Lissotriton

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 : 600-602

LISSOTRITON BELL, 1839

Species: Lissotriton italicus * (Peracca, 1898) , Lissotriton boscai * (Lataste, 1879) , Lissotriton graecus , Lissotriton helveticus * (Razoumovsky, 1789), Lissotriton maltzani , Lissotriton montadoni * (Boulenger, 1880) and Lissotriton vulgaris * (Linnaeus, 1758).

Otic–occipitum complex ( Fig. 5D )

The prominentiae semicircularis anterioris and posterioris are visible in dorsal view and rounded. The prominentia semicircularis lateralis is usually less visible, because it is covered by the parotic crest and process. Among the prominentiae, there is a deep and smooth middle depression. The prominentia semicircularis posterioris extends dorsally and mediolaterally from the cotyle. The circular or elliptical fenestra ovalis is ventral to the prominentiae semicircularis posterioris and lateralis, and between the cotyle and parotic process. The anterior edge of the fenestra ovalis is posterior to the mid-length of the complex. The parietal crest is variably developed from the mid-length of the proximal tectum synoticum to the anteriormost edge of the prominentia semicircularis anterioris. The parotic crest is lower close to the parotic process and higher in its anterior part. It is higher than the parietal crest, contacting it slightly anterior to the mid-length of the prominentia semicircularis anterioris. The parietal crest is higher anteriorly than the parotic crest. The parotic process is sub-triangular or rectangular in dorsal view, rectangular in posterior view and inclined in lateral view, with the ventral tip being more anterior than the dorsal one. The parotic crest is laterally inclined close to the parietal crest and laterally concave close to the parotic process. The anterior edge of the tectum synoticum is posterior to the mid-length of the complex. The tectum synoticum is almost as medially developed as the hypochordal commissure, extending slightly medially beyond the prefacial commissure. The short, subcylindrical otic process is anteriorly projecting, with an irregular articular surface, often covered by the prominentia semicircularis anterioris and by the high parietal crest anterior to the parotic crest. The foramen faciale is dorsolateral to the kidney-shaped articular surface of the processus basalis. This surface forms a laterally developed crest visible in ventral view, which does not extend beyond the main body of the complex. Between the processus basalis and the otic process, there is no deep sulcus petrosus. The basicapsular commissure is medially developed beyond the prefacial commissure and is as medially developed as the hypochordal commissure. The fenestra basicranialis is present between the basicapsular and hypochordal commissures. The elliptical postoticum foramen is posteriorly surrounded by the cotyle or by the lamina of the tectum synoticum. The foramen prooticum is C-shaped and not entirely surrounded by bone (but see Remarks). The auditory cavity is well defined and deep. The ventral surface is variably perforated, with the high medial crest either interrupted or not sigmoid by the sulcus carotis.

Remarks: In the examined specimens of Li. boscai and Li. helveticus , the parietal crest extends from the midlength of the distal end of the tectum synoticum (not proximal) to the anteriormost edge of the prominentia semicircularis anterioris. In the two available specimens of Li. helveticus , the foramen prooticum is completely surrounded by bone. In MDHC 259, an anteriorly pointing tip of the parietal crest forms the anterior end of the complex. In MDHC 135, the parotic process is dorsally convex in both anterior and posterior views and ventrally concave (slightly hook-shaped). In MNCN 18203, the parotic process is sub-triangular in posterior view. In MNCN 19267, the otic process is anteriorly projecting, with a circular articular surface.

