Bollettino della Società Paleontologica Italiana, 51 (3), 2012, 203-212. Modena, 30 dicembre 2012 A new species of Sangiorgioichthys (Actinopterygii, Semionotiformes) from the Kalkschieferzone of Monte San Giorgio (Middle Triassic; Meride, Canton Ticino, Switzerland) Cristina Lombardo, Andrea Tintori & Daniele Tona C. Lombardo, Dipartimento di Scienze della Terra Ardito Desio, Via Mangiagalli 34, I-20133 Milano, Italy; cristina.lombardo@unimi.it A. Tintori, Dipartimento di Scienze della Terra Ardito Desio, Via Mangiagalli 34, I-20133 Milano, Italy; andrea.tintori@unimi.it D. Tona, Corso Rigola 64, I-13100 Vercelli, Italy; baryonyx.walkeri@gmail.com KEY WORDS - Actinopterygii, Early Semionotidae, new taxon, Ladinian, Monte San Giorgio. ABSTRACT - The genus Sangiorgioichthys is one of the few Semionotidae known from the Middle Triassic. The type species S. aldae Tintori & Lombardo, 2007 has been found in Late Ladinian marine deposits of both the Italian and Swiss sides of Monte San Giorgio. A second species, S. sui López-Arbarello et al., 2011 described from the Pelsonian (Middle Anisian) of Luoping (Yunnan, South China) has extended the range of the genus both in time and space. A further species of Sangiorgioichthys, Sangiorgioichthys valmarensis n. sp., is described herein from the Late Ladinian Kalkschieferzone (Meride Limestone) of the Monte San Giorgio area, the same unit yielding the type species. Sangiorgioichthys valmarensis n. sp. differs from the already known species in number and arrangement of suborbitals, shape of the teeth and in shape and row number of the scales. The new species of Sangiorgioichthys increases the diversity of Semionotidae already in the Middle Triassic, indicating that the explosive radiation of Semionotidae during the Norian was preceded by a first phase of diversification during the Middle Triassic. RIASSUNTO - [Una nuova specie di Sangiorgioichthys (Actinopterygii, Semionotiformes) dalla Kalkschieferzone del Monte San Giorgio (Triassico Medio; Meride, Canton Ticino, Svizzera)] - Il genere Sangiorgioichthys è uno dei pochi Semionotidae noti dal Triassico Medio. La specie tipo S. aldae Tintori & Lombardo, 2007 è stata rinvenuta in depositi del Ladinico Superiore sia sul versante italiano che su quello svizzero del Monte San Giorgio. Una seconda specie, S. sui López-Arbarello et al., 2011, del Pelsonico (Anisico Medio) di Luoping (Yunnan, Cina meridionale) ha esteso la distribuzione del genere nello spazio e nel tempo. In questo lavoro viene descritta Sangiorgioichthys valmarensis, una nuova specie di Sangiorgioichthys rinvenuta nella stessa unità da cui proviene la specie tipo (Kalkschieferzone, Calcare di Meride) del Ladinico Superiore dell area del Monte San Giorgio. Il nuovo taxon differisce dalle specie già note per la forma e la disposizione dei suborbitali, la forma dei denti e per numero di file e forma delle scaglie. La nuova specie di Sangiorgioichthys mostra come i Semionotidae fossero già diffusi e diversificati durante il Triassico Medio, indicando come la loro radiazione esplosiva durante il Norico (Triassico Superiore) sia stata in realtà preceduta da una prima fase di diversificazione durante il Triassico Medio. INTRODUCTION The Monte San Giorgio area (Fig. 1) is one of the historically most important areas for marine vertebrates of the Middle Triassic. More than 150 years of scientific excavations in a sequence of several fossiliferous levels concentrated in a few square kilometres, led this site to be totally (Italian and Swiss sides) included in the UNESCO World Heritage List in 2010 for its unique outstanding palaeontological significance regarding the evolution of marine vertebrates during the Middle Triassic. The best known fossiliferous unit is the Besano Formation of latest Anisian - earliest Ladinian age, but since 25 years our research group is working on the poorly investigated uppermost part of Meride Limestone, the Kalkschieferzone (KSZ), of probable latest Ladinian age (see Stockar et al., 2012). During about 25 years of excavations lead by two of the authors (AT and CL), a number of interesting fossils has been reported from the lower/middle part of the upper member of the Meride Limestone, from both the Italian and Swiss sides of the Monte San Giorgio palaeontological area. However, the general biodiversity of the KSZ is quite low: about 20 fish species actually subdivided in at least two different assemblages (Tintori, 1990; Lombardo, 1999, 2001, 2002; Tintori & Lombardo, 1999, 2007; Lombardo & Tintori, 2004), the nothosaurid Lariosaurus (Tintori & Renesto, 1990; Renesto et al., 2003), three crustaceans (the mysidiacean Schimperella, the conchostracan Laxitextella and very rare