Kermitops gratus SO et al., 2025

Kermitops gratus SO et al. sp.nov.

Zoobank LSID: urn:lsid:zoobank.org:act:039A8C39-E226-4C54-9357-CB2161A07551 .

Holotype: USNM 407585 About USNM ( Figs 1–3 View Figure 1 View Figure 2 View Figure 3 ), a near complete skull roof, occiput with partial braincase, and mandibles preserved. Aside from partially preserved right vomerine teeth, the anterior palatal elements are not preserved. Marginal teeth are not well-preserved or exposed.

Etymology: Generic epithet is derived from a combination of ‘Kermit’ the famous lissamphibian and beloved Muppets’ character created and originally performed by Jim Henson, and the Greek suffix ‘- ops’, meaning face. Specific epithet ‘ gratus ’ meaning ‘gratitude’ in Latin for the contributions of specimen collector and former USNM vertebrate palaeontology curator Nicholas Hotton III, and other members of the USNM field party that were involved in the collection effort.

Locality and Horizon: East Coffee Creek , Lake Kemp (NE Quad), Wilbarger County, Lower Clear Fork Formation , Leonardian, Early Permian. USNM PAL 407585 About USNM was collected by Nicholas Hotton III and the USNM field party on 6 April 1984 (field number 84-).

Differential Diagnosis: An amphibamiform differentiated from all other amphibamiforms by the following autapomorphies: a small internarial fontanelle contained solely between the premaxillae and a double-pronged anterolateral process of the postparietal that incises the supratemporal. Further differentiated from Plemmyradytes , Micropholis , Pasawioops , Rubeostratilia , and Tersomius by anteroposteriorly shortened postorbital, resulting in a proportionally shorter postorbital bar. Differentiated from Platyrhinops , Amphibamus , Georgenthalia , Gerobatrachus , and branchiosaurids by a narrower skull width. Further differentiated from Platyrhinops , Amphibamus , and branchiosaurids by the participation of the frontal in the orbital margin. Shares with Platyrhinops , Amphibamus , Nanobamus , Tersomius , Pasawioops, Rubeostritalia , Georgenthalia , and Gerobatrachus , but differs from Doleserpeton , Micropholis , and branchiosaurids by, the presence of an anterior flaring of the frontal. Differs from at least Georgenthalia and Nanobamus in the absence of a keyhole-shaped external narial opening, where the lacrimal is emarginated.

DESCRIPTION

General morphology and preservation

The skull is approximately 3 cm long along the midline and 2 cm wide at the level of the occiput ( Figs 1–3 View Figure 1 View Figure 2 View Figure 3 ). There is some taphonomic distortion on both sides, making the orbits appear slightly more ovoid than they would have in life, and the left orbit is partially disarticulated. The anterior palate and braincase are lost but the remainder of the skull is well-preserved, even showing a full arrangement of palpebral ossicles in place and showcasing fine dermal ornamentation on the dorsal skull. The margins of the orbit are slightly raised, resulting in a differentiation of the orbital margin from the rest of the skull roof surface. The snout is long and parabolic in shape, consistent with the morphology seen in micropholids ( Fig. 1 View Figure 1 ; e.g. Fröbisch and Reisz 2008). However, the postorbital region of the skull is markedly shorter than that of all micropholids, including a foreshortened postorbital bar and a short postorbital skull table that is shared with Doleserpeton , Amphibamus , Platyrhinops , Gerobatrachus , and Georgenthalia ( Bolt 1979, Anderson et al 2008a, b, Clack et al 2009, Sigurdsen and Bolt 2010). The combination of a long parabolic snout and short postorbital skull table appears to be unique to this taxon ( Fig. 1 View Figure 1 ).

Premaxillae

The premaxillae are the anteriormost elements of the skull and are gently curved ( Figs 1A, B View Figure 1 , 3A, C View Figure 3 ). Laterally, the premaxillae contribute to the anteromedial wall of the narial opening. The dorsal processes terminate with long posteriorly projecting alary processes similar to Pasawioops ( Fröbisch and Reisz 2008) . There is a small internarial fontanelle between both premaxillae ( Fig. 1 View Figure 1 ). Internarial fontanelle are present among the amphibamiforms Pasawioops , Georgenthalia , Tersomius , and Doleserpeton , but their internarial fontanelles are larger and partially formed by a contribution of the nasal, which is not present here. Fine pitting adorns the premaxillae, though the ornamentation is not as distinct as in the dorsal skull roof. No teeth are preserved on the premaxillae.

