Marcopoloichthys mirigioliensis, Arratia & BÜrgin & Furrer, 2024

Genus Marcopoloichthys Tintori et al., 2007

Content. Five species known: Marcopoloichthys ani , M. andreettii , M. faccii , M. furreri , and Marcopoloichthys mirigioliensis sp. nov.

Geographical distribution. Eurasian distribution, including southern China (Yunnan and Guizhou Provinces), Northern Italy (Lombardy and Friuli) , southeastern Switzerland ( Ducan mountain , Canton Graubünden) , and southern Switzerland (Monte San Giorgio, Canton Ticino) .

Age. From the middle Anisian (Middle Triassic) to early Carnian (Late Triassic). [Remark: Tintori et al., (2007: p. 15) also mentioned not yet described specimens from the Norian of Northern Italy.]

Marcopoloichthys mirigioliensis sp. nov. http://zoobank. org

( Figs. 3 View Fig , 4 View Fig , 5 View Fig , 6 View Fig , 7 View Fig , 8 View Fig , 9 View Fig , 10 View Fig and 11 View Fig ).

Diagnosis. (Based on a unique combination of characters distinguishing it from other marcopoloichthyids.) Te smallest known marcopoloichthyid with a standard length (SL) of about 30–35 mm. Skull roof bones, infraorbitals and lower jaw covered with a thin layer of ganoine with rounded tubercles of different sizes. Large head, about 36% of SL; with a moderately large orbit, about 30% of head length and a moderately long preorbital length, about 33% of head length. With about 35 to 38 vertebral segments, which is an intermediary range compared to other marcopoloichthyids ( Table 1). Dorsal fin support including a compound and expanded anterior proximal radial, which is a massive, almost ax-shaped plate formed by the partial fusion of four proximal radials; eight or nine more proximal radials are present. First compound dorsal pterygiophore supporting at least one basal fulcrum and three or four lepidotrichia. Anal fin with six pterygiophores partially, and irregularly, fused between them. Last anal proximal radial elongate, plate-like, and supporting ca. five or six lepidotrichia. Caudal fin with ca. eight epaxial basal fulcra, less than M. furreri and M. ani ( Table 1). Short series of epaxial fringing fulcra associated with the proximal half of first principal ray, as in M. furreri . Between 20 or 21 principal caudal rays (as in M. furreri ). One short hypaxial procurrent ray (less than in other marcopoloichthyids; Table 1). Accessory hypaxial fulcrum present. About 11 hypaxial basal fulcra (12 in the holotype of M. furreri and seven in M. ani ). A series of ca. four oval-shaped urodermals present. With two large ovoid scales that are scute-like and associated to the urogenital region (three or four in M. furreri ).

Derivation of name. Te specific mirigioliensis for the excavation locality Point 902/Mirigioli at the southwestern crest of Monte San Giorgio (Meride, Canton Ticino), which was led by E. Kuhn-Schnyder (PIMUZ) from 1950 to 1968.

Holotype. PIMUZ T 3030 , a complete specimen that is preserved oriented to the right ( Fig. 3A, B View Fig ).

Paratypes. Five specimens: PIMUZ T 2976 , 4409 View Materials (part and counterpart), 4410 (part and counterpart), 4411, and 4424 .

Referred material. Eighteen specimens from the same locality, Point 902/Mirigioli ( PIMUZ T 4412 , 4413 View Materials , 4414 View Materials , 4415 View Materials , 4416 View Materials , 4417 View Materials , 4418 View Materials , 4419 View Materials , 4420 View Materials , 4421 View Materials , 4422 View Materials , 4423 View Materials , 4427 View Materials , 4428 View Materials , 4429 View Materials , 4430 View Materials , 4431 View Materials , and 4432); six of them with part and counterpart ( PIMUZ T 4416 , 4417 View Materials , 4420 View Materials , 4421 View Materials , 4422 View Materials , and 4428) .