undescribed decapods), a few insects mostly still undescribed (Krzeminski & Lombardo, 2001; Bechly & Stockar, 2011) and a few terrestrial plant remains. If we compare the fossil assemblages in the KSZ with those from the lower Meride Limestone Cava Inferiore, Cava Superiore and Cassina, we do not see many differences in the number of vertebrate and invertebrate taxa found in each single level (Bürgin, 1998, 1999); on the contrary, the Besano Formation assemblages are made of many more taxa, both vertebrates and invertebrates (Lombardo, 1999; Röhl et al., 2001) pointing to a strictly marine environment. TAPHONOMY AND PALAEOENVIRONMENT OF THE KALKSCHIEFERZONE In the KSZ no sure marine stenohaline organism has been found, leaving apart the nothosaurid Lariosaurus ISSN 0375-7633 doi:10.4435/bspi.2012.23
204 Bollettino della Società Paleontologica Italiana, 51 (3), 2012 Fig. 1 - The Monte San Giorgio area. The stout black line indicates the Besano Formation outcrops with small faults displacing the unit. The Meride Limestone outcrops South to the Besano Formation. Stars indicate the position of the two major sites for the Kalkschieferzone. After Lombardo (2002), modified. and the fishes, most of them strictly related to the marine environment: in fact, many of the KSZ fish genera have been found also in other localities that can be considered surely marine, such as Luoping, in southern China (Lombardo et al., 2011; Lopez-Arbarello et al., 2011) or Perledo along the eastern coast of the Lario Lake (Tintori & Lombardo, 1999; Lombardo et al., 2008) or even the Besano Formation in the same Monte San Giorgio area (Bürgin, 1999). During the deposition of the Meride Limestone, the fresh water influence became stronger: conchostracans and insects point to a quite close land with superficial freshwater ponds, permanent or seasonal, as suggested by the number of conchostracan-rich surfaces. Tintori (1990a) and Tintori & Brambilla (1991) proposed an alternation of dry and very rainy seasons, a monsoonal-like climate where heavy rains could suddenly affect the KSZ basin causing mass mortality events in the marine fauna, mainly fishes, as happened at least for Prohalecites, Peltopleurus and Allolepidotus, but also for the crustacean Schimperella (Tintori, 1990b). Furrer (1995) proposed that the fish mass mortalities were related to the dry season increase of salinity: this appears quite unlikely as a slow increase of salinity should allow fishes to leave the basin itself, while a strong sudden fresh water input can suddenly change the salinity. Also, increasing temperature should affect benthic organisms rather than nektonic ones (see for instance Cebrian et al., 2011). A further support to the fresh water hypothesis as causing mass mortality in a marine basin after flooding the nearby land, is provided by the assemblage yielding the apterygote insect Dasyleptus triassicus (Bechly & Stockar, 2011), from the upper KSZ. This assemblage, including three specimens of D. triassicus is here re-interpreted with respect to the hypothesis of Bechly & Stockar (2011). A surface of only two square meters yielding three specimens of this terrestrial insect together with diffuse small land plant remains, and five specimens of the fishes Peltopleurus and Prohalecites (Bechly & Stockar, 2011: p. 27), can be considered as a mass mortality one: a flood brought the insects and the plant remains in the basin and also killed the small fishes, which were used to dwell in marine salt waters. The presence of five fish specimens plus three insects are really worth of a mass mortality event interpretation, for such a restricted excavation surface: the number of fish specimens per square meter is actually very low in these levels, with the exception of surfaces with up to 50 Prohalecites specimens per square meter. The average richness in a fossiliferous level, following many years of field works in the KSZ, could be considered as one specimen every several dozens square meters for each lamina surface. Actually, Bechly & Stockar (2011) did not find any other fossil in the two meters thick sequence yielding Dasyleptus and the small fishes, proving that the fossiliferous surface in the whole is strictly related to the flooding. The lower and middle KSZ provide a very high number of specimens on mass mortality surfaces, compared to the regular (attritional) mortality ones. Fig. 2 shows the distribution of specimens in different beds of the site Meride-Val Mara D (lower part). The genus Peltopleurus is particularly interesting in its distribution as it amounts to 273 specimens on a total of 471 fishes recovered during the 1997-2001 excavations, for a bed surface of about 15 square meters (Fig. 