Nasals

Both nasals are preserved, roughly quadrangular in shape and are broad, occupying an expansive region of the snout similar to other amphibamiforms ( Fig. 1 View Figure 1 ). The nasals are ornamented with anastamosing ridges and pits. Anteriorly, the nasals are incised by the invading alary processes of the premaxillae similar to the condition seen in Pasawioops ( Fröbisch and Reisz 2008) . The midline nasal suture is slightly interdigitated as are the surrounding sutures with the frontal, prefrontal, and lacrimal. The nasals form the majority of the dorsomedial margin of the external nares.

Maxillae

The maxillae are preserved on either side of the skull as thin, elongated elements that reach from the anteriormost tip of the nares to the posteriormost portion of the postorbital bar ( Figs 1 View Figure 1 and 3B, D View Figure 3 ). Anteriorly, the maxillae bear a small but pronounced facial lamina that extends dorsally and forms the ventral margin of the external nares ( Fig. 3B, D View Figure 3 ). The facial lamina is slightly more pronounced than micropholids, such as Pasawioops and Tersomius texensis ( Fröbisch and Reisz 2008, Maddin et al. 2013). While there isn’t much ornament visible on the lateral surface of the maxillae, this is most likely due to poor preservation or over-preparation, and there are hints of rugose ornamentation present, similar to the rest of the skull. As the maxillae elongate towards the posterior, it underplates the lateral exposure of the palatine (LEP), and the jugal ( Fig. 3B, D View Figure 3 ). The maxillae terminates at the contact with the jugal, where it appears to taper to a point. No teeth are preserved on the maxillae.

Lacrimals

The lacrimals can be located on both sides of the skull as an elongate element that gently curves laterally on its anterior–posterior axis, leading to its contribution to both the dorsal and lateral skull roof similar to most micropholids. The elements reach from the posterior external nares to the antorbital margin ( Fig. 1 View Figure 1 ). The lacrimals are ornamented, though ventrally the ornamentation is subdued compared to more dorsal areas of the element ( Fig. 3A, C View Figure 3 ). They form the posterolateral margin of the external nares and the anterolateral margin of the orbit. The lacrimals emarginate the anterior and ventral margins of the orbit. The posterior process of the lacrimal ventral to the orbit narrows to the point and sutures to the LEP. The dorsal margin of the lacrimal bears a process that invades the suture between the nasal and the prefrontal resembling the condition in Pasawioops ( Fröbisch and Reisz 2008) . On the left lacrimal, the step is less pronounced. Laterally, the sutural contact between the lacrimal and the maxilla is straight.

Prefrontals

The prefrontals are falciform elements that comprise the majority of the anterodorsal margin of the orbit similar to most amphibamiforms ( Figs 1 View Figure 1 , 3B, D View Figure 3 ). The posterodorsal process of the right prefrontal narrows to a point between the frontal and the orbit and contacts the anterior half of the frontal. The posterodorsal process of the left prefrontal is more robust compared to the same process of the right prefrontals. The ventral process of the prefrontals is blunt and form a simple suture with the lacrimals, but invades into the lacrimal as a consequence of the medial lacrimal process ( Fig. 1 View Figure 1 ) This condition is unlike the less prominent ventral prefrontal process in Pasawioops and Tersomius ( Fröbisch and Reisz 2008, Maddin et al. 2013) but similar to Rubeostratilia ( Bourget and Anderson 2011) . The anterior suture of the prefrontals with the nasals are interdigitating, with the right prefrontal having more pronounced interdigitation ( Fig. 1 View Figure 1 ). The ornamentation of the prefrontals is well-defined with pits and ridges.

