Brouffia orientalis Carroll & Baird, 1972

Klembara, Jozef, Ruta, Marcello, Anderson, Jason, Mayer, Taran, Hain, Miroslav & Valaška, Daniel, 2024, A redescription of BroUffia orientaliS Carroll & Baird, 1972 from the Upper Carboniferous of the Czech Republic and the status and affinities of protorothyridid amniotes, Swiss Journal of Palaeontology (33) 143 (1), pp. 1-39 : 7-27

publication ID	https://doi.org/10.1186/s13358-024-00329-2
persistent identifier	https://treatment.plazi.org/id/6C5987DA-6943-FFC4-8C46-FBBA35D8F881
treatment provided by	Felipe
scientific name	Brouffia orientalis Carroll & Baird, 1972
status

Treatment

Figures 1 View Fig , 2 View Fig , 3 View Fig , 4 View Fig , 5 View Fig , 6 View Fig , 7 View Fig , 8 View Fig , 9 View Fig , 10 View Fig , 11 View Fig , 12 View Fig , 13 View Fig , 14 View Fig , 15 View Fig .

Gephyrostegus bohemicus Jaekel, 1902 ; Brough & Brough, 1967:147–158, specimen I, figs. 2A, B, 4, 5A, 6B, 7B, 8B, 10A, B.

Brouffia orientalis Carroll & Baird, 1972:337–341 , figs. 6, 11E.

Holotype

Part and counterpart blocks: M 4908a (formerly ČGH III B.21.C.587), dorsal aspect; M 4908b (formerly MP 451 ), ventral aspect (see Brough & Brough, 1967); National Museum , Prague, Czech Republic ( Figs. 1 View Fig , 2 View Fig , 3 View Fig , 4 View Fig , 5 View Fig , 6 View Fig , 7 View Fig , 8 View Fig , 9 View Fig , 10 View Fig , 11 View Fig , 12 View Fig ).

Locality and horizon

Nýřany ‘Gaskohle’, Nýřany Colliery, south-west of Plzeň, Czech Republic; apex of Lower Grey Beds, Plzeň- Manětín Basin; Upper Westphalian D (Asturian), Moscovian, Late Carboniferous (Middle Pennsylvanian) (see Klembara et al., 2014).

Amended diagnosis

In the following diagnosis, we focus on the principal characters that distinguish Brouffia from other protorothyridid genera. Additional anatomical differences among these genera are presented in the Discussion. We have not provided an exhaustive list of diagnostic features in Brouffia , because the polarity of several characters near the roots of crown-group Amniota is uncertain. Tis issue is compounded by the fact that the most recent, overarching analyses of early amniote phylogeny have yielded irreconcilable results for the intrinsic and extrinsic relationships of various clades.

Characters separating Brouffia from other protorothyridids: dermal skull roof sculpture consisting of clusters of tubercles of varying shape and size and accompanied by radiating ridges and grooves; dorsomedial surface of coronoid with extensive patch of densely arranged denticles; central portion of interclavicle plate covered in pebble-like, tubercular sculpture.

Main characters separating Brouffia from Paleothyris acadiana : three vs. two rows of palatal denticles; absence vs. presence of denticle patch on pterygoid transverse flange.

Main characters separating Brouffia from Coelostegus prothales: shallow vs. deep embayment of posterior margin of parietal; posterolateral process of frontal sturdy, finger-like, and blunt at its posterior extremity vs. narrow, elongate, and acuminate; anterior margin of supratemporal anterior vs. posterior to parietal posterior margin; larger number of maxillary teeth (~ 35 vs. ~ 24); single vs. multiple caniniform maxillary teeth.

Main characters separating Brouffia from Protorothyris archeri and P. morani : subelliptical vs. sliver-like supratemporal, with length greater than vs. smaller than greatest width of each of tabular and postparietal; absence vs. presence of conspicuous, posteromedial acuminate process on parietal posterior margin; absence vs. presence of transverse row of teeth on pterygoid flange.

Main characters separating Brouffia from Cephalerpeton ventriarmatum : small vs. large upper marginal teeth; absence vs. presence of strong interdigitation at rearmost end of prefrontal-lacrimal suture (also in Protorothyris archeri ).

Characters denoting immaturity: scapula and coracoid separately ossified; vertebral centra separate from neural arches; left and right halves of neural arches not co-ossified; humerus without well-developed processes.

Plesiomorphic characters in the context of crown-group amniotes: slightly raised patch of denticles on parasphenoid shaped like isosceles triangle; small exposure of coronoid in lateral view; single, posterior process of ilium; phalangeal counts of 2-3-4-5?-3.

Characters of uncertain polarity: nasal-frontal suture oblique; triangular posterior process of postfrontal accommodated by small, deep incisure between corpus and lappet of parietal, extending slightly posterior to transverse level of anterolateral corner of lappet; postorbital-parietal suture marginally longer than squamosal-parietal suture; triple sutural joint between frontal, parietal, and postfrontal occurring anterior to mid-length of pre-pineal portion of inter-parietal suture; carpals ossified; robust unguals on manus digits I and II; 31 presacral vertebrae.

Description

Skull roof

Most bones are well preserved, especially in the posterior part of the skull roof ( Figs. 1 View Fig , 2 View Fig , 5 View Fig , 6 View Fig ). In the snout region, several sutures are either disrupted or not recognizable as the lower jaws protrude against the ventral side of the overlying bones. Most skull roof bones feature a pronounced dermal sculpture of irregular tubercles of various sizes and radiating ridges and grooves. Generally, a few tubercles appear larger and more elongate than the rest. Smaller tubercles tend to be subcircular in outline. On several bones, isolated patches of tubercles are visible more peripherally (e.g., nasals; frontals; lacrimals; prefrontals; parietals; postparietals). Te portion of the external bone surface where the tubercles appear more densely arranged usually marks the position of the ossification centres. Grooves extend peripherally from these centres and cover most of the external bone surface. Tese grooves vary in density and depth across different regions of the skull. A system of alternating ridges and grooves is mainly observed on the anterior portions of the frontals and parietals. Changes in dermal sculpture are best conveyed with reference to Figs. 1 View Fig , 2 View Fig , 5 View Fig , 6 View Fig .

Both premaxillae are visible ( Figs. 1 View Fig , 5 View Fig ). Te nasal ramus, which is well preserved on the right premaxilla, gradually narrows posterodorsally and terminates in a smooth, rounded extremity. Te lateralmost portions of the ventral rami are not preserved on either premaxilla, although such rami appear to taper smoothly in a posterior direction. Te external surface of the premaxilla, at the junction between the nasal ramus and the ventral ramus, shows a small cluster of tubercles separated by irregular depressions ( Figs. 5 View Fig ).

On each side of the snout, in the region delimited by the nasals and the ventral rami of the premaxillae (corresponding to the external naris), a gently arcuate plate may represent a fragment of the septomaxilla

( Figs. 1 View Fig , 2 View Fig , 5 View Fig ), but no morphological details are discernible. Te left, wider fragment is L-shaped, with a posteriorly directed—as preserved—semielliptical extremity and a medially directed, subrectangular anterior process, and sits in the middle of the left external naris. Te narrower, right fragment is approximately crescent-shaped. It is close to the anterior margin of the right external naris, adjacent to the ventral ramus of the right premaxilla.

