Maghriboselache mohamezanei, Klug & Coates & Frey & Greif & Jobbins & Pohle & Lagnaoui & Haouz & Ginter, 2023

Klug, Christian, Coates, Michael, Frey, Linda, Greif, Merle, Jobbins, Melina, Pohle, Alexander, Lagnaoui, Abdelouahed, Haouz, Wahiba Bel & Ginter, Michal, 2023, Broad snouted cladoselachian with sensory specialization at the base of modern chondrichthyans, Swiss Journal of Palaeontology (2) 142 (1), pp. 1-28 : 4-19

Maghriboselache mohamezanei sp. n.

Figures 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , Additional file 1: Figs. 1 –40.

Holotype: AA.MEM.DS.12, which preserves the 3D neurocranium, teeth, shoulder girdle, and most fins, and hence most of the relevant body parts.

Etymology: Referring to Moha Mezane (El Khraouia & Merzouga, Morocco), French linguist and amateur geologist, specialized in fossils and minerals from the southern Tafilalt. He found many important specimens including some of the material described here.

Zoobank: LSID urn:lsid:zoobank.org:act:637BB65B-A77F-45DB-BCE2-383C66C46F82 .

Age: Tylacocephalan Layer, late early to early middle Famennian, Late Devonian.

Type locality: Mousgar (30°46`557``N, 4°41`257``W), southern Maïder, southeastern Anti-Atlas, Morocco (see material).

Material: Bid er Ras: PIMUZ A/I 5156, 30°45`606``N, 4°55`637``W; Mousgar : AA.MEM.DS.8, AA.MEM. DS.12, 30°46`557``N, 4°41`257``W, Tizi n`Aarrat: PIMUZ A/I 5160, Oufatene: PIMUZ A/I 5153, 30°47`057``N, 4°53`476``W, Madene: PIMUZ A/I 5152, 30°45`056``N, 4°42`829``W; PIMUZ A/I 5155, 5159, 30°43`235``N, 4°43`568``W; PIMUZ A/I, Jebel Aoufilal: PIMUZ A/I 5158, N30°56 ′ 25.2 ″, W4°01 ′ 14.9 ″. Most remains were found in the early/middle Famennian Tylacocephalan Layer. A complete list is provided in Additional file 1: Table S 1 .

Diagnosis: As for genus.

Description

Body form: Estimated in-life lengths of individuals available for study range between 0.8 and 2.5 m (based on proportions measured in the more or less complete specimens AA.MEM.DS.12, AA.MEM.DS.6, PIMUZ A/I 5153 and AA.BER.DS.01; Fig. 1 ), with the majority being slightly over one meter long ( Figs. 1 , 2 ). Te head, exclusive of the gill region, is rather short compared to, e.g., Akmonistion, and has a triangular appearance when flattened; in this respect, the material resembles the Cleveland Shale skeletons of Cladoselache . Te first dorsal fin spine is present in about half of those specimens preserving more than the head (PIMUZ A/I 5153, 5154, 5158, AA.BER.DS.01). Tis might suggest a sexual dimorphism like that proposed for certain Carboniferous chondrichthyans ( Lund, 1985), but we cannot be certain in the absence of clasper preservation.

Neurocranium Te neurocranium ( Figs. 3 , 4 , 5 , 6 ) is known from two specimens: AA.MEM.DS.12 ( Figs. 1 , 4 , 6 ; see also Additional file 1: Figs. S3 , S 4 ) and PIMUZ A/I 5159 ( Figs. 3 , 5 ; see also Additional file 1: Figs. S 38, S41). PIMUZ A/I 5159 exhibits a three-dimensionally preserved neurocranium measuring a total of 166.8 mm in length. Te nasal capsules and postorbital processes of AA.MEM.DS.12 are incomplete, but the specimen contains a cast of the cranial cavity that reveals exquisite anatomical detail ( Fig. 6 ) . PIMUZ A/I 5159 ( Figs. 3 , 5 ; see also Additional file 1: Fig. S 41) is smaller, 105 mm long and 81 mm wide, and includes a broad ethmoid cartilage enclosing widely separated nasal capsules flanking an internasal plate. Te postorbital wall and process is similarly complete, and the otico-occipital region is preserved in articulation with hyoid and mandibular arches as well as scattered gill arch cartilages. CT-scans of PIMUZ A/I 5159 are less contrasted (Additional file 1: Figs. S 29–S32, S35) than those of AA.MEM.DS.12 .

Te general shape and proportions of the neurocranium display a previously unknown combination of features: a symmoriiform core, cf. Dwykaselachus (Coates et al., 2017) , but with ethmoid and postorbital extremities almost meeting ventrally. Tis near-enclosure of the orbit in a cartilage ring is otherwise known only in the New Brunswick Doliodus ( Maisey et al., 2009) , a genus of interest because of the light it might shed on conditions close to the chondrichthyan crown node (Coates et al., 2017; Maisey et al. 2018). In lateral view, PIMUZ A/I 5159 is wedge-shaped ( Fig. 3C ), except for the bulging nasal chambers and near-circular orbits. Around one third of orbit diameter projects ventrally relative to neurocranial (ventral) midline ( Figs. 3–5 , Additional file 1: Figs. S29-S32, S35). In contrast, AA.MEM.DS.12

( Fig. 4C ) displays orbits with an oval outline, but this results from corrosion of its venter (including the postorbital processes) as well as a possible slight dorsoventral compression (not visible in the endocast).

