Institutional abbreviations

IGM, Colección Nacional de Paleontología (Instituto de Geología, Universidad Nacional Autónoma de México). CME, Colección de Material Extranjero, a subcolecction into IGM. UERJ PMB, Coleção de Paleozoologia (Universidade do Estado do Rio de Janeiro, Brazil). DNPM. DGM, Departamento Nacional de Producao Mineral.

Preparation methods abbreviations

The specimen studied here was recovered within a nodule from the Llano Yosobé site. It was prepared following different mechanical procedures. An air-powered micro-chisel was used to remove the superficial rock of the nodule, away from the fossil. Different needles and scrapers allowed the removal of sediments from the surface and near the fossil. The fossil was hardened with a plexigum solution in ethyl acetate and, when necessary, cyanoacrylate was used to bond detached fossil elements.

Anatomical nomenclature and abbreviations

The preserved osteological elements of the fossil described here were named following the nomenclature used in recent works for Aspidorhynchiformes (i.e. ^{Brito, 1997}; ^{Moody and Maisey, 1994}; ^{Taverne, 1969}; among others). In the same way, the abbreviations of these elements used in the figures of this work are based on similar works (^{Bartholomai, 2004}; Brito, ¹⁹⁸⁸, ¹⁹⁹²; ^{Gouiric-Cavalli 2015}; ^{Maisey, 1991}, ²⁰⁰⁰).

Comparative materials

Aspidorhynchus acutirostris^{Blainville, 1818}: CME 677, skull and fragments of the jaws from the Tithonian lithographic limestones of Solnhofen, Germany. Vinctifer sp.: CME 902 and CME 903 (five parts), scales from Aptian sediments of the Romualdo Formation, Brazil. Vinctifer comptoni (^{Agassiz, 1841}): UERJ PMB 1, 2, 3, 4, 5, 49, 52, 53, 54, 60, 61, 63, 64, 65, 66, and 80; as well as CME 872; these fossils include fragmentary and almost complete fishes 3-D preserved in nodules from the Aptian-Albian Santana Formation, Brazil. Vinctifer longirostris^{Santos, 1990}: DNPN. DGM 538-P, 460-P, 461-P, 462-P, and 463-P; UERJ PMB 74, 75, 76, 77, 78, and 79; these fossils include fragmentary and almost complete fishes preserved as impressions from the Aptian sediments of the Marizal Formation, Brazil.

SYSTEMATIC PALEONTOLOGY

Order ASPIDORHYNCHIFORMES ^{Bleeker, 1859}

Family ASPIDORHYNCHIDAE ^{Nicholson and Lydekker, 1889}

Genus VINCTIFER^{Jordan, 1919}

Vinctifer ferrusquiai sp. nov.

(Figures 2 and 3)

Nomenclatural Act. The new taxonomic name established in this article agrees with the requirements of the International Code of Zoological Nomenclature (ICZN); hence, this nomenclatural act is recorded in ZooBank, the online registration system of the ICZN. The Life Science Identifiers for this publication is also recorded in ZooBank as: urn:lsid:zoobank.org:pub:CD32D020-E5B7-4816-913C-EEE2E067A0D4

Holotype. IGM 8873, fish with part of the head and the anterior part of the trunk preserved and exposing the left and right sides (Figures 2 and 3).

Figure 2 IGM 8873, holotype of Vinctifer ferrusquiai sp. nov. from the Kimmeridgian deposits of the Llano Yosobé, near Tlaxiaco, Oaxaca, Mexico. 

Figure 3 Idealized line drawing of IGM 8873, holotype of Vinctifer ferrusquiai sp. nov. from the Kimmeridgian deposits of the Llano Yosobé, near Tlaxiaco, Oaxaca, Mexico (based on Figure 2). Abbreviations: ang, angular; cl, cleithrum; den, dentary; dfs, dorsal flank scale; dms, dorsal middle scale; ds, dorsal scale; dsp, dermosphenotic; ectp, ectopterygoid; exsc, extrascapular; fr+pa+dpt, fronto-parietal-dermopterotic (fusion of frontal, parietal, and demopterotic bones); g, gill elements; io 1-5, infraorbital; mtp, metapterygoid; mx, maxilla; op, opercle; pal, palatine; par, parasphenoid; pfr, pectoral fin ray; pmx, premaxilla; pmx (l + r), rostrum (including the terminal ends of both maxillae); pop, preopercle; ptt, posttemporal; q, quadrate; sc, sclerotic; scl, supracleitrum; sop, subopercle; so, supraorbital; suo, suborbital; rar, retroarticular; ro, rostral; srs, skull roof section; sy, sympletic; vfs, ventral flank scale; vs, ventral scale. Abbreviations enclosed in parentheses: e, external surface; i, internal surface; l, left side; r, right side. 

