taxonID	type	description	language	source
03E3CA2FFFC6E558FF77FF19FD71E91B.taxon	description	7: e 6799. Zverkov NG, Arkhangelsky MS, Pardo Perez JM, Beznosov PA. 2015 a. On the Upper Jurassic ichthyosaur	en	Zverkov, Nikolay G., Jacobs, Megan L. (2021): Revision of Nannopterygius (Ichthyosauria: Ophthalmosauridae): reappraisal of the ‘ inaccessible’ holotype resolves a taxonomic tangle and reveals an obscure ophthalmosaurid lineage with a wide distribution. Zoological Journal of the Linnean Society 191
03E3CA2FFFCBE553FF29FA78FAF3ED38.taxon	description	v. 2018 Ophthalmosauridae indet. – Delsett et al.: 34, figs 15, 16. Holotype: PMO 222.658, partial nasal and several fragments of cranial bones; several vertebrae, coracoids, distal part of the scapula, incomplete left forelimb and proximal portion of the right humerus (Fig. 22 A – L). Paratype: CCMGE 45 – 46 / 13328, right humerus and caudal vertebra (Fig. 22 M – Q). Diagnosis: Nannopterygius borealis differs from other species of Nannopterygius in the following combination of features: coracoids with relatively wide rounded posterior portions (wider than in the type species and N. yasykovi but still not as wide as in other ophthalmosaurids); intercoracoidal facet lenticular in outline and dorsoventrally thin (like that of N. enthekiodon and unlike those with complex outlines in N. saveljeviensis and N. yasykovi); humerus with accessory anterodistal facet (variable in N. enthekiodon, but also present in N. savelyeviensis and N. yasykovi); humeral ulnar facet larger than the radial facet in both anteroposterior and dorsoventral width (non-unique autapomorpy; nearly equal in all other species); radius markedly smaller than ulna (unambiguous autapomorpy; comparable in size to ulna in other species); ulna with convex posterior margin lacking perichondral ossification (non-unique autapomorpy; concave and completely ossified in other species); intermedium wedging between radius and ulna, and equally contacting them as in N. enthekiodon (not wedging and having a short contact with ulna compared to that with radius in N. saveljeviensis and N. yasykovi); limb elements rounded and loosely arranged in N. enthekiodon (polygonal and tightly packed in N. saveljeviensis and N. yasykovi). Occurrence: Late Volgian Jurassic – Cretaceous transitional interval (latest Tithonian or earliest Berriasian) of Svalbard; early Berriasian of Franz Josef Land. Remarks: The specimen described by Delsett et al. (2018) can be referred to Nannopterygius based on its modest size (coracoid anteroposterior length = 155 mm, humerus proximodistal length = 103 mm); elongated coracoids with intercoracoid facet shifted far anteriorly relative to scapular facet, primarily occupying the anteromedial process. Other features observed in PMO 222.658 are also well consistent with Nannopterygius: narrow anterior notch of the coacoid; large scapular facet clearly demarcated from the glenoid contribution; wide and mediolaterally flattened (strap-like) dorsal ramus of the scapula; three distal articular facets of the humerus and well-pronounced deltopectoral crest. The description of PMO 222.658 is provided by Delsett et al. (2018) and we do not consider it necessary to expand that description. The humerus CCMGE 45 / 13328 (Fig. 22 M – Q) is well consistent with that of PMO 222.658. PHYLOGENETIC ANALYSIS Our ‘ unordered’ parsimony analysis resulted in 112 most parsimonious trees of 416 steps in length with the consistency index (CI) = 0.373 and retention index (RI) = 0.665. The strict consensus (length of 435 steps; CI = 0.356; RI = 0.640) is poorly resolved (Fig. 22 A). The recovered topology differs from the results of Zverkov & Efimov (2019) and Zverkov & Prilepskaya (2019), and, to a greter degree, from those of Delsett et al. (2019) and Campos et al. (2020). Our results support the division of Ophthalmosauridae (Ophthalmosauria) into two clades: Ophthalmosaurinae and Platypterygiinae sensu Fischer et al. (2012) or, alternatively, interpreted as two families Ophthalmosauridae and Undorosauridae (see discussion in: Zverkov & Efimov, 2019). A clade that includes all species of Nannopterygius is no further positioned at the base of Ophthalmosauridae (Ophthalmosauria) as was recovered in the works of Zverkov & Efimov (2019) and Zverkov & Prilepskaya (2019). This clade is now recovered as a sister of Arthropterygius spp. within Ophthalmosaurinae. Contra to previous results, Gengasaurus is not in the Nannopterygius clade. This taxon is recovered in a polytomy with the other two main clades of ophthalmosaurines (ophthalmosaurids). The recovery of Arthropterygius within Ophthalmosaurinae (Ophthalmosauridae) supports the result of the pruned analysis of Zverkov & Prilepskaya (2019) and Barrientos-Lara & Alvarado-Ortega (2020). The Nannopterygius and Arthropterygius clades share seven synapomorphies: appearance of jugal / premaxilla contact (23.0 / 23.1; not unique); posterior margin of the jugal laterally excluded from contact with the quadratojugal by the postorbital (24.0 / 24.1; not unique); extremely reduced quadratojugal nearly unseen laterally (41.1 / 41.2; not unique); a weak condyle of the quadrate (45.0 / 45.1; not unique); dorsally shifted basioccipital facet of the basisphenoid (49.0 / 49.1; the only unique synapomorphy of this clade); articular that is longer than high (77.0 / 77.1; not unique); and a clavicle that is plate-like and high medially (105.0 / 105.1; not unique). The Nannopterygius clade is supported by 19 autapomorphies, including two unique characters: bulbous roots (4.0 / 4.1) and anteromedial process of coracoid strongly protruding anteriorly along with the intercoracoidal facet (92.1 / 92.2).	en	Zverkov, Nikolay G., Jacobs, Megan L. (2021): Revision of Nannopterygius (Ichthyosauria: Ophthalmosauridae): reappraisal of the ‘ inaccessible’ holotype resolves a taxonomic tangle and reveals an obscure ophthalmosaurid lineage with a wide distribution. Zoological Journal of the Linnean Society 191
03E3CA2FFFCBE553FF29FA78FAF3ED38.taxon	description	Our analysis of the dataset with some multistate characters set as ordered, resulted in 56 most parsimonious trees of 419 steps long (CI = 0.370; RI = 0.669). The strict consensus (length of 438 steps; CI = 0.354; RI = 0.645) is not much better resolved than in the previous analysis and the recovered topology remains similar (Fig. 23 B). The difference from the results of previous analysis is that Gengasaurus is recovered as sister to Arthropterygyus and Nannopterygius and that the Bremer support values for Ophthalmosauridae (Ophthalmosauria), Ophthalmosaurinae (Ophthalmosauridae) and Nannopterygius spp. are slightly higher (Fig. 23 B).	en	Zverkov, Nikolay G., Jacobs, Megan L. (2021): Revision of Nannopterygius (Ichthyosauria: Ophthalmosauridae): reappraisal of the ‘ inaccessible’ holotype resolves a taxonomic tangle and reveals an obscure ophthalmosaurid lineage with a wide distribution. Zoological Journal of the Linnean Society 191