Te ethmoid region is exceptionally broad and walled externally with cartilage. Uniquely among early chondrichthyans, the snout is the widest part of the neurocranium; wider than the total span of the postorbital processes ( Figs. 3A , 4B , 5D, G ). A large precerebral fontanelle is present (visible in photographs of PIMUZ A/I 5159 but absent from CT rendering; fontanelle margins damaged in AA.MEM.DS.12: Figs. 3A , 4B ), and extends posteriorly to the anterior level of the orbits. Nasal capsules are large, but capsule details are poorly resolved. Nostrils appear to be subterminal: a notch and depression on the right side of the PIMUZ A/I 5159 snout marks a plausible location ( Figs. 3A, F , 5C, D, G ). Furthermore, these nasal capsules appear to be anteriorly enclosed (except for narial apertures), quite unlike the anterolaterally directed cartilage cups present in other early chondrichthyans. Te subnasal space identified in Dwykaselachus and other symmoriiforms (Coates et al., 2017) seems to be absent.

Te rear wall of the ethmoid complex, anterior wall of the orbit, is strongly concave, thinning and extending posteriorly around the ventrolateral rim of the orbit

( Figs. 4D , 5D ). As in the New Brunswick Doliodus ( Maisey et al., 2009) , this cartilage resembles a neoselachian ectethmoid process (although homology is doubtful: these structures are very likely independently derived— see Maisey 1983 for comparison of this process in Egertonodus and Chlamydoselachus ) and terminates as a prong directed towards the tip of the postorbital process. Tus, like the New Brunswick Doliodus , the orbit is almost completely ringed in cartilage ( Figs. 4B , 5D ). Te ventral surface of the snout includes a distinct internasal plate, the lateral extremities of which project ventrolaterally, forming grooved attachment surfaces for the palatoquadrate (the orbital/ ethmoid articulation). Te form of the grooved surface closely resembles examples in symmoriiforms (Coates & Sequeira, 2001; Coates et al., 2017) and Cladodoides ( Maisey, 2005) .

Te orbits are not especially large and, in dorsal view, the roof of each is deeply embayed. Te supraorbital shelf is evidently much narrower than in Cladoselache (Harris 1938b; Maisey, 2007), Akmonistion (Coates & Sequeira, 2001), and Dwykaselachus (Coates et al., 2017) . Details within the orbit, observed in lateral aspect, are mostly obtained from specimen AA.MEM.DS.12 ( Fig. 4 ). A broad antotic pila divides a large optic nerve foramen from a prootic fenestra ( Fig. 4C ). In Pucapampella and Gydoselache ( Maisey et al., 2018), the pila support an optic pedicel (eye stalk) but no pedicel is evident in Maghriboselache . Te posteromedial recess of the orbit includes the exit of branches of the facial nerve (VII), preserved in detail in AA.MEM.DS.12 ( Fig. 4C ). Tere is no interorbital septum: unlike Dwykaselachus and other symmoriiforms, the medial wall of each orbit is separated widely from its counterpart. Te deeply concave surface of the postorbital wall is pierced by a circular foramen for the jugular (lateral head) vein close to the anteriormost portion of the otic wall; the foramen is strikingly similar to the same feature in Dwykaselachus . A suborbital shelf is present ( Fig. 4D ): narrow but slightly broader than the minimal examples in other symmoriiforms. Te efferent pseudobranchial foramen is marked by a slight dimple evident in rendered scans, located level with the optic nerve foramen.

Te postorbital process and wall (or arcade) of PIMUZ A/I 5159, although worn away both laterally and dorsally, is notably short in lateral extent ( Fig. 5D ) and quite unlike the slender, laterally elongate, examples in other symmoriiforms including Cladoselache ( Maisey, 2007: Figs. 58, 59, 61). In Maghriboselache , this robust, anteriorly concave process extends ventrally to rim the orbit floor, ultimately approaching the ‘ectethmoid’ process (as noted above). Once again, a similar process is present in the New Brunswick Doliodus ( Pradel et al., 2009) , and a further example might be found in Gladbachus (Coates et al., 2018) , which also appears to contribute to the orbit margin and floor. Te posterior wall of the process in Maghriboselache resembles those of Cladodoides and Dwykaselachus , bearing a gently angled ridge and groove for articulation with the palatoquadrate.

Unlike the ethmosphenoid, the otico-occipital division conforms closely to that of Dwykaselachus , resembling a low-resolution copy of standard symmoriiform shape. Te dorsal otic ridge ascends posteriorly to peak at a median, short rounded endolymphatic duct opening ( Figs. 4A–C , 5A–D ). Te lateral otic ridge, in this instance lacking a periotic process, broadens posteriorly to surround the posterior ampulla of the otic labyrinth. Tere is no lateral otic process cf. Tamiobatis ( Schaeffer, 1981) : the cartilage wall of the otic region simply bulges where it forms a broad convexity that encloses the posterior ampulla. Te occipital arch is short and embedded in the rear of the cranium; presence of an occipital fissure is evident from the endocast ( Fig. 6B ). Dorsal and ventral paroccipital processes are present, bracketing the cotylus.