2a). Four single surfaces can be considered as result of a mass mortality event, with 20 (Bed 15) to 151 specimens (Bed 1) each. All the remaining layers yield Peltopleurus too, but the number of specimens ranges from one to six for each one, widespread throughout the whole laminated bed. Not considering the genus Peltopleurus (Fig. 2b), mass mortality events are the only explanation for the unusual record of Coelatichthys meridensis Lombardo, 2001 (32 specimens in Bed 7) and Prohalecites porroi (Bellotti, 1857) (24, 26 and 30 specimens respectively in Bed a, 1, 3; the species is unknown in older beds). Owing to these quite common mass mortality surfaces P. porroi is by far the most common species across the whole KSZ: in the middle part of the unit (Ca del Frate site, Tintori, 1990), Prohalecites constitutes about the 95% of the collected specimens, but also in the upper part (Val Mara site D) it makes at least the 90% of the fish specimens (data based on 2003 excavation by CL and AT). Thus, it is evident that we can consider a mass mortality surface in the KSZ when we have only one specimen per square meter of a single surface, especially if they all belong to a single genus (Prohalecites, Peltopleurus, Coelatichthys) or to two genera. For the latter case, we know only mass mortality surfaces yielding Prohalecites and Peltopleurus together, in Bed 1 and 2 in Val Mara- Meride site D (lower part) and in surface yielding Dasyleptus. Furthermore, specimens from a mass mortality surface in the KSZ are usually of similar size (Tintori, 1990), while less common species, represented by sparse specimens, show a consistent pattern of size grouping (Tintori & Lombardo, 1999; Lombardo, 2002). As already pointed out (Tintori & Lombardo, 1999), this also implies that the mortality of marine dwellers was concentrated possibly in a single season of the year even if not always the adverse conditions led to mass mortality. If we do not take into consideration the specimens of Prohalecites and Coelatichthys, we obtain (Fig. 2c) the supposed attritional accumulation
C. Lombardo et alii - New actinopterygian from the Triassic of Monte San Giorgio 205 Interbedded to the fish-rich layers, there are levels showing massive quantity of Conchostracans: they are usually almost devoid of fishes (and vice-versa, Tintori, 1990), possibly because when the marine basin was too strongly affected by the fresh waters input from the nearby land for quite a long time, the marine fishes almost totally disappeared from the basin itself. Thus, apart from the mass mortality surfaces yielding usually Prohalecites, seldomly Peltopleurus and Coelatichthys, all the other fish genera are quite rare and their presence may be related to the attritional mortality in normal marine condition. Sangiorgioichthys spp. display this distribution pattern: for Sangiorgioichthys aldae we know only five specimens from four different outcrops (three from the lower and middle Kalkschieferzone in the Monte San Giorgio area, one from the Perledo-Varenna Formation in the Lario Lake area; Tintori & Lombardo, 2007) and the new species here described is represented only by the holotype. Possibly the Sangiorgioichthys species in the western Tethys had not a gregarious behaviour, while the eastern Tethys S. sui lived in very large schools, as it is proved by the several mass mortality surfaces extending for at least a few square kilometers in the Luoping area (Sun et al., 2009; Lòpez-Arbarello et al., 2011). Abbreviations MCSN: Museo cantonale di Storia Naturale, Lugano (Switzerland). b.f., basal fulcra; Br, branchiostegal rays; Cl, cleithrum; c.s., caudal scute; De, dental bone; d.f., dorsal fin; d.l.l.s., scales of dorsal lateral line; Dpt, dermopterotic; Dsph, dermosphenotic; Exsc, extrascapular; f.f., fringing fulcra; Fr, frontal; Io, infraorbitals; l.l.l.s., last lateral line scale; Mx, maxilla; Op, operculum; Pa, parietal; Pcl, postcleithrum; Pmx, premaxilla; Pop, preoperculum; Pt, posttemporal; Sbo, suborbital; Scl, supracleithrum; So, supraorbital bones; Sop, suboperculum. SYSTEMATIC PALAEONTOLOGY Fig. 2 - Number of fish specimens per bed from the lower part of Val Mara site D, Bed a being the top of the fossiliferous sequence. a) all genera considered; b) all genera but Peltopleurus, to allow a better definition of the distribution of the remaining genera; c) after clearing also Prohalecites and Coelatichthys, the left-over genera show the rarity of their finds. of specimens: it is quite clear that on average we have less than three specimens for each fish taxon (always for a surface of about 15 square meters), keeping in mind that the major peaks are due to indetermined/unprepared genera. We have also