03E3CA2FFFEEE566FF60F993FD61EF13.taxon	description	v * 1871 Ichthyosaurus enthekiodon Hulke: 440, pl. 17. v 1889 Ichthyosaurus entheciodon Hulke – Lydekker: 32, fig. 16. v 1922 b Nannopterygius entheciodon (Hulke) – von Huene: 91, 98, pl. 12, fig. 2. 1923 Nannopterygius euthecodon [sic.] (Hulke) – von Huene: 467. 1960 Nannopterygius enthekiodon. (Hulke) – Delair: 74. 1976 Nannopterygius enthekiodon (Hulke) – McGowan: 671. [v 1983 Nannopterygius enthekiodon (Hulke) – Kirton: 122 – 128, fig. 39, pl. 5.] 1992 Nannopterygius entheckiodon [sic.] (Hulke) – Bardet: 654. 1999 b Nannopterygius enthekiodon (Hulke) – Motani: 484. 2000 Nannopterygius enthekiodon (Hulke) – Maisch & Matzke: 81. v 2003 Nannopterygius enthekiodon (Hulke) – McGowan & Motani: 109, fig. 91. 2010 Nannopterygius enthekiodon (Hulke) – Maisch: 167. v 2018 Nannopterygius enthekiodon (Hulke) – Moon & Kirton: 110, pl. 39, figs 1 – 5; text-figs 43, 44. Holotype: NHMUK PV 46497, a largely complete embedded skeleton (see Supporting Information, Table S 1 and Fig. S 1). Referred specimens: NHMUK PV 46497 a, partial right hindlimb; MJML K 1776, several slabs with disarticulated skull, vertebra, ribs, pectoral girdle and a forelimb; MJML K 2010, scapulae, clavicles and forelimbs; CAMSM J 29421 and J 29422, scapulae (Dakosaurus in Seeley, 1869: 93); OUMNH J 10346, incomplete left and right forelimbs; OUMNH J 10360, right scapula; OUMNH J 10574 / 1 – 19, basioccipital, articulated parietals, nasals, quadrate, articular, surangular and eleven vertebrae; see Supporting Information, Table S 1 for details. Remarks: The basis for referral of additional specimens (excepting the isolated hindlimb NHMUK PV 46497 a) is primarily the morphology of the pectoral girdle and forelimbs. All the referred specimens with preserved scapulae, including isolated scapulae (CAMSM J 29421, J 29422 and OUMNH J 10360) have a peculiarly expanded and anteriorly rounded coracoidal facet, autapomorphic of N. enthekiodon. The forelimbs of MJML K 1776 and OUMNH J 10346 lack a contact of the anterior accessory epipodial element and humerus similarly to the holotype and unlike materials referred to other species of Nannopterygius, in which the contact is clearly present. The referred specimen, MJML K 1776, provides additional information on the morphology of cranial elements of N. enthekiodon; in particular, it has a parietal with a moderately slender supratemporal process bearing a well-pronounced and somewhat serrated dorsal ridge (autapomorphy), basioccipital with anteriorly bilobed floor of the foramen magnum and articular that is anteroposteriorly longer than dorsoventrally high. This allows the robust referral to N. enthekiodon of a partial skull, OUMNH J 10574 / 1 – 19, that is well consistent with MJML K 1776 in these overlapping elements. Occurrence: Kimmeridge Clay Formation, Upper Kimmeridgian to Lower Tithonian (Volgian), Upper Jurassic of southern England, UK. Revised diagnosis: Nannopterygius enthekiodon c a n b e d i a g n o s e d r e l a t i v e t o o t h e r s p e c i e s o f Nannopterygius by the following combination of characters: pronounced but not columnar processus narialis of the nasal (elongated and somewhat hook-like in N. saveljeviensis); moderately long medial articulation of parietals (shortened in N. saveljeviensis); absence of posterior medial notch of parietals (present in reduced form in N. yasykovi, extensive in N. saveljeviensis); supratemporal process of the parietal not as slender as in other species and bearing a well-pronounced and somewhat serrated dorsal ridge (autapomorphy); scapula with coracoidal facet extensive and rounded anteriorly, consistent in the dorsoventral width throughout much of its length (autapomorphy; coracoidal facet is triangular, markedly decreasing in dorsoventral width anteriorly, in N. saveljeviensis and N. yasykovi, as well as in other ophthalmosaurians); coracoids with spatulate posterior portions (not as wide as in N. borealis; tapered in N. saveljeviensis); intercoracoidal facet lenticular in outline as in N. b o r e a l i s (d i s t i n c t a n d c o m p l e x o u t l i n e s i n N. saveljeviensis and N. yasykovi); lack of direct contact of anterior accessory epipodial element and humerus (present in all other species); reduced dorsal trochanter and relatively poorly developed deltopectoral crest (large plate-like deltopectoral crest in N. saveljeviensis); radius roughly trapezoidal in dorsal outline (pentagonal in N. saveljeviensis and N. yasykovi) and comparable in size to ulna (markedly smaller than ulna in N. borealis); ulna with concave posterior margin (unlike convex in N. borealis); intermedium deeply wedging between radius and ulna and nearly reaching humerus in some specimens (similar condition in N. borealis, but not N. saveljeviensis and N. yasykovi); limb elements rounded and more loosely packed than in N. saveljeviensis and N. yasykovi; two demarcated distal femoral facets: preaxial accessory facet could be present but not clearly separated from the tibial facet (all three facets are demarcated in N. cf. saveljeviensis PRM 2836). Description The skull of the holotype specimen is poorly preserved and partially disarticulated (Fig. 3 A, B). In its orbital region, the postorbital, supratemporal, squamosal, lacrimal and jugal can be distinguished, although their preservation is too poor for a detailed description. Additional data are available from the referred specimens MJML K 1776 and OUMNH J 10574. Premaxilla (Fig. 3 A, B): The premaxilla is partially preserved in the holotype (Fig. 3 A, B). It is elongate and slender, bearing a longitudinal groove along much of the lateral surface. Nasal (Figs. 3, 5 M, N): In general morphology, the nasal is similar to that of Ophthalmosaurus icenicus (Moon & Kirton, 2016). The ridge bordering the dorsal excavation is well pronounced (Fig. 5 M). The descending process of the nasal on the dorsal border of the external naris is present and the lateral ‘ wing’ overhanging it posterodorsally (Fig. 5 N). Lacrimal (Fig. 3 A, B): The lacrimal is similar to that of Arthropterygius and Ophthalmosaurus (Moon & Kirton, 2016; Zverkov & Prilepskaya, 2019). It is L-shaped in lateral view and participates in the posterior border of the external naris, forming an extensive and shallow posterior margin of the narial opening (see Supporting Information, Table S 4, character 20, state 0; Fig. 3 A, B). The posteroventral process of the lacrimal is elongated; it follows the dorsal surface of the jugal and forms the anteroventral margin of the orbit (Fig. 3 B). Laterally, along the orbital margin, the lacrimal develops a high ridge (part of the circumorbital crest) that is continued around the orbit by other elements. Prefrontal (Fig. 3 A, B): The prefrontal forms the anterodorsal margin of the orbit. Its preservation is too poor for a detailed description. It is possible that anteroventrally, the prefrontal contributed to the external naris (Fig. 3 B). Parietal (Figs. 4 A, B, 5 A – E): Both the parietals are preserved in articulation in OUMNH J 10574 (Fig. 5 A – E). The interparietal suture is moderately long anteroposteriorly (Fig. 5 B); it is not as long as in Ophthalmosaurus icenicus (Moon & Kirton, 2016) and not as short as in Arthropterygius (Zverkov & Prilepskaya, 2019). The dorsal surface of the parietal is slightly concave along the midline in lateral view with no sagittal eminence (Fig. 5 D). The supratemporal process is slender (Fig. 5 B – E), similar to that of Ophthalmosaurus icenicus (Moon & Kirton, 2016) and Arthropterygius spp. (Zverkov & Prilepskaya, 2019). The posterodorsal surface of the supratemporal processes bears an irregular ridge that borders the supratemporal facet anteriorly (Figs. 4 A, 5 B, D, E). The anterior border of the parietal bears two clearly demarcated facets for the frontal and postfrontal (Fig. 5 A, B). The frontal facet is faced anteromedially and reaches the interparietal symphysis, thus the parietal unlikely contributed to the posterior border of the parietal foramen. The impression of the cerebral hemisphere forms a deep and extensive cup in the anterior half of the ventral surface of the parietal (Fig. 5 A, C); posterior to it is the impression of the optic lobe, which is approximately equal in anteroposterior length and is roughly circular in outline. Supratemporal (Figs. 3 A – D, 4 A, B): The supratemporal forms the posterodorsal skull roof. In dorsal view, it articulates with the parietal posteromedially and with the postfrontal anteromedially; in lateral view, it articulates with the postfrontal anteriorly and with the squamosal and postorbital ventrally. In general morphology, it has no marked differences from Ophthalmosaurus icenicus (Moon & Kirton, 2016). The disarticulated supratemporal of MJML K 1776 demonstrates a long medial lamina of the ventral ramus (Fig. 4 A, B). It is possible that when articulated, this ramus was in contact with the stapes as in Ophthalmosaurus (Moon & Kirton, 2016). Squamosal (Fig. 3 A, B): The squamosal is large compared to other ophthalmosaurids and is most similar to that of Stenopterygius (e. g. Godefroit, 1993; McGowan & Motani, 2003; Motani, 2005). It is a thin plate-like element triangular in outline and well exposed in lateral view. An extensive facet of the supratemporal for the squamosal could be observed in MJML K 1776 (Fig. 4 A, B) Postorbital (Fig. 3 A, B): The postorbital is lunate in lateral view; it forms much of the posterior margin of the orbit. Its preservation in the holotype is too poor for further observations. Jugal (Fig. 3 A, B): The jugal is a gracile J-shaped element with slender mediolaterally compressed posterior process and thin suborbital bar. In the holotype, the orbital region is disarticulated and the jugal has its anterior end rotated dorsally (Fig. 3 B). Pterygoid (Figs. 3 C, D, 4 F): Both pterygoids are nearly completely preserved in MJML K 1776, lacking only the anteriormost portions. The lateral margin of the anterior ramus, which contacted the palatine, is nearly straight with no evidence of a process postpalatinus (Figs. 3 C, D, 4 F). The quadrate ramus of the pterygoid is slender, forming three wing-like flanges for the basisphenoid and quadrate. The medial flanges are elongate and were possibly in articulation, covering the basisphenoid ventrally (Fig. 4 F), but this posteromedial contact could be a taphonomic artefact. The anterior socket for the basipterygoid process of the basisphenoid is a small pit, indicating a poor development of the basipterygoid process of basisphenoid. The dorsal and lateral flanges of the quadrate ramus are short and weak, forming a concave lateral surface for articulation with the quadrate. Quadrate (Fig 5 F – I): The fragmental right quadrate is preserved in OUMNH 10574 (Fig. 5 F – I). It has a gracile articular condyle with nearly equal in size bosses: the articular boss is slightly more shifted ventrally than the surangular boss (Fig. 5 G). The stapedial facet is dorsoventrally elongate (Fig. 5 F). The anteromedial protrusion is pronounced (Fig. 5 F, I), unlike that of Arthropterygius chrisorum (Zverkov & Prilepskaya, 2019). Basioccipital (Figs. 4 D, E, 5 R – U): The basioccipital is preserved in MJML K 1776 and OUMNH 10574. The element is similar to that of the Cretaceous Acamptonectes densus, including the feature that has previously been considered as an autapomorphy of Acamptonectes – an anteriorly bilobed floor of the foramen magnum (Fischer et al., 2012). The condyle is oval in outline, although it is likely due to a diagenetic compression. The vertical incision of the posterior notochordal pit is raised close to the dorsal edge of the condyle, right under the floor of the foramen magnum (Fig. 5 T). The condyle is slightly deflected peripherally by an excavate extracondylar area. The extracondylar area is reduced, but can be observed in posterior view both laterally and, in a lesser degree, ventrally (Fig. 5 T); it lacks a ventral notch. The excavate peripheral ring of the extracondylar area is incomplete, being separated ventrally by a crest in OUMNH 10574 (Fig. 5 S), but it is continuous in MJML K 1776 (Fig. 4 D). The anterior margin of the extracondylar area is obliquely S-curved in lateral view (Fig. 5 U). The opisthotic and stapedial facets are semi-oval in shape and occupy nearly equal height in lateral view. On the dorsal surface, there are exoccipital facets oval in outline. The posterior borders of the exoccipital facets are rounded, unlike those tapered in Undorosaurus (Zverkov & Efimov, 2019). The facets are medially separated by a wide floor of the foramen magnum, which is bilobed anteriorly (Figs. 4 E, 5 R). The anterior surface of the basioccipital is irregularly pitted forming the basisphenoid facet. Hyoid apparatus (Fig. 3 A, B): The paired hyoid elements are partially exposed in the holotype and one element can be observed in MJML K 1776. The element is a short and strongly bowed rod. The exposed anterior end is compessed and expanded (Fig. 3 B). Mandible (Figs. 3, 4 G, 5 O – Q): The mandible is nearly complete, but disarticulated, in the holotype. In this regard, the previously reported mandibular length of 60 cm (e. g, Moon & Kirton, 2016) is likely overestimated. Additional data on the morphology of surangular and articular are available from MJML K 1776 and OUMNH J 10574. Dentary (Fig. 3 A, B): The dentary is slender and bears a longitudinal groove on its lateral surface. Splenial (Fig. 3 A, B): The splenials are partially exposed in the holotype and demonstrate a typical anterior bifurcation with dorsal and ventral rami being nearly equal in length and slender. Angular (Fig. 3 C, D): Only a posterior fragment of the left angular is preserved in MJML K 1776. Based on this fragment it could be said that the posterior portion of the angular is expanded and covered the surangular externally, thus giving the angular a pronounced lateral exposure. Surangular (Figs. 3, 4 G, 5 O – Q): The surangular is generally similar to that of Ophthalmosaurus icenicus (Moon & Kirton, 2016), although more gracile and