Te ventral surface is poorly preserved posteriorly in PIMUZ A/I 5159 and AA.MEM.DS.12. Te likely division of the lateral dorsal aortae anterior to the occiput is inferred from a mid-line depression in the rendering of PIMUZ A/I 5159. Directly posterior to the level of the postorbital process, the basicranium exhibits the characteristic waist of symmoriiforms. Level with the posterior of this restriction, the basicranium shows a large, laterally directed foramen ( Fig. 4D ) marking the likely emergence of a lateral dorsal aorta and union with the efferent hyoid artery (cf. Dwykaselachus in Coates et al., 2017; “ Cobelodus ” in Maisey, 2007). Just anterior to the base of the postorbital processes, a simple, midline, basicranial fenestra marks the buccohypophyseal foramen ( Fig. 4D ).

Endocast. Tis description is largely based on AA.MEM.DS.12 ( Fig. 6 ) with additions from PIMUZ A/I 5159. Te overall appearance ( Fig. 6 ) of the endocast resembles Cladodoides ( Maisey, 2005) , with a broad endocranial space running from anterior to posterior extremities. Te nasal chambers ( Fig. 6B–D ) are similarly proportioned to those of Dwykaselachus (Coates et al., 2017) but with greater separation across the midline contributing to the exceptional width of the entire ethmoid region. Tere is no extreme narrowing of the space for the telencephalon between the orbits. Mesencephalon and vestibulolateral chambers are marked only by modest lateral expansions of the pre-otic region ( Fig. 6D ). Te transition between telencephalon and mesencephalon spaces lacks any distinct boundary; the endocranial roof rises gently, lacking the almost step-like rise evident in Dwykaselachus . Te mesencephalon chamber is proportionally broader than in Cladodoides , and both dorsal and lateral views show a shallow constriction ( Fig. 6B, C ) preceding the domed vestibulolateral chamber seated between the anterior semicircular canals.

Symmoriiform endocasts described thus far show a marked elevation of the endocranial floor reflecting the angle and extent of the dorsum sellae posterior to the hypophyseal space. In Maghriboselache , although steeper than in Cladodoides , the angle of inclination is much less than in Dwykaselachus . Similarly, the roof of the hindbrain-midbrain chamber junction is lower than the height of the otic labyrinth in Cladodoides , slightly higher in Maghriboselache , and considerably higher in Dwykaselachus , in which the bulk of the vestibulolateral chamber is nested above the anterior semi-circular canals. Little is known of the hindbrain region, sandwiched between the otic capsules. An occipital fissure persists, arched anteriorly between the posterior semi-circular canals ( Fig. 6B ). Te occipital division of the braincase is short, barely projecting beyond the posterior limit of the otic capsule and including three spino-occipital nerve foramena (unlike five in Dwykaselachus ).

Te otic labyrinth ( Fig. 6B–E ) conforms closely to the pattern present in Dwykaselachus and ‘ Cobelodus’ / Ozarcus except in one key respect: the anterior ampulla is ventral to the level of the external ampulla as in Cladodoides and outgroups ( Schaeffer, 1981). In symmoriiforms and extant holocephalans, the anterior ampullae is level with or the slightly dorsal to the external ampulla. Te endolymphatic duct of Maghriboselache is entirely separate from the occipital fissure and projects vertically level with the crus commune, in this regard consistent with Dwykaselachus and ‘ Cobelodus’ / Ozarcus . Ventral to the external semicircular canal, the saccular chamber is visible, with the glossopharyngeal canal extending along its ventrolateral margins. Unlike Cladodoides , endocasts of specimen AA.MEM.DS.12, Dwykaselachus and Cobelodus’ / Ozarcus show no distinct pipe (in-fill) for the exit of the vagus nerve.

Te ventral side of the endocast of AA.MEM.DS.12

( Fig. 6D ) preserves imprints of chambers and ducts for several cranial nerves and blood vessels. Te exit of the optic nerve (II) is positioned ventral to the posterior part of the telencephalon. Directly ventral to this, an infilled forked channel marks the likely entry for the efferent pseudobranchial artery. Te hypophyseal chamber includes the foramen for the pituitary vein. Ventrolateral to the vestibulolateral chamber, the openings for the paired facial nerve (VII) are present. Te anterior palatine branch of the facial nerve projects anteriorly, the posterior palatine branch extends posteroventrally, and the hyoid ramus extends posterodorsally.

