New holostean fishes (Actinopterygii: Neopterygii) from the Middle Triassic of the Monte San Giorgio (Canton Ticino, Switzerland)

Braincase, parasphenoid and vomers

The braincase is partially exposed in several specimens, but only a few bones are recognizable. MCSN (8317) shows an approximately circular prootic with only one large foramen for the hyomandibular trunk and the jugular vein (Allis, 1897; Bjerring, 1972; Bjerring, 1977); posterior to this foramen there is a deep excavation corresponding to the subtemporal fossa (Appendix S1: Fig. 2). The sphenotic is pyramidal and sutures to the dermopterotic posteriorly. The orbitosphenoid is preserved in MCSN 8072 (Fig. 7). The bone has a rounded convex dorsal border and a notch in the anterior border. Comparable notches are visible in the orbitosphenoid of Isanichthys lertboosi (Deesri et al., 2014: Figs. 7–8), gars (Grande, 2010) and amiiforms (Grande & Bemis, 1998).

The parasphenoid has well-developed basipterygoid and ascending processes (= processus ascendens anterior and posterior, respectively—see ‘Discussion’; MCSN 8008, 8072, 8086, 8317, 8351; Fig. 7, Appendix S1: Figs. 3–4). The orbital portion of the parasphenoid is broader than the postorbital portion and there are no teeth and no foramina. On the dorsal surface there is a median flattened strong ridge extending forward from the ascending process widening and becoming shallower in anterior direction to completely form the dorsal surface of the parasphenoid (MCSN 8008, 8086; Appendix S1: Fig. 4).

The paired vomers are disarticulated and nicely exposed in MCSN 8007 and PIMUZ T 4785 (Fig. 8, Appendix S1: Fig. 5A). Each vomer has a relatively large rectangular anterior head and a posterior process that sutures with the parasphenoid. The length of the anterior head represents almost half of the total length of the bone and its width is about 1.3 times the maximal width of the posterior process. The vomerine dentition is heterogeneous. There is a marginal row of four small teeth followed by a median patch of four irregularly arranged slightly larger teeth and a posterior row of two large fangs.

Skull roof and snout

The dermal bones of the skull roof are ornamented with numerous tubercles and short ridges covered with ganoin. The frontals cover most of the skull roof and both frontals are of similar size except in MCSN 8072, in which they are asymmetrical, the left frontal being somewhat larger (Figs. 7–10; Appendix S1: Figs. 3–5). The two frontals do not extend far beyond the anterior margin of the orbit, but they do posteriorly, covering the anterior half of the temporal region of the skull, so that the postorbital portion of the frontal is about 35–40% of the total length of the bone. The bones are rather wide; their length is between 2.5 and 3 times its maximal width, which is in the temporal portion approximately at the level of the anterior border of the dermopterotic. The interorbital constriction is nicely curved and deep and the frontals are expanded again anteriorly. The anterior border of the frontals is oblique in posterolateral to anteromedial direction. The posterior border of the frontal is rounded to almost rectangular and the suture between the frontals is mainly smooth though it forms one or two strong indentations approximately at the level of the posterior rim of the orbit. The form of this indentation varies from clearly indenting processes (MCSN 8009, 8072, PIMUZ T 4785; Figs. 7 and 12, Appendix S1: Fig. 5A) to an almost quadrangular step (MCSN 8007, PIMUZ T 4788; Fig. 8, Appendix S1: Fig. 5B). The path of the supraorbital sensory canal is preserved in the lateral half of each frontal and is marked by a strong ridge in the medial surface of the bone (MCSN 8007, 8008). It is straight and close to the central longitudinal axis of the frontal in the anterior half of the bone and it curves laterally approaching the lateral border and the dermosphenotic at the beginning of the temporal portion of the bone. Only the posterior half to two thirds of the frontals is ornamented with tubercles and short ridges resembling dropping water radiating from the postorbital curvature of the path of the supraorbital sensory canal.

Both quadrangular parietals are of comparable size and their length is between 25 and 30% of the length of the frontals. The suture between both parietals is straight and smooth in some specimens (MCSN 8072; Fig. 7), but forms a posterior indentation in others (MCSN 8009, PIMUZ T 4788; Fig. 12, Appendix S1: Fig. 5B). The parietals are completely and densely ornamented and the tubercles and ridges are approximately radiating from the posterolateral region of the bone. Laterally, the parietals and frontals suture with the dermopterotics, which are elongate, more than two times longer than deep, narrowing anterolaterally following the posterior edge of the frontal. The dermopterotics are about 1. 5 times longer than the parietals extending forwards lateral to the frontals for 40–45% of their total length in the larger specimens (MCSN 8009, 8072, PIMUZ T 4987; Figs. 7 and 12, Appendix S1: Fig. 6). In this anterior portion, the medial margin of each dermopterotic forms a step, which is overlapped by the frontal (MCSN 8072; Fig. 7). In medial view, the dermopterotics are longitudinally traversed by a well-developed descending lamina, which runs mostly through the middle of the bone and bends laterally rather abruptly close to the posterior border (MCSN 8007, 8008; Fig. 8, Appendix S1: Fig. 4). On the dorsolateral surface, only the posteromedial portion of the dermopterotics is ornamented and the posterior portion of each dermopterotic is traversed by a transversal groove housing the middle pit line. There is no groove for the middle pit line in the parietals. The supraorbital sensory canal does not enter the parietals.

Parietals and dermopterotics articulate posteriorly with a single pair of large extrascapular bones. Each extrascapular is sub-triangular, but only slightly narrowing towards the midline where it meets its counterpart forming a smooth suture. The extrascapulars are tightly bound to the large and similarly shaped posttemporals, and both bones are also similarly and densely ornamented.