Type locality and age. Point 902/ Mirigioli ( Monte San Giorgio , Meride , Canton Ticino, southern Switzerland; 45.9110713N / 8.940217E). Lower Besano Formation (late Anisian, Illyrian, R. reitzi Ammonoid Zone). Holotype from bed 10, paratypes from beds 10 and 17, referred material from beds 4 to 19. GoogleMaps

Description

Te new fish, Marcopoloichthys mirigioliensis sp. nov., is small, about 30 to 35 mm SL (with 32 mm being the most frequent value), with an elongate, torpedo-like body, a moderately large head that occupies about 36% of the SL, and a narrower caudal peduncle that is followed by a deeper caudal fin. Te orbit is moderately large; its diameter is about 30% of the head length, and the preorbital length is moderately long, about 33% of the head length. Te insertion of the dorsal fin is located slightly in front of the middle of the body length and is opposed ventrally to the origin of the pelvic fins; the insertion of the anal fin is placed opposite to the posterior part of the dorsal fin. Te insertion of the anal fin is just in front of the last pterygiophore of the dorsal fin or slightly posterior; thus, the insertion of the moderately short anal fin is closer to that of the pelvic fins than to the caudal fin. Consequently, the new fish, as in other marcopoloichthyids, has a relatively long caudal peduncle (about 38% of standard length in the holotype PIMUZ T 3030). Te small pectoral fins, poorly preserved, have a low position, closer to the ventral margin of the body than to the middle region of the flank. Te caudal fin has both lobes of nearly the same size with its posterior margin deeply forked. Te distal portions of all fin rays are commonly crushed or not preserved.

Skull roof and braincase Te skull roof is incompletely preserved in all specimens and does not allow a detailed description of its shape, nor of specific bones. Remains of the parietal [= frontal] bones are exposed laterally, i.e., above the orbits, and they have a gentle incurvation when the fish is preserved with closed jaws. Te region where the nasals would be placed is poorly preserved, but an elongate rectangular nasal bone and a shorter accessory or additional nasal bone are preserved in PIMUZ T 3030 ( Figs. 3 View Fig , 4 View Fig ). An incomplete, elongate bone, the mesethmoid, is preserved at the most anterior tip of the snout. It has a similar T-shape, as in Marcopoloichthys furreri , but commonly one of its lateral processes is destroyed in the available specimens; the preserved process is distinct, well developed, and laterally extended.

Te postparietal [= parietal] and supratemporotabular [= dermopterotic] are poorly preserved so that a proper description is not possible, but the supratemporotabular would be forming the lateral border of the skull roof in PIMUZ T 3030 ( Fig. 4 View Fig ); but its suture with the postparietal is not preserved, while the autosphenotic and its sutures with the supratemporotabular and parietal show that the bone is unfused in the holotype. Because of poor preservation, it is unclear whether the skull roof bones are independent or whether they are partially fused in available specimens. A fragment of a possible extrascapula is preserved in PIMUZ T 3030 . Te external surface of the skull roof bones is covered by ornamentation, consisting of small, irregular ridges and tubercles. Information on the cephalic sensory canals and pit-lines is not available because of the ornamentation covering the skull roof bones; however, traces of sensory canals are not observed in places where the ornamentation is missing .

Te orbitosphenoid is not preserved in the available material. Te lateral ethmoid is well ossified and slightly bent. Little information is available about the parasphenoid and vomer, although the parasphenoid is partially exposed in the holotype ( Fig. 4 View Fig ) and is preserved as an imprint in PIMUZ T 4411 .

Orbit and circumorbital bones Te new species has a moderately large orbit ( Figs. 3 View Fig , 4 View Fig ) of about 30% of head length. All specimens studied herein were not feeding at the moment of their death, and their orbit is preserved almost rounded; in contrast, in other marcopoloichthyids preserved during feeding, the orbit and the mouth are protracted anteriorly, and the orbit is oval-shaped ( Arratia, 2022: Figs. 4 View Fig , 7B View Fig ).