Mandibular and hyoid arches. In PIMUZ A/I 5159, mandibular and hyoid arches are nearly complete and articulated ( Figs. 3 , 5 , Additional file 1: Fig. S30, S33, S34). Notably, the jaws are much shorter relative to the neurocranium than in Akmonistion (Coates & Sequeira, 2001), Ozarcus ( Pradel et al., 2014) , and Ferromirum (Frey et al., 2020a, b), where the jaw joint is offset posteriorly, well behind the occiput. Te palatoquadrate exhibits the cleaver shape ( Schaeffer, 1975), which is characteristic of many early chondrichthyans; it has an otic process some 40% of total jaw length ( Fig. 5B, D, E ). Te otic process is both concave laterally, forming a deep space to house adductor muscles, and concave anteriorly where it articulates with the postorbital process rear wall. Te anterior, palatine, ramus is dorsoventrally flattened and gently concave dorsally where it contributes to the orbit floor (Additional file 1: Fig. S33). Te medial rim of the ramus ethmoid extremity bears, ventrally, a short sequence of three transverse ridges with intervening grooves where it engages with the orbital/ethmoid articulation (correspondingly corrugated) of the neurocranium. Te labial margin of the ramus is gently scalloped on the ventral surface to form a dental platform with spaces for at least eight tooth families (estimated from the number of depressions in the scalloped margin). Palatoquadrate proportions resemble the flattened specimen of Cladoselache kepleri figured by Harris (Harris, 1938) but differ from the Tennessee cladoselachian ( Maisey, 1989) in which the otic process is only 30% of total length with perhaps a dozen tooth families per jaw ramus. Maisey (1989) argued that cladoselachians lack a condylar jaw joint, but Maghriboselache displays, laterally, a ventrally prominent quadrate condyle and mesially a concavity to receive the mandibular knob (Additional file 1: Fig. S33). Te jaw articulation is not as well preserved as that of Ferromirum (Frey et al., 2020a, b), but appears to have been quite similar, thus it might well have driven the mesio-lateral mandibular rotation described by Frey et al., (2020a, b).

In ventral aspect, the body of Meckel’s cartilage ( Figs. 3 , 5 , Additional file 1: Fig. S33) exhibits a gradual anteromesial curvature towards the symphysis, but in dorsal view, the tooth-bearing platform is straighter, curving mostly in the parasymphysial region. Te tooth platform is gently scalloped; there is no continuous dental groove (Additional file 1: Fig. S33E to G). A rounded ventrolateral ridge delimits a shallow adductor fossa on the lateral surface, the fossa extending for almost 60% of mandible length. Te jaw articulation resembles Ferromirum (Frey et al., 2020a, b) with the quadrate condyle articulating with a well-formed outer (lateral) glenoid posterior and lateral to the mandibular knob ( Figs. 3 , 5 , Additional file 1: Figs. S30, S33). Tus, both primary and secondary components of the jaw joint are present. Te mandibular symphysis, although shallow, is deeper than that of Ferromirum (Frey et al., 2020a, b), and flexibility was possibly reduced by the presence of large symphyseal teeth in the lower jaw.

Te hyoid arch, like that of Ozarcus ( Pradel et al., 2014) , includes hyomandibula, ceratohyal, and hypohyal (Additional file 1: Fig. S33). In Maghriboselache the hyomandibula is gently curved, anteriorly expanded, and~ 50% of ceratohyal length. Te ceratohyal is slender, broader and slightly flattened anteriorly, but without the posterolateral flange present in Ferromirum (Frey et al., 2020a, b). Te lateral fossa is similarly developed as in Ferromirum (Additional file 1: Fig. S34). Te hypohyal is a simple rod, around 20% of ceratohyal length. Maisey (1989) debated the possible presence of an interhyal in cladoselachians; PIMUZ A/I 5159 corroborates his conclusion that none is present.

Dentition. Te dentition is partially visible in several specimens, including PIMUZ A/I 5160, 5161 and PIMUZ A/I 5154 ( Fig. 7 ). Generative tooth sets are spaced nearly equidistantly along Meckel`s cartilage, with a gap of about 10% of tooth base width between each set (Additional file 1: Fig. S37, S38, S39). Palatoquadrate tooth sets are positioned to oppose those on Meckel’s cartilage. PIMUZ A/I 5162 and AA.TJR.DS.1 show 11 sets per jaw ramus with a distinctive symphyseal set (Additional file 1: Figs. S38, S39), about twice the linear dimensions of teeth in adjacent sets (PIMUZ A/I 5159), capping the mandible. A symphyseal tooth set is reported present in Cladoselache , but without the enlarged size relative to the rest of the dentition ( Jacquemin et al., 2020; Williams, 2001). Te dentition is “cladodont” ( Fig. 7 ): each tooth has a large, finely striated, gently sigmoidal main cusp with one to three pairs of smaller lateral cusps (the outermost being the largest). Tere appears to be ontogenetic variation in lateral cusp number. As in Cladoselache and non-symmoriiform cladodonts, crown material appears to be continuous between cusps ( Fig. 7C ). Notably, each tooth base includes a deep basolabial depression with adjacent projections, recognized by Ginter et al. (Ginter et al., 2010, p. 58) as the outstanding characteristic of Cladoselache teeth. In articulated tooth sets, this depression brackets the main cusp of the preceding (ontogenetically older) tooth. Te orolingual surface of the tooth base bears two rounded buttons ( Fig. 7C, D ). Tis surface in Cladoselache is unknown, but symmoriiforms usually bear a single button (Coates & Sequeira, 2001; Ginter et al., 2010; Zangerl, 1990).