There is a large and broad pair of nasal bones and a median rostral. The three bones articulate with each other covering the ethmoidal region completely (MCSN 8072, 8073, 5827; Figs. 7 and 9, Appendix S1: Fig. 7). The nasals are very broad posteriorly, with the posterior border as broad as the anterior borders of the frontals and anterior supraorbital together in large specimens (MCSN 5827, 8469; Figs. 9–10). From this broad posterior portion, the nasals narrow anteriorly and bent laterally at the anterior end. Thus, in the anterior region, the median border of the nasals is convex and the lateral border is deeply concave, probably surrounding the anterior external nares. The shape of the large nasals does not provide any clear indication of the position of the posterior nares, but they were probably placed between the nasals and the frontals as in Amia (Grande & Bemis, 1998). An excavation on the posteromedial corner of the nasals is present in medium size individuals (e.g., MCSN 8007, 8009, 8072, 8413; Figs. 7–8 and 12), but it is not present in larger specimens. In some of the largest specimens one pair of small rounded bones are placed, one on each side, between the frontal and the nasals on the area where the notch is placed in the smaller fishes (MCSN 5827, 8469; Figs. 9–10). In one of the largest specimens, this small bone is ornamented with a ganoin patch (MCSN 8469; Fig. 10). The dorsal surface of the nasals is traversed by a longitudinal ridge, which enclosed the anterior portion of the supraorbital sensory canal and bents laterally towards the antorbital in the anterior portion of the nasal. There are a few scattered tubercles ornamenting the nasals. The rostral is roughly tubular, fitting the curve formed by the two articulated nasals, and it is concave anteriorly (MCSN 5827, 8001, 8007, 8073, 8413, PIMUZ T 4987; Figs. 8–9 and 14; Appendix S1: Figs. 6–7). There are no lamellar expansions underlying the nasals and there is a tube for the ethmoidal commissure.

Circumborbital series and cheekbones

The circumborbital series consists of supraorbitals, dermosphentoic, infraorbitals, anterior infraorbitals and antorbital bones. There are two (MCSN 8073, 8469, PIMUZ T 4783, 4788; Fig. 10, Appendix S1: Figs. 5B and 7) or three (MCSN 5827, 8009, 8072; Figs. 7, 9 and 12) supraorbital bones. The supraorbital bones are ornamented with tubercles and short ridges. The dermosphenotic is a little larger than the last supraorbital and strongly sculpture with ridges and shelves, probably following the paths of the sensory canals (MCSN 8072; Fig. 7). It is tightly attached to the sphenotic at the posterodorsal corner of the orbit in several specimens, but it is not incorporated into the skull roof. The junction between the supraorbital, infraorbital and temporal canals most probably occured in the dermosphenotic. In medial view the dermosphenotic is traversed by a strong ridge (MCSN 8007, 8008; Fig. 8C, Appendix S1: Fig. 4).

There are three infraorbital bones forming the ventral rim of the orbit and one (e.g., MCSN 5827, PIMUZ T 4987) or two (e.g., MCSN 8009, 8073) small, almost tubular infraorbitals in the posterior border of the orbit. The first infraorbital bone is subrectangular, somewhat longer than it is deep, and does not contact the first supraorbital so that the orbit is not closed anteriorly (MCSN 8072, 5827; Figs. 7 and 9). The second infraorbital is notably the largest in the series and it is longer than it is deep, expanded ventrally in an almost fan-shaped lamina, which is distinctly traversed by ventrally directed grooves radiating from a main longitudinal groove related to the infraorbital sensory canal. Similar main longitudinal and minor radiating grooves are more poorly preserved in the first infraorbital bone. The second infraorbital alone makes most of the ventral rim of the orbit and it is followed by a small infraorbital, which is forming the posteroventral corner of the orbit. This third infraorbital is only slightly larger than the infraorbitals forming the posterior border of the orbit, which are the smallest in the series, subrectangular, slightly deeper than long. The infraorbitals are ornamented with a few scattered tubercles.

Anterior to the first infraorbital there are two anterior infraorbitals. The large nasals are displaced over the anterior infraorbitals in most of the specimens. However, the anterior infraorbitals are visible in MCSN 8072 and 5827 (Figs. 7 and 9). The posterior anterior infraorbital is longer than deep, and its lateral surface is traversed by a longitudinal groove and, although not well preserved, numerous radiating grooves, as is the case of the first two infraorbital bones. The antorbitals are very slender, crescent-shaped tubular bones with slightly larger dorsal and smaller anterior arms (MCSN 5827; Fig. 9).

Between the infraorbitals and preopercle the cheek is covered with numerous suborbital bones. The most dorsal suborbital bone is the largest and occupies the whole length between the preopercle and the circumborbitals, with a depth of about 75% of its length. Ventral to this large suborbital, the other suborbitals form a mosaic of numerous and very small bones extending up to a level at the centre of the orbit. The pattern of suborbitals is variable and in several specimens the second and sometimes the third suborbital are as long, though less than half the depth of the dorsalmost suborbital (MCSN 5827, 8009, 8083; Figs. 9 and 12). All of the suborbital bones are ornamented.

The preopercle is very slender and crescent-shaped, but only slightly curved anteriorly, and oriented almost vertically. A series of pores close to the posterior border of the bone indicate the exits of tubules branching from the preopercular sensory canal. These tubules are clearly visible in the largest specimens (e.g., MCSN 8448). The posterior suborbital bones overlap the anterior margin of the preopercle and the dorsal portion of the preopercle is almost completely hidden by the suborbitals in the largest specimens.