Te circumorbital series is incompletely preserved in the holotype and partially destroyed or not preserved at all in other specimens so that it is not possible to describe the anatomical characteristics of all bones. Additionally, the ornamentation obscures most of the boundaries between bones in the holotype. As in other marcopoloichthyids, the circumorbital series is open dorsally due to the absence of supraorbital bones. Anteroventrally, a possible antorbital and infraorbitals 3–5 ( Fig. 4 View Fig ) are observed, while a possible small, squarish dermosphenotic is preserved at the posterodorsal corner of the orbit in PIMUZ T 3030 . A faint remnant of an anterior sclerotic bone is preserved. Posterior to the dermosphenotic and posterodorsal infraorbitals, one or two suborbitals are preserved, but the ornamentation obscures details on

(See figure on next page.)

Fig. 3 View Fig Marcopoloichthys mirigioliensis n. sp. A, photograph and (B) drawing of holotype in lateral view ( PIMUZ T 3030 , reversed to the left). C, photograph and (D) drawing of paratype ( PIMUZ T 2976 ). Scale bars: 5 mm. Abbreviations: an.f, anal fi; a.v, abdominal vertebrae; bsp, basipterygium or pelvic plate; cau.f, caudal fin; cl, cleithrum; c.v, caudal vertebrae; dor.f, dorsal fin; l.j, lower jaw; max, maxilla; met, mesethmoid; orb, orbit; sk,skull roof; op.r, opercular region; pec.f, pectoral fin; pel.f, pelvic fin these bones, as well as on infraorbital 3 and the trajectory of the infraorbital canal .

Upper jaw Te upper jaw ( Figs. 4 View Fig , 5 View Fig ) consists of a moderately long premaxilla and a long maxilla, which are poorly preserved. A supramaxilla has not been observed and is considered absent as in other marcopoloichthyids. Te premaxilla and maxilla either are broken or not preserved in the available specimens. Te premaxilla is about half of the length of the maxilla, and when the mouth is closed, the premaxilla is placed anteroventrally to the maxilla. Te premaxilla is elongate, and its anterior thin process is incompletely preserved in the available material and slightly gently curved and edentulous

( Fig. 6B View Fig ). Te longer and larger maxilla ( Fig. 5 View Fig ) is narrow anteriorly and widens caudally into a plate-like posterior part. Its posterior margin is slightly oblique. Both bones, premaxilla and maxilla, lack teeth. If ornamentation was present, no remains are visible in any specimen.

Lower jaw Te lower jaw ( Figs. 4 View Fig , 5 View Fig ) is not well preserved in the available material, and only the anterior margin and ventral part are visible. As in other marcopoloichthyids, the jaw is prominent, relatively short, deep, and somewhat triangular-shaped, with the quadrate-mandibular articulation placed at a point roughly below the mid-orbit ( Fig. 4 View Fig ) when the mouth is closed. Te oral margin lacks teeth as in other marcopoloichthyids. Te ventral margin is almost straight and has a parallel running ridge below which a series of small pores indicate the course of the mandibular sensory canal (see specimens PIMUZ T 2976, 4411 and 4428). Te lower jaw narrows anteriorly at the symphyseal region, which is anteroventrally placed and widens dorsally, producing a very high coronoid process that is covered by lateral bones in the available material ( Fig. 5 View Fig ). Tus, the elements forming the coronoid process are unknown in this species, but it is expected to be formed by the dentary and surangular, as in other marcopoloichthyids (see Arratia, 2022: Figs. 4B View Fig , 8 View Fig ). Te anteroventral margin of the jaw has the characteristic shape described for Marcopoloichthys furreri , due to the presence of a slightly rounded anteroventral process ( Fig. 4 View Fig ). Te posterior part of the right lower jaw is preserved medially in PIMUZ T 2976, and because only one ossification is observed, this is interpreted here as the result of fusion among the articular, angular and retroarticular. Te postarticular process of the angular bone

( Fig. 4 View Fig ) is rudimentary or non-existent.

Te jaw ornamentation is very characteristic in Marcopoloichthys furreri ; however, the lateral surface of the jaw is covered by other bones in this new fish material, and the exposed portion is not very informative, so that the condition of the ornamentation remains unclear for Marcopoloichthys mirigioliensis sp. nov.