Etymology. The specific name honors our colleague, Dr. Ismael Ferrusquía Villafranca, for his contributions to the knowledge of the geology and paleontology of Oaxaca.

Locality and Age. The Llano Yosobé site, near Tlaxiaco, Oaxaca, southern Mexico; Kimmeridgian marine deposits belonging to the Sabinal Formation (^{Alvarado-Ortega et al., 2014}).

Diagnosis. Vinctifer species with an estimated maximum standard length of 261 mm and exhibits a unique combination of characteristics including the enamel of dermal bone of the skull strongly ornamented with tubercles and ridges as in V. comptoni; and flank scales smooth and not serrated as in V. longirostris.

Description

The specimen was recovered from a nodule. This is somewhat laterally compressed. After the preparation, this exhibits bones of both sides of the orbital and postorbital sections of the head and the anterior part of the trunk (Figures 2 and 3).

According to ^{Brito (1997, p. 688)}, the body proportions of Vinctifer show that the head plus the rostrum is one third of the standard length, and the head without the rostrum is two times longer than high. In IGM 8873, the part of the head (including the opercle) preserved is about 60 mm of length, from the ethmoid region to the posterior opercle rim; the terminal end of the preserved rostrum (maxillae) is 13 mm long; and the head height is close to 37 mm. These data suggest that the head length (without the rostrum) of IGM 8873 was, at least, 87 mm. Therefore, the estimated standard length of this specimen is 261 mm.

Skull. The anterior part of the skull of IGM 8873 is obscured or lost. The preserved part exhibits that the skull roof is almost flat, somewhat laterally compressed, and largely occupied by the frontals, parietals, and dermopterotic bones that are fused to each other (Figure 3). This forms a couple of fronto-parietal-dermopterotic bones that are asymmetrically extended in their middle edge; therefore, their suture is practically harmonic until passing the orbital region and deeply sinuous beyond. Both, fronto-parietals-demopterotic are almost three times longer than wide. Anteriorly, in front of the orbit these bones taper and form a slightly sinuous anterior edge. A small, displaced fragment of bone joint with the anterior edge of the right fronto-parietal-dermopterotic is here tentatively interpreted as a part of the rostral. Posteriorly, these composed bones are partially separated from the anterior edge of the extrascapular bones, which joint with fronto-parietals-dermopterotic just above the middle of the opercle. The supraorbital sensory canal runs all along the lateral edge of the fronto-parietal-demopterotic. The extrascapulars are rectangular, almost twice wider than long. Also, these are medially attached to each other throughout an asymmetrical sinuous suture. Behind these, the pair of postemporal bones are elongated bones with rounded posterior edges (Figure 3).

Bones of the skull roof are covered by ganoine and distinctly ornamented. The anterior third of the fronto-parietals are rather smooth while the posterior part is covered with tubercles as well as sinuous and somewhat reticular longitudinal grooves. The extrascapulars share the same ornamentation with ridges.

Jaws. Only the posterior portion of the bones that are part of both jaws are preserved. Among these, the posterior part of the maxilla is an ovoid, extended, flat, and smooth structure that displays a strongly curved dorsal edge and a slightly curved ventral edge. No teeth or alveoli are preserved in the maxillae. A possible posterior fragment of the right premaxilla is preserved. The anterior tip of the rostrum of this fish is preserved; this consists of the anterior ends of both maxillae that are strongly attached to each other and ornamented with fine longitudinal striae. Unfortunately, the premaxillar bones only show the dorsal surface; hence, the presence or absence of teeth or alveoli in this structure cannot be confirmed (Figure 3).

