage of the spinal nerve. The dorsal crest of the urostyle is present and well-developed, but it remains high only throughout its anterior half. Laterally positioned transverse processes are absent in the urostyle, whereas an anterodorsal process located on the anterior margin of the dorsal crest is present.

Pectoral girdle The elements associated to the pectoral girdle of Mariliabatrachus navai ( Fig. 7 ) are present in the holotype and MZSP-PV 25 , but are better preserved in the paratype MZSP-PV 26 . The pectoral girdle is arciferal and slightly shifted laterally in MZSP-PV 26 . The omosternum is present and mineralized (Supporting Information, Fig. S6 ). The clavicle, coracoid, and scapula are fused. In MZSP-PV 26 , the clavicles are well preserved but are overlapping each other due to the shifting that occurred during the fossilization process. Both are strongly curved and their medial edges have no expansions, whereas their lateral margins are fused to the scapula and coracoid. Despite their shift, the clavicles are oriented anteromedially, and this condition is better observed in the right clavicle of MZSP-PV 26 .

The coracoids bear an expanded lateral margin fused anteriorly with the clavicle.These bones are arranged horizontally, presenting wide medial margins and an anterior edge slightly expanded anteriorly. The sternal ends are asymmetrical and only slightly expanded (less than half) in relation to the total length of the bone. The posterodorsal process is absent. Both scapulae (total length of 5.50 mm) are present in MZSP-PV 26, but the right one is damaged and only its proximal margin is known, whereas the left one is more complete, showing a concave anterior margin, without processes or crests, and a roughly straight posterior margin.

The pars acromialis is well developed. The glenoid fossa (total length of 1.94 mm) is completely ossified and closed by the fused clavicle lateral margins, coracoid, and proximal margins of the scapula. The scapula is relatively elongated, as the maximum width of the glenoid fossa is less than half of the total width of the scapular shaft. The medial cleft of the scapula is absent. The cleithra are only barely visible in the specimen MZSP-PV 26 , whereas in the holotype only a fragment assigned to the left cleithrum was preserved. This bone shows a straight lateral (scapular) margin and a bifurcated posterior margin, in which the anterior and posterior branches are separated by a distinct notch. Forelimbs The preserved components of the Mariliabatrachus navai are the humeri, radioulna, carpal elements, and some phalanges. Both humeri are preserved and complete in the holotype and paratype MZSP-PV 26 . The humerus ( Fig. 8A–D ) is elongated and presents a well-developed crista ventralis that reaches the median portion of the relatively narrow diaphysis. The crista medialis and the crista lateralis are absent. The humeral condyle is spherical, only slightly shifted laterally, well ossified, and large (its total diameter in relation to the total distal width at the epicondyle level is more than 0.58). The ulnar epicondyle is relatively well-developed, whereas the radial one is small. The cubital fossa is located immediately above the humeral condyle, being small and shallow. The radioulna ( Fig. 8E, F ) is present in both limbs of the holotype. This bone bears a deep and concave olecranon fossa, and the olecranon process is well developed. Carpal bones (including pre- and postaxial elements) of both limbs were preserved in the holotype; however, due to shifts that occurred during the fossilization and their damaged condition, the following morphological assignments are tentative. Based on the positioning of the carpals 4 * 5 and the morphology of the metacarpals, we interpret that the left manus ( Fig. 9 ) was completely flipped during fossilization. The carpal torsion is apparently present. Regarding the postaxial carpals, the ulnare and the distal carpal 3 are free (i.e. not fused), but the distal carpals 4 * 5 are fused into a single element, whereas the preaxial carpals (element Y and distal 2) are free. The morphology and the total number of the prepollical elements cannot be given, as only one element tentatively assigned to the prepollex was preserved. In the holotype, all the four metacarpals were preserved in the left manus but their distal margins are broken and the proximal ones are damaged, whereas in the right manus only two indeterminate metacarpals are still present, despite their highly damaged condition. As the left manus was flipped, the order of the metacarpals is reversed. The metacarpal II has a proximal margin (1.16 mm of width) wider than the one of the metacarpal III (0.88 mm of width). The proximal margin of the metacarpal III exhibits only one articulation surface. In the right manus ( Fig. 10 ), five elements were tentatively identified as the proximal and terminal phalanges. There is no evidence of the presence of intercalary elements between the only proximal and terminal phalanges still articulated. The terminal phalanges are conical and straight, presenting a rounded distal tip and a planar to convex proximal epiphysis.