observed that usually, but not always, when a mass mortaly event happened, there are also a high number of specimens belonging to other species, apart from the dominant one. Furthermore, it can be observed that the total number of specimens has a sudden increase around Bed 8, which implies a possible improvement in the environmental conditions, allowing a much larger number of individuals to dwell in the lagunes of the KSZ. Subclass Actinopterygii Cope, 1887 Infraclass Neopterygii Regan, 1925 Order Semionotiformes Arambourg & Bertin, 1958 Family Semionotidae Woodward, 1890 pro parte Genus Sangiorgioichthys Tintori & Lombardo, 2007 Type species - Sangiorgioichthys aldae Tintori & Lombardo, 2007 Other species - Sangiorgioichthys sui López-Arbarello et al., 2011; Sangiorgioichthys valmarensis n. sp. (this paper). Diagnosis (emended from López-Arbarello et al., 2011) - Small semionotiform with dermal bones covered with ganoine; broad postemporal and supracleithral bones; elongate anterior supraorbital; large infraorbital at the postero-ventral corner of the orbit; several suborbitals, arranged in two or single rows anteriorly to the crescentshaped preoperculum and one or two suborbitals
206 Bollettino della Società Paleontologica Italiana, 51 (3), 2012 occupying a triangular area ventral to the infraorbital bones and lateral to the quadrate; elongate supramaxilla fitting in a notch on the dorsal border of the maxilla; small dorsal fin, limited to the area between the origin of the pelvic and anal fins; complete row of scales in the body lobe above the last scale of the lateral line; dorsal ridge of scales conspicuous, but only with a small spine. Geographic distribution - Rio Vallone and Ca del Frate (Viggiù, Varese, Italy), Perledo (Italy), Val Mara D (Meride, Canton Ticino, Switzerland), and Dawazi (Luoping County, Yunnan Province, South China). Stratigraphic distribution - Kalkschieferzone of the Meride Limestone and Perledo Member of the Perledo- Varenna Formation (Ladinian, late Middle Triassic), and Vertebrate Level of the upper member of Guanling Formation (Pelsonian, Middle Anisian, early Middle Triassic). Remarks - As already stated by Tintori & Lombardo (2007) and López-Arbarello (2008), the presence of anterior infraorbital bones, premaxilla with long nasal process, several suborbital bones, conspicuous dorsal ridge scales (with posterior spine) and the lack of gular plates support the referral of Sangiorgioichthys to the Semionotiformes sensu Olsen & McCune, 1991. The phylogenetic relationships within Semionotiformes is still controversial. Tintori & Lombardo (2007) referred Sangiorgioichthys to the family Semionotidae, but López- Arbarello (2008) stressed the poor definition of this group, which most probably represents a non-monophyletic assemblage, therefore considering Sangiorgioichthys a rather primitive form among semionotiforms. The new species of Sangiorgioichthys here described seems to confirm the interpretation given by Tintori & Lombardo (2007), with this genus included within Semionotidae, owing to the series of characters typical of the family indicated by Olsen & McCune (1991), Arratia & Schultze (1999) and Wenz (1999): a ridge of medio-dorsal scales with a prominent posterior spine, several infraorbital bones, a large antero-dorsal process on suboperculum, a narrow and forward-curved preoperculum, a high coronoid process on dentary, rostral and nasals roughly tubular, and a single supramaxilla. Sangiorgioichthys valmarensis n. sp. (Figs 3-7) Diagnosis - Small species of Sangiorgioichthys with four suborbitals arranged in a single row anteriorly to the preoperculum, and a fifth one placed ventrally to the large infraorbital at the postero-ventral corner of the orbit; narrow maxilla with long and upward bending anterior region, bearing thin and conical teeth; button-like teeth on palatal bones; scale covering made by 34 vertical rows and at least 23 horizontal rows of thin scales; belly region covered by scales longer than deep, with a rounded posterior margin; flank scales deeper than long, with a slightly rounded and serrated posterior margin; few scales of the lateral line with one or two pores; dorsal lateral line on the third horizontal row. Holotype - MCSN 8425, the only known specimen. Type locality - Bed n. 76, Site D (upper part), Val Mara (also called Gaggiolo Valley) near Meride, Unesco WH Monte San Giorgio, Canton Ticino, Switzerland. Etymology - From Val Mara, the locality where the specimen has been found. Geographic distribution - Monte San Giorgio (Canton Ticino, Switzerland). Fig. 3 - Sangiorgioichthys valmarensis n. sp. The holotype MCSN 8425 from Bed 76 of the Val Mara site D (upper part). Scale bar: 10 mm.
