Euproctus

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 : 597-598

EUPROCTUS GENÉ, 1839

Species: Euproctus montanus * (Savi, 1838) and Euproctus platycephalus * (Gravenhorst, 1829) .

Otic–occipitum complex ( Fig. 5B )

The prominentiae semicircularis anterioris and posterioris are visible and rounded, whereas the prominentia semicircularis lateralis is less evident. The middle depression is deep, with smaller foramina in its floor. The elliptical fenestra ovalis is ventral to the parotic process, and its anterior edge is posterior to the mid-length of the otic–occipitum complex. The parietal crest is interrupted in its mid-length. The posterior half runs from the posterior half of the distal edge of the tectum synoticum to the mid-length of the prominentia semicircularis anterioris, and it is more medial than the anterior half. The anterior half starts from the midlength of the prominentia semicircularis anterioris and is higher than the posterior half, forming a dorsolateral tip at the mid-length of the prominentia semicircularis anterioris. The parotic crest is low and slightly visible. The parotic process is sub-triangular in dorsal view and rectangular in both anterior and posterior views. The anterior edge of the tectum synoticum is posterior to the mid-length of the otic–occipitum complex. The tectum is as developed medially as the hypochordal commissure, and slightly medially extended beyond the prefacial commissure, but a concavity is visible between the two commissures. The otic process is not anteriorly extended on the prominentia semicircularis anterioris, and in dorsal view the prominentia semicircularis anterioris is visible anterior to the otic process. The articular surface of both the otic process and the processus basalis are not clearly visible. Those processes respectively form a dorsolateral spine and a small ventrolateral spine that do not extend beyond the main body of the complex. The sulcus petrosus is not visible between the processus basalis and the otic process. The elliptical postoticum foramen is surrounded posteriorly by the cotyle. A lamina connects the parotic process with the cotyle and is sinusoidal, running along the posterodorsal edge of the fenestra ovalis. The foramen prooticum is entirely surrounded by bone. The basicapsular commissure extends medially beyond the prefacial commissure, being developed medially as the hypochordal commissure. The basicapsular commissure shows an anterior spine, shorter than that in Pleurodeles (see below) but still present. The fenestra basicranialis is clearly visible between the basicapsular and hypochordal commissures. The ventral surface is variably perforated, bearing a medial crest running from the posteriormost point of the basicapsular commissure to the posteriormost point of the hypochordal commissure, and is crossed by the sulcus carotis.

Atlas ( Fig. 7B )

The neural canal is circular in anterior view and is twice as high as each occipital joint. The occipital joints are circular or elliptical, with the major axis being horizontal (or sub-horizontal). 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 wider than each occipital joint. The neural crest is blade-like and not posteriorly enlarged, whereas the secondary crests are present and anteriorly enlarged, and they converge slightly towards the neural crest. The neural spine is present. The lateral surface of the atlas is variably perforated. The incisura vertebralis cranialis is high and narrow. In lateral view, the dorsal edge of the neural arch is moderately inclined (<40° relative to the horizontal). The neural arch between the wide incisura caudalis and the cotyle is convex. The maximum concavity of the incisura vertebralis caudalis is dorsal to the horizontal plane of the maximum concavity containing the incisura cranialis. Posteriorly, the well-developed lateral crests reach the wide incisura caudalis. The inferior crests are low or marked. In posterior view, the neural arch is dorsally convex (inverted U-shaped) or flat. Less than half of the postzygapophyses posteriorly extends beyond the cotyle in lateral view. In dorsal view, the neural arch is anteriorly straight or concave (U-shaped), and posteriorly, the incisura dorsalis, if present, is interrupted by the neural spine. In dorsal view, the cotyle can be visible or not. The ventral surface bears more than two foramina.

Remarks: In MDHC 507, the neural spine is absent.

Precaudal vertebrae ( Fig. 11A )

The precaudal vertebrae are opisthocoelous. The neural canal is pentagonal, higher than the condyle. The condyle is circular or elliptical. 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 slightly posteriorly oriented, partly covering or not covering the posterior edge of the neural arch between the postzygapophyses and the centrum. In the same view, the neural arch dorsal to the prezygapophyses is generally 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, and posteriorly it becomes broader and then forked. The neural spine is absent. The anterior zygapophyseal crests contact the dorsal part of the diapophyses. The posterior zygapophyseal crests are well developed and horizontal, contacting the diapophyses distally or at their mid-length. The ventral lamina is trapezoidal anterior to the transverse processes, and it is triangular posteriorly. 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 parapophyses). In lateral view, the dorsal edge of the neural arch is dorsally concave in its anterior part or horizontal. The incisura vertebralis caudalis is deep, and the neural arch ventral to it is inclined or, in some vertebrae, convex. In posterior view, the dorsal edge of the neural arch is dorsally convex (inverted V- or U-shaped). In lateral view, the neural arch dorsal to the postzygapophyses is sinusoidal or vertical. Less than half of the postzygapophyses is extended posteriorly beyond the cotyle in lateral view. In dorsal view, the neural arch is straight anteriorly. The condyle is visible in dorsal view (usually along its entire length), whereas the cotyle is not visible (or in rare instances, slightly visible through the incisura dorsalis). The ventral surface is generally perforated.

Caudal vertebrae ( Fig. 13B )

The caudal vertebrae are higher than long (height/ length ratio ~1.3–1.4). The neural canal is pentagonal or circular, and the haemal canal is elliptical, U-shaped or triangular. The neural canal is wider than the haemal canal. The transverse processes are triangular in both anterior and dorsal views, such that the vertebra is generally rhomboidal in shape. The neural and haemal crests are high and posteriorly forked.The lateral surface is not smooth, because several crests and small foramina are present, but there is no large foramen on the haemal arch. The zygapophyseal crests are low and horizontal or ventrally concave. The anterior ventral crests are low and, in general, do not reach the anterior edge of the haemal arch. The posterior ventral crests start from the posteroventral edge of the haemal crest in lateral view. In this view, the anterior and posterior ventral crests form an angle> 130°. In lateral view, the anterior margin of the haemal arch is convex (or anteriorly inclined) between the centrum and the anterior ventral crest, and ventral to the latter. The haemal crest does not project anteriorly beyond the haemal arch. The haemal arch and crest are posteriorly convex and rounded in lateral view, with both lacking a posterior tip.

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 7. Atlantes of European urodeles. A, Calotriton asper (MNCN 16122). B, Euproctus montanus (BSPGM 4202). C, Ichthyosaura alpestris (MDHC 407). D, Ichthyosaura alpestris (MDHC 391). From left to right: anterior, dorsal, lateral (left lateral for A; right lateral for B–D), 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.