Both nasals are preserved. Although their lateral margins are not entirely visible, their overall shape can be determined reasonably accurately based upon the shape of surrounding elements ( Figs. 1 View Fig , 2 View Fig , 3 View Fig , 4 View Fig , 5 View Fig ). Each nasal is elongate and subrectangular, and slightly shorter than the frontal. Its anterolateral margin contributes to the posterodorsal margin of the external naris. Its anteromedial portion forms a stout subtrapezoidal process articulated with the nasal ramus of the premaxilla. Anterior and posterior to the triple sutural joints between the nasals, the lacrimals, and the prefrontals, the width of the nasals decreases imperceptibly. Te nasal-frontal sutures are markedly oblique and, as a result, the frontals appear wedged between the posterolateral portions of the nasals. Part of the ventral surface of the left nasal, interpreted by Brough & Brough (1967) as a prevomer, forms a narrow strip of bone on the ventral side of the skull ( Fig. 7 View Fig ), visible between the anteriormost extremities of the lower jaws. Tis strip of bone shows impressions of a tubercular sculpture. A similar sculpture has been observed on the ventral surface of the nasals in premetamorphic stages of the seymouriamorph tetrapod Discosauriscus austriacus ( Klembara, 1997) . Although only the posterior rami of both prefrontals are preserved ( Figs. 1 View Fig , 2 View Fig , 5 View Fig ), the complete outline of the expanded anterior portion of the left prefrontal and a small section of the anterior portion of the right prefrontal are traceable as impressions. Te prefrontal has a triangular shape. Its long posterior ramus has a robust construction and terminates in a blunt posterior extremity, as shown on the right-hand side of the skull. Tis extremity is separated from the anterior ramus of the postfrontal by a small contribution of the frontal to the orbit margin. Te posterior ramus of the prefrontal contributes to the anterodorsal margin of the orbit. Te expanded anterior portion of the bone forms an isosceles triangle narrowly inserted between the nasal and the lacrimal and entering the anterior margin of the orbit. A short, but distinct posteroventral process, particularly visible on the left prefrontal, extends for a short distance ventral to the mid-height of the orbit.

Te elongate, subrectangular frontals are complete

( Figs. 1 View Fig , 2 View Fig , 5 View Fig ). Tey are slightly narrower than the nasals, with posterolaterally to anteromedially orientated anterior margins, and transversely orientated posterior margins. Te configuration of the anterior margin was already noted by Brough & Brough (1967) in their drawing of the left frontal. Te frontals contact each other along the anteriormost portions of their medial margins. Posterior to this level, they are slightly separated. Slightly posterior to its mid-point, the interfrontal suture presents a distinct inflexion, where the medial margin of the right frontal produces a small triangular process that fits into a small, embayed section along the medial margin of the left frontal. Similar inflexions observed in a variety of early tetrapods indicate that the process generally overlaps an underlying lamella (surface of bone overlap) associated with the recess ( Klembara, 1997). Te posterolateral corner of the frontal forms a gracile, digitiform process situated between the parietal and the postfrontal. Tis process extends posteriorly, reaching the level of the anterior one-third of the pre-pineal inter-parietal suture. It is accommodated by a small notch along the lateral margin of the parietal corpus (see below), a short distance anterior to the point where the parietal lappet merges into the parietal corpus. Te frontal has a very short contribution to the dorsalmost part of the orbit margin, especially visible on the left-hand side of the skull.

Both postfrontals are represented, but only the left element appears complete and un-disrupted ( Figs. 1 View Fig , 2 View Fig , 5 View Fig ). It is an approximately triangular bone that contributes to most of the posterodorsal margin of the orbit. A very short section of the smooth-surfaced and vertically orientated orbital wall is seen on the left postfrontal. Te medial margin of the bone forms an extensive sutural contact with the frontal but only a short contact with the parietal. Te suture between the lateroventral process of the postfrontal and the postorbital is approximately half as long as the latter bone. A slightly shorter sutural contact occurs between such process and the anterior margin of the parietal lappet. Te postfrontal forms a small, acuminate triangular projection at its posterior extremity, inserted between the parietal corpus and lappet.

Te left parietal is nearly intact and well preserved

( Figs. 1 View Fig , 2 View Fig , 5 View Fig , 6 View Fig ). In contrast, the right parietal is damaged as the right pterygoid protrudes dorsally against its ventral surface. Te entire medial sculptured surface of the right parietal is missing, and the sutural margins of its lateral portion cannot be observed ( Figs. 5 View Fig , 6 View Fig ). Te parietal is divided into two elongate, subtrapezoidal portions: a medial corpus and a lateral lappet. Te lappet is delimited from the corpus by an anteromedial and a posteromedial notch which accommodate, respectively, the posterior projection of the postfrontal and the anterior margin of the supratemporal. Although the parietal-frontal suture is scarcely visible, it appears to follow an irregularly interdigitating course, and occurs approximately at the same transverse level as the postfrontal mid-length. Te slightly subelliptical parietal foramen is situated either at the same level as, or anterior to, the mid-length of the inter-parietal suture. Te lappet forms a long suture with the postorbital and a marginally shorter suture with the squamosal. Te triple sutural joint where the parietal, the postorbital, and the squamosal meet lies just posterior to the parietal foramen. Anterior to the foramen, the inter-parietal suture is nearly straight. Posterior to it, the suture is very gently sinuous. Te posteriormost portion of the parietal accommodates the tabular and postparietal ( Fig. 6 View Fig ), as established by Carroll & Baird (1972). A slightly oblique ridge along the posterior margin of the left parietal marks the position of the sutural seam between the left parietal and the left tabular. Posterior to this ridge is a flat and slightly depressed area for the left tabular ( Fig. 6 View Fig ). Most of its surface is smooth, except for its anteromedial portion which is covered in fine, anteroposteriorly orientated striations. Medial to this area is a second, slightly depressed area that underlapped the left postparietal. Tis area is smooth medially but covered in small, irregular tubercles laterally ( Figs. 5 View Fig , 6 View Fig ).

Te left supratemporal is complete and preserved in situ ( Figs. 1 View Fig , 2 View Fig , 5 View Fig , 6 View Fig ), whereas the right supratemporal is slightly less complete and appears to have been displaced posteriorly, in a manner analogous to the displacement incurred by the two postparietals and by the right tabular (see below). Te right supratemporal is marginally smaller and narrower than the left one, but this may be the result of preservation. Te bone has an ellipsoid outline. Its greater axis is orientated anteromedially to posterolaterally. Its anterior one-third is accommodated by the posterolateral corner of the parietal. Its ossification centre occupies the posterior half of the bone.

Te tabular has a subtrapezoidal outline ( Figs. 1 View Fig , 2 View Fig , 5 View Fig , 6 View Fig ). A bony element preserved just posterior to the left parietal almost certainly represents the left tabular. Its identification is based upon the fact that its outline matches that of the slightly depressed lateral articulation area along the posterior portion of the left parietal, described above. Te right tabular is also preserved ( Figs. 5 View Fig , 6 View Fig ), but rotated by 90 degrees, such that its narrow lateral extremity faces anteriorly. Te tabular narrows abruptly to a point laterally. Its dorsal surface bears distinct tubercles and ridges located mostly on its medial surface. Te suture between the tabular and the postparietal is orientated anteroposteriorly. A smooth, strip-like occipital flange is visible posterior to the ornamented surface. Te right tabular is smooth. For this reason, we speculate that its exposed surface might be ventral. According to Carroll & Baird (1972), the tabular is of similar shape to the supratemporal, but our findings suggest otherwise.

Both postparietals are complete and in articulation, and visible a short distance behind the parietals ( Figs. 1 View Fig , 2 View Fig , 5 View Fig , 6 View Fig ). Tey are rectangular and only marginally wider than long, and their posteromedial corners form acuminate posterior processes. Posterior to their sculptured surface is a smooth, narrow occipital flange. Whereas the posteromedial process is not shown in Brough & Brough’s (1967) drawing of the skull, it does appear in Carroll’s (1970) as well as Carroll & Baird’s (1972) drawings, but it does not appear in their skull reconstruction.