Opercular series and branchiostegal rays

The opercle is 10–30% deeper than it is long, with almost straight dorsal and anterior borders. The ventral border is only very slightly convex, the posterior border is convexly curved, so that the bone is longest at the middle or at its ventral margin. On the medial surface there is a relatively large ovoid articular facet for the hyomandibula (PIMUZ T 486; Fig. 11A). The subopercle is smaller than the opercle, with a maximal depth of 35–40% of the maximal depth of the opercle. The dorsal border is only slightly concave and the ventral border is convex, so that the bone is roughly sickle shaped. It has a well-developed ascending process, which is tapering dorsally, but rather low; its height is about 20% of the maximal length of the subopercle and also c. 20% of the height of the anterior border of the opercle (MCSN 8469, 8001; Figs. 10 and 14). The anterior border of the subopercle is oblique, anteroventrally inclined. Both the opercle and subopercle are densely ornamented with ganoin tubercles and small ridges or patches. The interopercle is triangular, tapering rostrally, with a gently convex ventral border and straight dorsal and posterior borders. The maximal length of the interopercle is 1.2–1.5 times its maximal depth. Only the posterior margin of the interopercle is sparsely ornamented.

Medioventral to the subopercle there is the largest branchiostegal ray, which is distinguished as a branchiopercle because of its notably larger size and much stronger ornamentation than the remaining branchiostegals. Also, differing from the other branchiostegals and resembling the branchiopercle of Amia, this bone in T. longaeva has a broad and flatly truncated anterior end (MCSN 8009, 8469; Figs. 10 and 12; Hubbs, 1919; Grande & Bemis, 1998). The dorsal margin of the branchiopercle is overlapped by the subopercle and the ventral margin is densely ornamented in the same way as the opercular bones. The branchiopercle is followed by six branchiostegal rays, which decrease in size anteriorly and are not or only very slightly ornamented. A gular plate is absent.

Hyomandibula and hyoid arch

The hyomandibula is partially exposed in lateral view in several specimens (MCSN 8001, 8008, 8317, 8351; Fig. 14, Appendix S1: Figs. 2–4) and completely in medial view in PIMUZ T 486 (Fig. 11). The dorsal portion, representing about a third of the bone, is almost quadrangular with a long and oblique articular facet and straight vertical posterior border. There is a large and pronounced opercular process, which is very strong and broadens towards the opercle. Ventrally, the opercular process is connected with the vertical shaft through a thin lamina of bone. The vertical shaft is well ossified and broadens ventrally. The ventral border forms a posteroventrally directed facet probably for the articulation with a medial subopercular process, which is a cartilage that links the hyomandibula to the medial surface of the subopercle in living gars (Grande, 2010). The hyomandibular trunk enters the bone medially at the level of the opercular process and exits through a large opening on the lateral surface, approximately at the centre of the bone (MCSN 8317, PIMUZ T 486; Fig. 11, Appendix S1: Fig. 2).

A small symplectic is partially exposed and articulated in MCSN 8073 and PIMUZ T 4987 (Fig. 13A, Appendix S1: Fig. 6) and disarticulated and well exposed in MCSN 8009 (Figs. 12 and 13B). Based on these two fossils, we interpret the condition in T. longaeva as similar to the mode of articulation of the symplectic in Pachycormus curtus described by Patterson (1973: 274, Fig. 18; Fig. 13C, see below). Although there is no quadratojugal in this later taxon there is also a step on the medial surface of the quadrate, towards which the symplectic is attached (partially fused to the quadrate in the specimen NHMUK 32434 studied by Patterson, though he considered this might not be the typical condition).

There is a single, but large and approximately quadrangular hypohyal on each side (best preserved in MCSN 8008 and 8469; Fig. 10, Appendix S1: Fig. 4). The anterior ceratohyals are rather massive and well preserved in several specimens (MCSN 8001, 8008, 8009, 8351, 8469, PIMUZ T 486; Figs. 10–12 and 14, Appendix S1: Figs. 3–4). Each of these bones is subrectangular with strengthen and rather straight ventral border and gently curved antero- and posterodorsal corners. The bone is 2–2.5 times longer than it is deep. The posterior ceratohyal is only partially exposed and its shape cannot be reconstructed.

Palatoquadrate

The palatoquadrate is fully ossified, but it is only partially exposed and the individual bones cannot be described in detail (MCSN 8009, 8011, 8073, 8083, 8351; Fig. 12, Appendix S1: Figs. 3 and 7). The pars autopalatina is ossified. Dermo- and ectopterygoids bear the most powerful teeth, which are conical. The ectopterygoid is only exposed in the lateral view as a crescent-shaped bone with tapering anterior and posterior ends and only two teeth in the most anterior portion. The posteroventral portion of the ectopterygoid is articulating with the quadrate caudally. The quadrate is relatively small. The quadratojugal is also small and in some specimens it is tightly bound or partially fused (MCSN 8009, 8073) to the posteroventral border of the quadrate, but it is completely fused to the quadrate in PIMUZ T 4987 (Figs. 12 and 13A–13C, Appendix S1: Fig. 7). Immediately above the condyle, the inner surface of the quadrate forms a posterodorsally directed rounded shelf (Fig. 13B). Based on the conditions observed on the specimens MCSN 8009, 8073 and PIMUZ T 4987, we think that the anterior strengthened portion of the symplectic articulated and was able to slide on this inner shelf of the quadrate (Fig. 13C). The well-defined condyle for the articulation with the lower jaw is formed by the quadrate and quadratojugal together (Figs. 13A–13B).

Jaws

The two premaxillae are disarticulated and displaced in MCSN 8007, 8009 (Figs. 8, 12 and 13D–13E). The nasal processes are relatively short, with a depth less than two times the width of the toothed portion of the bone. The passage of the olfactory nerve is indicated by a broad groove and an open fenestra at the posteromedial portion of the nasal process. None of the specimens shows a complete olfactory foramen and the right premaxilla in MCSN 8007 seems to be completely preserved, so we think that the nasal process does not form a complete olfactory foramen in T. longaeva (Fig. 13D). A foramen at the base of the nasal process probably corresponds to the passage of the palatine ramus of the facial nerve (Allis, 1898; Fig. 13D). The left premaxilla is very nicely exposed in medial view in MCSN 8009 showing a broad medial “ascending” process at the anteromedial corner of the bone (Fig. 13E). This “ascending” process is much shorter than the nasal process and has a very irregular border. The premaxilla has 6 pencil-like teeth, which are notably smaller than the teeth on the dentary, but larger than the ones on the maxilla.