Frontals

The paired frontals are quadrangular elements in the interorbital skull roof. They are asymmetric, with the right frontal narrower than the left ( Fig. 1 View Figure 1 ). The midline is a simple wavering suture until the posterior quarter, where the suture becomes a significantly interdigitating suture. Anteriorly, the frontals widen; the anterior of the left frontal is twice as wide as its posterior, while the anterior of the right frontal is only marginally wider than its posterior. Anterior flaring of the frontals can be seen in Rubeostratilia , Tersomius , Nanobamus , Gerobatrachus , and Georgenthalia ( Anderson et al. 2008a, b, Gee and Reisz 2020). A small process of the frontals contacts a very small portion of the medial orbital margin, restricted by the supraorbital processes of the prefrontal and postfrontal ( Fig. 1 View Figure 1 ). The posterior contact with the parietals forms an interdigitating suture. Some of the most well-defined ornamentation can be observed on the anterior half of the frontals.

Palpebral ossifications

PalpebralossificationsarecommonlyfoundinAmphibamiformes, and a well-preserved series of these mosaic plates line the orbit adjacent to the frontals in Kermitops . These plates vary in size and are mostly unornamented, but bear a very slight pitting on some of the largest plates ( Fig. 1 View Figure 1 ). Amphibamiforms that preserve similar palpebral ossifications include Tersomius texensis ( Maddin et al. 2013) , Rubeostratilia texensis ( Bourget and Anderson 2011) , and the likely amphibamiform ‘ Broiliellus ’ hektotopos ( Berman and Berman 1975) .

Postfrontals

Based on the right postfrontal, the postfrontals are the smallest elements of the interorbital region and contribute to a small posteromedial segment of the orbital margin, most similar to Plemmyradytes ( Huttenlocker et al. 2007) , Pasawioops ( Fröbisch and Reisz 2008) , and Rubeostratilia ( Bourget and Anderson 2011) , but vastly different than the expansive postfrontals of Nanobamus ( Gee and Reisz 2020) . They are subtriangular in shape, with the anterior terminus of the supraorbital process narrowing to a point between the frontal and the orbit ( Fig. 1 View Figure 1 ). The contacts with the surrounding elements—the frontal, parietal, supratemporal, and postorbital—are straight.

Postorbitals

The postorbitals are falciform elements that form a significant portionofthepostorbitalmarginandaremostsimilarto Plemmyradytes ( Huttenlocker et al. 2007) and Georgenthalia (Anderson 2008) . Anterodorsally, the dorsal process of the postorbitals narrows to a point between the postfrontal medially and the orbit laterally ( Figs 1 View Figure 1 , 3B, D View Figure 3 ). The ventral process of the postorbitals tapers to a point anterior of the jugal, forming the posterior margin of the orbit. The postorbitals form simple and straight sutures with the postfrontal, supratemporal, and jugal, and form an undulating suture with the squamosal that is not preserved on the right.

Jugals

The jugals are subtriangular in shape in lateral view and most similar in shape to other micropholids, such as Micropholis and Rubeostratilia ( Bourget and Anderson 2011) ( Fig. 3B, D View Figure 3 ). They contribute to the posteroventral margin of the orbit. The anterior process of the jugals narrows to a points in between the orbit dorsally and the maxilla ventrally. The posterior termination marks the posterior extent of the postorbital bar. Well-defined pit and ridge ornamentation is present on the left jugal, whereas on the right it is either eroded or over-prepared and partially obscured by matrix.

Parietals

The parietals are both preserved; however, the left side is much less distorted ( Fig. 1 View Figure 1 ). The parietals are quadrangular and narrow anteriorly, as in most amphibamiforms (e.g. Pasawioops Fröbisch and Reisz 2008 and Doleserpeton Sigurdsen and Bolt 2010 ; but unlike Micropholis Schoch and Rubidge 2005 ). The interparietal suture is highly interdigitated and a small pineal foramen is located on the anterior third of its length. The parietals meet the frontals anteriorly at a narrow contact and form an interdigitated suture. Laterally, the parietals contact the postfrontals and supratemporals at a broad amplitude and shallow suture. Posteriorly, the parietals are at their widest and contact the postparietals at a wavy but not interdigitated suture. The parietals share the same dermal ornamentation as the rest of the skull but do not appear to have as deep grooves as the frontals and some of the snout region.

Postparietals

The postparietals are both preserved at the occiput as the posteriormost bones of the skull roof alongside the tabulars ( Figs 1 View Figure 1 , 3A, C View Figure 3 ). The postparietals are anteroposteriorly extended, unlike the narrower postparietals in Georgenthalia and Eoscopus . The postparietals have double-pronged processes that protrude anterolaterally and intrude into the supratemporal. They form complex, undulating sutures with their surrounding elements, particularly the supratemporal. The occipital margin of the right postparietal is complete but fragmented. Similar to the rest of the posterior skull table, dermal ornamentation is present on the postparietals.