Pelvic girdle Elements of the pelvic girdle ( Fig. 11 ) are well preserved in the holotype and the paratypes MZSP-PV 1328 and MZSP-PV 1329 . They are still articulated with the vertebral column and hindlimbs in the holotype, and there is only a faint suture line between the ilium, ischium, and pubis, and so they are fused. In acetabular view, the ilial shaft is moderately elongated (~3.5 times longer than the ilial body) and slightly arched dorsally. The ilial shaft bears a moderately high dorsal crest (~ 0.84 in relation to the total high of the ilial shaft) extending almost throughout its entire length, except for the distal end. In medial view, there is a relatively deep and elongated sulcus between the dorsal portion of the shaft and the ventral portion of the dorsal crest. The cross-section of the ilial shaft is oval in anterior view, but the dorsal crest forms a thin projection dorsomedially oriented. In the ilial body, the dorsal prominence is present but low, being rounded and confluent with the dorsal crest of the ilial shaft, and also bears a laterally projected and elongated dorsal protuberance. The dorsal acetabular expansion is moderately developed (1.1 mm in length), posterodorsally oriented, and positioned at the same height in relation to the dorsal prominence–protuberance complex. There is no supraacetabular fossa. The acetabular fossa is relatively shallow, wide (1.95 mm length, 2.32 mm width), and has a roughly cordiform outline, being located posteroventrally in relation to the dorsal prominence–protuberance complex. A well-pronounced acetabular rim surrounds almost entirely the margins of the fossa, except for its dorsalmost portion. The preacetabular zone is well-developed and leads to moderately wide ventral acetabular expansion (1.45 mm in length) anteroventrally directed, slightly broader than the dorsal one. There is an angle of ~90º between the anterior margin of the ventral acetabular expansion and the ilial shaft. In ventral view, the surface of the ilial body is smooth, and there is no sign of a spiral groove. The ischium bears a well-developed posterodorsal region, which has a quadrangular outline, whereas its portion located posterior to the acetabular fossa is short and has a relatively straight margin. The portion of the pubis located below the acetabular fossa is short, except for the region next to the ventral acetabular expansion, which is elongated and forms a rounded projection oriented anteroventrally.

Hindlimbs The elements that comprise the hindlimbs of Mariliabatrachus navai were preserved only in the holotype and the specimen MZSP-PV 1326 . Among the preserved bones in the holotype, there are the entirely preserved right femur ( Fig. 12 ) and tibiofibular, and the partially preserved left femur and the right tibiale and fibulare.

In MZSP-PV 1326, the left tibiale, fibulare, distal tarsals, metatarsals, prehallux, and some phalanges were preserved at least partially ( Fig. 13 ). The remaining skeletal elements (i.e. the left tibiofibula and the right distalmost portions of the hindlimb) are absent. Both femora are completely ossified, exhibiting a roughly straight outline and a conspicuous femoral crest positioned along the proximal half of its length. The femur has a slightly short total length when compared with the tibiofibula (14.32 mm and 15.59 mm, respectively). The tibiofibula is nearly straight. Regarding the proximal tarsals ( Fig. 13 ), the tibiale and fibulare (total length of 7.45 mm), they are partially fused proximally (width at proximal epiphysis equal to 2.37 mm) and distally (width at distal epiphysis equal to 2.48 mm), and so there is a gap between their diaphyses. The distal tarsals 2 and 3 are fused, and another adjacent tarsal was tentatively interpreted as formed by the fusion of element Y and tarsal 1. Near to this element, there is a completely preserved element and a bone fragment tentatively identified as proximal and distal prehallical elements. Toes of the left pes were partially preserved in MZSP-PV 1326 ( Fig. 13 ), including portions of metatarsals and proximal phalanges. Distal phalanges of the toes II, III, IV, and V are present but highly damaged. The only terminal phalanx present was tentatively associated with the toe II. This phalanx is roughly straight and its distal end is slightly knobbed. There is no evidence of the presence of intercalary elements.

Phylogenetic analyses

The morphology-based analysis under equal weights and unordered multistate characters resulted in 140 mostparsimonious trees (MPTs) of 1380 steps (CI = 0.172, RI = 0.554), the strict consensus of which is illustrated in Figure 14 . Bremer and jackknife support values for the nodes of the consensus are indicated at the base of each branch. Under these analytical conditions, the monophyly of Neobatrachia (i.e. a clade sister to Heleophryne ) was not recovered. Mariliabatrachus navai was retrieved nested among a large clade of well-ossified hyloid neobatrachians (including both living and extinct species), although with weak support. In our analysis, the monophyly of this clade is supported by a single synapomorphy, Ch. 85: transverse processes/associated ribs of vertebra III lacking uncinate processes. A complete list with the common synapomorphies of all MPTs is available in the Supporting Information, Fig. S13 .

There are some differences between the topology obtained from this analysis and those generated under different analytical conditions (e.g. treating multistate characters as ordered or using implied weighting). Further details on these alternate analyses are provided in the Supporting Information, Figs. S7–S 12 . The strict consensus of the analysis using ordered multistate characters resulted in a large polytomy, with only a few clades emerging as monophyletic (e.g. a subgroup of ranoids and the species of Telmatobius ). On the other hand, the other analyses (treating multistate characters as unordered but using implied weighting with different values of k) produced better-resolved topologies (e.g. Neobatrachia was recovered as monophyletic), although typically with low support. Additionally, neither Ranoidea nor Hyloidea have been retrieved as monophyletic. The phylogenetic positioning of Mariliabatrachus also varies depending on the analysis. In some cases, it was recovered as the sistertaxon of Uberabatrachus and Beelzebufo (k = 3), Eurycephalella (k = 7), or a group containing Late Cretaceous species and Calyptocephalella (k = 10; k = 20).