The maxillae have a strong and very long rod-like anterior articular process and a deep supramaxillary notch (MCSN 5827, 8001, 8009, 8072; Figs. 7, 9, 12 and 14). The maxillary paddle is between 3 and 3.5 times longer than deep and covers the anterior half of the coronoid process of the lower jaw laterally. The articular process of the maxilla is very long and rod-like. The dorsal border of the maxilla elevates very rapidly posterior to the articular process and turns abruptly downwards producing a deep supramaxillary notch. The single supramaxilla accommodates along the dorsal border behind the supramaxillary notch. The two bones together make an almost perfectly paddle shaped element. Small conical maxillary teeth are preserved in a few specimens (MCSN 8001, 8009, 8072, 8073; Figs. 7, 12 and 14, Appendix S1: Fig. 7), but their total number and distribution are unknown. The maxillary teeth are notably smaller than the dentary teeth and the smallest marginal teeth in the mouth (Fig. 14).

The lower jaw is formed by the dentary, angular, surangular, retroarticular, articular, prearticular and coronoid bones. The dentary has a long toothed anterior portion and forms well-developed coronoid and posteroventral processes (MCSN 8009, 8072, 8351; Figs. 7 and 12, Appendix S1: Fig. 3). There are 9–10 dentary pencil-like teeth, which are the largest marginal teeth on the jaws. The height coronoid process is 40–45% of the total length of the lower jaw. Above the posteroventral process, the posterior border of the dentary is almost perpendicular to the major longitudinal axes of the bone. Along the toothed portion of the dentary, the dorsal margin forms a medial shelf on which the coronoids are attached (MCSN 8008, 8001, 8413; Fig. 14, Appendix S1: Fig. 4). There are two coronoid bones bearing strong pencil-like teeth similar in shape to those of the dentary. There are two rows of teeth on the coronoids. The teeth on the lateral row are larger, approximately of the same size as the dentary teeth, but the teeth on the medial row are small. The prearticular is located on the medial surface of the dentary posterior to the coronoids (MCSN 8001; Fig. 14). The prearticular teeth are roughly arranged in two rows and are of similar size than the lateral coronoid teeth. The posteroventral process does not reach the posterior border of the lower jaw and the posterior portion of the ventral border of the lower jaw is formed by the retroarticular. The retroarticular is very large and it is exposed in several specimens (MCSN 8072, 8083, 8469; Figs. 7 and 10). It is sutured to the angular and forms the ventral border of the lower jaw caudal to the posteroventral process of the dentary. The surangular is relatively large, articulating dorsal to the angular and posterior to the dentary, and the dorsal border is convex. The concave articular facet is directed posterodorsally and it is formed by the articular alone.

Girdles and paired fins

The pectoral girdle is formed by the posttemporal, supracleithrum, presupracleithrum, cleithrum, and four postcleithra. The posttemporal is approximately triangular resembling the large extrascapular, but it is larger and anteriorly overlapped by this bone. Therefore, the exposed portion of the posttemporal is extremely similar in size and shape to the extrascapular. Also like the extrascapulars, the two posttemporal bones meet at the dorsal midline. Each posttemporal has a rounded ventral process for the articulation with the supracleithrum (MCSN 8001, 8009, 8072, 8073, PIMUZ T 486, 2848, 4785; Figs. 7, 11–12 and 14A).

The supracleithrum is only completely exposed in PIMUZ T 486, where it is preserved in medial view (Fig. 11). There are no medial dorsal or ventral processes as in the gars (Grande, 2010). The bone narrows ventrally and is broadest at its dorsal end, where it forms a concave articular facet directed dorsally, which receives the rounded process of the posttemporal forming a ball-and-socket articulation (Wiley, 1976). Directly anterior to this facet, a small ovoid bone, which is here named subposttemporal bone, places between the flattened anterodorsal border of the supracleithrum and a concave facet in the medial ventral margin of the posttemporal. A subposttemporal bone has been otherwise only observed in the callipurbeckiid semionotiform Macrosemimimus fegerti (A López-Arbarello, pers. obs., 2011). In the latter species this bone sits directly on the concave articular facet of the cleithrum indicating that it is an aid to the ball and socket articulation. The lateral line enters the supracleithrum at the middle of the bone and obliquely runs to exit through the dorsal border entering the posttemporal for a brief trajectory through the anteroventral portion of this bone. The lateral surface of the posterodorsal margin of the supracleithrum is variably ornamented with short ridges and tubercles. A small presupracleithrum is preserved in several specimens (MCSN 8009, 8072, 8073, PIMUZ T 486, 4790, 4987; Figs. 7 and 11–12, Appendix S1: Figs. 6–7).

The cleithrum is crescent-shaped in lateral view and has a single row of denticles lining the limit between the lateral and branchial surfaces of the bone (MCSN 8072, 8073, PIMUZ T 486; Figs. 7 and 11, Appendix S1: Fig. 7). The branchial portion of the cleithrum consists of a very broad lamina of bone (PIMUZ T 8001, 8009; Figs. 12 and 14A), which is probably homologous to the medially directed lamina of the cleithrum in Boreosomus (Nielsen, 1942) or the medial wing of the cleithrum in gars (Wiley, 1976; Grande, 2010). Posterior to the cleithrum there are four postcleithra, three of which are tightly articulated and form together a half crescent shape (MCSN 8072, 8073; Fig. 7; Appendix S1: Fig. 7). The dorsalmost postcleithrum is the largest and tapers dorsally. The second postcleithrum is almost rectangular and the third and much smaller postcleithrum is oval shaped. The fourth postcleithrum is also oval and a little smaller than the third postcleithrum. This most anterior postcleithrum is detached from the others and it is usually not preserved.