Both maxillae are exposed. Te right maxilla is particularly well preserved, and only its anterior extremity is disrupted ( Figs. 1 View Fig , 2 View Fig , 3 View Fig , 4 View Fig , 5 View Fig , 7 View Fig ). Morphological details of the lateral surfaces of both elements are visible. Teir medial surfaces are damaged or obliterated ( Figs. 3 View Fig , 4 View Fig , 7 View Fig ). Te anteriormost portion of each maxilla is dorsoventrally narrow. Te bone deepens rapidly in a posterior direction, reaching its greatest depth about halfway along its length. From this point, it decreases gradually in depth towards its posterior extremity. In its posterior half, it exhibits two subparallel sulci ( Figs. 1 View Fig , 5 View Fig ). Te lower sulcus is distinctly deeper than the upper sulcus and terminates at the posterior end of the maxilla. On its medial surface, the bone has a well-developed supradental shelf ( Figs. 3 View Fig , 4 View Fig ).

Te lacrimal is a large, elongate bone ( Figs. 1 View Fig , 2 View Fig , 5 View Fig ) extending from the anteroventral margin of the orbit to the external naris. Te right lacrimal is almost completely preserved. Its lateroventral portion is partially overlapped by the right maxilla and its posteroventral process is concealed. On the left side of the skull, the maxilla covers the middle part of the lacrimal, but the anteriormost and posteriormost portions of the latter are exposed. If our interpretation is correct, the posteroventrally orientated process of the lacrimal (jugal process) appears as a posteriorly tapering, robust strut tucked between the left maxilla and the left prefrontal ( Fig. 5 View Fig ). In their drawing of the right lacrimal, Brough & Brough (1967) illustrated a jugal process, but we are unable to confirm their observation. Te lacrimal-prefrontal suture is sinuous and marginally longer than the lacrimal-nasal suture. Te lacrimal attains its greatest depth at the level of its triple sutural joint with the nasal and the prefrontal. Anterior to this level, the bone narrows imperceptibly and forms a subrectangular bony sheet. Posterior to the sutural joint, it narrows slowly up to the orbit margin, then more rapidly ventral to the anteroventral section of the orbit margin.

Although both postorbitals are observed, only the left element provides useful data on the morphology of the bone and its relationships with neighbouring elements ( Figs. 1 View Fig , 2 View Fig , 5 View Fig , 6 View Fig ). The postorbital is subtriangular and forms the second smallest contribution to the margin of the orbit, after the frontal. The medial margin of the postorbital is sutured with the parietal lappet. The posterior extremity of the postorbital-parietal suture extends posterior to the mid-point of the lateral margin of the lappet. The lateroventral ramus of the postorbital narrows to a point. The postorbital-jugal suture is slightly longer than the postorbital-squamosal suture and its anterior extremity is situated slightly below the mid-height of the orbit in lateral view. The right postorbital features a well-preserved orbital margin with a slightly raised and sharp peripheral rim.

Te jugals are vaguely cleaver-shaped in outline

( Figs. 1 View Fig , 2 View Fig , 5 View Fig , 6 View Fig , 7 View Fig ) although in neither is the posteriormost portion fully preserved. Te bone consists of a broad posterior corpus and a slender anterior process. Across the transition between these two regions, the jugal decreases rapidly in depth up to the mid-point of the orbit length. Anterior to this point, the process is of approximately constant thickness and contacts the lacrimal at a level between the anterior and middle one-thirds of the orbit’s anteroposterior diameter. Te orbital margin is thick and with a smooth texture. Te posterior margin of the bone forms a markedly sinuous suture with the squamosal. Te ventral margin of the corpus is gently convex and probably lay flush with the ventral margin of the posterior extremity of the maxilla.

Te shape and proportions of the squamosals can be inferred with some confidence, in part based upon the shape of surrounding bones, although its anterior and ventral margins are disrupted ( Figs. 1 View Fig , 2 View Fig , 5 View Fig , 6 View Fig ). Te dorsal margin is visible on the right squamosal. It displays a thick peripheral rim along its anterior and middle one-thirds, where it contacts the postorbital along an anteroventrally slanting suture as well as the parietal lappet along a nearly horizontal suture, respectively. In this region, the dorsal margin of the squamosal is gently arcuate ( Fig. 5 View Fig ). Te posterodorsal portion of the bone forms a shallow embayment for the supratemporal. At this level, the posterodorsal margin slants posteroventrally. Te straight posterior margin is subvertical and bears a shallow groove, broadest towards its dorsal extremity and gradually narrowing ventrally ( Fig. 5 View Fig ).

Te complete right quadratojugal and the posterior portion of the left quadratojugal are visible ( Figs. 1 View Fig , 2 View Fig , 5 View Fig , 6 View Fig , 7 View Fig ). Te posterior, subcircular articulation part of the bone continues into a club-shaped, stout anterior process with a nearly straight dorsal margin and a gently convex ventral margin. Te boundary between these two regions is represented by a small constriction. Te process is deepest at its mid-length and becomes dorsoventrally narrower anteriorly and posteriorly, terminating in a blunt anterior extremity. Carroll & Baird (1972) figured the quadratojugal as a strap-shaped element with acuminate anterior and posterior extremities and attaining its greatest depth in its anterior one-fourth. We have not been able to find evidence in support of their interpretation. We suspect that the bony sliver that appears next to the right squamosal in their drawing is either part of the squamosal or a small chunk of matrix ( Figs. 5 View Fig , 6 View Fig , 7 View Fig ).

Sclerotic ring

Several dorsal and ventral sclerotic plates occur as faint impressions in both orbits ( Figs. 1 View Fig , 2 View Fig , 5 View Fig ). At least five plates are visible in the left orbit ( Fig. 2 View Fig ) and nine in the right orbit ( Figs. 1 View Fig , 5 View Fig ). Tey appear as mediolaterally elongate and rectangular elements ( Fig. 5 View Fig ), about half as wide as long, but with no obvious surface details.

Palate

Most of the palate surface is visible, except for its lateralmost portions which are partially overlapped by the lower jaws ( Figs. 3 View Fig , 4 View Fig , 7 View Fig ). Te left pterygoid is completely preserved ( Fig. 7 View Fig ). Te posterior half of the right pterygoid is also clearly visible. Te posterior half of the palatal ramus of the pterygoid narrows gradually anteriorly. At this level, its lateral margin is sinuous, being gently convex anterior to the point where the ramus detaches from the corpus of the pterygoid and then broadly concave up to the level where the two palatal rami contact each other. Further anteriorly, the palatal ramus widens slightly, and its lateral margin becomes convex. Tis convexity occupies the anterior one-third of the lateral margin. More anteriorly, this margin becomes very gently concave. Te anterior part of the palatal ramus is narrowly triangular and carries an elongate and acuminate anteromedial projection and a subtriangular and abbreviated anterolateral projection. Between these two projections is a broadly V-shaped notch that accommodates the posterior extremity of the vomer ( Fig. 7 View Fig ). Te square transverse flange is well developed and carries a robust transverse ridge along its posterior margin. Te articulation socket has a subtriangular outline. Both quadrate rami are preserved. A strong arcuate ridge occurs on the anteroventral portion of the quadrate ramus, close to its lateral margin, and continues smoothly into the transverse ridge. Te narrow and elongate interpterygoid vacuities extend for more than half of the length of the palatal rami.

Carroll & Baird (1972) did not identify a vomer in Brouffia . However, the left-hand side of the palate shows a narrow space between the anteriormost tip of the left pterygoid and an elongate, narrow bony plate visible immediately lateral to it ( Figs. 3 View Fig , 4 View Fig , 7 View Fig ). Tis plate fits into the above-mentioned V-shaped notch of the palatal ramus. We identify this bony plate as the posterior portion of the left vomer. Te anteriormost extremity of the vomer is extensively overlapped by the anterior portion of the right splenial ( Fig. 7 View Fig ). However, small denticles present immediately anterior to the anteriormost portion of the right splenial provide an indication of the possible anterior extent of the right vomer ( Figs. 3 View Fig , 4 View Fig , 7 View Fig ).

