Ommatotriton

Macaluso, Loredana, Wencker, Lukardis C M, Castrovilli, Maria, Carnevale, Giorgio & Delfino, Massimo, 2023, A comparative atlas of selected skeletal elements of European urodeles (Amphibia: Urodela) for palaeontological investigations, Zoological Journal of the Linnean Society 197 (3), pp. 569-619 : 602-604

OMMATOTRITON GRAY, 1850

Species: Ommatotriton ophryticus * (Litvinchuk, Zuiderwijk, Borkin & Rosanov, 2005) and Ommatotriton vittatus * (Gray, 1835) (not European).

Otic–occipitum complex ( Fig. 5E )

The prominentiae semicircularis anterioris and posterioris are clearly visible, whereas the prominentia semicircularis lateralis is generally covered by the parietal crest and process. Among the prominentiae, there is a smooth and deep middle depression. The circular or elliptical fenestra ovalis is ventral to the parotic process and visible in posterior view. Its anterior edge is posterior to the mid-length of the complex. The parietal crest is low, extending from the posterior or middle point of the distal tectum synoticum to the anteriormost edge of the prominentia semicircularis anterioris. The parotic crest is variably developed, but generally low and either equally high throughout its length or dorsally concave. It contacts the parietal crest in the anterior one-third of the prominentia semicircularis anterioris and is laterally concave close to parotic process, where it generally forms a dorsal tip. The parietal crest is lower anterior to the parotic crest. In dorsal view, the parotic process is rectangular in the two specimens of O. vittatus and sub-triangular in the two specimens of O. ophryticus . In posterior and anterior views, this process is triangular, and in lateral view it is almost horizontal or with the ventral tip more anterior than the dorsal one. The tectum synoticum is slender, and its anterior edge is posterior to the midlength of the complex. The tectum synoticum is almost as medially extended as the hypochordal commissure and extends medially beyond the prefacial commissure, and only a slight concavity is visible between the two commissures. In both available specimens of O. ophryticus , the prefacial commissure also extends medially. The cylindrical otic process projects anteriorly from the prominentia semicircularis anterioris and bears a circular articular surface. The foramen faciale is particularly visible in ventral view as a large foramen on the posterior part of the basicapsular commissure, being posterodorsal to the kidney-shaped articular surface of the processus basalis. The processus basalis forms a small lateral crest visible in ventral view. The sulcus petrosus between the processus basalis and the otic process is hidden by a sharp process ventral to the prominentia semicircularis anterioris. The elliptical postoticum foramen is surrounded posteriorly by the cotyle alone. Usually, the foramen prooticum is almost completely surrounded by bone. The auditory cavity is well defined but not deep. The basicapsular commissure extends medially beyond the prefacial commissure and is almost as medially extended as the hypochordal commissure. The fenestra basicranialis is present between the basicapsular and hypochordal commissures.The ventral surface is variably perforated, and the medial crest is interrupted by the sulcus carotis posterior to the basicapsular commissure.

Remarks: In MNCN 13193, the deep middle depression bears a single foramen posterior to the mid-length of the prominentia semicircularis lateralis.

Atlas ( Fig. 8C )

The neural canal is circular in anterior view and is twice as high as each occipital joint or slightly less. In posterior view, the neural canal is at least twice as wide as the circular cotyle or slightly less. The occipital joints are circular or elliptical, with a horizontal (or sub-horizontal) major axis. The articular facets of the odontoid process are separated by a narrow groove on the ventral surface. In ventral view, the base of the odontoid process is as wide as each occipital joint or slightly wider. The forked or posteriorly enlarged neural crest is low or absent, whereas the secondary crests are absent or variably developed. If present, the secondary crests run parallel to the neural crest for most of their length. Close to the posterior edge of the neural arch, they converge and contact the neural crest; hence, they do not reach the end of the arch. The neural spine is generally present. The lateral surface of the atlas is variably perforated. The incisura vertebralis cranialis is present. In lateral view, the dorsal edge of the neural arch is inclined or sub-horizontal. The neural arch between the wide incisura caudalis and the cotyle is convex or sub-vertical. The maximum concavity of the incisura vertebralis caudalis is dorsal to the horizontal plane containing the maximum concavity of the incisura cranialis. The well-developed lateral crests extend posteriorly beyond the postzygapophyses, almost reaching the posterior edge of the neural arch. The inferior crests are marked. In posterior view, the neural arch is dorsally convex (inverted U-shaped). In lateral view, the postzygapophyses extend posteriorly beyond the cotyle for more than half of their length. In dorsal view, the neural arch is anteriorly straight, and the incisura dorsalis is posteriorly deep, formed by the forked neural crest or by the neural arch. The cotyle is not visible (or slightly visible) in dorsal view. The ventral surface is smooth or bears more than two foramina.

Remarks: MNCN 40462 is the only examined specimen of O. ophryticus preserving the atlas. In this specimen, the dorsoposterior edge of the atlas is formed by the neural arch, producing a huge posterior concavity. In addition, the secondary crests do not contact the short and blade-like neural crest, and the lateral crests do not extend beyond the postzygapophyses.