Atlas ( Fig. 8A, B )

The neural canal is circular in anterior view, twice as high as each occipital joint. In posterior view, the neural canal is 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 narrower than each occipital joint. The posteriorly enlarged neural crest is low or absent, whereas the secondary crests are variably developed, but always 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 can be present or absent. The lateral surface of the atlas is variably perforated. The incisura vertebralis cranialis is small or absent. In lateral view, the dorsal edge of the neural arch is sub-horizontal (inclination of 10–30° above the horizontal). The neural arch between the incisura caudalis and the cotyle is convex or subvertical. The maximum concavity of the incisura vertebralis caudalis is dorsal to the horizontal plane of the maximum concavity of the incisura cranialis. Posteriorly, the lateral crests reach the elliptical postzygapophyses or run dorsally to the latter, but without reaching the posterior edge of the neural arch. The inferior crests are low or absent. In posterior view, the neural arch is dorsally convex (U- or V-shaped), but the incisura dorsalis is sometimes visible. Less than half of the postzygapophyses extends posteriorly beyond the cotyle in lateral view. In dorsal view, the neural arch is anteriorly straight or concave (U- or V-shaped concavity); posteriorly, the incisura dorsalis is deep and formed by the neural arch. In dorsal view, the cotyle may or may not be visible. The ventral surface is smooth, although it can also be pierced by more than two foramina.

Remarks: Secondary crests are absent in MDHC 135. In NHMW 34075, the lateral crests are low.

Precaudal vertebrae ( Fig. 11C )

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. Diapophyses and parapophyses are distinguishable, connected by a smooth lamina reaching their distal ends. Distally, the lamina is smooth. The transverse processes are subperpendicular to the centrum or with a slightly posterior orientation, covering the incisura caudalis only slightly in lateral view or not covering it. In the same view, the neural arch dorsal to the prezygapophyses is either visible or not. 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 and being posteriorly broadened and forked. The neural spine is low or absent. The medial edges of the prezygapophyses are usually parallel in dorsal view. 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 mid-length. 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 small foramen is visible in the ventral half of the proximal edge of the transverse processes (at the base of the parapophyses). In lateral view, the dorsal edge of the neural arch is dorsally concave in its anterior part. The incisura vertebralis caudalis is deep, and the neural arch ventral to it is inclined or rarely convex. In posterior view, the dorsal edge of the neural arch is horizontal or dorsally convex (inverted U-shaped). The neural arch dorsal to the postzygapophyses is sigmoid or vertical in lateral view. Less than half of the postzygapophyses extends posteriorly beyond the cotyle in lateral view. In dorsal view, the neural arch is anteriorly concave (U-shaped) or flat. The condyle and the cotyle may or may not be visible in dorsal view. The ventral surface is generally perforated.

Remarks: In Li. boscai , the neural crest is dorsally pitted and bears moderate lateral lips (much less evident than in Salamandrina ). In this species, the condyle is slightly visible in dorsal view, and in ventral view the ventral lamina is commonly trapezoidal. The ventral lamina differs from other congeners, in which it is common for the ventral lamina to be asymmetrically rhomboidal. The same pitted surface of the neural crest is visible in the extinct species Li. rohrsi .

Caudal vertebrae ( Fig. 13E )

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. The neural and haemal crests are high and posteriorly enlarged or forked; if they are enlarged, their dorsal surface is perforated. The lateral surface is not smooth, because several crests and small foramina are present. There is no large foramen on the haemal arch. The zygapophyseal crests are marked and horizontal or ventrally concave. 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 posteroventral edge of the haemal arch in lateral view. 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) between the centrum and the anterior ventral crest, and convex or anteriorly inclined ventral to the anterior ventral crest. The haemal crest does not project anteriorly beyond the haemal arch. The haemal arch and crest are posteriorly convex and rounded in lateral view, without having a posterior tip.

Remarks: The caudal vertebrae of Li. vulgaris are particularly high (height/width ratio ~1.8), whereas in the other species the height/width ratio is lower (~1.4). In Li. boscai , the neural crest has no lateral lips (different from the precaudal vertebrae).

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 13. Caudal vertebrae of European urodeles.A, Calotriton asper (MNCN 16122). B, Euproctus platycephalus (MDHC 405). C, D, Ichthyosaura alpestris (MDHC 391). E, Lissotriton Ʋulgaris (MDHC 135). From left to right: anterior, dorsal, lateral (left lateral for A, E; right lateral for B–D), posterior and ventral views. Scale bars: 1 mm.