strongly mediolaterally compressed, resembling the surangulars of juvenile specimens of O. icenicus (NGZ pers. obs. on NHMUK specimens, April 2019). Among the principal differences from O. icenicus are a pronounced curvature of the surangular posterior part, which is uncommon for ophthalmosaurids but occurs in some basal thunnosaurians (e. g. Hauffiopteryx and some specimens of Ichthyosaurus; McGowan, 1973; Marek et al., 2015), and a markedly better pronounced and more horizontally oriented process (Fig. 2 N, O), which is commonly interpreted as a point of attachment of M. adductor mandibulae externus group (e. g. Moon & Kirton, 2016). This process is well visible in dorsal view as in Grendelius mordax (NGZ pers. obs. on the holotype CAMSM J 68516, December 2018) and unlike in Ophthalmosaurus, Undorosaurus and Arthropterygius (Moon & Kirton, 2016; Zverkov & Efimov, 2019; Zverkov & Prilepskaya, 2019). Articular (Figs. 4 C, 5 J – L): The articular is preserved in MJML K 1776 (Fig. 4 C) and OUMNH J. 10574 (Fig. 5 J – L). It is a small and isometric element with a saddle-shaped medial surface and flattened lateral surface. The anteroposterior length exceeds the dorsoventral heigth of the element with H / L = 0.70 – 0.78. The posterior margin is convex, as well as dorsal and ventral margins, which are nearly parallel (Figs. 4 C, 5 K). There is a small emerging bony bulge in the dorsal half of the medial surface. The anterior surface for the articulation with the quadrate is concave and lenticular in outline (Fig. 5 J). Dentition. It was impossible to assess the teeth of the holotype during its distant examination; and in the referred specimens, the teeth are not preserved, exept for one partial tooth in MJML K 1776 (Fig. 4 B). However, Hulke (1871) considered the teeth of the holotype identical to those of ‘ Enthekiodon ’ (see Fig. 2 and Remarks above). Thus, the teeth might be small (not exceeding 13 mm in their apicobasal length, including root), with slender and poorly ornamented crowns and markedly expanded bulbous roots: width of the root nearly twice exceeding the maximum diameter of the crown. Vertebral column (Fig 6): In the holotype, 66 vertebra are present, presumably 45 of which are presacral, as was originally identified by Hulke [45 th centrum is the first in which the diapophysis and parapophysis are merged; cf. 42 identified by Kirton (1983) and by Moon & Kirton (2018)]. Posterior to them, at least six more vertebra in the transitional region bear a fused 8 - shaped rib facet. Isolated presacral vertebral centra are present in MJML K 1776 and OUMNH J. 10574 (Fig. 6). Their morphology is similar to those of Ophthalmosaurus. Anteriormost centra are tapered ventrally, and more posteriorly located centra have circular articular faces. The atlas – axis complex preserved in MJML K 1776 bears a marked lateral suture between the atlas and axis (Figs. 3 D, 6 A). Ribs: The ribs are long (the longest rib of the holotype is c. 60 cm when measured directly from proximal to distal end. Thus, it is as long as the skull and comprises c. 20 % of the total animal length). We found no support for the suggestion of Moon & Kirton (2018) that the ribs bear only a single groove proximally. Instead, in the holotype, the observed proximal cross-sections are characteristically 8 - shaped with longitudinal grooves running on both the anterior and posterior faces terminating close to the midlength; distally, the rib becomes circular in cross-section. Identical condition could be observed in MJML K 1776. Pectoral girdle (Fig. 7): The pectoral girdle elements of the holotype were recently characterized in detail by Moon & Kirton (2018), but not all of the interpretations proposed in that work can be supported by our observations. Primarily, this concerns the medial contact of the coracoids, which is present only in the anterior half of the medial border (Fig. 7 A, B), but not along the entire medial length, as was supposed by Moon & Kirton (2018). The posterior portions of the coracoids are slightly divergent and their posterior edges are rounded (Fig. 7 A, B). The anterolaterally faced scapular facet is relatively large (only slightly shorter than the glenoid contribution) and clearly separated from the glenoid contribution forming an angle of c. 120 °. The glenoid contribution is concave and faces posterolaterally, unlike laterally facing and parallel to the medial facet in most other ophthalmosaurids. The coracoids available for MJML K 1776 and MJML K 1174 (here referred to as Nannopterygius sp.) (Fig. 7 P, Q) show no marked differences from those of the holotype, except for minor variation in size and proportions, which is partially due to deformation and also could partially reflect an intraspecific variation. Compared to a wide range of coracoid shape variation reported for Ophthalmosaurus icenicus (Moon & Kirton, 2016), the morphology of the coracoid in Nannopterygius is remarkably stable. The intercoracoidal facet could be observed from MJML K 1776: it has a simple lenticular outline with the ventral edge more convex than the dorsal edge. The left scapula of the holotype is completely preserved and exposed in the lateral view and the right scapula could be observed only in its proximal part, which is articulated to the corresponding coracoid (Fig. 7 A, B). The left scapula of the holotype demonstrates a peculiar morphology among ophthalmosaurids, so that several isolated scapulae from the Kimmeridge Clay Formation that, having comparable size and identical morphology, could be referred to this taxon (see Supporting Information, Table S 1) and are used below to supplement the description, along with MJML K 2010 and MJML K 1776. The scapula of Nannopterygius is peculiar in its extensive and concave coracoid facet, which is wide and rounded anteriorly, and a small glenoid contribution, as well as in an extensive notch of finished ossification between the coracoid facet and the acromial process. The coracoid facet of the scapula is dorsoventrally thickened and terminates anteriorly with the rounded edge being clearly separated from the acromial process by an extensive notch. This condition is autapomorphic among ophthalmosaurians, as typically the coracoidal facet tapers anteriorly. Although scapular notches were reported as a rare condition for several mature individuals of Ophthalmosaurus (Moon & Kirton, 2016), in Nannopterygius this appears to be a typical state. The acromial process is well pronounced and extends anteriorly, curving ventrally for articulation with the clavicle. Another characteristic feature of the scapula in Nannopterygius is its mediolaterally compressed and distally expanded shaft. This latter condition is similar to that of Ophthalmosaurus icenicus, although in most of the referred specimens of O. icenicus the distal end of the scapular shaft is markedly less expanded anteroposteriorly, whereas in N. enthekiodon the marked distal expansion is a typical condition (Fig. 7 C, L, T, U). The clavicle is described based