The endochondral elements of the pectoral girdle are only partially exposed, but there are at least five radials (MCSN 8001, 8007, 8072, 8073; Figs. 7–8 and 14A, Appendix S1: Fig. 7). The pectoral fin web is made up of 17–18 lepidotrichia (MCSN 8009, 8073; Fig. 14A, Appendix S1: Fig. 7). There are numerous fringing fulcra along the first pectoral fin ray, which have the typical ganoin ‘nail’ that characterizes the genus. The fringing fulcra are fused to each other towards the base of the fin, but they are not fused to the base of the first pectoral ray. The shape of the base of the first pectoral fin ray is variable between individuals and probably represents ontogenetic variation (see below).

The basipterygia are exposed in MCSN 8001 and 8475 (Appendix S1: Fig. 1). They are elongated and slender bones almost equally expanded proximally and distally. The pelvic fins are always imperfectly preserved so that the total number of rays is uncertain but seven rays are preserved on the right pelvic fin of MCSN 4974, 8072, and 8475 and this is most probably the complete set of pelvic rays. A series of fringing fulcra garnished with ganoin ‘nails’ lay on the first pelvic ray.

Dorsal and anal fins

The dorsal fin web is made of 14–16 rays extending backwards a little behind the vertical level at the end of the anal fin (Fig. 15A; Appendix S1: Figs. 4A and 7). There are a variable number of small basal fulcra at the origin of the dorsal fin, which are usually fused to each other at their bases and carry the first fringing fulcrum, and a series of small though garnished with ganoin ’nails’ fringing fulcra lay along the first dorsal fin ray. The anal fin is relatively small consisting of six rays (Fig. 15B). There are a few small basal fulcra at the origin of the fin and a series of fringing fulcra on the leading edge of the fin. The first ray in both dorsal and anal fins is unbranched and much shorter than the second ray.

Caudal fin and body lobe

The caudal fin is abbreviated heterocercal with a well-developed body lobe including 8 to 9 inverted rows of scales and a median dorsal scute (Figs. 12 and 15C; Appendix S1: Figs. 3 and 6–7). There is a marginal row of seven scales that merges with the adjacent inverted row distally. This second inverted row is the longest, made up of 11 to 14 scales, varying in the number of the most distal scales forming the sharp tip of the body lobe.

The caudal fin web is forked with equally long ventral and dorsal lobes. There is a variable number (1–5) of small paired and unsegmented basal fulcra followed by 3–5 short segmented rays which are bearing fringing fulcra. The first principal ray is the first ray, which is unbranched, but as long as the following ray and bears fringing fulcra. There are 11 principal caudal fin rays in the ventral lobe below the lateral line, and 11 to 12 rays in the dorsal lobe. Except for one or two rays placed in the central part of the fin, the basal segment of the dorsal principal rays are very long and located oblique to main axis of the ray, approximately following the orientation of the body lobe scale rows (MCSN 8475; Fig. 14C). The basal segment of the dorsal principal rays of the body lobe have small dorsal processes (MCSN 8009, 8073, 8413, PIMUZ T 4987; Fig. 12; Appendix S1: Fig. 6–7). The caudal fin rays are laterally covered with patches of ganoin.

Body squamation

The body of Ticinolepis longaeva is covered with numerous and relatively small thick rhomboid scales. There are 39–40 scales along the lateral line and between 14 and 22 scales above the lateral line along the vertical row immediately anterior to the dorsal fin (intraspecific variation, see below). In the most anterior portion of the flank, in the first three or four vertical rows, the scales are approximately quadrangular, but they are shallow, longer than deep in the rest of the body. As usual, the scales are gradually smaller starting from the most anterior scales of the lateral line in dorsal, ventral and posterior directions, but in Ticinolepis the ventrum is covered with extremely shallow scales (Figs. 5 and 11–12; Appendix S1: Figs. 3–4 and 6–7). This feature is especially noticeable in this species.

The scales are rhomboid, with smooth surface and variably serrated posterior border, that is to say that scales with serrated borders are found in some, but not all of the specimens and in some regions, but not all over the body. The distribution of these serrated scales is capricious and we have not been able to identify any particular pattern. The scales have the usual peg-and-socket articulation and a broad smooth anterior surface devoid of ganoin for the articulation with the adjacent scales, but there are no distinct longitudinal processes.

There is no distinct dorsal ridge of scales and only one specimen has distinct, though small preanal and precaudal scutes (MCSN 8073; Fig. 15B; Appendix S1: Fig. 7). All the fins are preceded by one or a few small basal fulcra and fringed with numerous small fringing fulcra, which are distinctly ornamented with a thick oval patch of ganoin.

p v. 1998 Archaeosemionotus sp. Bürgin: Fig. 8H, Table p. 7

p v. 1999a Archaeosemionotus sp. Bürgin: Appendix 1

Holotype. PIMUZ T 273 (Fig. 5B).

Paratypes. PIMUZ T 237, 240, 248, 256, 257, 265, 277, 278, 315, 331, 341, 358, 401, 413, 438, 638, and 4350.

Type locality. P. 902/Mirigioli, Monte San Giorgio (Meride, Canton Ticino, Switzerland; Fig. 1).

Type horizon. Upper Besano Formation, early Ladinian, lowermost E. curionii Ammonoid Zone.

Etymology. The species name crassidens derives from the latin crassus, thick, and dens, tooth, referring to the strongly tritoral dentition of this species.

Referred specimens. PIMUZ T 2823 and 2835 from the uppermost Besano Formation (Val Porina mine).