Precaudal vertebrae ( Fig. 11D )

The precaudal vertebrae are opisthocoelous. The neural canal is pentagonal or circular, slightly higher or lower than the condyle. The condyle is circular or elliptical, with a horizontal major axis. In lateral view, the anterior edge of the neural arch between the condyle and the elliptical prezygapophyses is inclined. The diapophyses and parapophyses are distinguishable, connected by a smooth lamina reaching their distal ends.The transverse processes are subperpendicular to the centrum or with a slightly posterior orientation, covering the incisura caudalis only marginally in lateral view or not covering it. In the same view, the neural arch dorsal to the prezygapophyses is visible. One-third of the height of the vertebra is formed by the neural arch dorsal to the postzygapophyses. The neural crest is blade-like and high, starting posterior to the anterior edge of the neural arch, being broadened and forked posteriorly. The neural spine is low or absent. The anterior zygapophyseal crests contact the dorsal part of the diapophyses. The posterior zygapophyseal crests are well developed and horizontal, contacting the diapophyses proximally or at their midlength. Anterior and posterior ventral crests are well developed and form an asymmetrically rhomboidal or trapezoidal ventral lamina. The lateral surface of the vertebrae is generally perforated. In anterior view, a wide foramen is visible in the ventral half of the proximal edge of the transverse processes (at the base of the parapophyses). The incisura vertebralis caudalis is deep and contacts the centrum or, alternatively, the neural arch ventral to it is inclined. In posterior view, the dorsal edge of the neural arch is horizontal or dorsally convex (inverted U-shaped). The neural arch is posteriorly forked dorsal to the postzygapophyses, and each branch in lateral view shows a posterior concavity ventrally and a tip dorsally. In lateral view, the postzygapophyses extend posteriorly beyond the cotyle for more than half of their length. In dorsal view, the neural arch is anteriorly concave (U-shaped) or flat. The condyle is visible in dorsal view (usually for most of its length), whereas the cotyle is not visible (or, rarely, it is slightly visible through the incisura dorsalis). The ventral surface is generally perforated.

Remarks: In O. ophryticus , the cotyle is slightly visible in dorsal view.

Caudal vertebrae ( Fig. 14A )

The caudal vertebrae are high (height/length ratio> 1.4). The neural canal is pentagonal or circular, and the haemal canal is elliptical or U-shaped. The neural canal is wider than the haemal canal and higher than or as high as the haemal canal. The transverse processes are rectangular (with the longest side vertical) in anterior view; in dorsal view, they are triangular, and in lateral view, they form an inclined lamina, formed posterodorsally by the transverse process itself and anteroventrally by the anterior middle crest. The neural and haemal crests are high and posteriorly forked, with a large foramen corresponding to the bifurcation point; if they are enlarged, the dorsal surface is perforated. The lateral surface is not smooth, because several crests and small foramina are present, and a large foramen perforates the haemal arch. The zygapophyseal crests are marked and horizontal or ventrally concave. They are poorly connected with the transverse processes. The anterior ventral crests are low and generally do not reach the anterior edge of the haemal arch. The posterior ventral crests start from the posterior edge of the haemal crest. In lateral view, the anterior and posterior ventral crests form an angle>130°. In lateral view, the anterior margin of the haemal arch is concave (or posteriorly inclined) or convex (or anteriorly inclined) between the centrum and the anterior ventral crest, and concave (or posteriorly inclined) ventral to the latter crest. The haemal crest does not project anterior to the haemal arch. The haemal arch and crest form a sharp or rounded tip posteriorly in lateral view.

Remarks: In O. vittatus , the posterior tip of the haemal crest is more ventral than in O. ophryticus , commonly forming the ventralmost part of the vertebra.

Figures

Figure 5. Otic–occipitum complexes of European Pleurodelinae.A, left complex of Calotriton asper (MNCN 16122). B, right complex of Euproctus montanus (BSPGM 4202). C, left complex of Ichthyosaura alpestris (MDHC 416). D, right complex of Lissotriton Ʋulgaris (MDHC 133). E, left complex of Ommatotriton Ʋittatus (MNCN 13193). F, right complex of Pleurodeles aealtl (MDHC 253). G, right complex of Triturus carnifex (MDHC 38). H, left complex of Triturus carnifex (MDHC 299). From left to right: anterior, dorsal, lateral, posterior and ventral views. Scale bars: 1 mm.

Figure 8. Atlantes of European urodeles. A, Lissotriton Ʋulgaris (MDHC 135). B, Lissotriton Ʋulgaris (MDHC 133). C, Ommatotriton Ʋittatus (MNCN 13193), with right postzygapophyses missing. D, Pleurodeles aealtl (MDHC 253). E, Triturus carnifex (MDHC 38). From left to right: anterior, dorsal, lateral (right lateral for A, D; left lateral for B–C, E), posterior and ventral views. Scale bars: 1 mm.

Figure 11. Precaudal vertebrae of European urodeles. A, Euproctus platycephalus (MDHC 405). B, Ichthyosaura alpestris (MDHC 352). C, Lissotriton Ʋulgaris (MDHC 135). D, Ommatotriton Ʋittatus (MNCN 13193). E, Pleurodeles aealtl (MDHC 253). F, G,Triturus carnifex (MDHC 38): F, one of the first trunk vertebrae; and G, trunk vertebra close to the pelvis. From left to right: anterior, dorsal, lateral (left lateral for A–C, E, F; right lateral for D, G), posterior and ventral views. Scale bars: 1 mm.

Figure 14. Caudal vertebrae of European urodeles. A, Ommatotriton ophryticus (MNCN 40462). B, C, Pleurodeles aealtl (MDHC 253). D, Triturus carnifex (MDHC 299). E, Triturus carnifex (MDHC 145). From left to right: anterior, dorsal, lateral (right lateral for A, C; left lateral for B, D, E), posterior and ventral views. Scale bars: 1 mm.