Below, covered by the maxillae, the terminal parts of the lower jaws are preserved. The angular bears a well-developed articular process that externally is almost totally covered by the retroarticular bone. The articular fossa for the quadrate and symplectic is located below the middle orbit. Although a small fragment of the dentary is observed below the maxilla, this and other lower jaw bones are obscured or lost.

Suspensorium. Bones of this series are partially covered by the postorbital bones (Figures 2 and 3). The quadrate is a triangular structure that lacks the posterior process and bears a stout articular head leaned downwards and forwards. This bone meets the ectopterygoid anterodorsally and the metapterygoid dorsally. The joint between the quadrate and the hyomandibula is obscured. The symplectic bone is a thick-nail like bone, strongly attached to posterior edge of the quadrate. The symplectic is short; its height does not exceed the dorsal edge of the quadrate. Large part of the quadrate bone was lost during the preparation. Symplectic and quadrate bones form part of the articular head of lower jaw and these articulate directly with the articular facet of the lower jaw.

The ectopterygoid is a flat and smooth boomerang shaped bone (Figure 3). Although the anterior end of this bone is lost and both ectopterygoids expose their external surface; some small conical teeth of uniform size is observed below the ventral rim of the right ectopterygoid. The endopterygoid and hyomandibular bones are not exposed. Only part of the metapterygoid is visible below the postorbital bones and joined with the dorsal edge of the quadrate. A possible fragment of the right palatine bone is present in front of the orbit.

Circumorbital bones. Although the circumorbital bones are scattered in around the orbit of both side of IGM 8873; it seems that these bones constitute an enclosed ring of five infraorbitals plus the dermosphenotic, one supraorbital, and two large suborbitals (Figure 3).

The infraorbitals are slender, rectangular, and flat bones. The infraorbital 1, located anteriorly in the series, is the longest; it lies on the ethmoid region of the skull and is leaned upward; its main axis is about three times its minor one. The infraorbitals 2 and 3, located below the middle part of the orbit, are shorter but at least two times longer than high. The infraorbital 4 and 5 are rectangular flat bones bordering the posterior edge of the orbit.

There are two large suborbital bones located behind the posterior infraorbitals; these flat smooth bones cover part of the cheek and the entire postorbital lateral region of the skull. The ventral suborbital is trapezoidal and the dorsal suborbital is rectangular with rounded corners, about 1.2 times longer than high (Figure 3).

One supraorbital and a single dermosphenotic dorsally enclose the orbital ring. Both are long triangular bones directed downward, which are about equal in length, and have rounded corners. These flat smooth bones are approximately three times longer than high and meet to each other above the middle of the orbit. At least one right sclerotic bone is preserved (Figure 3); however, in life this fish must have a couple of symmetric sclerotic bones occupying both eyeballs as it occurs in well preserved specimens of Vinctifer.

The infraorbital sensory canal runs near the orbital edge of the infraorbital bones, where it is intensely branched. It seems that this canal also penetrates the dermosphenotic before to meet with the supraorbital canal.

Opercular bones. The opercular series consists of three laminar bones and lacks interopercle (Figure 3). The opercle is the largest element in the series; it is kidney shaped, higher than long, with a straight anterior edge, sinuous ventral edge, and posterior and dorsal edges curved. The ventral region of the opercle is more extended backwards than the dorsal one. Below, the subopercle is present as an inverted isosceles triangle, about two times longer than deep, in which the dorsal edge is equally extended than the opercle.

The preopercle is a roughly triangular bone, equally high as the opercle. Whereas its upper quarter forms a sharp projection, the rest of the bone is shaped like an equilateral triangle in which the anterior edge is convex while the ventral and posterior ones are straight and somewhat sinuous, respectively. The preopercular sensory canal runs along this bone, near to its ventral and posterior edges, forming a posteroventral acute angle. This sensory canal is strongly branched all along its horizontal section and in the ventral half of its vertical section; each of these branches opens in a pore (Figure 3).