Branchial skeleton. Where the branchial arch cartilages are present and preserved, they are mostly exposed in ventral view revealing ceratobranchials and what might be a small, lanceolate, copula (Additional file 1: Fig. S2 , S 11 , S28). Other, smaller, branchial cartilages are preserved, but in all specimens with branchial skeletons the components are jumbled and/or compacted, prohibiting a full reconstruction. PIMUZ A/I 5155 exhibits four to five pairs of ceratobranchials arranged in an anteromedial to posterolateral direction, extending 56 mm posterior to occipital level (measured at the midline); individual ceratobranchial lengths range from 65 to 73 mm. In contrast, the ceratobranchials of PIMUZ A/I 5152 extend some 155 mm beyond the braincase, and a likely copula measures 93 mm long and 40 mm wide.

Vertebral Column. PIMUZ A/I 5156 and 5153 preserve 30 to 40 pre-caudal neural arches (Additional file 1: Fig. S21) in original position, distributed above the likely path of an unconstricted notochord: there are no traces of centra. As in Akmonistion (Coates & Sequeira, 2001) axial regionalization is evident, especially so in PIMUZ A/I 5156. Te cervical region (preceding the pectoral girdle) is the most poorly preserved. Where visible, the neural arches are anteroposteriorly broad: at least ten members are evident. Neural arches become leaner and longer in the thoracic region (see also Cobelodus, Zangerl & Case, 1976 ), but preservation is insufficient to describe finer details of the regional transition. In general, trunk neural arches are slender and tightly packed between their anterior and posterior neighbors. All arches lean posteriorly. Te peduncular, pre-caudal, region extends posteriorly from the level of the pelvic girdle to the anterior boundary of the tail. Not as well preserved as the trunk neural arches, these arches are thinner, inclined more posteriorly, and decrease in size towards the tail.

Pectoral girdle and fins. As in Cladoselache (Bendix-Almgreen, 1975; Dean, 1909a; Tomita, 2015), the pectoral girdle and fins are large and well developed. Te scapulocoracoids ( Fig. 8A–E ) are best preserved in PIMUZ A/I 5155 (146 mm long from anteroventral to dorsal extremities), PIMUZ A/I 5152 (194 mm long) and PIMUZ A/I 5158 (104 mm). However, like most Paleozoic chondrichthyan specimens, these cartilages are flattened and distorted, although those of Maghriboselache are more robust than other symmoriiform examples (Additional file 1: Fig. S48). Te distinctively shaped scapular process approximates to a right-angled triangle, the posterior edge of which (the hypotenuse) is slightly convex. A deep embayment in the posterior margin divides the bulk of the process from the articular region. Te process forming the posteroventral extremity of the scapular region (or posterodorsal angle of the embayment) might be the homologue of the posterior process present in other symmoriiforms pectoral girdles, but here present in an unusually ventral location. A small diazonal foramen is located dorsal to the horizontal articular crest, which projects posteriorly to terminate as a condyle for the metapterygial plate ( Fig. 8E ). Te coracoid region is less well preserved than the scapular process but appears to project ventro-medially for a substantial distance. A small, separate, L-shaped procoracoid cartilage is present, well-preserved in PIMUZ A/I 5156.

Te pectoral fin is known from five specimens ( Figs. 8 , 9 , Additional file 1: Fig. S49). Te overall shape is strikingly like that of Cladoselache , resembling an elliptical wing with a strongly convex leading edge. Around fifteen or sixteen pre-metapterygial radials largely fill the fin envelope ( Figs. 8A–D , 9D ), with a distal fringe of ceratotrichia contributing to the trailing edge (Additional file 1: Fig. S23). Excluding the first three or four unsegmented members, each radial consists of a short proximal and much longer distal segment. Te proximal segments are cylindrical, but the distal segment, although cylindrical proximally, broadens and flattens distally into a strap-like form ( Fig. 8D ) also evident in Cladoselache (Bendix-Almgreen, 1975; Tomita, 2015) and Fadenia ( Zangerl, 1981) . In PIMUZ A/I 5156 (Additional file 1: Fig. S22) and PIMUZ A/I 5154 (Additional file 1: Fig. S13 ), there appear to be additional articulations within the single rays, indicating the presence of intercalated segments. Te metapterygium (preserved in PIMUZ A/I 5158) is small and bears three facets for radials and a distal articulation for a presumably short, trailing whip

( Fig. 8 , Additional file 1: Fig. S28). Te articulation surface with the scapulocoracoid is a shallow concavity. Unlike Cladoselache ( Tomita, 2015) , there are likely segments of a metapterygial whip, around six pieces in total. Where the pectoral fin skin is preserved (PIMUZ A/I 5154), dermal denticle size changes from larger (0.8 mm) to smaller (c. 0.4 mm) distal denticles with polygonal outline.

Pelvic girdle and fins. Te pelvic girdle is preserved in several specimens (AA.MEM.DS.12, PIMUZ A/I 5155, 5156, 5158). Each half (left and right) consists of a fanshaped, or subtriangular, plate ( Fig. 8F–I ). In many reconstructions of similar pelves, the narrow process of such plates is restored directed dorsally. It seems more likely that this process was directed medially and horizontally towards its counterpart, contributing to a divided pelvic bar (as suggested by the dorsoventrally flattened remains of PIMUZ A/I 5155. In this orientation the distal, broadest side of the plate, serving as articular surface for the pelvic fin, is directed more-or-less laterally, like the articular crest for the pectoral fin.