Diagnosis. Species of Ticinolepis differing from the other species of this genus in the following combination of characters: tritoral teeth on dermopalatin, ectopterygoid, coronoids and dentary; lower jaw and skull roof bones totally or partially fused; 6 infraorbital bones; 8–9 principal caudal fin rays below the lateral line; only 8–9 flank scales above lateral line; marginal row of body lobe with 9 scales; second and third inverted rows of body lobe equally long, merging distally, made up of 9–10 scales in each row and two common scales forming the tip of the body lobe.

Pterygial formula:

${\displaystyle \frac{\mathrm{D}17\text{–}19}{\mathrm{P}6\text{–}7\mathrm{A}15\text{–}16\mathrm{C}26\text{–}28}\mathrm{T}31\text{–}34.}$

Braincase, parasphenoid and vomers

The braincase is very well preserved and partially exposed in left lateral view in PIMUZ T 273 (Fig. 16). The exposed portion is remarkably similar to the braincase of the specimen NHMUK 37795a of Ionoscopus cyprinoides (Maisey, 1999), except that sutures are not discernible and all the bones seem to be fused, including the large and high ascending process of the parasphenoid (= processus ascendens posterior; see ‘Discussion’), which is almost perpendicular to the parasphenoid bar, being only slightly inclined posteriorly. It is tightly bound to the sphenotic dorsally and fused to the prootic posteriorly. At the base of the ascending process there is an anteriorly directed triangular process that resembles the pterosphenoid process of the parasphenoid of Amia (indicated with a red dot in Figs. 16 and 22; Grande & Bemis, 1998), but it is not sutured to the pterosphenoid. Similar free processes, not articulated with other bones, are present in the ionoscopiforms Ionosocpus cyprinoides and Oshunia brevis (Maisey, 1999). We interpret this process as the processus ascendens anterior, which corresponds to the basipterygoid process (see ‘Discussion’ below). Ventral to this process there is a notch related to the passage of the efferent pseudobranchial artery (Patterson, 1975: 531) or the posterior palatine branch of the cranial nerve VII (Grande & Bemis, 1998), or both (Allis, 1897; Bjerring, 1972; Bjerring, 1977; Jarvik, 1980). Posteriorly, at the base of the ascending process, there is a notch corresponding to the passage of the internal carotid artery (Allis, 1897; Patterson, 1975; Grande & Bemis, 1998) and probably also the pharyngeal brunch of the glossopharyngeal nerve (Bjerring, 1972; Bjerring, 1977; Jarvik, 1980). The lateral wall of the otic region is completely ossified embracing the areas corresponding to the prootic, opisthotic and pterotic. In the prootic area there is a large foramen corresponding to the passage of the hyomandibular trunk and the jugular vein, and more dorsally a smaller foramen corresponding to the spiracular canal (Allis, 1897; Bjerring, 1972; Bjerring, 1977; Patterson, 1975; Jarvik, 1980; Grande & Bemis, 1998). The opening of the spiracular canal is placed immediately anteroventral to the hyomandibular facet, which is completely ossified between the areas corresponding to the prootic, pterotic and sphenotic. The facet is anteroventrally inclined in approximately 35°respect to the longitudinal axis of the parasphenoid + basioccipital. In the occipital region, the exo- and basioccipitals are coossified. Immediately posterodorsal to the vagus foramen there is a cranio-spinal process, which is homologous to the intercalar in basal teleosts according to Patterson (1975). The dorsal portion of the occipital region is not well visible and, thus, an epioccipital is not discernible.

In the orbital region, anterior to the ascending process of the parasphenoid the pterosphenoid is visible, but no details can be described. The pyramidal sphenotic is tightly bound to the prootic and the ascending process of the parasphenoid. Some specimens have badly preserved remains of the orbitosphenoid, which was large, reaching the parasphenoid ventrally (PIMUZ T 2823). The ethmoidal region is strongly ossified, with large lateral ethmoids. The vomers are not exposed, but the strongly tritoral vomerine dentition (Fig. 16) indicates that the bones were probably fused.

Skull roof and snout

The frontals, parietals and dermopterotics are tightly ankylosed or partially fused and the sutures are almost indistinguishable (best preserved in PIMUZ T 438, 2835; Fig. 17). Therefore, it is not possible to describe the shape and proportions of the individual bones. As a whole, the skull roof is c. 35% broader posteriorly than anteriorly. There is an approximately rectangular interorbital constriction and the anterior portions of the frontals make rounded lateral antorbital processes. The middle and posterior pit lines are indicated by grooves at the rear of the skull roof. The middle pit lines run through the dermopterotics and parietals, the posterior pit lines are indicated by grooves almost parallel to the posterior margin of the parietals. The dermopterotics project forward forming distinct anterolateral processes (PIMUZ T 438; Appendix S1: Fig. 8). Resembling the type species of the genus, there is a single pair of extrascapulars in T. crassidens. They are large and triangular, articulating with the dermopterotics and parietals and reaching the dorsal midline (PIMUZ T 256, 257, 277, 401, 638; Fig. 18, Appendix S1: Fig. 10).

The nasals are less strongly ossified and narrower than in the type species (PIMUZ T 413, 2823 and 2835; Figs. 17 and 19). They are neither ornamented nor tightly articulated with the frontals, the rostral or between them, so they were most probably imbedded in the skin, apparently only attaching to the longitudinal median ridge made by the large nasal processes of the premaxillae. They are thin laminar bones and their margins are generally broken and incompletely preserved, except in PIMUZ T 4350 (Fig. 19), where they are exceptionally well preserved. Each nasal is broadest posteriorly, with slightly laterally curved anterior end and, thus, the lateral margin is deeply concave in the anterior portion, probably surrounding the anterior external nares. Longitudinally, each nasal is traversed by a tube carrying the supraorbital sensory canal, which turns laterally close to the anterior margin of the bone. The rostral is roughly rhomboidal with two lateral horns including a tube for the ethmoidal commissure and a medial caudally directed knoll producing a roughly V-shaped dorsal border (PIMUZ T 277; Fig. 20).