Te left palatine is almost complete, although its posterolateral portion is overlapped by the lower jaw ( Figs. 3 View Fig , 4 View Fig , 7 View Fig ). It is an elongate plate with two robust anterior processes. Te lateral maxillary process is longer than the medial vomerine process. Between the processes is a wide notch representing the posterior margin of the choana. Although only partly visible, the outline of the choana suggests that this opening was substantial and probably extended posteriorly close to the level of the posterior extremity of the vomers.

Carroll & Baird (1972) interpreted an elongate piece of bone overlying the transverse flange of the left pterygoid as a fragment of the ectopterygoid ( Figs. 3 View Fig , 4 View Fig , 6 View Fig , 8 View Fig ). Whereas we are unable to support or reject this interpretation, we think it is plausible. Te fragment forms a slender strip of bone and carries two large teeth close to one of its extremities (presumably, anterior) and probably also small denticles.

Te parasphenoid plate is completely preserved and exposed in ventral view ( Figs. 3 View Fig , 4 View Fig , 7 View Fig ). It is vaguely flaskshaped and with a distinct constriction immediately posterior to the basipterygoid processes. It reaches its greatest width at its posterior margin. Te cultriform process is a narrow, stiletto-like structure gradually narrowing to an acuminate tip anteriorly.

Palatoquadrate ossifications

Te internal surfaces of both quadrates are exposed. Te left element is slightly better preserved than its antimere

( Figs. 3 View Fig , 4 View Fig , 7 View Fig ). A lateral and a medial ridge cross the surface of the quadrate, running in an anterodorsal direction from the condylar portion. Te ridges converge gradually, but do not meet. Further anteriorly, they appear to diverge slightly. Te internal surface of the quadrate consists of small tubercles and ridges probably representing unfinished bone. If so, these elements were probably not fully ossified. Te condylar portion is well preserved on the left quadrate.

Neural endocranium

Te supraoccipital is preserved in dorsal view ( Figs. 1 View Fig , 2 View Fig , 5 View Fig ). It consists of large right and left plates of approximately quadrangular shape. Te right plate is slightly damaged. Both plates are joined by an anteroposteriorly short, median bony bridge. Te posterior margin of the bridge constitutes the dorsal margin of the foramen magnum. Te basioccipital is well-preserved and visible posterior to the parasphenoid ( Figs. 3 View Fig , 4 View Fig , 7 View Fig ). It is a quadrangular plate with its posterolateral margins slightly converging posteromedially. Te ventral surface of the basioccipital bears two anteroposteriorly orientated ridges with slightly convex lateral edges. Only the basipterygoid processes of the basisphenoid are visible

( Figs. 3 View Fig , 4 View Fig , 7 View Fig ). Tey are short, with their articular surfaces directed at an angle of about 45˚ relative to the longitudinal axis. Carroll & Baird (1972) described a bony element preserved lateral to the basioccipital as an exoccipital. Te same element was interpreted by Brough & Brough (1967) as a stapes. We can neither confirm nor reject either identification, due to the rather poor preservation of the element in question ( Fig. 7 View Fig ).

LoWer jaW

Carroll & Baird (1972) provided diagrammatic sketches of both lower jaws as well as a reconstruction of the right ramus in lateral aspect. However, no description of the lower jaw was supplied. In contrast, Brough & Brough (1967) illustrated the rami but gave only a limited account of their morphology. Our description differs from Brough & Brough’s (1967) in several respects and we have been able to amend many of their original observations. Both rami are appressed against the ventral surface of the skull and are largely exposed in lateral aspect ( Figs. 3 View Fig , 4 View Fig , 7 View Fig ). Small portions of their medial aspect, including details of some constituent bones, are visible inside the orbits in dorsal view ( Figs. 1 View Fig , 2 View Fig , 5 View Fig ). Te left ramus is almost fully articulated whereas the right ramus is disrupted.

Te dentary is long and slender and occupies a little over two-thirds of the jaw length ( Figs. 3 View Fig , 4 View Fig , 7 View Fig ). Te posterior extremities of both dentaries are discernible within the orbits in dorsal view ( Figs. 1 View Fig , 2 View Fig , 5 View Fig ). Te external surface of the dentary is covered in longitudinal sulci and grooves, the course of which is disrupted by a network of cracks. One of these grooves is slightly deeper than the others and its course can be followed along most of the length of the dentary. Tis groove is situated in the dorsal one-third of the bone’s external surface and is of approximately constant width. Near the anterior extremity of the ramus, this groove widens slightly and becomes shallower, merging indistinctly into the surrounding bone surface. At its posterior extremity, the groove approaches the upper margin of the dentary. Slightly posterior to its mid-length, the dentary is deepest, as reported by Carroll & Baird (1972). Te posterior extremity of the dentary tapers abruptly, such that the portion of the bone that extends behind the last tooth forms a stout and subequilateral triangle wedged into the anterior portion of the surangular.

Te angular is spindle-shaped ( Figs. 7 View Fig , 8 View Fig ) and reaches its greatest depth at the level of the posterior extremity of the dentary. Its anterior half gradually narrows dorsoventrally in an anterior direction. As preserved, it is tightly tucked between the dentary and the splenial at the level of its acuminate extremity. Te posterior half of the bone also becomes increasingly narrow dorsoventrally, albeit less gradually than the anterior half. Te external surface of the posterior portion of the angular is sculptured. Te sculpture, which is better observed on the right angular

( Figs. 3 View Fig , 4 View Fig , 7 View Fig , 8 View Fig ), features subcentral tubercles and abbreviated ridges alternating with grooves, the latter increasing in length posteriorly.

Both surangulars form subrectangular, elongate plates

( Figs. 3 View Fig , 4 View Fig , 7 View Fig , 8 View Fig ). Immediately dorsal to the posterior process of the dentary, the anterodorsal extremity of the surangular is visible as a blunt semicircular process in contact with the coronoid along a small subvertical suture, visible in lateral view. Ventral to the posterior process of the dentary, the surangular extends anteriorly forming a triangular, pointed projection wedged between the dentary and the angular. A short distance behind the surangular-coronoid suture, the surangular attains its greatest depth and forms a distinct crest. Immediately posterior to the crest, the dorsal margin of the bone slopes gently posteroventrally, following a slightly convex course. At its posterior end, the margin becomes gently concave.

Te posterior portion of the left coronoid is visible inside the left orbit in dorsal aspect ( Figs. 1 View Fig , 2 View Fig , 5 View Fig ) and part of its external surface is exposed in ventral view ( Figs. 7 View Fig , 8 View Fig ). Te coronoid extends posterodorsally as a narrow, rod-like strut attached to a plate-like, anterior portion

( Fig. 5 View Fig ). Tis morphology suggests that this bone corresponds to the posterior coronoid. Te dorsomedial surface of this plate is covered in closely packed denticles. Protorothyris archeri is the only other ‘protorothyridid’ in which the internal surface of the lower jaw is known ( Carroll & Baird, 1972; Clark & Carroll, 1973). Te single coronoid of Protorothyris ( Clark & Carroll, 1973) lacks denticles. Tus, although incomplete, the coronoid of Brouffia clearly differs from that of Protorothyris and resembles closely that of Gephyrostegus ( Klembara et al., 2014) . Te total number of coronoids is unknown in Brouffia .