In PIMUZ A/I 5155 and 5158, a few short, rod-shaped proximal radials articulate to the pelvic girdle; in PIMUZ A/I 5153, the total reaches 10. Proximal segments are short and cylindrical and distal segments are long and slender, tapering distally. Anterior and posterior radials are the shortest with length increasing gradually towards the midpoint of the fin. No trace of pelvic clasper has been found.

Caudal fin. Te caudal fin is known from specimens AA.MEM.DS.12, PIMUZ A/I 5152, 5153 and AA.BER. DS.01 ( Fig. 8J–M ). None of these preserves a complete articulated tail. Te restoration is modelled after Akmonistion (Coates & Sequeira, 2001) rather than Cladoselache ( Zangerl, 1981) because individual parts display proportions resembling those of the former rather than the latter example.

Specimen AA.BER.DS.01 ( Fig. 8M ) includes a caudal skeleton with six to eight neural arches or spines in the upturned chordal, dorsal lobe, and eleven or more elongate hypochordal radials in the ventral lobe. Te angle between dorsal and ventral lobe axes exceeds 90 degrees, consistent with a caudal fin outline resembling that of Akmonistion, and the high aspect ratio tails of symmoriiforms and edestids in general. Te neural arch/ spine and supraneural cartilages are broad (three examples preserved in AA.MEM.DS.6) but not as broad as those of Cladoselache . A scatter of subjacent cartilages might be the remains of dorsal lobe hypochordal arches and spines. A scattering of short proximal radials and hypochordal arches lie proximal to the elongate radials of the ventral lobe. Some of these have the characteristic elbow-shape of those situated directly beneath point of notochordal upturn in Akmonistion (Coates & Sequeira, 2001) and Cobelodus ( Zangerl & Case, 1976) . In AA.MEM.DS.12 a dorsal, oval to subrectangular supraneural structure some 50 mm long and 17 mm wide lies directly anterior to the dorsal lobe. A similarly position cartilage in the most complete specimen of Akmonistion (Coates & Sequeira, 2001: Fig. 9A ) is a displaced radial. In AA.MEM.DS.12, the item appears to be part of the caudal axial skeleton.

Dorsal fin spines and fins. Te anterior dorsal fin spine is known mostly from a natural mold in PIMUZ A/I 5154 ( Fig. 10 ); spine fragments are present in PIMUZ A/I 5153, 5157 and 5158. Te general shape resembles spines-forms Ctenacanthus major and C. varians ( Maisey, 1981) : stout, broad-based, and curved posteriorly. As in other spine-bearing symmoriiforms, surface ornament is absent but the mold suggests presence of an anterior keel. Furthermore, at least four well-formed, non-overlapping denticles are present on the trailing edge close to the spine apex ( Fig. 10B ). Te spine base is in poor condition, but it appears that it was inserted at an angle of about 50° to the dorsum. Longitudinal striations marking the spine base are probably weathering artefacts or remains of internal structures rather than ornament. Te cast surface in PIMUZ A/I 5154 shows fine details of blood vessel imprints ( Fig. 10D ). Tese originate near the trailing edge (0.1 to 0.2 mm thick) and finely branch anteriorly (ca. 0.01 mm wide), entering the fin spine behind the putative keel. Tis suggests that in life much of the spine was covered by living tissue.

Te posterior dorsal fin spine is preserved in AA.MEM. DS.12, AA.MEM.DS.6 and AA.BER.DS.01 (Additional file 1: Figs. S19, S24). Te spine is squat and approximately one third of first dorsal fin spine height. Te most complete specimen AA.BER.DS.01 is preserved with the leading edge uppermost (Additional file 1: Fig. S19). Te course textured surface shows no ornament and no anterior keel; denticles presence is unknown.

Presence of an anterior dorsal fin is uncertain ( Fig. 11 ). No radials are preserved; hence this fin is likely absent in specimens lacking an anterior dorsal spine. Fin evidence is limited to the shape of basal cartilage associated with the fin spine. Te partially preserved basal cartilage in PIMUZ A/I 5158 articulates with the entire fin spine base (Additional file 1: Fig. S28). Visible over a length of about 33 mm, the cartilage ventral, dorsal and anterior edges are covered by phosphatized musculature; thus, the outline is obscured. It appears to be subrectangular, elongate, and projects for about a third of its length posterior to the fin spine. Tis suggests service as fin support as well as spine support.

Te posterior dorsal fin is preserved in most of the skeletons; in some positioned nearly vertically or obliquely relative to the bedding plane (AA.MEM.DS.12, PIMUZ A/I 5155, 5156; Fig. 1 , Additional file 1: Figs. S1 , S 7–S 9 , S26). Te fin has a conventionally rounded outline with a steeper leading edge and more gradually inclined, convex, trailing edge. AA.MEM.DS.12 preserves 19 radials and PIMUZ A/I 5156 at least 16, with 8 + contributing to the leading edge. Radials are divided into proximal (short) and distal (long) segments, with the single intraradial articulations more-or-less aligned with the level of the body outline. A broad basal cartilage supporting the diminutive fin spine articulates with at least the anteriormost 10 radials. Tere is no evidence of a delta-shaped cartilage (cf. the ‘V’-shaped element noted by Zangerl and Case (1976).