on holotype, MJML K 1776 and MJML K 2010 (Figs. 3 E, F, 4 B, S). The clavicle is robust and similar to that of Arthropterygius (Zverkov & Prilepskaya, 2019). It is high dorsoventrally, having a dorsoventral height to mediolateral length ratio of 0.26 (estimated from MJML K 1776). However, unlike in Arthropterygius, it is not thickened anteroposteriorly but thin. Forelimb (Figs. 3 C, D, 8): The incomplete left forelimb of the holotype is exposed in dorsal view [cf. interpreted as being exposed in ventral view by Moon & Kirton (2018)]. This interpretation is supported by the shape and orientation of the process that originates close to the posterior edge and is obliquely directed to the radial facet, thus having a typical position and morphology of the trochanter dorsalis (see e. g. McGowan & Motani, 2003), whereas the left humerus of this specimen, exposed in ventral view, has a welldeveloped deltopectoral crest typically shifted to the anterior edge of the humeral proximal end (Fig. 7 A, B). The humerus is stocky with proximal and distal ends of nearly equal anteroposterior width and robust diaphysis. The humerus is slightly compressed along its posterior edge (Fig. 8 C, I). There are two distal articular facets: a posterodistally deflected ulnar facet and anterodistally facing radial facet. The radial facet is slightly anteroposteriorly longer than the ulnar facet. The presence of a small facet anterior to radial facet is equivocal. The forelimbs are also preserved in MJML K 2010 and MJML K 1776. Additionally, several isolated humeri and one incomplete forelimb are deposited in the OUMNH collection (Supporting Information, Table S 1). All these materials are consistent with the holotype in their morphology and size, and thus herein referred to the same taxon (see Supporting Information, Table S 1). All the referred humeri have a poorly developed dorsal trochanter and deltopectoral crest, but in OUMNH J. 10346 and MJML K 2010 the deltopectoral crest is better pronounced than the dorsal trochanter (Fig. 8 E, Q). The distal facets have equal dorsoventral width and similar outline, although the radial facet slightly tapers anteriorly, while the ulnar facet is more rounded posteriorly (Fig. 8 J, P). Judging from MJML K 1776 and OUMNH J 10346, there was no contact between the humerus and anterior accessory epipodial element (Fig. 8 F, L). However, anterior to the contact with the radius there is a small, free surface, poorly demarcated from the radial facet. This may be interpreted either as a part of the radial facet or as the rudimentary facet of the anterior accessory epipodial element. At least five elements are preserved in articulation with the right humerus of the holotype. These are the radius, ulna, ulnare, intermedium and presumably the distal carpal four (Fig. 8 A – C). Seven epipodial and mesopodial elements are in articulation in the limb of MJML K 1776 (Fig. 8 F), and a number of isolated forelimb elements, including the radius, ulna and intermedium, are preserved in association with forelimbs in MJML K 2010 and OUMNH J. 10346. The ulna is characterized by a tapered and concave posterior edge (Fig. 8 B, C, D, F, E, L), which is a synapomorphy of ophthalmosaurines (Fischer et al., 2012). The element is roughly pentagonal in dorsal outline and bears three distal facets for the intermedium, ulnare and pisiform. The proximal articular surface is slightly convex. The radius is anteroposteriorly longer and proximodistally shorter than the ulna. It is roughly trapezoidal in dorsal outline with the widest surface for articulation with the humerus (Fig. 8 A, D, F, L). Distally it articulates with the anterior accessory element, radiale and intermedium. The medial articulation with the ulna was probably poorly developed in the holotype; it is relatively short in MJML K 2010 and MJML K 1776, and is nearly lost in OUMNH J. 10346 (Fig. 8 B, D, F, L). The anterior edge of the radius is not involved in ossification. In some specimens, a short, free surface (facet) separates the facet of the anterior accessory epipodial element from the humerus proximally (Fig. 8 F, L). The anterior accessory epipodial element preserved in MJML K 1776 and MJML K 2010 is semicircular in outline with straight anterior edge lacking ossification (Fig. 8 E, F). The intermedium wedges between the ulna and radius so that it is nearly in contact with the humerus (Fig. 8 A, B, F, L). The element is roughly pentagonal in dorsal view and bears six facets for the following elements (clockwise for the right limb in dorsal view): ulna, ulnare, distal carpal three, distal carpal two, radiale and radius. Hindlimb: Based on photographs, Zverkov & Efimov (2019) suggested that the femur of NHMUK PV 46497 a could be in articulation with three epipodial elements. Our personal examination of the specimen confirmed the interpretations of previous workers (Kirton, 1983; Lyddeker, 1889; Moon & Kirton 2018) that only the two elements are articulated with the femur. However, anterior to the tibia there is a free surface of the distal femur that may or may not serve as a facet for an anterior accessory element (Supporting Information, Fig. S 2). For details on the morphology of NHMUK PV 46497 a we direct the reader to Moon & Kirton (2018). It is worth mentioning that the fibula of NHMUK PV 46497 a lacks posterior perichondral ossification, which is present in the fibula of the holotype (NHMUK PV 46497). Similar variation occurs in Ophthalmosaurus (NGZ pers. obs. on NHMUK specimens, April 2019).	en	Zverkov, Nikolay G., Jacobs, Megan L. (2021): Revision of Nannopterygius (Ichthyosauria: Ophthalmosauridae): reappraisal of the ‘ inaccessible’ holotype resolves a taxonomic tangle and reveals an obscure ophthalmosaurid lineage with a wide distribution. Zoological Journal of the Linnean Society 191
03E3CA2FFFEAE570FC5AFA7FFD73EE5A.taxon	description	1889 Ichthyosaurus – Lydekker: 32 [pars.]. 1922 Nannopterygius von Huene, 91. 1960 Nannopterygius – Delair: 73. 1976 Nannopterygius – McGowan: 671. [1983 Nannopterygius – Kirton: 122.] 1986 Ophthalmosaurus – Delair: 133 [pars.]. 1992 Nannopterygius – Bardet: 654. 1997 Paraophthalmosaurus Arkhangelsky: 87. [1997 Jasykovia Efimov, 97.] 1998 Paraophthalmosaurus – Arkhangelsky: 87 [pars.]. 1999 a Yasykovi a Efimov: 93.	en	Zverkov, Nikolay G., Jacobs, Megan L. (2021): Revision of Nannopterygius (Ichthyosauria: Ophthalmosauridae): reappraisal of the ‘ inaccessible’ holotype resolves a taxonomic tangle and reveals an obscure ophthalmosaurid lineage with a wide distribution. Zoological Journal of the Linnean Society 191
03E3CA2FFFEAE570FC5AFA7FFD73EE5A.taxon	description	2000 Ophthalmosauru s Seeley, 1874 – Maisch & Matzke: 78 [pars.]. 2000 Nannopterygius von Huene – Maisch & Matzke: 81.	en	Zverkov, Nikolay G., Jacobs, Megan L. (2021): Revision of Nannopterygius (Ichthyosauria: Ophthalmosauridae): reappraisal of the ‘ inaccessible’ holotype resolves a taxonomic tangle and reveals an obscure ophthalmosaurid lineage with a wide distribution. Zoological Journal of the Linnean Society 191