Palatoquadrate, suspensorium, hyoid and branchial arches, and urohyal Most of these elements are partially hidden by other bones or are destroyed so that the description is restricted to a few of them. Although part of the entopterygoid is preserved in PIMUZ T 3030 nothing special can be said about it; there is no information available on the ectopterygoid and palatine regions. A urohyal has not been observed in any specimen, and it is assumed to be absent as in other marcopoloichthyids. Of the hyoid arch, only the rectangular plate-like anterior ceratohyal is identifiable (but left and right elements are superposed in PIMUZ T 4411), and the hypohyal region is not preserved. Remnants of branchial arch elements are preserved in a single specimen (PIMUZ T 4432; Fig. 6 View Fig ), but a description is not possible.

Specimen PIMUZ T 4411 is an interesting specimen that provides information on the suspensorium, but there is a problem in that the left and right quadrates and hyomandibulae ( Fig. 6B View Fig ) are preserved and overlapping each other, making the interpretation of the cranial bones difficult. Te suspensorium is only partially preserved. Te left hyomandibula is almost vertically oriented, with a slight anteroventral inclination on its shaft. Because of the position of the bone, its cranial facet seems to articulate largely with the supratemporotabular region [= dermopterotic]; because of the poor preservation or no preservation of the braincase (which probably was not ossified in life), other components of the cranial facet are unknown. Tere is a significant distance between the ventral ossified part of the hyomandibula and the quadrate and it is expected that this space was filled with the symplectic or hyosymplectic cartilage

( Fig. 6B View Fig ), because no ossified section is observed between the lower part of the hyomandibula and the ossified lower part of the symplectic (which is not preserved in the specimen illustrated in Fig. 6 View Fig , probably due to its cartilaginous condition). Te quadrate is a triangular bone, with a well-defined rounded condyle for articulation with the lower jaw; it is unclear how large the metapterygoid was. An elongate, triangular-shaped symplectic is observed in PIMUZ T 3030 ( Fig. 4 View Fig ). A quadratojugal has not been observed as well as in other marcopoloichthyids.

Opercular and branchiostegal series, and gular plate Te preopercle is described here, although it is a bone associated with the suspensorium. Te opercular and branchiostegal series are poorly preserved or incomplete so that their descriptions are also incomplete. Te preopercle is a large and L-shaped bone, which is slightly expanded postero-ventrad at the confluence of both of its arms. No specimen preserves the complete bone; its dorsal arm is slightly longer than the ventral one when the mouth is closed and almost reaches the lateral side of the supratemporotabular [= dermopterotic] dorsally ( Fig. 3C, D View Fig ), and the ventral arm seems to be mainly carrying the preopercular canal. Tis canal is positioned along a slightly broad groove and blind-ending tubules are clearly visible in PIMUZ T 2976, T 4415, and especially in T 4419, where the preopercles are partially preserved.

A description of the opercle, subopercle and interopercle is not possible, because the bones are damaged or not preserved in the available material (see Figs. 3 View Fig , 4 View Fig , 5 View Fig ). A similar situation is observed in relation to the branchiostegal series, whose number of rays remains unknown, as in other marcopoloichthyids. A gular plate has not been observed and is interpreted as absent, as in other marcopoloichthyids.

Vertebral column, intermuscular bones, and ribs A few specimens provide partial information on the vertebral column. Te caudal vertebrae are better preserved than the abdominal ones, including the holotype PIMUZ T 3030 ( Fig. 3 View Fig ) and paratypes PIMUZ T 4410 ( Fig. 7B View Fig ) and PIMUZ T 4411 ( Fig. 6A View Fig ) .

Te vertebral column is aspondylous (see Arratia et al., 2001 for the different types), with well-developed dorsal and ventral arcocentral elements forming the centra, and a persistent, functional notochord in adults. Tere are about 35–38 vertebrae, including five hypural segments, making the count comparable with those of Tintori et al. (2007) and Arratia (2022). Tere are about 19–21 caudal vertebral segments ( Fig. 3 View Fig ); small interdorsal and interventral arcocentral elements alternating irregularly with the well-developed basidorsal and basiventral arcocentral elements have been observed, as in Marcopoloichthys furreri . No remains of centra are present in the ural region (see description of caudal fin).