C. Lombardo et alii - New actinopterygian from the Triassic of Monte San Giorgio 207 Fig. 4 - Sangiorgioichthys valmarensis n. sp. a) skull of the holotype MCSN 8425; b) drawing of the skull. Scale bar: 5 mm. Stratigraphic distribution and age - Uppermost part of the lower Kalkschieferzone (upper member of Meride Limestone), latest Ladinian (Middle Triassic). Description - The specimen is about 8 cm long in standard length and about 2.5 cm deep in the region immediately behind the skull. It is preserved with the right side exposed. The specimen is almost complete, except for a slight disarticulation of the bones of the anterior part of the snout, of the distal elements of the fins and of the scales of postero-ventral region of the body. Skull - Both the frontal bones are visible; they are about two and a half times longer than the single parietal left. They are characterized by an elongated shape, with an irregular anterior margin ending with a tip and a straight and endented posterior one. The lateral margin shows only a slight orbital constriction, where the long supraorbital is placed. The interfrontal suture is slightly wavy. The pores of the supraorbital sensory canal open along the lateral margin of each element reaching the suborbitals. Ornamentation consists of tubercles mostly concentrated along the lateral margin and of short ridges arranged perpendicularly to the posterior margin of these elements. The parietal is rectangular, ornamented by tubercles near the lateral margin and the interparietal suture, which shows an irregular profile. The lateral and posterior margins of the bone are quite straight, contacting respectively the dermopterotic and extrascapular bones. The large dermopterotic is trapezoidal in shape, with tubercles in the anterior-dorsal region of the bone. Extrascapular is roughly triangular, longitudinally crossed by a series of large pores corresponding to the supratemporal commissure and surrounded by a row of tubercles. The partly preserved postemporal is roughly subtriangular (Figs 3-4). The opercular region is broad, with a semicircular posterior outline. It is made by an oval-shaped operculum and a sickle-shaped suboperculum with a well-developed antero-dorsal process, with a depth equaling about one fourth of that of the operculum; a small sub-triangular and fragmentary element, ventrally placed to the suboperculum, but detached from it, can be interpreted as the interoperculum. The bones of opercular region are not ornamented, being covered by a smooth layer of ganoine. The narrow and crescent-shaped preoperculum is vertical and bends forwards; it is slightly wider in its ventral region than in the dorsal one. Two rows of pores, corresponding to the preopercular sensory canal, are visible; on the posterior margin of the element these openings are larger than those arranged on the anterior one. The preoperculum is not ornamented (Figs 3-4). The circumorbital ring comprises supraorbitals and infraorbitals. There are two subrectangular supraorbitals; the anterior element is long about one time and a half the length of the posterior one. Owing to the preservation of the specimen, the supraorbitals of both sides of the skull are visible. Their ornamentation is made of scattered tubercles, while two pores are visible on the postero-dorsal corner of the posterior right element. The dermosphenotic is roughly diamond-shaped, with irregular margins, and it is dorso-ventrally oriented. Pores of the infraorbital sensory canal are visible along its anterior margin, and ganoine tubercles are scattered on its surface. At least three infraorbitals are recognizable. The element placed below the dermosphenotic is rectangular in shape and it is dorso-ventrally crossed by the pores of the infraorbital sensory canal, which ran near the anterior margin; ventrally, there lies the biggest infraorbital, a trapezoidal bone placed on the postero-ventral corner of the circumorbital ring; the sensory canal ran in craniocaudal direction along the ventral margin, then bending toward the dorsal region. The last visible infraorbital is triangular and it is placed caudally to the maxilla. All the elements are covered by scattered tubercles, limited to the dorsal margin in the anterior one. The region between preoperculum and infraorbitals is occupied by five suborbitals. Four elements are placed caudally to the infraorbitals: they are arranged in a single row which, proceeding dorso-ventrally, is made by a small semicircular, a broad trapezoidal, a small rectangular and a