03E3CA2FFFEAE570FC5AFA7FFD73EE5A.taxon	description	2018 Macropterygius Huene – Moon & Kirton: 117 [pars.].	en	Zverkov, Nikolay G., Jacobs, Megan L. (2021): Revision of Nannopterygius (Ichthyosauria: Ophthalmosauridae): reappraisal of the ‘ inaccessible’ holotype resolves a taxonomic tangle and reveals an obscure ophthalmosaurid lineage with a wide distribution. Zoological Journal of the Linnean Society 191
03E3CA2FFFEAE570FC5AFA7FFD73EE5A.taxon	materials_examined	Type species: Ichthyosaurus enthekiodon Hulke, 1871. Referred species: Nannopterygius saveljeviensis (Arkhangelsky, 1997) comb. nov.; Nannopterygius yasykovi (Efimov, 1999 a) comb. nov.; N a n n o p t e ry g i u s b o re a l i s s p. n o v. from the lowermost Cretaceous (Berriasian) of Arctic Islands (Svalbard and Franz Josef Land). Emended diagnosis: Medium-sized ophthalmosaurid (up to 3.5 m in maximum estimated length) characterized by the following autapomorphies: teeth with bulbous roots and slender crowns (width of the root nearly twice exceeds maximum diameter of the crown); marked curvature of the posterior mandible similar to that of Hauffiopteryx and unlike in any ophthalmosaurid; well-pronounced Musculus adductor mandibulae externus process (unique, although similar condition present in Grendelius mordax, pers. obs); coracoids markedly elongate (anteroposterior length to mediolateral width ratio = 1.7 – 1.4), with divergent posterior ends and large, square anteromedial processes; intercoracoidal facet shifted anteriorly and occupying anteromedial process. Nannopterygius is also characterized by the following combination of features: gracile and elongated rostrum as in Aegirosaurus and Sveltonectes (less robust than in Arthropterygius, Caypullisaurus, Grendelius, Ophthalmosaurus and Undorosaurus); snout ratio of c. 0.64, orbital ratio 0.25 – 0.28; supranarial process of premaxilla well developed and projecting into the external naris (supranarial process reduced in Arthropterygius, Opthalmosaurus and Undorosaurus); subnarial process contacts the jugal (as in Grendelius and Undorosaurus); narial process of nasal present and, in the type species, similar in shape to that of Acamptonectes, Ophthalmosaurus and Undorosaurus, although in N. saveljeviensis narial process is more columnar as in Sveltonectes; prefrontal contributing to the external naris as in Sveltonectes; prefrontal forming anteromedial expansion as in Caypullisaurus, Leninia, Simbirskiasaurus and Sveltonectes; narrow supratemporal anteromedial tongue protruding far anteriorly and covering the postfrontal as in Ophthalmosaurus and unlike that wide of Athabascasaurus and Arthropterygius; jugal bowed ventrally similarly to that of Arthropterygius; jugal posterior process anteroposteriorly narrow (unlike that of Caypullisaurus, Grendelius, Platypterygius and Undorosaurus); extremely narrowed postorbital bar due to extreme reduction of quadratojugal lateral exposure (as in Arthropterygius and Ophthalmosaurus); squamosal is present and triangular in shape as in Ophthalmosaurus (less dorsoventrally narrow than in Arthropterygius and Undorosaurus); parietal lacking sagittal eminence and having a slender supratemporal process (as in Arthropterygius and Ophthalmosaurus); basioccipital with reduced extracondylar area (as in Acamptonectes, Ophthalmosaurus and Undorosaurus, but to a lesser degree than in Grendelius and Platypterygius); quadrate with reduced occipital lamella and pronounced angular process (unlike in Arthropterygius); expanded and bilobed anterior portion of the foramen magnum floor (uniquely shared with Acamptonectes); posteriorly rounded edges of the exoccipital facets of the basioccipital (unlike in Acamptonectes, Sveltonectes and Undorosaurus); basisphenoid with extremely reduced basipterygoid processes (width to length ratio 1.2); basioccipital Region); 3, bank of the Volga near Gorodischi village, Slantsevy Rudnik village and ‘ Detskiy sanatorium’ (Ulyanovsk Region); 4, Kashpir (Samara Region); 4, Gorny (Krasnopartisansky District, Saratov Region); 6, Kutseba (Perelyub District, Saratov Region). Zonal correlation of the Volgian regional stage of the European part of Russia, Svalbard, Franz Joseph Land and England. Distribution of Nannopterygius spp. is shown in grey. Correlation of ammonite zones after Casey (1973), Rogov & Zakharov (2009), Rogov (2010 a, b, 2017) and Kiselev et al. (2018). facet of the basisphenoid facing posterodorsally, occupying in dorsal view area nearly equal to that of dorsal plateau (uniquely shared with Arthropterygius); stapes with moderately stout shaft (like that of Ophthalmosaurus and Undorosaurus); short and robust paroccipital process of the opisthotic, poorly demarcated from the main body of the element (unlike that of Ophthalmosaurus and Acamptonectes); pronounced stapedial curvature as in basal parvipelvians Ichthyosaurus and Hauffiopteryx and, among ophthalmosaurids, uniquely shared with Arthropterygius; articular markedly anteroposteriorly longer than dorsoventrally high in all species excepting N. yasykovi (height to length ratio less than 0.8 as in Arthropterygius and unlike in Grendelius, Mollesaurus and Ophthalmosaurus); pronounced bony boss on the articular medial surface (as in Undorosaurus nessovi Efimov, 1999); teeth comparatively small with crowns either lacking ornamentation, or bearing rare and fine striations (as in Ophthalmosaurus natans (Marsh, 1879), Arthropterygius lundi, Acamptonectes, Athabascasaurus, Sveltonectes and Muiscasaurus); 45 presacral vertebrae [42 in Ophthalmosaurus; 47 in Platypterygius australis (McCoy, 1867), 52 in Undorosaurus and? Aegirosaurus]; angle between the dorsal surfaces of articulated coracoids is nearly straight (180 – 170 º); scapular and glenoid facets of coracoid clearly demarcated and comparable in size similarly to those of Sveltonectes; well-developed acromial process of scapula unlike that of Undorosaurus; in some specimens, acromial process and anteromedial process of the coracoid could be in contact as observed in some Stenopterygius and Leptonectes specimens; mediolaterally compressed scapular shaft, oval in cross-section (as in Acamptonectes, Arthropterygius, Ophthalmosaurus and Undorosaurus, and distinct from the thick and rod-like cross-section in Grendelius and Platypterygius); scapular notch present as in Sveltonectes, Grendelius pseudoscythicus, G. zhuravlevi and, as a rare variation, in Ophthalmosaurus icenicus; scapular glenoid contribution reduced compared to coracoid facet as in Sveltonectes and Ophthalmosaurus natans; dorsoventrally high and relatively robust clavicles (as in Arthropterygius); interclavicle with narrow posterior median stem as in Arthropterygius and Ophthalmosaurus (mediolaterally wide in Grendelius and Undorosaurus); interclavicle ventral knob present as in Undorosaurus and Grendelius; two or three distal humeral facets: for radius and ulna, and, in some species, for an anterior accessory epipodial element; poorly developed dorsal