Tabulars

The tabulars are small, quadrangular elements contributing to the margin of the otic notch and to the occiput of the skull roof, as in most amphibamiforms ( Figs 1 View Figure 1 , 3A, B View Figure 3 ). They are much more anteroposteriorly foreshortened compared to the postparietals, similar to Pasawioops ( Fröbisch and Reisz 2008) and Tersomius texensis ( Maddin et al. 2013) . The ornamentation on the tabulars is very fine and not as well-defined as in other elements. A short posterolateral rim of the tabulars contributes to the margin of the otic notch. The occiput is dorsoventrally compressed and the right tabular especially so, making it difficult to discern any more of the otic notch participation by the tabulars. A paroccipital process of the left tabular is partially preserved and sutures to a possible opisthotic ( Fig. 3A, B View Figure 3 ).

Squamosals

The squamosals are elements that frame the majority of the anterior and ventral otic notch, found on either side of the cranium ( Figs 1 View Figure 1 , 3 View Figure 3 ). The exact shape of the squamosals is uncertain, due to dorsoventral deformation of the posterior skull roof. They form continuous sutures with the quadratojugals ventrally and postorbitals anteriorly. There is a short suture anterolaterally with the jugals. There is poorly defined pitting on the squamosals. Due to the deformation, it is difficult to discern their sutures with the supratemporals dorsally, but the dorsal processes of the squamosals appear to underplate the supratemporals. The transition between the skull roof surface and the otic notch surface of the squamosals is poorly defined due to dorsoventral compression. However, the squamosals exhibit a lack of ornamentation similar to other amphibamiforms that allows us to infer how the otic notch may have been constructed in life.

Supratemporals

The supratemporals are preserved on either side of the cranium and are large, subrectangular-shaped elements that contact the parietals and postparietals medially, the postfrontal anteriorly, the squamosal and postorbital ventrally, and the tabular posteriorly ( Fig. 1 View Figure 1 ). On either side, the medial sutures with the parietals and postparietals are noticeably wavering and slightly interdigitated. The supratemporals are highly ornamented with anastomosing ridges and pits similar to the other dorsal skull elements. In general, the morphology of the supratemporals resembles the condition found in Micropholidae , more so than the condition in Amphibamidae .

Quadratojugals

The quadratojugals frame the otic notch ventrally. The better preserved left quadratojugal is laterally triangular and dorsally quadrangular ( Figs 1 View Figure 1 , 3 View Figure 3 ). The quadratojugals overplate the respective quadrates. The quadratojugals are ornamented with light pitting on both of the exposed lateral surfaces.

Quadrates

The quadrates are found underplating the quadratojugals ( Fig. 3 View Figure 3 ). They are identified on the basis of their contact with the quadrate process of the pterygoid. This position is potentially a result of the element’s craniomandibular articulation being shoved anterior relative to their original position. The left quadrate is not well-preserved enough to further discern additional features of the element. The right quadrate appears to be fractured into two fragments and is similarly difficult to discern further features of its anatomy.

Septomaxillae

The septomaxillae are small bony elements found in the ventrolateral margin of the nares ( Figs 1 View Figure 1 , 3B, D View Figure 3 ). They are small and fragmented; few features of the elements can be noted besides their positions.

Vomer

Although the vomer is mostly obscured, what appears to be cross-sections of the vomerine fangs may be visible on the area of the palate where the right vomer would lie ( Fig. 2 View Figure 2 ).

Parasphenoid

The base of the parasphenoid is partially crushed, distorting its original shape ( Fig. 2 View Figure 2 ). However, a general shape can be described; the posterior margin of the parasphenoid laterally flares out, and narrows towards the basipterygoid processes, which jut out laterally, forming a steep incision on the lateral margins of the parasphenoid. Only the base of the cultriform process is preserved; it is parallel-sided, narrow, and keel-shaped. A field of denticles is preserved at the interface between the cultriform process and the base of the parasphenoid, as well as further anterior on what remains of the cultriform process, differing from the condition in Pasawioops ( Fröbisch and Reisz 2008) and Micropholis (Schoch and Rubidge 2005) but similar to most other amphibamiforms. The base of the parasphenoid bears shallow depressions for the attachment of muscles ( Fig. 2 View Figure 2 ).