208 Bollettino della Società Paleontologica Italiana, 51 (3), 2012 Fig. 5 - Sangiorgioichthys valmarensis n. sp. a) dorsal ridge scales and scales of dorsal lateral line in the holotype MCSN 8425; b) drawing of dorsal ridge scales and dorsal lateral line scales; c) ventral scales of the holotype MCSN 8425; d) drawing of the ventral scales. Scale bar: 5 mm. triangular bone. A large triangular element lies ventrally to the largest infraorbital. All the elements show a smooth surface (Figs 3-4). Jaws - The upper jaw is made of premaxillary and maxillary bones. The specimen shows both premaxillae, shaped like a scalene triangle with the longest side forming the oral margin, and the shortest one facing anteriorly. Near the right premaxilla lies a single small and thin tooth, probably belonging to this bone. The elongate maxilla has a subtriangular shape, with a long and narrow ethmoid process projecting antero-dorsally from the anterior end. Near the ventral margin of the maxilla there are a few small, conical and slightly curved teeth. The lower jaw shows a broad coronoid process posteriorly to the narrow and elongated anterior region of the dentary, whose oral Fig. 6 - Sangiorgioichthys valmarensis n. sp. a) drawing of lateral line scales from 16 th to 23 rd transverse scale row of the holotype MCSN 8425; b) drawing of a few lateral line scales of the holotype MCSNIO P457 of Sangiorgioichthys aldae, from Tintori & Lombardo (2007). Scale bar: 5 mm. margin is provided with long and thin teeth only on the anterior half of the bone. The ventral margin shows very large pores of the mandibular sensory canal, but the state of preservation of this region of the bone prevents to determine their exact number. In the palatal region, dorsal to the first visible infraorbital, small cylindrical teeth with a flattened cap, probably related to crushing dietary habits, are detectable. Branchiostegal rays form a row of seven elongated and partially overlapping triangular bones, decreasing in size anteriorly (Fig. 4b). Pectoral girdle - Cleithrum is curved and dorsoventrally elongated; it is crossed by a row of small tubercles. Posteriorly to cleithrum there are two postcleithra: a shorter and broader ventral element and a more elongated dorsal bone, which extends dorsally beyond the dorsal end of cleithrum. Supracleithrum is subrectangular and slightly curved forward, partially overlapping the ventral margin of the dorsalmost element of postcleithrum (Figs 3-4). Squamation - The squamation is made by ganoid scales covering the entire body. They are arranged in 34 transverse and at least 24 horizontal scale rows, all of them showing a smooth surface. The shape of the scales varies according to their position on the body. The scales of the lateral region of the trunk are subexagonal, deeper than broad up to the insertion of the dorsal fin. Their posterior margin is serrated. The scales decrease in size proceeding posteriorly, becoming subrectangular to rhombic and reducing the serration. In the ventral region, between pectoral and pelvic fins, the scales are as long as deep, with a rhombic shape and a round posterior margin. The region of the belly between the pelvic fins is covered by large scutes. Scales of the caudal peduncle have a rhombic shape, as long as deep; those covering the axial body lobe, extending up to half of the dorsal lobe of the fin, have a leaf-like shape, longer than deep. The posterior margin of the axial body lobe are made of
C. Lombardo et alii - New actinopterygian from the Triassic of Monte San Giorgio 209 Fig. 7 - Sangiorgioichthys valmarensis n. sp. a) dorsal fin of the holotype MCSN 8425; b) drawing of the dorsal fin; c) caudal fin of the holotype; d) drawing of the caudal fin. Scale bar: 5 mm. rhombic scales arranged in a single row beginning from the last scale of the lateral line. There is a mid-dorsal ridge scale row made of lanceolate scales, with a marked median keel (Figs 3, 5, 7). The passage of the lateral line sensory canal is marked by a single pore on most of the corresponding scales of the flank region; some of them show two pores, while others lack