Te splenial appears as a slender bony splinter that contributes to the ventral margin of the jaw ramus

( Figs. 3 View Fig , 4 View Fig , 7 View Fig ). In external view, its anterior extremity is estimated to have reached the level of the 7th dentary tooth, whereas its posterior extremity occurs slightly posterior to the last tooth. In the right lower jaw, the splenial is dislodged from its anatomical position and its external surface is fully exposed ( Fig. 7 View Fig ). Its middle section is overlapped by several pieces of matrix. It is a flat, narrow, and fusiform bone with a thick ventral margin, reaching its greatest depth about halfway along its length. From this point, the splenial tapers gently towards its anterior and posterior extremities. Its anterodorsal portion is occupied by a deep notch ( Fig. 7 View Fig ). Tis notch resembles a similar structure in the splenial of Discosauriscus austriacus ( Klembara, 1997) and, perhaps, Karpinskiosaurus ultimus ( Klembara, 2011) . In these two seymouriamorphs, the splenial contributes to the posteroventral margin of a medial excavation situated immediately posterior to the lower jaw symphysis.

Both prearticulars are visible in the part and counterpart slabs ( Figs. 1 View Fig , 2 View Fig , 3 View Fig , 4 View Fig , 5 View Fig , 7 View Fig ). Te posterior portion of the bone is robust but appears to be only partly ossified. Its quadrangular posterior portion is separated by a narrow constriction from a dorsoventrally narrow, anterior bony strip. Tis strip deepens gradually anteriorly, building the medial wall of the adductor fossa. However, its full anterior extent cannot be determined ( Fig. 7 View Fig ).

Te articulars are substantial elements ( Figs. 3 View Fig , 4 View Fig , 7 View Fig ). Te left articular is preserved as an irregularly ovoid bony patch, visible immediately posterior to the posterior extremity of the lower jaw ( Fig. 7 View Fig ). Its exposed, presumably ventral surface is unfinished, similar to the condition noted for the posterior extremity of the prearticular. If confirmed, this observation would corroborate Carroll & Baird’s (1972) conclusion that the holotype of Brouffia is not a mature individual. Te right articular is preserved as a subrectangular fragment occupied by a subcentral transverse ridge. Its anteromedial corner forms a slender process, tucked between the quadrate and the quadratojugal, that extends anteriorly. However, no other information is available.

Dentition

Most upper and lower marginal teeth are visible ( Figs. 1 View Fig , 2 View Fig , 3 View Fig , 4 View Fig , 5 View Fig , 7 View Fig ), albeit slightly compressed. Te teeth are subconical with their tips inclined posteriorly in different degrees. At least four teeth are visible in the left premaxilla, and there is space for one possible additional tooth. Tey differ little in proportions and decrease uniformly in height towards the front and the back of both the maxilla and the dentary. Many of the maxillary teeth ( Figs. 1 View Fig , 2 View Fig , 3 View Fig , 4 View Fig , 5 View Fig , 7 View Fig ) are covered in fine lingual striations close to their crown tips and a sharp crest runs along their anterior edge ( Fig. 9 View Fig ). We found no evidence of a basal enamel folding, including in the largest teeth. Te large depression visible in the mid portion of several tooth crowns results from crushing. Twenty-seven teeth can be observed in the left maxilla, with space for approximately three additional teeth. However, the anterior end of the bone is not preserved so that an accurate count is not possible. A large “caniniform” tooth is present in the anterior one-third of the left maxilla ( Figs. 7 View Fig , 8 View Fig ), as opposed to two “canines”, such as were reported by Carroll & Baird (1972). None of the teeth that occur just anterior and posterior to the caniniform tooth matches the size of the latter ( Figs. 4 View Fig , 7 View Fig , 9A View Fig ). Twenty-four teeth occur in the right maxilla. A further nine additional teeth may have been present, although, as in the case of the left maxilla, the anterior end of the bone is missing ( Figs. 1 View Fig , 2 View Fig , 3 View Fig , 4 View Fig , 5 View Fig , 7 View Fig ). Our estimate of the maxillary tooth number is higher than that given by Carroll & Baird (1972) and closer to that of Palaeothyris (estimated 35 teeth; Carroll, 1969). Te left dentary shows 28 teeth, with room for another seven ( Figs. 1 View Fig , 2 View Fig , 3 View Fig , 4 View Fig , 5 View Fig , 7 View Fig ). Twenty-five teeth are visible in the right dentary, plus space for another eight or nine, with an estimated count of 35.

Most of the ventral surface of the vomer is covered by small and densely arranged denticles ( Figs. 3 View Fig , 4 View Fig , 7 View Fig ). Te denticles situated along the medial margin of the choana appear to be smaller than those covering the medial surface of the vomer.

Te ventral surface of the palatal ramus of the pterygoid shows three elongate fields covered in small and closely spaced denticles. Tese three fields are separated by wide smooth surfaces that radiate out from the basicranial articulation ( Figs. 2 View Fig , 4 View Fig , 7 View Fig ). Within these fields, the denticles form diverging rows. Te posterolateral surface of the transverse flange bears a shagreen of irregularly arranged denticles. An anteroposteriorly elongate denticle field is present on the ventral surface of the left palatine ( Fig. 7 View Fig ), and a large part of the dorsomedial surface of the left coronoid ( Fig. 5 View Fig ). Te fragment of bone identified as a left ectopterygoid carries three large, tusk-like teeth in its anterior portion and, possibly, a set of small denticles ( Figs. 7 View Fig , 8 View Fig ).

Lastly, a triangular field of small denticles occupies the middle one-third of the parasphenoid ( Fig. 7 View Fig ). Tis field is shaped like an isosceles triangle, terminating in a narrow, pointed anterior extremity that extends a short distance anterior to the basipterygoid processes, ~ 21% of the length of the cultriform process. Te patch widens posteriorly, nearly reaching the mid-length of the parasphenoid plate, where its greatest width is ~ 60% of the width of the plate at the same transverse level.

Postcranial skeleton

As in the case of the skull, the postcranial skeleton has undergone considerable diagenetic compression

( Figs. 10 View Fig , 11 View Fig ). Several sections of the vertebral column are difficult to discern due to poor ossification, disarticulation of individual elements, and/or obstruction from overlying structures. Te details of the ventral surface of the vertebrae are partly obscured by the impressions of gastralia, which are arranged in elongate rows running anteromedially to posterolaterally from the ventral midline. In addition to gastralia, there are impressions of minute, round bony elements that appear irregularly scattered on the dorsal surface of the skeleton. Carroll & Baird (1972) regarded these elements as dorsal scales, but we have not been able to confirm or reject this interpretation.

Vertebrae

Various elements of the atlas/axis complex can be seen immediately behind the skull, although the precise identification of each is problematic ( Figs. 10 View Fig , 11 View Fig ). Two small, triangular fragments posterior to the supraoccipital may represent the paired proatlases. Both sides of the atlas neural arch, together with its posteriorly directed spine, are visible. A poorly preserved, rectangular bony fragment underlying the left atlas neural arch may represent one of the atlas centra. Te axis centrum is the first centrum visible on the ventral surface. It is recognizable because it is slightly longer than the following centra ( Fig. 11 View Fig ). Te axis arch is visible on the dorsal surface ( Fig. 10 View Fig ). Subtle variation in the morphology and proportions of the arches can be gleaned from Fig. 10 View Fig .

Te largest pleurocentra are approximately 3 mm long

( Figs. 10 View Fig , 11 View Fig ). Te neural arches are in place but are not suturally attached to the pleurocentra, nor are they fused along the ventral midline. Small, sliver-like intercentra are especially discernible in the mid-trunk and pelvic regions. As Carroll & Baird (1972) noted, the ventral lip of some pleurocentra is beveled, indicating that it would have accommodated a small intercentrum. Tere are 31 presacral vertebrae, including the atlas and axis. Te sacral vertebrae are not very dissimilar from adjacent vertebrae, except for the presence of a larger articulation area for the rib head. Two sacral ribs are visible on the left side of the specimen in dorsal aspect, corroborating the occurrence of two sacral vertebrae, as noted by Brough & Brough (1967). In contrast, only a single sacral vertebra was identified by Carroll & Baird (1972). Only the first four caudal vertebrae are preserved on the slabs and these resemble the last thoracic vertebrae ( Figs. 10 View Fig , 11 View Fig ).