Figures

Figure 1. Geological map of Bauru Basin showing its positioning in South America and highlighting the type locality of Mariliabatrachus navai gen.et sp. nov..

Figure 2. The hypodigm of Mariliabatrachus navai gen. et sp.nov.. A, B, holotype MZSP-PV 25 (still articulated and almost complete skeleton). C, paratype MZSP-PV 26 (broken portions of skull, lower jaw fragments, and postcranial elements, including pectoral girdle, and parts of the forelimbs and vertebral column). D, paratype MZSP-PV 27 (fragment of a braincase). E, paratype MZSP-PV 28 (fragment of the posterior portion of the skull).F, paratype MZSP-PV 1326 (partially preserved hindlimb). G., paratype MZSP-PV 1327 (partially preserved skull). H, paratype MZSP-PV 1328 (elements of the pelvic girdle and distal column). I, paratype MZSP-PV 1329 (fragments of maxilla,scapula, and sacral vertebra).J, paratype MZSP-PV 1330 (isolated fragment of a pterygoid). K, paratype MZSP-PV 1331 (isolated vertebra). Scale bar = 1 cm.

Figure 3. Details of MZSP-PV25, the holotype of Mariliabatrachus navai gen. et sp.nov.. All the abbreviations are listed in the Appendix.Scale bar = 1 cm.

Figure 4. Skull of the holotype (MZSP-PV 25) of Mariliabatrachus navai gen. et sp. nov. in dorsal (A), ventral (B), anterior (C), posterior (D), and right lateral (E), and left lateral (F) views. Scale bars = 2 mm.

Figure 5. Lower jaw of the holotype (MZSP-PV 25) of Mariliabatrachus navai gen. et sp. nov. in dorsal (A), labial (B), and lingual (C) views. Details of the right dentary and mentomeckelian in labial (D) and lingual (E) views.All the abbreviations are listed in the Appendix. Scale bar = 1 mm.

Figure 6. Articulated vertebral column of the holotype (MZSP-PV 25) of Mariliabatrachus navai gen. et sp. nov. in dorsal (A), ventral (B), and right lateral (C) views. Sacral vertebra in dorsal (D), ventral (E), anterior (F), and posterior (G) views.Urostyle in anterior (H), left lateral (I), and dorsal (J) views.All the abbreviations are listed in the Appendix.Scale bars = 1 mm.

Figure 7. Pectoral girdle of the paratype (MZSP-PV 26) of Mariliabatrachus navai gen. et sp. nov. in ventral (A) and dorsal (B) views. All the abbreviations are listed in the Appendix.Scale bar = 2 mm.

Figure 9. Interpretative reconstitution of the left manus of the holotype (MZSP-PV 25) of Mariliabatrachus navai gen. et sp.nov.in dorsal (A) and ventral (B) views. Left manus as preserved in the holotype in ventral (C) and dorsal (D) views.All the abbreviations are listed in the Appendix.Upper scale bar = 2 mm, lower scale bar = 1 mm.

Figure 10. Right manus of the holotype (MZSP-PV 25) of Mariliabatrachus navai gen.et sp. nov.in ventral (A), dorsal (B), and lateral (C) views.Details of the terminal and penultimate phalanges in lateral (D) and ventral (E) views. All the abbreviations are listed in the Appendix. Upper scale bar = 2 mm, lower scale bar = 1 mm.

Figure 11. Pelvic girdle of the holotype (MZSP-PV 25) of Mariliabatrachus navai gen. et sp. nov. in acetabular (A) and dorsal (B) views. All the abbreviations are listed in the Appendix.Scale bar = 2 mm.

Figure 12.Hindlimb bones of the holotype (MZSP-PV 25) of Mariliabatrachus navai gen.et sp. nov.. Right femur in dorsal (A), lateral (B), and ventral (C) views.Right tibiofibula in lateral (D) view.All the abbreviations are listed in the Appendix. Scale bar = 1 mm.

Figure 13. Tibiale, fibulare, and pes of the paratype (MZSP-PV 1326) of Mariliabatrachus navai gen. et sp. nov. in ventral (A) and dorsal (B) views. All the abbreviations are listed in the Appendix.Scale bar = 1 mm.

Figure 14. Strict consensus of the 140 most-parsimonious trees retrieved in the phylogenetic analysis (using equal weighting and unordered multistate characters, rooted in Ascaphus truei). The solid circle indicates a clade formed by well-ossified frogs.

Figure8.Forelimb bones of the holotype (MZSP-PV 25) of Mariliabatrachusnavaigen.et sp.nov.. Left humerus indorsal (A),medial (B), ventral (C), andlateral(D)views.Radioulnainventral (E)anddorsal (F)views.All the abbreviationsare listed inthe Appendix.Scalebar = 1 mm.