Circumborbital series and cheekbones

The dermosphenotic and the series of supraorbitals are most completely preserved in PIMUZ T 4350 (Fig. 19). Each dermosphenotic is small, usually rectangular, but it might have an anteriorly directed arm extending above the orbit. The posterodorsal portion of the bone fits into the ‘notch’ formed by the lateral border of the frontal and the anterior border of the anterolateral process of the dermopterotic (PIMUZ T 438). This area is also probably sitting on the lateral process of the sphenotic. Along the dorsal rim of the orbit, the dermosphenotic is followed by four small supraorbitals, which are gradually larger in anterior direction. The supraorbitals are weakly ornamented on their external surfaces, but the whole supraorbital series produces a longitudinal ridge along the internal surfaces of the bones, probably for attachment to the rim of the frontal.

Ventral to the dermosphenotic, the circumborbital series is completed with a series of 6 infraorbital and at least two anterior infraorbital bones (PIMUZ T 277, 315; Fig. 20). The anterior infraorbitals are very delicate and thin laminar bones, and are thus only rarely preserved. The anterior infraorbitals are approximately rectangular in shape, a little longer than deep and gradually shallower in anterior direction. The first infraorbital, placed at the anterior rim of the orbit, does not contact the anterior supraorbital and, thus, the orbit is open anteriorly. The first infraorbital is small and has no particularly distinct features. As in the type species of Ticinolepis gen nov., the second infraorbital is the largest in the series, but differing from this other species, the bone in T. crassidens is not fan-shape but approximately rectangular and similar to the other infraorbitals. The infraorbitals three to six complete the posteroventral and posterior rim of the orbit. Their relative size and shape are somewhat variable from rectangular to tubular between specimens, but the infraorbital immediately adjacent to the dermosphenotic is always very small (best exposed in PIMUZ T 277 and 4350; Figs. 19–20). The antorbitals are small crescent shaped bones, with the anterior arm longer than the depth of the dorsal arm (PIMUZ T 277).

As in the other species of the genus, there is a mosaic of small suborbitals covering the cheek posteroventral and posterior to the circumborbital series in T. crassidens. Also as in T. longaeva, the dorsalmost suborbital is notably larger than the other suborbitals, covering the area between the infraorbitals and the preopercle approximately up to the level of the parasphenoid. This largest suborbital is also about 30% longer than it is deep. The number and arrangement of the other suborbital bones is variable between individuals, but the whole mosaic of suborbitals completely covers the palatoquadrate laterally, reaching up to the level of the coronoid process of the lower jaw, at the centre of the orbit (PIMUZ T 277; Fig. 20).

All suborbitals and circumborbital bones are densely ornamented with small, adjacent ganoin patches. In the dermosphenotic and infraorbitals the ornamentation is not complete and the orbital margin of the bones is smooth. Similarly, only the posterodorsal margin of the most anteroventral suborbitals is ornamented (PIMUZ T 277, 331, 2823).

The preopercle is very slender and crescent-shaped (best preserved in PIMUZ T 277, 331 and 4350; Figs. 19–20). The anterior margin is overlapped by the suborbitals and the preopercular sensory canal is indicated by a series of pores at the posterior border of the bone.

Opercular series and branchiostegal rays

The opercle is large and about 50% deeper than long and has almost straight rostral and ventral borders and gently convex dorsal and caudal borders (Figs. 18 and 21). It is shortest at the dorsal margin and longest at about two thirds of its depth. The subopercle is relatively large and sickle-like shape with a maximal depth (excluding the anterodorsal process) of about 30% of the depth of the opercle. The ascending process is robust, with long base, reaching up to a level at about half of the depth of the opercle. The anterior border of the subopercle is oblique, slightly inclined anteroventrally. Both the opercle and subopercle are densely ornamented with small, adjacent patches covered with ganoin (PIMUZ T 257, 277, 413, 2823). The interopercle is triangular, rather large, but relatively short, with a maximal length only about 20% of its maximal depth, and with a blunt rostral tip (PIMUZ T 413; Fig. 21). Only the posterior margin of the interopercle is ornamented in the same way as the opercle and subopercle (PIMUZ T 257, 277, 413, 2823). There is no evidence of a median gular. A branchiopercle is preserved in PIMUZ T 315 and 413. The complete set of six branchiostegal rays is only preserved in PIMUZ T 315.

Hyomandibula and hyoid arch

The hyomandibula is partially exposed in lateral view in PIMUZ T 273 and 4350 (Figs. 16 and 19). In the later it is partially covered by suborbitals and the preopercle, but in the first of these specimens the dorsal portion of the hyomandibula is well exposed. It is well ossified, rather slender and trapezoid. There is a broad and blunt opercular process. The ventral shaft is almost vertical, slightly inclined posteroventrally, and rather slender. There are two dorsoventrally directed parallel grooves ending in small foramina on the lateral surface of the hyomandibular shaft. These two grooves represent the curse of the hyomandibular trunk, which includes three main branches in Amia. The two grooves suggest that the r. mandibularis facialis and the r. mandibularis lateralis separated from the posterior r. hyoideus bevore exiting the lateral surface of the hyomandibula (see description of the curse of these branches in Jarvik, 1980: 51). Better preserved material is needed to confirm this interpretation.

There is a robust quadrangular hypohyal visible in PIMUZ T 315 and 4350 (Fig. 19B). The anterior ceratohyal is well visible in several specimens (PIMUZ T 277, 315, 438, 2823, and 4350; Figs. 19–20, Appendix S1: Figs. 8 and 11) and is roughly rectangular with no median constriction. The bone is less than two times longer than deep and, thus, it is relatively shorter than in the other species of Ticinolepis. The posterior ceratohyal is only partially exposed in PIMUZ T 277 and 2823.