these openings, apparently without a pattern. The dorsal lateral line is detectable by a pore and a slit visible on two scales placed in the antero-dorsal region of the body, belonging to the third scale row, counting from the mid-dorsal ridge (Figs 5-6). Fins - The only visible pectoral fin is the right one; it is composed by at least six lepidotrichia. Each ray is made of elongated proximal segments and short distal ones. Due to the disarticulation of the distal end of the fin, it is not possible to evaluate how many times lepidotrichia branch. Along the anterior margin of the fin there are 2-3 basal fulcra and a few fringing fulcra. The right pelvic fin inserts at the level of the 12 nd transverse scale row: it is badly preserved, showing only 5-6 proximal segments of lepidotrichia (Fig. 3). The triangular dorsal fin inserts at the level of the 20 th transverse scale row and it is made by at least 12 lepidotrichia. Each lepidotrichium is composed by a long proximal segment, followed by shorter distal segments branching at least twice, becoming very thin and delicate. The anterior margin shows 2-3 basal fulcra and a few thin fringing fulcra (Figs 3, 7a-b). The anal fin seems to be placed at the same level of the dorsal one, but due to partial disarticulation of the ventral region of the body, this cannot be exactly determined. At least 9-12 rays have been counted: they are composed by long proximal segments, followed by shorter segments branching at least twice into narrow and cylindrical elements (Fig. 3). The tail is hemiheterocercal, with an axial body lobe reaching about half the length of the dorsal lobe. The number of rays is about 23-24: disarticulation and dispersal of the ventralmost rays makes difficult to give their exact number. Each ray is made by a relatively
210 Bollettino della Società Paleontologica Italiana, 51 (3), 2012 elongated and stout proximal segment followed by shorter and narrower distal ones, which branch at least twice. The dorsal lobe shows at least 6 dorsal caudal scutes, a basal fulcrum on the dorsal lobe and a row of fringing fulcra along the dorsal margin of the fin. Ventral margin is badly preserved and only a basal fulcrum and very few fringing fulcra are detectable (Figs 3, 7c-d). Discussion - The genus Sangiorgioichthys, erected by Tintori & Lombardo (2007) on the basis of material coming from Monte San Giorgio, was so far represented by two species only: the type-species, Sangiorgioichthys aldae Tintori & Lombardo, 2007, found also in material coming from Perledo, and a second one from the Middle Triassic of China, Sangiorgioichthys sui López-Arbarello et al., 2011. The skull pattern, particularly the peculiar arrangement of circumorbital bones, and the morphology of both upper and lower jaws allow to put the new taxon within this genus. Although the attribution of the new taxon to the genus Sangiorgioichthys is clear, many characters distinguish Sangiorgioichthys valmarensis n. sp. from the other two species. The new taxon shows fewer suborbitals than S. aldae, having five elements instead of the nine of the type-species of the genus; furthermore, the dorsalmost suborbitals of Sangiorgioichthys valmarensis n. sp. are arranged in a single dorso-ventral row, instead of two. Moreover, in S. aldae there are two distinct suborbitals placed ventrally to the large infraorbital at the posteroventral corner of the orbit, whereas in Sangiorgioichthys valmarensis n. sp. there is only one suborbital. Anyway, it should be noted that a specimen of S. aldae (MCSNL 5050) shows an incomplete separation of the suborbitals placed ventrally and posteriorly to the third, large infraorbital, therefore this character could be considered as related to intraspecific variability. The ethmoid process on the maxilla of Sangiorgioichthys valmarensis n. sp. is longer than in S. aldae and forms an obtuse angle with the dorsal margin of the bone. In the new taxon this angle is 110, while in Sangiorgioichthys aldae is >120. A few small and conical scattered teeth have been observed along the oral margin of the maxilla of Sangiorgioichthys valmarensis n. sp.; all specimens belonging to Sangiorgioichthys aldae have a clearly edentulous maxilla. Concerning dentition, another significant difference is the presence in Sangiorgioichthys valmarensis n. sp. of palatal teeth