Ribs

Te slender and double-headed ribs do not show expanded distal extremities ( Figs. 10 View Fig , 11 View Fig ). Te distal extremities of the short, straight, and flattened cervical ribs appear gently rounded. Tese ribs are approximately twice the length of an adjacent centrum. Most of the thoracic ribs are long and curved and terminate in somewhat squared-off extremities. Teir length (in the mid-trunk region) corresponds to that of four to five centra. Te two rib heads merge indistinctly. Te last eight pairs of thoracic ribs are considerably shorter than more anterior thoracic ribs and decrease rapidly in length towards the pelvic girdle, where they are reduced to slender and straight spurs. Te articulation areas on both sacral ribs is surrounded by a slightly raised peripheral rim. Te anterior sacral rib has a flared, trapezoidal, flattened distal end, a gently concave anterior margin, an almost straight (except proximally) posterior margin, and a gently convex distal margin. Te posterior rib has a rectangular profile and a comparatively less expanded distal end. Its anterior and posterior margins have similar proportions to those of the anterior sacral rib ( Fig. 10 View Fig ). Te caudal ribs appear short (although longer than the sacral ribs), sturdy, and sharply angled. Tey do not appear to be fused to the centra, although most occur close the latter. No obvious traces of chevrons could be detected.

Pectoral girdle

Te well-developed pectoral girdle shows no fusion of its endochondral elements ( Figs. 10 View Fig , 11 View Fig ). Te clavicle is long, flat, and gently curved. Its lightly sculptured and subelliptical blade is only slightly wider than the widest portion of the clavicular stem. Te stem has subparallel margins and terminates dorsally in a blunt parabolic extremity. As far as we can tell, the clavicle is marginally longer than four anterior trunk centra. We concur with Carroll & Baird (1972) that the bony rod occurring lateral to the left clavicle may represent a cleithrum. It is incomplete and nearly straight as preserved. Its identification is uncertain as it is similar in width to the adjacent ribs. In dorsal view, it shows an elongate, narrow triangular depression, possibly representing a sutural surface for the scapular blade (assuming its correct identification).

Te interclavicle consists of a long, slender stem (as is typical of primitive amniotes and several amniote-like groups), and a broad, diamond-shaped plate. Te posterior extremity of the stem is concealed underneath a trunk centrum. Te stem changes in width along its length. Its posterior half shows nearly straight margins and increases very slightly in width posteriorly. Its central section, as preserved, is narrowest. Its anterior half has gently concave lateral margins and widens gradually anteriorly, merging almost indistinctly with the plate. Te plate is approximately twice as wide as long and attains its greatest width at the level of the transverse axis that connects its lateral subtriangular processes. Anterior to these processes, the plate has a broadly semicircular outline. Posterior to the processes, at the transition between the stem and the plate, the posterolateral margins of the plate converge strongly posteromedially and present an irregularly sigmoid course. Te densely sculptured central portion of the plate consists of irregular, pebble-like, and densely packed tubercles generally decreasing in size peripherally. Tis sculpture extends a short distance posteriorly, occupying a central strip on the anterior half of the stem. It also extends onto the medial half of the lateral subtriangular processes and becomes less conspicuous in the lateral half of these processes where the tubercles tend to be small and produce a low and irregular relief. Te anterior and anterolateral portions of the plate are either smooth or covered in light striations.

Te scapula is flat and sturdy. Its dorsal and ventral margins are gently convex, the former being marginally shorter anteroposteriorly than the latter. Its anterior margin forms a smooth, rounded convexity (more pronounced on the left scapula) immediately ventral to the mid-height of the bone. Dorsal and ventral to this convexity, the anterior margin is straight or irregular sinuous. Te posterior margin features a shallow embayment slightly dorsal to the mid-height of the scapula. Dorsal and ventral to this embayment, the profile of the margin is nearly straight. Te coracoids are represented by flat, featureless, and poorly defined bony masses visible on either side of the interclavicular stem. It is not clear whether one or two coracoids are present ( Fig. 10 View Fig ).

Forelimb

Both left and right humeri are preserved, the right one being the more complete of the two. At about 15.5 mm, its length matches that of approximately five thoracic centra. Te shaft merges smoothly into the proximal and distal extremities of the bone. Te shaft reaches its minimum width slightly proximal to the mid-point of the total humerus length. It has an asymmetric profile, its posterior margin being slightly shallower than its anterior margin. Te right and left humeri show subtle proportional differences and these may not be solely due to preservation. Tus, the posterior margin of the shaft of the left humerus appears to be gently sigmoid where it transitions to the proximal extremity. In contrast, the posterior margin of the right humerus is straight at the same level. Distally, a reverse arrangement is observed: at the transition between the shaft and the distal extremity, the right humerus has a gently concave posterior margin while the left humerus is markedly sigmoid. Te distal extremity is gently expanded and fan-shaped and distinctly wider than the proximal extremity, which exhibits an irregularly trapezoidal outline ( Figs. 10 View Fig , 11 View Fig ). Te abbreviated entepicondyle forms a blunt and triangular projection. A large and proximodistally elongate entepicondylar foramen is present. In extensor view, the foramen reveals an asymmetrical, teardrop-shaped outline and lies very close to the posterior margin of the entepicondyle. At its proximal end, the foramen narrows rapidly to a point. At its distal end, it shows a blunt, rounded profile. In flexor view, the foramen appears as an indistinct, comparatively shorter, more distally placed subelliptical depression. Te proximal and distal articulation surfaces of the humerus are orientated at an angle of 90˚ relative to one another, as in several early amniotes. Neither an ectepicondylar ridge nor a supinator process are present. Te distal articulation surface is indistinct and does not show obvious condylar projections or surfaces and was probably largely cartilaginous in life, though we cannot rule out a preservation artefact.

Te radius and ulna are relatively simple and undifferentiated elements. Te margins of the shaft are shallow and concave, and their proximal and distal extremities are subrectangular. Te two bones are of comparable lengths, and roughly equivalent to the combined lengths of three mid-thoracic vertebral centra. Te slightly more gracile of the two bones may represent the radius. Te bone identified as an ulna has more flattened proximal and distal extremities.

Combined information from part and counterpart slabs provides a substantial amount of morphological detail for the right manus, which we therefore describe in great detail. We are confident about the number of phalanges on digits I–III, as these are fully articulated. On digit V, the first phalanx as well as the proximal portion of the second can be seen on both slabs. A partly preserved ungual is also visible ( Fig. 11 View Fig ). Te space between the preserved portion of the second phalanx and the remnant of the ungual is likely to have been occupied by the distal part of the second phalanx. As for digit IV, we have expressed uncertainty as to the number of phalanges. Tree articulated phalanges are clearly visible in flexor view ( Fig. 11 View Fig ). In extensor view ( Fig. 10 View Fig ), the proximal two-thirds of the first phalanx can be seen, as well as the distal extremity of the penultimate phalanx in articulation with an ungual. When the extensor and flexor views of the manus are superimposed, the length of digit IV appears to be consistent with the occurrence of five phalanges.