Scales. Te integument bears small individual ‘polyodontode’ ( Ørvig, 1977) scales, approximately 0.3 mm wide to 0.8 mm long ( Figs. 9C , 12 , Additional file 1: Fig. S16.—PIMUZ A/I 5156). Scale crowns are mostly flattened with two to four longitudinal striations on the external surface. Some crowns are not completely flat, but with a convex surface.

Specialized lateral line scales are present ( Fig. 12 ). Tese scales are neither crescent- nor ring-shaped, as in fossil taxa such as Akmonistion (Coates & Sequeira, 2001) and Orestiacanthus ( Lund, 1984) , and extant holocephalans. In contrast, the scales have more angular bases combining in pairs to form the lateral line groove. Te scale crowns (single pointed cusps) are oriented away from the groove, directed dorsally or ventrally.

Soft tissues. Soft tissue-remains are frequently preserved (Additional file 1: Figs. S9 , S 14 , S20, S26 to S28). Muscle fibers can be seen in several specimens. PIMUZ A/I 5156 preserves still distinguishable V-shaped myomeres and collagenous myosepta (Additional file 1: Figs. S20, S26–S28). Tese haematized muscle tissues (Frey et al., 2019, 2020a, b) appear as elongated black rolls with fine longitudinal striations. Consequently, the body outline is discernible in most specimens ( Fig. 1 ). In specimen PIMUZ A/I 5153, the posterior tip of one lobe of the liver is preserved in a position just anterior to the pelvic fins. In PIMUZ A/I 5155, the stomach contains a more or less articulated small actinopterygian (40 mm long).

Phylogenetic analysis

Bayesian tip-dated analyses were performed in BEAST 2.6.3 (Bouckaert et al., 2019) with a data matrix developed from Coates et al., (2017, 2018), Dearden et al. (2019) and Frey et al., (2020a, b). Te Nexus- files are available as Additional files 7, 8, 9 and 10. We added characters capturing body proportions (see Additional files 2 to 6) as well as some tooth characters used by Hodnett et al. (2021). Accordingly, we ran separate analyses with between 230 ( Fig. 13 ; details see Additional file 1) and 238 characters, respectively. Te results of both analyses using 230 and 238 characters recovered Maghriboselache mohamezanei as sister taxon of Cladoselache ( Fig. 13 , Additional file 1: Figs. S41, S42). In the analysis of the 230-character matrix, this clade was recovered as sister group to all other total-group holocephalans ( Fig. 13 ). Te analysis using the 238-character matrix resulted in Maghriboselache and Cladoselache as sister group to symmoriids, with holocephalans as sister group to symoriids and cladoselachiids (Additional file 1: Fig. S42). Cladoselache and Maghriboselache share the distinctive tooth morphology and the shape of the central and posterior part of the neurocranium. Te known neurocrania of Cladoselache are mostly flattened, usually with poor detail of the ethmoid region ( Maisey, 2007: Fig. 60, CMNH 5611). However, Dean (1909b: pl. 288) figured a specimen displaying the narrow V-shaped arrangement of the lower jaw and the broad nasal capsule of the neurocranium in a flattened state. Maghriboselache has a broad anterior rim of the internasal plate and nasal chambers. Te two genera share the large paired fins with a similar outline, but relative to body size, the pectoral fins are bigger in Cladoselache . In both genera and the pectoral radials are strap-like, although in Cladoselache , this morphology is present from leading to trailing edge.

In Maghriboselache , two dorsal fin spines are present at least in one sex, while the posterior fin spine in Cladoselache is ‘hypothetical’ ( Zangerl, 1981: Fig. 73). Tis character might be shared with some symmoriids like Falcatus and perhaps Stethacanthus . Te overall shape of the caudal fin (lunate, high aspect ratio) is characteristic for symmoriiform taxa. Accordingly, we suggest that Cladoselache and Maghriboselache form a monophylum, which likely is sister to all other symmoriids, all are geologically younger except Ferromirum , which is of identical age. Maghriboselache was found in the Tylacocephalan layer, which is older (middle Famennian, 369 – 369.5 Ma; Frey et al., 2018, 2020a, b; Jobbins et al., 2020) than the Cleveland shale (late Famennian, 360 – 358.9 Ma; Cushing, 1912) from where Cladoselache is provenant. Presuming our phylogenetic scheme is correct, Maghriboselache and Ferromirum are the oldest stem holocephalans known from articulated material.

Te presence of two dorsal fin spines in association with the corresponding basal fin cartilage is possibly the plesiomorphic condition in early chondrichthyans (Frey et al., 2019, 2020a) because it occurs in several Famennian representatives of the main clades of the chondricthyan crown group. Te overall shape of the anterior fin spine resembles that of Ferromirum in the caudally oriented curvature close to the apex and the smooth surface (Frey et al., 2020a). By contrast, symmoriiforms may have spine brush complexes, ctenacanths and phoebodontids have nearly straight and striated anterior fin spines.