made of cylindrical pedicles with flattened crowns, visible in the area dorsal to the infraorbitals. In Sangiorgioichthys aldae palatal bones bear conical teeth of different size, not supported by pedicles. Tintori & Lombardo (2007) in fact note that S. aldae is devoid of specialized crushing teeth, as seen, e.g., in Lepidotes tendaguruensis Arratia & Schultze, 1999, L. elvensis (de Blainville, 1818), L. deccanensis (Sykes, 1851) (see also Wenz, 1967 and Jain, 1983) and L. microrhis Wenz, 2003. The palatal teeth of Sangiorgioichthys valmarensis n. sp., although clearly not highly specialized, considering their small size, show that the lacking of crushing teeth is a character peculiar of S. aldae but not of the genus as a whole. Another remarkable distinctive feature of Sangiorgioichthys valmarensis n. sp. concerns the squamation: the scales of the new taxon appear in fact thinner and more delicate respect to the thick ones of S. aldae. Only some scales in the type-species show a posterior margin characterized by few denticles with no precise topographic distribution, while in Sangiorgioichthys valmarensis n. sp. almost all scales are serrated. Concerning the shape, the ventral scales of Sangiorgioichthys valmarensis n. sp. have a clear rounded posterior margin, contrasting the rhombic outline of S. aldae. Lastly, the scales of the middle dorsal ridge row of Sangiorgioichthys valmarensis n. sp. are narrower and more lanceolate than those of S. aldae. Sangiorgioichthys valmarensis n. sp. differs from the older species Sangiorgioichthys sui López-Arbarello et al. 2011, as well. In Sangiorgioichthys valmarensis n. sp., a single pair of extrascapulars has been observed, instead of the two present in S. sui. The pattern of the infraorbital series is also quite different: both species have a large infraorbital at the postero-ventral corner of the orbit, but in some specimens of S. sui there is an elongate element anterior to it, while in Sangiorgioichthys valmarensis n. sp. the same element has a triangular shape. Suborbitals show even greater differences: S. sui has two or more ventral elements and two caudal elements to the infraorbitals, while Sangiorgioichthys valmarensis n. sp. has only one large, triangular ventral and four elements caudal to the infraorbitals. Marginal teeth of S. sui are bigger but shorter, on both upper and lower jaws, than those of Sangiorgioichthys valmarensis n. sp.; moreover, the dentition of the lower jaw of Sangiorgioichthys n. sp. is different from that of S. sui, having teeth only on the anteriormost end of the dentary. No crushing teeth have been reported in S. sui. The maxilla of Sangiorgioichthys valmarensis n. sp. also differs from that of S. sui having a longer ethmoid process, much more inclined backwardly and pointing to the anterior end of the frontals, whereas in S. sui it is short and points forwards, almost aligned with the dorsal margin of the bone. The dermal bones of S. sui are much more ornamented than those of Sangiorgioichthys valmarensis n. sp.: in the new species small ganoine tubercles are mostly concentrated on the surface of infraorbitals, supraorbitals and the posterior region of skull roof, while the rest of the skull bones are almost smooth. S. sui shows an ornamentation more homogeneously distributed, made of small tubercles, ridges and patches of ganoine (López- Arbarello et al., 2011). Scale covering in Sangiorgioichthys valmarensis n. sp. differs from that of S. sui, especially in the belly region: ventral scales of Sangiorgioichthys valmarensis n. sp. show a rounded posterior margin; in S. sui these are rhombic in shape. Some of the lateral line scales of Sangiorgioichthys valmarensis n. sp. present the pores of the corresponding sensory canal randomly arranged in single or coupled openings; concerning this character, it apparently differs from S. sui, where the scales show only a single pore and a notch along the posterior margin. Sangiorgioichthys valmarensis n. sp. shows therefore a set of characters that indicates the need to erect a new species distinct from the already known S. aldae and S. sui. The presence of three species of this genus confirms once more the diversification of Semionotiformes, and more specifically Semionotidae, during the Middle Triassic. 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