Palatoquadrate

The palatoquadrate is fully ossified, but it is not possible to delimit the individual bones. Although an autopalatine bone cannot be delimited, the pars autopalatina is clearly ossified (PIMUZ T 273; Fig. 16). At least one dermopalatine and the ectopterygoid bear powerful molariform teeth (PIMUZ T 4350; Figs. 19C–19D). These bones are relatively large and powerful. The quadrate has a distinct massive irregularly shaped body and a well-defined condyle. There is a splint-like quadratojugal firmly attached to the posteroventral border of the quadrate.

Jaws

The two premaxillae are incompletely exposed in the studied specimens and only the toothed portion is visible. The nasal processes are hidden and, thus, their length is unknown.

The maxillae and supramaxillae are very poorly preserved. Based on the few specimens, in which these bones are almost completely preserved (PIMUZ T 315, 341, 2823; Appendix S1: Fig. 11), they are very similar to the maxillae and supramaxillae of T. longaeva, with approximately the same proportions and similar shape variation.

The lower jaw is always exposed in lateral view and the bones are all fused together forming a massive jaw with a very strong and high coronoid process (Figs. 17–18 and 20–22; Appendix S1: Figs. 8 and 11). The maximal depth of the bone at the coronoid process is c. 60% of the maximal length of the jaw. The symphysis is relatively shallow with a depth of about 20% of the maximal length of the jaw. The almost horizontal toothed portion of the dentary is c. 55% of the maximal length of the jaw. The anterior edge of the coronoid process is concave (PIMUZ T 273, 277).

Except for the maxillary teeth, the dentition is very strong (Figs. 17–22; Appendix S1: Figs. 8 and 11). Each premaxilla bears 4–5 teeth (Appendix S1: Fig.9) and there is a marginal row of 7–8 teeth on the dentary (Fig. 21D). Two prearticular teeth are laterally exposed posterior to the dentary teeth in PIMUZ T 273 and 277 (Figs. 20 and 21D). The coronoid bones are only partially exposed and are never found detached from the jaw and, thus, they were probably fused to the dentary. Large molariform coronoid teeth are well exposed in most of the specimens. These and the vomerine teeth are the largest teeth in this species (Figs. 21E–21D).

Girdles and paired fins

Like in the type species, the pectoral girdle of T. crassidens includes a posttemporal, a supracleithrum, a small presupracleithrum, a cleithrum, and an unknown number of postcleithra (Figs. 17–18; Appendix S1: Figs. 9–11). The posttemporal is also large, subtriangular, and reaches the dorsal midline. As in the type species, the posttemporal of T. crassidens presents a rounded process for articulation with the supracleithrum (indicated with an orange dot in Fig. 19B). The posttemporal bears along its ventral margin a short streak of the sensory canal, which represents the connection of the lateral line with the cephalic sensory canal system. A further part of this connection pierces the supracleithrum obliquely (Appendix S1: Fig. 9). This latter element has a deep, almost rectangular shape, with ventral part tapering into a slightly pointed tip. A small notch at the caudal margin of the supracelithrum marks the entering of the lateral line. The presupracleithrum is exposed in PIMUZ T 256 and 2835 (Figs. 17–18). The large cleithrum is only partially preserved and shows a distinct medial ridge with denticles running along its lateral surface. There is a shallow incurvation on the caudal edge, just behind the pointed tip. The posttemporal and presupracleithrum are fully and the supracleithrum is partially ornamented by irregular ridges and tubercles, whereas no ornamentation is found on the external surface of the cleithrum. The pectoral fin is composed of 13–16 segmented and, with the exception of the first, distally branched fin rays (Appendix S1: Fig. 11). The leading edge of the fin is composed of a spinous basal fulcrum and a paired series of well-developed fringing fulcra.

The pelvic bones are not exposed or preserved. The small pelvic fins consist of four to five distally segmented and branched rays. A single spinous basal fulcrum precedes the leading edge of the fin, which bears a series of fringing fulcra.

Dorsal and anal fins

The dorsal and anal fins are very poorly preserved in the material of T. crassidens (Figs. 5B, 18 and 21; Appendix S1: Fig. 8). They are generally similarly built as in the other species. The dorsal fin includes 13 rays in PIMUZ T 256 and there are eight anal fin rays in PIMUZ T 237.

Caudal fin and body lobe

The caudal fin is abbreviated heterocercal with a body lobe including 8–9 inverted rows of scales and a median dorsal scute. Differing from the other species, in T. crassidens the marginal row includes nine scales and the second and third inverted rows are equally long, merging distally, made up of 9 (PIMUZ T 256) to 11 (PIMUZ T 413) scales in each row and two common scales forming the tip of the body lobe (Figs. 17C, 18F and 20C).

The caudal fin web is forked with equally long ventral and dorsal lobes. There three to four small unsegmented basal fulcra followed by three short segmented rays, which might bear fringing fulcra. The first principal ray is the first ray, which is unbranched, but as long as the following ray and bears fringing fulcra. There are only nine principal caudal fin rays in the ventral lobe, below the lateral line, and ten rays in the dorsal lobe.

Body squamation

Like in the type species, the body of T. crassidens is covered with thick rhomboid scales, which are generally quadrangular, slowly changing from deeper than long in the anterior vertical rows, to slightly longer than deep in the centre of the body and the caudal peduncle. As usual in Ticinolepis the ventrum is covered with extremely shallow scales, though in this species the longitudinal rows of shallow scales are not as numerous as in the type species (Figs. 5B, 18 and 21; Appendix S1: Fig. 8). The scales have smooth surfaces and smooth posterior border, except for the scales traversed by the lateral line, which might have a posterior excavation. The scales have the usual peg-and-socket articulation and a broad smooth anterior surface devoid of ganoin for the articulation with the adjacent scales, but there are no distinct longitudinal processes. There is no distinct dorsal ridge of scales and no preanal scute.