Pterygoids

The pterygoids are poorly preserved but, based on the components preserved, the pterygoids are triradiate elements composed of at least three rami: the palatal ramus, the quadrate ramus, and the basicranial process ( Fig. 2 View Figure 2 ). The connection between both basicranial processes of the pterygoids and the basipterygoid processes of the parasphenoid seems to form a suturalbasicranial articulation. Both quadrate rami of the pterygoids are distorted, but the sutures between the rami and the quadrates are well-preserved and tight. Both palatal rami of the pterygoids are poorly preserved. Only a disarticulated proximate segment is preserved in the left pterygoid. In the right pterygoid, the process is broken at the base where it extends from the pterygoid and is rotated posteriorly. On the process itself, there appears to be a preserved shagreen of denticles similar to those seen in Pasawioops ( Fig. 2 View Figure 2 ; Fröbisch and Reisz 2008).

Exoccipitals

The exoccipitals are paired elements of the occiput. Both exoccipitals preserve the ascending columns and the occipital condyles ( Figs 3A, C View Figure 3 ). They are strongly sutured to the posterior margin of parasphenoid ventrally ( Fig. 2 View Figure 2 ). The dorsal processes of the exoccipitals extend dorsally towards the postparietals. They meet the descending ventral process of the postparietal, but it is unclear where the suture lies, if it exists, making it hard to delimit the ventral process of the postparietals. Laterally, a facet for the opisthotic is present on both exoccipitals similar to Pasawioops ( Fröbisch and Reisz 2008) ; the right opisthotic is sutured ( Figs 3A, C View Figure 3 ).

The shape of the foramen magnum is roughly subrectangular and slightly taller than wide. It is framed laterally by the dorsal processes of the exoccipitals, ventrally by a separate ossification from the exoccipitals, and dorsally by the postparietals ( Figs 3A, C View Figure 3 ). This additional ventral, unpaired ossification is separated from the lateral exoccipitals by fine sutures, and tightly sutures to anteriorly located parasphenoid. We tentatively identify this ossification as the basioccipital.

Mandible

The skull roof is accompanied by paired mandibular rami. While most of the elements of the mandibles are obscured by matrix, the elements that are observable indicate that the hemimandibles possess the usual amphibamiform complement of the dentary, splenial, post-splenial, coronoids, angular, surangular, pre-articular, and articular ( Fig. 2 View Figure 2 ). The dentaries are the longest and largest element of the mandibles ( Fig. 2 View Figure 2 ). Although the teeth are not visible, they are probably the sole tooth-bearing element of the mandibles. The surface of the dentary that is exposed is worn, but it does not seem to preserve prominent ornamentation. Sutured ventrally to the dentaries are the splenials and post-splenials ( Fig. 2 View Figure 2 ). These elements are narrow, parallel-to-subparallel rectangles that follow the curvature of the mandibles; they form a trough shape as the element cups the ventral hemimandibles. Predominantly elements of the lingual surface, narrow slivers of the splenials and post-splenials are visible on the labial surfaces. The dentaries and the splenials both meet and contribute to a well-defined mandibular symphysis, similar to Pasawioops ( Fröbisch and Reisz 2008) . The post-splenials terminate at the same level at which the dentaries terminate posteriorly. Posterior to the post-splenials are the angulars. The angulars are significant components of the posterior labial surface of the hemimandibles; they wrap around the ventral aspect of the ramus and contribute to the lingual surface of the hemimandibles as well ( Fig. 2 View Figure 2 ). Dorsally, on the labial surface, the angulars form a simple suture to the surangulars ( Figs 3B, D View Figure 3 ). The surangulars occupy a thin strip at the posterior mandible. Lingually, the coronoids and a pre-articular are visible in the left hemimandible, but the exact boundaries and shapes of these elements cannot be delimited. The splenials suture to the coronoids and the pre-articular dorsally.