Te neural and haemal spines ( Figs. 3 View Fig , 7 View Fig , 9 View Fig , 11 View Fig ) of the caudal region are narrow, except for those of the preural centra (see below). Te neural and haemal spines are moderately inclined toward the body axis, increasing slightly their caudal inclination posteriad. Te first haemal spines are short, not extending between the anal pterygiophores or just reaching them.

Due to the poor preservation of the abdominal or precaudal vertebrae, the presence and structure of the “supradorsal carrier” found in Marcopoloichthys furreri ( Arratia, 2022: Fig. 9 View Fig ) could not be confirmed. Te total number of parapophyses ( Fig. 3 View Fig ) is unclear due to poor preservation of the precaudal region. Te first ones would be covered by the opercle and the dorsal bones of the pectoral girdle. Te parapophyses are lightly squarish in shape, and each bears a small articular cavity close to its ventral margin. No ribs are preserved in the studied specimens. Tey were not reported or illustrated in Marcopoloichthys ani (Tintori et al., 2007: Fig. 4 View Fig ) or in Marcopoloichthys furreri ( Arratia, 2022: Fig. 9 View Fig ), and it is accepted here that marcopoloichthyids do not have ossified ribs.

Tere is no reliable information on the neural arches of the abdominal vertebrae, which are distorted, disarticulated, or not preserved at all in the available specimens. Consequently, it is not possible to confirm the presence of a stout and short epineural process emerging at the posterolateral margin of the arch, as in Marcopoloichthys furreri .

Te series of supraneural bones is commonly either not preserved, distorted, or displaced and covered by other structures. Te total number of supraneural bones is unknown. Te series extends up to the expanded, plate-like, compound first dorsal proximal radial, and it does not extend between the most anterior proximal radials, as in Marcopoloichthys furreri .

Pectoral girdle and fins Te pectoral girdle is poorly preserved or not preserved in the available specimens. Te dermal bones forming the teleostean girdle are the posttemporal (linking the girdle with the posterior region of the cranium), supracleithrum, cleithrum, clavicle, and postcleithra. Te posttemporal, supracleithrum, and clavicle are incompletely preserved or not preserved in the available material ( Figs. 3 View Fig , 4 View Fig , 6 View Fig ). Chondral bones, including the scapula, coracoid, and proximal and distal radials, are not preserved in the available material.

Te sigmoidal-shaped cleithrum ( Figs. 4 View Fig , 6 View Fig ) is an elongate, narrow bone forming most of the pectoral girdle and is a heavily ossified bone, with a long and narrow dorsal limb and a slightly expanded and curved ventral limb. Due to the poor preservation of the cleithrum it is unclear whether a serrated appendage is on its anteromedial surface. Remains of the scapula and coracoid are preserved in the available material, but they are not informative.

Te pectoral fin ( Figs. 3 View Fig , 4 View Fig , 6 View Fig , 7 View Fig ) is positioned near the ventral margin of the body. Te total number of pectoral rays is unknown, because the fins are incomplete or disarticulated, but one thick, first pectoral ray and nine to 11 rays are preserved in PIMUZ T 3030. All rays have long, delicate bases and are scarcely branched and segmented distally. Basal fulcra or fringing fulcra have not been observed.

Pelvic girdles and fins Te pelvic girdles are exposed in a few specimens (e.g., Figs. 3 View Fig , 7 View Fig , 8 View Fig and 9 View Fig ). A large, elongate plate-like basipterygium (or pelvic plate) is slightly curved medially; its posterior part is slightly broader than the anterior one and presents an elongate posteromedial process that it is longer than the one present in Marcopoloichthys furreri . Te rays per fin are difficult to count due to their poor preservation, but seven or eight rays are preserved in specimen PIMUZ T 4409 and nine in PIMUZ T 4432. Tis last specimen is preserved with the pelvic fin expanded so that it is possible to observe that the two most inner rays are thinner than the preceding rays.