Te shape and proportions of the five metacarpals (Mc) are gleaned from combined observations of the part and counterpart slabs. Only McIII and IV are visible in extensor and flexor views ( Figs. 10 View Fig , 11 View Fig ), whereas McI and II are fully exposed in extensor view only and McV in flexor view only. Te longest metacarpal, McIV, measures a little more than half of the length of the radius and ulna ( Fig. 10 View Fig ). It is distinctly more robust than each of the other metacarpals and the width of its shaft (about halfway along the length of the bone) is slightly smaller than the width of its proximal and distal extremities. McI-III and V exhibit a slightly more pronounced ‘waisting’ along their shafts than McIV. Furthermore, McII-V are vaguely sigmoid in their overall shape. Tis feature is made apparent by the changing curvature of the anterior and posterior margins of those metacarpals proximodistally and by the fact that the peripheral rims of their extremities are inclined at different angles relative to the main axis of the bones ( Figs. 10 View Fig , 11 View Fig ). McI differs from the other metacarpals in that its anterior margin is markedly concave, while its posterior margin appears straight through most of its length. Its proximal extremity shows two distinct sections, recognizable by their differently orientated peripheral rims. Te posterior section (articulated with the most anterior distal carpal; Fig. 11 View Fig ) shows a straight rim, whereas the anterior section forms a robust and smoothly convex process with an anteroventrally oblique rim. Where the two rims merge, they form an obtuse angle between them. In terms of their absolute lengths, the metacarpals are arranged in the following order: McI <McV <McII <McIII<McIV. Using McI as a reference, the lengths of McV and McII represent an increase of ~ 9.67% and ~ 13.06%, respectively, relative to the length of McI, while those of McIII and McIV are~ 36.35% and~ 37.8%, respectively. Te proximal ends of adjacent metacarpals McII-V are tightly appressed and there is no evidence that this pattern is an artefact of preservation.

Te phalanges reveal considerable morphological variation, both within and between digits ( Figs. 10 View Fig , 11 View Fig ). Combined information from both the extensor and flexor views indicates that in the first phalanx of each digit, the proximal extremity is slightly more expanded than the distal extremity. Te difference in width between the two extremities is more apparent in digits II-V. In those digits, the proximal extremity is broadly spatulate or fan-shaped, with a nearly straight or very gently convex peripheral rim and a slightly asymmetrical profile. Te distal extremity, in contrast, is subrectangular and only marginally wider than the minimum width of the shaft. Te anterior and posterior margins of those phalanges are gently concave, but their profiles differ. Tus, on digits III and V, the posterior margin is more deeply arcuate than the anterior margin. Te reverse situation characterizes the proximal phalanx of digit IV. On digit II, both margins of the proximal phalanx are gently concave and with a comparable curvature. Te first phalanx of digit I is of nearly constant thickness and shows a more robust build than the proximal phalanges of digits II–V. Its proximal extremity is only ~ 20% broader than its distal extremity. Its anteroproximal corner is slightly protruding, while its anterodistal corner is abbreviated and bluntly round. Its anterior and posterior margins appear moderately concave in their proximal one-third. Te penultimate phalanges of digits II and III also have a robust aspect ( Fig. 10 View Fig ). Tat of digit II is squat and vaguely sigmoid, with a gently concavity in the middle one-third of its anterior margin and a similar, shallow concavity along the distal half of its posterior margin. Its proximal and distal extremities are, respectively, squarish and subtrapezoidal. Te phalanx is slightly shorter than the more proximal element on the same digit. Te penultimate phalanx of digit III is subrectangular, with a straight posterior margin, and a small concavity along the distal half of its anterior margin. It is slightly longer than the more proximal phalanx in the same digit and its extremities are approximately rectangular, as preserved. Subtle morphological details of the other phalanges, particularly on digits III and IV, are best conveyed by the illustrations in Figs. 10 View Fig and 11 View Fig .

Te slender digits terminate in short, sturdy, and claw-like unguals, visible on digits I-IV in extensor view

( Fig. 10 View Fig ). In flexor view ( Fig. 11 View Fig ), only the tip of the ungual on digit V is visible. Te rest of this ungual is partly concealed underneath the first and second phalanges of digit IV. As preserved, the unguals are about half the length of the next most distal phalanx ( Fig. 10 View Fig ). Tey show an asymmetric profile, presumably indicating that they lie on the plane of mediolateral flattening. Teir length (distance from their apex to their proximodorsal part, the latter approximately coinciding with the base of the extensor tubercle; see Mann et al., 2021) increases imperceptibly from the first to the third ungual, then decreases slightly from the third to the fourth. Te unguals on digits I and II are robust, due to the occurrence of a well-developed flexor tubercle (proximoventral part of the ungual) forming a sturdy, gently convex eminence on the second ungual, but reduced to a small process on the first. Both the first and second ungual terminate in a thick, beak-like extremity. Te third and fourth unguals are vaguely talon-shaped and feature smoothly curved dorsal (convex) and ventral (concave) margins, although their distal tips are not markedly hooked (e.g., see Mann et al., 2021). Only the tip of the fifth ungual is visible in flexor view ( Fig. 11 View Fig ). Its curvature resembles that of the third and fourth unguals, as far as we can tell.

Te construction of the manus in Brouffia has few analogues among early reptiles. In a quick literature survey, we identified some general similarities with the Early Permian captorhinid Romeria prima (see Clark & Carroll, 1973, fig. 10), e.g., in the shape and proportions of McI (although this shows a comparatively shorter shaft in R. prima ), the robust aspect of the first phalanx of digit I (slightly longer than McI and with a narrower, more demarcated waist in R. prima ), and the sturdy unguals on digits I and II (but with a less pronounced curvature of the distal extremity in R. prima ). Te functional and/or phylogenetic implications of these traits are presently uncertain (see main text for a brief consideration of the lifestyle of Brouffia ). Te well-ossified wrist shows no fewer than seven carpals. In flexor view

( Fig. 11 View Fig ), three large proximal carpals may be identified as the radiale, intermedium, and ulnare. More distally, four smaller bones occur, but their exact spatial arrangement is unclear. In extensor view, a single large carpal, presumably the ulnare, and five smaller carpals are visible ( Fig. 10 View Fig ). It is likely that the full complement of centrals and distal carpals is present, although in a slightly disrupted arrangement. Te phalangeal count is probably 2-3-4-5?-3, the generalized condition for early amniotes.

Pelvic girdle

Te pelvic girdle is disarticulated. Its constituent elements are unfused, presumably indicating immaturity

( Figs. 10 View Fig , 11 View Fig ). As in the case of the pectoral girdle, the individual pelvic elements are preserved as flat bony plates with little surface detail. Te stout ilium carries a single, short, and sturdy rectangular process directed posteriorly. Te neck of the ilium is robust, with a nearly straight anterior margin and a smoothly concave posterior margin and is inclined posteriorly at about 45˚. Where the anterior margin of the neck terminates dorsally, it joins the dorsal margin of the posterior process at an obtuse angle. Te acetabulum has an asymmetric, subparabolic profile with a longer and gently sigmoid anterior margin and a shorter and ‘stepped’ posterior margin. Te ischium is a broad plate resembling a quarter of a crescent in outline. It is deepest at its anterior extremity, which terminates in a smoothly convex anterior margin. Its posterior extremity forms a blunt and subtriangular process. Te pubis is a round plate, again without obvious surface features.

Hindlimb

Te right hind-limb is almost complete, but exhibits little anatomical detail ( Figs. 10 View Fig , 11 View Fig ). Te femur is 17 mm long, only slightly longer than the humerus but somewhat more robust through the shaft. Te proximal articulation is flat and strap-shaped, and there is little indication of an intertrochanteric fossa on the ventral surface. A narrow adductor crest is discernible. It extends from the proximal articulation almost to the distal articulations. Little can be seen of the distal articulation surface. Te posterior condylar prominence appears to be folded over to a small extent.

Te tibia and fibula are both similar in size and of comparable length to the radius and ulna. Te tibia has a much wider proximal extremity than the fibula, terminates in a narrower, slightly flared distal end, and exhibits a nearly straight anterior margin and a gently arcuate posterior margin, attaining its greatest curvature along its proximal half. Te peripheral rim of the proximal extremity consists of a shorter anterior section and a longer posterior section at an obtuse angle relative to one another. Te fibula is rod-shaped and shows a subrectangular proximal extremity and a slightly more expanded, spatulate distal extremity than the tibia. Its anterior margin has a similar curvature to that of the posterior margin of the tibia, except that its greatest curvature occurs distally. Te posterior margin of the fibula is nearly straight.