Phylogenetic analysis

We explored the phylogenetic relationships of Kermitops gratus among Dissorophoidea using a modified version of the character–taxon matrix recently published by Schoch and Werneburg (2023) and Werneburg et al. (2023). We added four additional taxa: Plemmyradytes shintoni ( Huttenlocker et al. 2007) , Rubeostratilia texensis ( Bourget and Anderson 2011) , Milnererpeton huberi ( Hunt et al. 1996, Werneburg et al. 2021), and Nanobamus ( Gee and Reisz 2020) . Several inconsistencies were present in the original matrix and corrected before the analysis was performed (see Supporting Information, S2 and S3 for details). We made the addition of six characters concerning the variation found in the circumorbital elements of the prefrontal, postorbital, postfrontal, jugal, lacrimal, and, when applicable, the LEP:

113. Shape of the prefrontal at its circumorbital contribution: (0) wide body of the element; or (1) some or all of the element is reduced, becoming narrower and near splint-like at the anterior or dorsal orbital margin.

114. Shape of the postfrontal at its circumorbital contribution: (0) wide body of the element; or (1) some or all of the element is reduced, becoming narrower and near splint-like as it wraps around the dorsal or medial orbital margin.

115. Shape of the postorbital at its circumorbital contribution: (0) wide body of the element; or (1) some or all of the element is reduced, becoming narrower and near splint-like at the posterior orbital margin.

116. Shape of the lacrimal at its circumorbital contribution: (0) wide body of the element; or (1) some or all of the element is reduced, becoming narrower and splint-like at the ventral or anterolateral orbital margin.

117. Shape of the jugal at its circumorbital contribution: (0) wide body of the element; or (1) some or all of the element is reduced, becoming narrower and near splint-like at the ventral or posterolateral orbital margin.

118. Depth of the LEP, if present: (0) LEP tall, at least half as tall as maxilla in orbital margin; or (1) facial exposure of palatine a narrow sliver.

The final character–taxon matrix, consisting of 46 taxa and 118 characters (Supporting Information, S4) was analysed using TNT 1.5 (https://cladistics.org/tnt), utilizing the same conditions as reported in Schoch and Werneburg (2023). All characters were equally weighted and unordered. We used the New Technology Search option with 1000 replicates under Ratchet. Due to the possible presence of a basioccipital, we ran two different analyses—one with the basioccipital interpreted as absent and another with the basioccipital interpreted as present. Strict consensus trees were calculated from the most-parsimonious trees from each analysis ( Fig. 4 View Figure 4 ). Bootstrap analyses were also run, producing 1000 replicates for each condition and generating a strict consensus tree from each bootstrap analysis (Supporting Information, S5, S6).

Bayesian inference was conducted using MrBayes 3.2.7 ( Huelsenbeck and Ronquist 2001, Ronquist et al. 2012) under the Mkv model ( Lewis 2001), independent gamma branch rates, and equal rate of change between character states for two analyses with alternate codings of the presence of the basioccipital. The analysis was parameterized to initiate four runs with six Markov chain Monte Carlo chains and run for 10 million generations with sampling every 1000 generations and a relative burn-in of 25%. A consensus tree with posterior probabilities mapped on to the nodes was generated ( Fig. 5 View Figure 5 ; Supporting Information, S7, S8).

The parsimony analysis assuming the presence of a basioccipital produced five equally parsimonious trees of 360 steps each ( Fig. 4A View Figure 4 ). The recovered trees had a consistency index of 0.367 and a retention index of 0.694. The strict consensus of the most-parsimonious trees recovered monophyletic Amphibamiformes; however, the majority of relationships among them form a polytomy, with the exception of strong support for monophyletic branchiosaurids and lissamphibians. Micropholis was found to be the sister-taxon of Pasawioops , and Kermitops was part of the amphibamiform polytomy ( Fig. 4A View Figure 4 ). The parsimony analysis assuming absence of a basioccipital produced four equally parsimonious trees of 359 steps each ( Fig. 4B View Figure 4 ). The recovered trees had a consistency index of 0.368 and a retention index of 0.696. The strict consensus produced several relationships that departed from previously recognized topologies. Nanobamus and Milnererpeton were recovered as sister-taxa, which in turn are sister to the Georgenthalia , Gerobatrachus , and Lissamphibia clade. This relationship replaces amphibamids as the previously recovered closest relatives to the latter clade ( Schoch 2019, Schoch and Werneburg 2023). A polytomy consisting of micropholids, Kermitops , Plemmyradytes , and Eoscopus was recovered with the clade of Nanobamus , Milnererpeton, Gerogenthalia , Gerobatrachus , and Lissamphibia ( Fig. 4B View Figure 4 ). Amphibamids and branchiosaurids are sister to each other and in turn are sister to the previous clade.