Dorsal fin and radials Te insertion of the dorsal fin is almost at the same level of the insertion of the pelvic fins and the fin does not overlap the anal fin ( Fig. 9 View Fig ). Te dorsal fin ( Figs. 3 View Fig , 6A View Fig , 7 View Fig , 9 View Fig ) and its radials are not well preserved, with all bones partially displaced or damaged so that a precise total number of dorsal fin rays and radials cannot be provided. Te holotype PIMUZ T 3030 has ca. 15 rays preserved, but the radials are destroyed; in contrast, PIMUZ T 4411 has nine proximal radials, but only 10 incomplete or broken rays are preserved. Medial and distal radials are not preserved in the available specimens. In all specimens, except one, the first dorsal proximal radial is destroyed or incomplete; this plate-like proximal radial is nicely shown in Fig. 9 View Fig . It is an ax-shaped element, with an anteriorly expanded, slightly rectangular bony plate that is partially separated proximally of a posterior bar-like radial; this morphology suggests that this compound element may be the result of fusion and modification of at least three proximal radials. All other proximal radials are slightly expanded distally, with the last one more so, having a broader distal articular surface. However, it is unknown how many rays are supported by this last pterygiophore.

Anal fin and radials Te anal fin and its pterygiophores are not well preserved in the available material, making a description difficult. Additionally, there is variation in number of proximal radials and amount of fusion involved between proximal radials. Te most complete series of proximal anal radials, or the most informative, is that present in PIMUZ T 4424 ( Fig. 10 View Fig ). In this specimen, the first proximal radial is broader and apparently formed only by a single expanded proximal radial. Tis first proximal radial is long and curves anterodorsally giving the bone a characteristic shape in marcopoloichthyids ( Arratia, 2022; Tintori et al., 2007). Tis first proximal radial is followed by four elongate, but shorter and narrower radials in this specimen. Te last radial is an elongate element, bearing a narrow, thin anterior process that extends dorsally between the distal tips of the haemal spines and has a broad distal portion for articulation with about four lepidotrichia ( Fig. 10 View Fig ). In specimen PIMUZ T 4410a ( Fig. 9 View Fig ), the first proximal radial is expanded ventrally, giving the impression that this is a result of fusion of two radials; the bone is very elongate and curves markedly anterodorsally. Tis element is followed by three shorter and simple proximal radials, and the last one is a shorter proximal radial that expands posteroventrally in an elongate, somewhat triangular-shaped plate, which supports about four rays that are poorly preserved in this specimen. Te holotype has relatively well preserved anteriormost radials, but the last, expanded one is partially destroyed. In total, the anal series of proximal radials includes five separate elements and ca. nine rays.

Caudal fin and endoskeleton Te caudal fin and endoskeleton are preserved in several specimens. Te homocercal caudal fin ( Figs. 3 View Fig , 7A View Fig ) is deeply forked, with a few shorter and thinner middle principal rays compared to the long, marginal segmented and branched principal rays ( Fig. 11 View Fig ). As in Marcopoloichthys furreri , many rays still preserve a thin layer of ganoine on their surfaces.

Two or three preural vertebrae support the anterior basal fulcra. Te preural vertebrae, as well as the ural ones, are supported by a functional notochord. Consequently, except by the arcocentra, no centra are formed, and the region is monospondylous, in contrast to the irregular diplospondylous vertebral segments present in some of the mid-caudal vertebrae ( Fig. 11 View Fig ). Te two preural segments (corresponding to preural centra 1 and 2) are characterized by the presence of well-developed ventral arcocentra with moderately broad and flat haemal spines, which distally support the last principal rays, one procurrent ray and the series of hypaxial basal fulcra

( Fig. 11 View Fig ). Dorsally, the neural arches or arcocentra and spines of these two preural vertebrae are missing, and their space is partially occupied by the uroneural plate, a condition different to that in Marcopoloichthys furreri ( Arratia, 2022: Figs. 13, 14). Te neural spines of the last caudal and preural vertebrae 3 and 4 are inclined posteriorly, closer to the body axis, and they do not support the most anterior basal fulcra.