Bones of the opercular series are covered with ganoine that is well ornamented with tubercles and ridges (Figures 2 and 3). In the opercle, the surface is almost entirely ornamented with tubercles aligned in concentric lines. The focus of these lines is located just at the beginning of the last quarter of the height of its anterior edge, apparently opposite to the articular facet exposed on the inner surface of this bone. The tubercles are progressively greater toward the edges of this bone; they are ankylosed near to the ventral edge forming short and sinuous ridges. The subopercle is covered with sinuous ridges of variable size and randomly arranged. Although, most of the preopercle surface is smooth; relative few small tubercles are between the preopercular sensory canal and ventral and posterior edges. Also, a small surface located in front of the ventral half of horizontal section of preopercular sensory canal is ornamented with large tubercles and sinuous short ridges.

Branchial arch. Disarticulated and scattered elements of the branchial arch on the left are preserved in the left side of the specimen. These bear numerous, elongated thread-like gill filaments and robust, elongated gill rakers are also visible (Figure 3).

Pectoral and pelvic fins. Only the cleithrum and supracleithrum elements are persevered in the pectoral girdle. Other bones of this girdle are not exposed. The pectoral fin of this fish comprises at least five rays, whose bases are flat and wide. The terminal ends of these rays are obscured (Figure 3).

In lateral view, the cleithrum seems an inverted “L” structure, almost uniformly thin throughout (Figure 3). The horizontal limb of this bone is almost as long as the vertical limb height and the joint of its limbs form rounded posterior corner. The terminal third of the vertical limb of this bone is thinner than the rest of the bone. The entire surface of the horizontal limb and the lower half of the vertical limb are strongly ornamented with long sinuous crests that in some cases are fused forming a net.

The supracleithrum is a high triangular bone, noticeably wider than the dorsal end of the cleithrum (Figure 3); it covers the laterally surface of the body behind the opercle and slopes dorsally covering the occiput. In IGM 8873 the left supracleithrum bone is dislocated, rotated, and exhibit its internal surface where it is clear that this bone encloses the sensitive canal of the lateral line. The right supracleithrum is in life position in this fish; the ganoine on the surface of this bone is entirely ornamented with tubercles and sinuous ridges.

Scales. The part of the trunk preserved in IGM 8873 is entirely covered of thick ganoine scales arranged in longitudinal rows (Figures 2 and 3). The dorsal region of the trunk is covered with a row of middle dorsal scales associated with two rows of dorsal scales placed laterally on each side of the trunk. Additionally, there are two rows of flank scales covering the lateral sides of the trunk and at least five rows of ventral scales on the abdominal region. At least the flank and ventral scales have a dorsal middle large spine-like articular process and a small central depression in the ventral one; therefore, the dorsal process of one scale inserts within the ventral depression of the immediate superior scale.

The general shape of scales of the middle dorsal row is not clear because they are amply overlapping; however, these seems to be elongated and ovoid. Contrary, the shape of scales of the associated dorsal rows is elongated and rectangular. The ganoine of dorsal scales is strongly ornamented with remarkable tubercles and sinuous longitudinal ridges (Figure 3).

The scales of both flank rows are flat, rectangular plates, higher than long. The scales on the dorsal flank row are hypertrophied; in these, the height is between four and five times the length. The upper sixth part of each dorsal flank scale tapers dorsally forming a triangular wing tilted forward, which is also leaned inward participating in the covering of the dorsal trunk region. Contrary, the scales on the ventral flank row are also remarkable: these are equally long but about almost half high than those placed immediately above (Figures 2 and 3).

In both flank scales, the edges are practically harmonious, straight, and without serration. In these scales, the ganoine is practically smooth except for some inconspicuous tubercles present in the posterior half on the inward wing of the dorsal flank scales, as well as, for the middle straight ridge that runs from top to bottom in dorsal and ventral flank scales. This middle straight ridge represents the posterior limit of the overlapping of the flank scales. In opposite position to this middle straight ridge, the internal surface of flank scales, shows a shallow and wide groove, in which the little thickened anterior edge of the subsequent posterior scale is accommodated (Figures 2 and 3).

In IGM 8873, at least five rows of ventral scales are covering the abdominal region of the trunk (Figure 3). Overall, these are rectangular, about two times longer than high, and its dorsal edge bears a prominent spiny dorsal process. These scales are almost entirely smooth, except for a small keel at the base of the dorsal process.