process of the humerus; deltopectoral crest commonly better developed than the dorsal process; metacarpal five contacting ulnare posterodistally (i. e. ‘ longipinnate’ condition); intermedium bearing extensive distal facet for distal carpal three and anteriorly contacting distal carpal two (as in Undorosaurus and unlike in Aegirosaurus, Arthropterygius, Brachypterygius and Ophthalmosaurus); ischiopubis slender and rod-like with small obturator foramen; two or three distal femoral facets; ventral process of the femur is more developed than the dorsal process, although the latter is also well pronounced. Occurrence: Upper Kimmeridgian to lower Volgian (Lower Tithonian, Upper Kimmeridge Clay) of the UK; Middle to Upper Volgian (Tithonian to Lower Berriasian) of European Russia and Upper Volgian to Ryazanian (Berriasian) of the Arctic. Remarks: In 1870, Hulke described fragmentary jaws with associated teeth from the Kimmeridge Clay Formation of Kimmeridge Bay. Based on peculiar teeth with ‘ great development of the cementum, which gives the fang the appearance of being inserted in a bulbous sheath’ (Hulke, 1870: 172), he proposed the provisional name ‘ Enthekiodon ’. Later he used this as a specific name for an ichthyosaur skeleton newly discovered in the same locality and horizon, and having teeth that ‘ agreed so closely with those of Enthekiodon as to leave no reasonable doubt of their identity’ (Hulke, 1871: 440). The skeleton was designated as the holotype of Ichthyosaurus enthekiodon. The location of the first described ‘ Enthekiodon ’ material was considered unknown (Moon & Kirton, 2018). Some authors suggested that the specimen was ‘ destroyed through an action of pyrites’ (Delair, 1960: 74). However, during the examination of the NHMUK collection in April 2019, NGZ observed an uncatalogued specimen from the Kimmeridge Clay Formation (Fig. 2) that according to the label is part of Hulke’s collection and perfectly agrees with the description of Hulke (1870). Thus, it is likely that this is the ‘ lost’ specimen of ‘ Enthekiodon ’. Indeed, the preserved portions of rostrum indicate that it was slender. Teeth are small, not exceeding 13 mm in their apicobasal length (including root). The crowns are slender and poorly ornamented; some of them lack the ornamentation entirely (Fig. 2 B, C), whereas others are ornamented by slight, rare striations (Fig. 2 D, E). The base of the crown is 2.4 mm in diameter and the root is 4.6 mm in maximum width, thus nearly twice exceeding the maximum diameter of the crown. This agrees well with the morphology of teeth observed in other specimens of all species of Nannopterygius. In this regard, the species-level identification of this material is impossible, but its affinity to Nannopterygius is highly plausible. The concept of the genus composition performed in the current contribution is based primarily on peculiar morphology of the pectoral girdle found in all referred specimens, where preserved, but not seen in any other ophthalmosaurid. Other osteological traits and results of the phylogenetic analysis (see below), in our opinion, are substantial support for the presented taxonomic decision.	en	Zverkov, Nikolay G., Jacobs, Megan L. (2021): Revision of Nannopterygius (Ichthyosauria: Ophthalmosauridae): reappraisal of the ‘ inaccessible’ holotype resolves a taxonomic tangle and reveals an obscure ophthalmosaurid lineage with a wide distribution. Zoological Journal of the Linnean Society 191
03E3CA2FFFF5E557FCBBFD73FC60ED98.taxon	description	[v. 1997 Jasykovia sumini V. Efimov: 107, fig. 7.9 в – ж.]. v * 1999 a Yasykovia yasykovi Efimov, 1999: 94, fig. 1 [pars.]. v. 1999 a Yasykovia sumini Efimov, 1999: 94, figs 4 в, г, 6 а, в.	en	Zverkov, Nikolay G., Jacobs, Megan L. (2021): Revision of Nannopterygius (Ichthyosauria: Ophthalmosauridae): reappraisal of the ‘ inaccessible’ holotype resolves a taxonomic tangle and reveals an obscure ophthalmosaurid lineage with a wide distribution. Zoological Journal of the Linnean Society 191
03E3CA2FFFF5E557FCBBFD73FC60ED98.taxon	materials_examined	Holotype: UPM EP-II- 7 (1235), anterior portion of skeleton embedded in matrix (Fig. 17). R e f e r r e d s p e c i m e n: U P M I I - 1 1 (3 - M), p a r t i a l disarticulated skeleton, holotype of Yasykovia sumini (Figs. 17 – 20, 21). Remarks: The clarification of specimen composition of the presented hypodigm is provided in the Discussion. Diagnosis Nannopterygius yasykovi differs from other species of Nannopterygius in the following combination of features, including two autapomorphies (marked with ‘ * ’): medial articulation of parietals strongly dorsoventrally thickened (unlike in any other species), anteroposteriorly long and bipartite * (short in N. saveljeviensis); slender supratemporal process of the parietal, as in N. saveljeviensis (more robust and bearing a rugose dorsal ridge in the type species); prominent anteromedial protrusion of the quadrate (present, but less pronounced, in N. enthekiodon and N. saveljeviensis); coracoids with spatulate posterior portions as in the type species (not as wide as in N. borealis; strongly mediolaterally constricted and tapered in N. saveljeviensis); intercoracoidal facet trapezoidal in outline with straight ventral margin bearing protrusions posteriorly and anteriorly *; relatively small scapular facet of the coracoid (proportionally larger in all other species of the genus); more pronounced curvature of the scapular shaft; comparable in size coracoidal facet and glenoid contribution of the scapula; radius comparable in size to ulna (radius markedly smaller than ulna in N. borealis); ulna with concave posterior margin (unlike convex in N. borealis); intermedium not wedging between radius and ulna, and having a short contact with ulna compared to that with radius as in N. yasykovi (wedging between the two elements and equally contacting them in N. enthekiodon and N. borealis); limb elements polygonal and tightly packed (rounded and loosely arranged in N. enthekiodon and N. borealis). Occurrence: Middle to Upper Volgian (Epivirgatites nikitini and Kachpurites fuigens ammonite biozones), Upper Jurassic of European Russia. Description The skull is incomplete and partially disarticulated in the holotype and is represented by several isolated elements in the referred specimen. In general, the skull is similar to that of Nannopterygius saveljeviensis, although some differences do exist. Premaxilla (Fig. 17): The partial premaxilla preserved in the holotype UPM EP-II- 7 (1235) has two elongated processes posteriorly (Fig. 17). The process supranarialis is well pronounced and slender, the process subnarialis extends posteriorly and contacts the jugal on the level of the posterior margin of the external naris (Fig. 17 D). femur of Nannopterygius cf. saveljeviensis PRM 2836 in distal (J), proximal (K), anterior (L), dorsal (M) and ventral (N) views. Abbreviations: dp, dorsal process; faae, facet for the preaxial accessory epipodial element; ffi, facet for the fibula; fti, facet