Figures

Fig. 1 Skeletons of Maghriboselache mohamezanei n. gen. et sp. Famennian,eastern Anti-Atlas (for locality details,see supplement). Homologous body regions are indicated by colored fields. Only J is from the southern Tafilalt,all others are from the southern Maïder region. A PIMUZ A/I 5152;B AA.MEM.DS.12;C, AA.MEM.DS.6; D PIMUZ A/I 5153;E PIMUZ A/I5154; F PIMUZ A/I 5155; G AA.BER.DS.01; H PIMUZ A/I 5156; I PIMUZ A/I5157;J PIMUZ A/I 5158

Fig. 2 Photo and drawing of a nearly complete skeleton of Maghriboselache mohamezanei n. gen. et sp., AA.BER.DS.01.The marked fin spine belongs to the posterior fin

Fig. 3 Head of Maghriboselache mohamezanei n. gen. et sp., PIMUZ A/I 5156 with neurocranium, jaws, hyoid arches and disarticulated gill remains. A dorsal posterior,B detail of D, C right lateral anterior, D left lateral, E ventral, and F anterior views

Fig. 4 Neurocranium of Maghriboselache mohamezanei n. gen. et sp. A to E holotype, AA.MEM.DS.12. A anterior, B dorsal (other specimen: PIMUZ A/I 5156), C left lateral (C2: detail of C1, marked by rectangle in C1), D ventral,and E posterior view. F PIMUZ A/I 5156, posterior view

Fig. 5 Head of Maghriboselache mohamezanei n. gen. et sp., PIMUZ A/I 5156 with neurocranium, jaws, hyoid arches and disarticulated gill remains. A posterior, B right lateral, C anterior, D dorsal, E left lateral, F ventral, G anterior views.Note the color-coded cranial elements

Fig. 6 Endocast of Maghriboselache mohamezanei n. gen. et sp., holotype, AA.MEM.DS.12. Nasal chambers (in grey) copied from PIMUZ A/I in A, B and D. A anterior, B dorsal, C left lateral, D ventral, and E posterior views

Fig. 7 Photos and drawings of the teeth of Maghriboselache mohamezanei n. gen. et sp., PIMUZ A/I 5160. 2 tooth rows. A, C, E, photos and B, D, F interpretative drawings of these photos

Fig. 8 Fins of Maghriboselache mohamezanei n. gen. et sp. A left pectoral fin of the holotype AA.MEM.DS.12. B, C right and left pectoral girdle elements and pectoral fins of PIMUZ A/I 5155; D left pectoral girdle elements and left pectoral fin of PIMUZ A/I 5156, E left scapulocoracoid of PIMUZ A/I 5152.F to I Pelvic girdle and pelvic fins. F PIMUZ A/I 5156, G PIMUZ A/I 5163, H PIMUZ A/I 5155, I PIMUZ A/I 5153. J to M Caudal fins. J AA.MEM.DS.12,K isolated fin, PIMUZ A/I 5163, L PIMUZ A/I 5153, M AA.BER.DS.01. Photos of the fins are in Fig. 1 and in Additional file 1: Fig. S5 to S11, S13, S14, S16 to S18, S20 to S25, S27, S28

Fig. 9 Details of the pectoral fins of Maghriboselache mohamezanei n. gen. et sp., PIMUZ A/I 5154.A tip of the left fin with articulated, though weathered integument, showing the localization of figure B. B detail of the fin with dermal denticles. C detail of the right pectoral fin showing the dermal denticles overlying the radials. D overview over the right fin, showing the localization of figure C and E. E detail showing the integument at the distal tip of the fin. Note the reduced denticle size

Fig. 10 Details of the fin spine of the anterior dorsal fin of Maghriboselache mohamezanei n. gen. et sp., PIMUZ A/I 5154.A overview, showing the localization of figures B to E. B detail of the tip with denticles at the posterior edge.C detail showing the fine longitudinal striation.D, E details showing imprints of blood vessels

Fig. 11 Skeletal reconstruction of possibly a male (A dorsal. B lateral) and possibly a female (C bottom, lateral) of Maghriboselache mohamezanei n. gen. et sp.The according details were collected from the mentioned specimens.Note the presence of anterior dorsal fin spine in the supposed males,possibly serving a role during copulation.Claspers are not present in the supposed males of our sample.The photos show the according regions of specimens displayed in Fig. 1 and the Additional file 1

Fig. 12 Detail of thorax of Maghriboselache mohamezanei n. gen. et sp., PIMUZ A/I 5156, showing the modified scales of the lateral line

Fig. 13 Phylogeny based on the emended character matrix from Coates et al. (2017) and Frey et al., (2020a, b). Bayesian tip-dating analyses of 230 characters were performed using the fossilized birth–death model. Early Silurian species after Zhu et al. (2022)

Fig. 14 Endocasts of various extinct and extant chondrichthyans of the main chondrichthyan clades and evolutionary change in the holocephalan branch.A Overlain labyrinths of the genera in F (note the increase in height and decreasing length). B Overlain endocasts of the genera in C (note the increasing volume of the mesencephalon and the dorsal bulging). C Outlines of endocasts of some chondrichthyans. D Evolution of neurocrania, sensory organs, brain endocasts and labyrinths exemplified with seven genera. Eyes reconstructed in blue, labyrinth in red, neurocranium outline in grey. Most endocasts after Coates et al. (2017), Phoebodus after Frey et al. (2019), and unpublished data, Maghriboselache after this paper