Te preservation of the neural spines of preural vertebrae 3–4 suggests that they have a central core of cartilage surrounded by a thin, perichondral ossification. An anterior process at the base of neural spines is apparently absent. Te haemal spines of preural centra 1–2 are broader than most anterior spines. Te haemal spine of preural vertebra 4 and more anterior ones are narrower. Te haemal spines of the most preural vertebrae are thinly perichondrally ossified. Te haemal spines of preural vertebrae 1–3 ( Fig. 11 View Fig ) bear a short and narrow process dorsally at their limit with the expanded ventral arcocentra, which is often broken. A hypurapophysis on the lateral wall of the ventral arcocentrum or haemal arch of preural centrum1 is absent.

Posterior to the neural spine of preural centrum 3, a large chondral neural plate is positioned ( Fig. 11 View Fig ). In many specimens, this region is damaged or the elements are displaced, except for PIMUZ T 3030, which is illustrated in Fig. 11 View Fig . Because of its position as part of the ural region and the lack of neural arches or arcocentra, the bony plate is considered here as a uroneural plate or “a uroneural of special kind” following Arratia and Schultze (2013; see section of Discussion). Certainly, due to its position and shape, such an element in Marcopoloichthys mirigioliensis n. sp., increased the stiffness of the tail during locomotion, which is a function of the uroneurals.

No epurals are present, and there is no space left for them between the distal tips of the enlarged uroneural plate and the bases of the epaxial basal fulcra. Five hypurals ( Fig. 11 View Fig ) are present, all of them close together so that a hypural diastema between hypurals 2 and 3 is absent. Hypural 1 is expanded at its proximal region and seems to have preserved part of the ventral arcocentrum as in M. furreri . Hypural 1 is the longest and broadest element of the series, whose size diminishes posteriorly. Hypural 1 ( Fig. 11 View Fig ) supports the lowest principal rays, while hypurals 2 and 3 support the thin and short middle principal rays. Several thin and narrow bases of the principal rays articulate directly with one hypural without producing a special angle.

Tere are ca. eight epaxial basal fulcra, which are followed by an incomplete series of fringing fulcra, which only reach to the mid-region of the dorsal margin of the first unsegmented principal ray. Te most anterior basal fulcra are bifurcated at their bases ( Fig. 11 View Fig ). Tere are 20 or 21 principal rays with narrow bases that are segmented and branched distally as in Marcopoloichthys furreri ( Arratia, 2022) . Teir most distal segments are commonly not preserved, except for the shorter rays of the middle region of the fin, which have thin and narrow bases branching once or twice distally. Te articulation between segments of the principal rays is straight.

Ventrally, there are about 12 hypaxial basal fulcra. Tere is one short procurrent ray that is followed by a short series of hypaxial fringing fulcra ( Fig. 11 View Fig ). In addition, an accessory fulcrum is present between the procurrent ray and the hypaxial basal fulcra ( Fig. 11 View Fig ).

One incomplete dorsal scute and another incomplete ventral scute precede the epaxial and hypaxial lobes, respectively. A series of four slightly displaced ovoid and circular urodermals is present ( Fig. 11 View Fig ).

Scales Te body is devoid of scales, except for two large oval cloacal scales or scute-like elements ( Figs. 7 View Fig , 8 View Fig , 9 View Fig and 10 View Fig ) placed around or close to the urogenital region as in other marcopoloichthyids.

Stomach content In the region between the anterior most anal pterygiophore, pelvic fins and enlarged scales or scutes of specimen PIMUZ T 4410, there is a series of small structures that are herein interpreted as stomach content remains ( Fig. 7B View Fig ). Tese remains are represented by tiny phosphatic elements (length about 0.2–0.3 mm) that probably are hooks of a coleoid cephalopod (see Rieber, 1970). Tese hooks are smaller than the ones found in the holotype and only specimen of Phragmoteuthis? ticinensis Rieber, 1970 recovered in bed 17 and are currently under study to identify them taxonomically.