The Bayesian inference permutation considering the presence of a basioccipital in Kermitops produced a topology that differs starkly from the results of both of the maximum parsimony analyses ( Fig. 5A View Figure 5 ). Kermitops and Plemmyradytes once again form a clade; however, in this permutation this clade is the sister-taxon of all other amphibamiforms. Rubeostratilia forms a clade with Micropholidae , which is the sister-taxon of the clade formed by branchiosaurs, Nanobamus , Milnererpeton , Georgenthalia , Gerobatrachus , and Lissamphibia. Georgenthalia formed a clade with Gerobatrachus ; they are recovered as the sister-group to Lissamphibia to the exclusion of Milnererpeton and to the further exclusion of Nanobamus . This clade was recovered as a sister to Branchiosauridae . Further this topology recovered Platyrhinops forming a clade with Amphibamus to the exclusion of Doleserpeton as sister-taxon to the clade of Nanobamus , Milnererpeton , Georgenthalia Gerobatrachus , and Lissamphibia, plus the branchiosaurid clade. Eoscopus was found as the sister-taxon to the Kermitops and Plemmyradytes clade, plus all other amphibamiforms. The posterior probability of Amphibamiformes clades is low (posterior probability = 0.1904) and the posterior probability of the node that unites Kermitops and Plemmyradytes with amphibamiforms is similarly low (posterior probability = 0.2492) ( Fig. 5A View Figure 5 ; Supporting Information, S7).

IntheBayesianinferencepermutationconsideringtheabsence of the basioccipital, Kermitops is nested within amphibamiformes as sister-taxon to Plemmyradytes ( Fig. 5B View Figure 5 ). They are sister to a monophyletic group consisting of branchiosaurs, Nanobamus , Milnererpeton , Georgenthalia , Gerobatrachus , and Lissamphibia (posterior probability = 0.1401) (Supporting Information, S8). Micropholids were recovered as the sister-group to Kermitops and Plemmyradytes , plus the branchiosaurs, Nanobamus , Milnererpeton , Georgenthalia , Gerobatrachus , and Lissamphibia. Eoscopus is once again found as the earliest divergent amphibamiform ( Fig. 5B View Figure 5 ).

An additional Bayesian inference permutation was conducted for the absent state of the basioccipital under a FBD ( Heath et al. 2014) and a uniform distribution tree age prior between 312 and 330 Mya following a previous time-calibrated analysis ( Jones et al. 2022). Three extant lissamphibians were added to the dataset for this analysis ( Epicrionops bicolor , Cryptobranchus alleganiensis , and Leiopelma hamiltoni ). The fossil ages for tip-calibration were obtained from the Paleobiology Database (paleobiodb.org) and supplemented with the age of the reported stage of occurrence from the publications of a taxon when needed (Supporting Information, S9). The resultant topology also recovered micropholids and micropholid-like amphibamiforms as more closely related to lissamphibians than previously expected ( Fig. 6 View Figure 6 ). Kermitops was found as the sister-taxon to Plemmyradytes . The Kermitops – Plemmyradytes clade was found as the sister-taxon to the clade including Rubeostratilia and Micropholidae , to the exclusion of Eoscopus . Sister to this clade, another clade of amphibamiforms was recovered containing Lissamphibia, Gerobatrachus , Georgenthalia , and Nanobamus with Milnererpeton at the base. Within Lissamphibia, the three extant lissamphibians were recovered as a monophyletic group sister to Karaurus ( Fig. 6 View Figure 6 ). This position is probably recovered due to the minimal coverage of lissamphibian morphology and to focus on amphibamiform characters. Branchiosaurs were found as the sister-taxon to amphibamids. The amphibamid–branchiosaur clade was recovered as the sister-taxon to the clade formed by micropholids, micropholid-like amphibamiforms (e.g. Kermitops , Plemmyradytes ), and Milnererpeton , Nanobamus , Georgenthalia , Gerobatrachus , and lissamphibians ( Fig. 6 View Figure 6 ).