for the tibia; obtf, obturator foramen vp, ventral process. Scale bar = 3 cm. Nasal (Fig. 17): Based on the exposed part, the nasal has no significant differences from that of the type species and is similar to that of N. saveljevensis. The morphology of the narial process cannot be assessed. Frontal (Fig. 17): The frontal is also similar to that of N. saveljevensis with the medial facet for the counterpart located in the anterior half and the elongated margin of the parietal foramen. Parietal (Figs. 17, 18 A – F): The parietal is similar to that of the type species in a moderately anteroposteriorly long interparietal articulation, unlike that shortened symphysis in N. saveljeviensis. The interparietal facet is massive, triangular in outline and has a rugose surface (Fig. 18 E). There is a rudimentary notch posterior to the main interparietal facet, but posterior to this notch the medial edge of the parietal forms an additional contact with the counterpart. A low ridge along the posterior margin of the parietal marks a border of a posterior parietal shelf (Fig. 18 A, D). In lateral view, the dorsal surface of the parietal is straight along the midline with no sagittal eminence (Fig. 18 A, F). The supratemporal process is slender, unlike that of the type species, and similar to that of N. saveljeviensis. The impression of the cerebral hemisphere forms a deep, circular cup on the anterior part of the ventral parietal (Fig. 18 C). The impression of the optic lobe is extensive and circular in outline, occupying a posterior part of the parietal ventral surface (Fig. 18 B). Prefrontal (Fig. 17): The prefrontal is similar to that of the other species, in having a well-developed dorsomedial expansion and contributing to the external naris. The lateral curcumorbital crest is also well developed. Lacrimal (Fig. 17): The lacrimal is similar to that of the type species. The dorsal process of the lacrimal contacts the narial process of the prefrontal in a comparatively simple, sinusoidal suture with no marked interdigitation. The anteroventral tip of the lacrimal is in contact with the premaxilla. The posteroventral process of the lacrimal follows the dorsal edge of the jugal and shapes the anteroventral margin of the orbit. Laterally, along the orbital margin, the lacrimal develops a ridge that is continued around the orbit by other elements. Postfrontal (Fig. 15 G – I): The postfrontal has no marked difference from that of the type species and N. saveljeviensis. It is curved and widest anteriorly, grading into a narrower and mediolaterally facing posterior strut. Supratemporal (Fig. 17): The supratemporal is too poorly preserved for detailed observations. Squamosal and quadratojugal: At present, these elements are unknown for the species. Jugal (Fig. 17): The jugal is similar to that of other species: it is a gracile J-shaped element markedly bowed ventrally. It has a lender posterior process and thin suborbital bar laterally bearing a ventral continuation of the circumorbital crest. Pterygoid (Fig. 18 O – Q): The preserved posterior portion of the pterygoid with lateral, dorsal and medial lamellae is gracile. Quadrate (Fig. 19 Q – T): The quadrate of UPM II- 11 (3 - M) has a well-developed angular protrusion. The articular condyle is similar to those of other species, with saddle-shaped articular surface and rounded ventral edge of the articular boss (Fig. 19 Q, T). The stapedial facet is oval in outline and surrounded by a raised peripheral area. Basioccipital (Fig. 19 F – J): The floor of the foramen magnum of the basioccipital is anteriorly expanded and bilobed (Fig. 19 H). The condyle is circular in outline, slightly wider than high, with the posterior notochordal pit located in its dorsal half (Fig. 19 G). The extracondylar area is smooth and lacks peripheral excavation and a ventral crest, present in other species of the genus (Fig. 19 H, I). The facets for opisthotic and stapes both shifted anteriorly and nearly equal in dorsoventral height in lateral view (Fig. 19 I). The exoccipital facets have rounded posterior borders. The anterior protrusion in the middle of the anterior surface is pronounced and with a deep vertically oriented medial groove in its center (Fig. 19 J). Parabasisphenoid (Fig. 19 A – F): The parabasisphenoid is square in ventral view due to an extremely reduced basipterygoid processes. In lateral view, it is irregularly pentagonal due to a dorsally raised basioccipital facet and an additional free posterior surface ventral to it, similar to the condition observed in some specimens of Arthropterygius (Zverkov & Prilepskaya, 2019). The anterior vertical wall is high, being only slightly less than the anderoposterior length of the element. The posterior foramen for the internal carotid arteries is located in the posterior half of the ventral surface, close to its middle, and is continued posteriorly by a groove. The anterior impessions of a cartilaginous continuation of the cristae trabecularis are pronounced, forming a curved smooth surface ventral to the anterior foramen of the internal carotid arteries canal. Opisthotic (Fig. 19 K – O): The opisthotic is similar to that of N. saveljeviensis in every aspect, although it is slightly less massive. Supraoccipital (Fig. 19 P): Only the exoccipital processes of the supraoccipital are preserved and are less massive than in N. saveljeviensis. The impression of the otic capsule is a deep L-shape curve. Hyoid apparatus (Fig. 17 A, B): A hyoid element is short and bowed. It is 87 mm in maximum length and shows no differences from that of N. saveljeviensis. Mandible (Figs. 17, 18 J – W): The morphology of the mandibular elements is typical of the genus. The dentary is slender; it terminates approximately at the middle of the orbit. The surangular demonstrates a typical curvature in its posterior part. The paracoronoid process is poorly developed, whereas the process for M. adductor mandibulae externus group is a large ridge (Fig. 18 J – L). The articular is similar to those of other Nannopterygius species in general outline, differing in that it is more isometric (H / L = 0.86) and narrowed posteriorly (Fig. 18 R – W). The muscular knob on the medial surface is poorly pronounced as in the type species, and unlike that of N. saveljeviensis. Vertebral column (Fig. 20): The atlas – axis complex and two anterior presacral vertebrae are preserved in UPM II- 11 (3 - M); they are similar to those of N. saveljeviensis. The atlas and axis are fused with a marked suture and lack a ventral keel (Fig. 20 A, B). The anterior presacral vertebral centra are rounded in articular view and slightly flattened at the dorsal margin (Fig. 20 C). Ventrally, they bear a rudimentary keel (Fig. 20 D).	en	Zverkov, Nikolay G., Jacobs, Megan L. (2021): Revision of Nannopterygius (Ichthyosauria: Ophthalmosauridae): reappraisal of the ‘ inaccessible’ holotype resolves a taxonomic tangle and reveals an obscure ophthalmosaurid lineage with a wide distribution. Zoological Journal of the Linnean Society 191