Some anatomical details are available for the pes, permitting a slightly more complete description than in previous works. Te remains of a few tarsals and the entire first digit are preserved on the slab where the specimen is orientated in dorsal view ( Fig. 10 View Fig ). Two large tarsals, presumably astragalus and calcaneus, are present, one in articulation, the other in the form of a poorly ossified bony mass occurring some distance from the distal end of the tibia and visible on both part and counterpart ( Figs. 10 View Fig , 11 View Fig ). Based upon its proximity to the tibia, this bony mass may represent a remnant of the astragalus. Although poorly ossified, it has a roughly pentagonal shape. Tere is no indication that it originates from the fusion of multiple ossification centres. While the juvenile condition of Brouffia would lead us to expect sutures (or traces of sutures) to occur in the astragalus if the latter did indeed originate from multiple ossifications, its poor preservation and the precocious ossification of the tarsals and carpals relative to the rest of the skeleton suggest caution in drawing a conclusion either way.

Only the first pedal digit is preserved ( Fig. 10 View Fig ). It is somewhat longer and more robust than the first digit of the manus and terminates in a stout and claw-shaped ungual. Te digit proportions are notable in that they are very different from those of stem amniotes, such as Gephyrostegus , in which an extremely shortened first pedal digit is present ( Brough & Brough, 1967).

Scales

Te ventral surface of the vertebrae is obscured by impressions of numerous ventral scales (gastralia)

( Fig. 12 View Fig ). Te ventral scales are flat, subrectangular plates with thick lateral margins, and are arranged in posterolaterally orientated rows. According to Brough & Brough (1967), there are two types of scales. Te first and larger type, described by them as being ‘oat-shaped’, includes scales that are approximately three times longer than wide and with a weakly pronounced ridge along one side. Te second, smaller type of scales includes ‘rhomboidal’ elements, about four times longer than wide. Tese two types of scales are not easily distinguishable, although we are able to confirm variation in size. Te impressions of some scales, particularly in the middle portion of the trunk, suggest that some of the largest elements exhibited a much higher length:width ratio than that reported by Brough & Brough (1967). Tere appears to be little scale imbrication in both anteroposterior and mediolateral directions. We have not been able to confirm Brough & Brough’s (1967) observation that the ribs cover the scales on both part and counterpart slabs, which would suggest the presence of a complete dermal armor.

Skull and loWer jaW reconstructions

We present a new reconstruction of the skull of Brouffia orientalis in dorsal ( Fig. 13 View Fig ), ventral ( Fig. 14 View Fig ), and lateral views ( Fig. 15A, B View Fig ) and of the lower jaw in lateral view ( Figs. 15C, D View Fig ). In dorsal aspect, the skull is broadly parabolic, and the anterior margin of the snout is gently curved ( Fig. 13A View Fig ). As reconstructed, its length (measured from the anterior extremity of the conjoined premaxillae to a transverse line joining the rearmost projections of the squamosals) is slightly more than twice its width (greatest distance between the jugals). Te nostrils are large and transversely elongate, and their distance is slightly less than half of the mediolateral nostril width. Te anteroposterior diameter of the orbit is a little over 30% of the total skull length. Te orbit centres are situated slightly posterior to the skull mid-length. Te distance between the posterior margins of the orbits and the rearmost projections of the squamosals is approximately 73% of the distance between the anterior margins of the orbits and the snout. Te width of the skull table (the greatest distance between the lateral margins of the parietal lappets) is a little over 57% of the total skull width.

Aside from overall skull proportions, our reconstruction ( Fig. 13A View Fig ) differs in several aspects of bone morphology from Carroll & Baird’s (1972). Details of the antorbital region of the skull are scanty or non-existent in Carroll & Baird’s (1972) reconstruction and, therefore, meaningful comparisons are not possible. In Carroll & Baird (1972), the anteromedial corner of the tabular projects slightly anterior to the anterolateral corner of the postparietal, whereas in our reconstruction the anterior margins of these two bones occur approximately at the same transverse level, except for the lateralmost tract of the anterior margin of the tabular. Tey are also slightly wider than long, and the postparietal is mediolaterally marginally narrower than the tabular ( Figs. 1 View Fig , 2 View Fig , 5 View Fig , 13A View Fig ) and with a small, spur-like posteromedial process. Te parietal lappet appears indistinct anteromedially in Carroll & Baird (1972), who illustrated the suture between the lappet and the posteromedial part of the postfrontal as being smoothly curved. In our reconstruction, the posteromedial corner of the postfrontal is narrowly triangular and sits in a deep incision of the parietal, which marks the transition between the corpus and lappet of that bone. Crucially, Carroll & Baird (1972) did not recognize the slender, long, and finger-like posterolateral process of the frontal that separates the anterolateral margin of the parietal corpus from the medial margin of the postfrontal. In Carroll & Baird (1972), the morphology of the frontal, postfrontal, and parietal on the right-hand side of the skull differs from that on the left-hand side. However, the right parietal is heavily disrupted, and we have not been able to discern its precise shape and contacts with neighbouring elements ( Figs. 1 View Fig , 2 View Fig , 5 View Fig ). For this reason, we have opted for a conservative approach in our reconstruction, such that the spatial arrangement of bones on the right-hand side of the skull mirrors that of their antimeres ( Fig. 13A View Fig ).

In lateral view ( Fig. 15A View Fig ), the skull is deepest slightly posterior to the mid-length of the orbit, as also shown by Carroll & Baird (1972). However, the course of sutures between the jugal, squamosal, and quadratojugal differs substantially between their reconstruction and our own. Te dorsal and ventral corners of the posterior portion of the jugal are smoothly round and delimit a gently embayed posterior margin ( Figs. 5 View Fig , 15A View Fig ). Carrol & Baird (1972, fig. 6A) also showed this margin in their drawing of the posterior portion of the left jugal. However, in their reconstruction of the skull in lateral aspect (Carrol & Baird, 1972, fig. 7D), the jugal features a slightly convex posterior margin. Our reconstruction also features a slenderer and strap-shaped quadratojugal than that figured in Carroll & Baird (1972) as well as a less deep squamosal and a more extensive postfrontal ( Fig. 15A View Fig ).

In ventral view ( Fig. 14A View Fig ), the pterygoids dominate the palatal surface. Together with the parasphenoid, they are the best-preserved bones of the palate. Most of the left palatine is also discernible, including the denticles covering its surface. Although the ectopterygoids are not preserved, their proportions may be estimated from the morphology of the surrounding bones. Te posteroventral portions of the premaxillae are not preserved. For this reason, the lengths of their vomerine processes are only hypothetical. Our reconstruction does not differ in any substantive way from Carroll & Baird’s (1972). Te interpterygoid vacuities are comparatively narrower in our reconstruction and taper to a lesser degree anteriorly. Teir length (from the medial ends of the basipterygoid processes to the posterior extremity of the inter-pterygoid suture) is approximately half of the distance from the basipterygoid processes to the anterior extremity of the inter-pterygoid suture. Te choanae are proportionally wider and show a more gently curved posterior margin than in Carroll & Baird (1972).

Te left lower jaw is reconstructed in external view

( Fig. 15C View Fig ). It is dorsoventrally slender and appears slightly more gracile than in Carroll & Baird’s (1972) reconstruction. A detailed comparison between their reconstruction and our own is necessarily limited, in that they showed the posterodorsal portion of the lower jaw covered by the corresponding portion of the cheek in lateral view. Lastly, although the splenial is fully visible in internal view, the length of its exposure on the external surface of the lower jaw is only estimated ( Fig. 15C View Fig ).