Calotriton

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 : 595-596

CALOTRITON GRAY, 1858

Species: Calotriton arnoldi and Calotriton asper *.

Otic–occipitum complex ( Fig. 5A )

The three prominentiae (anterioris, lateralis and posterioris) are not evident or rounded in dorsal view, and the middle depression is smooth, but not deep. In lateral and posterior views, the elliptical fenestra ovalis is visible. The fenestra ovalis is ventral to the parotic process, and its anterior edge is in the middle of the complex or slightly anterior. The fenestra is particularly small in this genus, being only slightly wider than the postoticum foramen, elliptical and surrounded posteriorly by the cotyle. The parietal crest is higher in its posterior half, forming a tip at the midlength of the prominentia semicircularis anterioris, and is low anterior to the latter; the anterior end of the parietal crest corresponds to the anteriormost edge of the prominentia semicircularis anterioris. The parotic crest is low and ends in the middle of the proximal or distal end of the parotic process. This latter process is particularly long and wide, rectangular in dorsal view and posteriorly curved, forming a posterior concavity with the cotyle. In dorsal view, the parotic process covers the fenestra ovalis. In lateral view, the parotic process is laminar and ventrally concave, such that in posterior view the shape of this process is not precisely recognizable as either rectangular or triangular. The anterior edge of the tectum synoticum is posterior to the mid-length of the complex. The tectum synoticum is almost as developed medially as the hypochordal and prefacial commissures, with a rectangular concavity between the latter and the tectum. The cylindrical otic process is anteriorly projecting, bearing a circular articular surface. The foramen faciale is dorsolateral to the elliptical articular surface of the processus basalis. In general, the processus basalis extends laterally into a short spine that is visible in anterior and ventral views and does not extend beyond the main body of the complex. The articular surface of the processus basalis is well posterior to the otic process. In anterior view, the sulcus petrosus is not visible because it is covered by a wide lamina ventral to the otic process. The foramen prooticum is entirely surrounded by bone. The basicapsular commissure is extended medially beyond the prefacial commissure and is as medially extended 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, with no crista retrosellaris. The ventral surface shows one or two foramina (other than the foramen faciale), with a medial crest, starting from the posteriormost point of the hypochordal commissure. There is a high crest connecting the posterolateral edge of the processus basalis with the mid-length of the medial crest and forming the anterior edge of the sulcus carotis. The medial crest is absent anterior to the medial crest.

Atlas ( Fig. 7A )

The neural canal is circular in anterior view and is as high as each occipital joint or slightly higher. 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 the major axis being horizontal. The articular facets of the odontoid process are separated by a narrow groove visible in ventral view. In this view, the base of the odontoid process is as wide as each occipital joint. The neural crest does not start from the anterior edge of the neural arch and is blade-like and high without being posteriorly broadened. The secondary crests broaden anteriorly. Posteriorly, they converge towards the neural crest, thus, ending far more anterior than the posterior edge of the neural arch; in this way, in dorsal view, the three crests form a Y-shape. The neural spine is absent. The lateral surface of the atlas bears two or more foramina per side. The incisura vertebralis cranialis is wide. In lateral view, the dorsal edge of the neural arch is strongly inclined. The neural arch between the wide incisura caudalis and the cotyle is concave or inclined. In general, the lateral crests end ventrally to the postzygapophyses without reaching them. The inferior crests are absent or low. Less than half of the postzygapophyses extends posteriorly beyond the cotyle in lateral view. In dorsal view, the neural arch is anteriorly straight or with a V-shaped notch, and the cotyle is visible posteriorly. The ventral surface is variably perforated.

Precaudal vertebrae ( Fig. 10E )

The vertebrae are opisthocoelous. In lateral view, one-third of the height of each vertebra is formed by the neural crest and neural arch dorsal to the prezygapophyses. The neural canal is pentagonal or circular, and the condyle is circular or elliptical, with the major axis being horizontal. Diapophyses and parapophyses are connected by a lamina reaching their distal ends. The lamina is distally linear or only slightly concave. The neural crest is blade-like and posteriorly forked, and it starts anteriorly from the anterior edge of the neural arch or more posteriorly. The neural spine is absent. The lateral surface of the vertebra shows more than one foramen, meaning that the surface is generally not smooth. The anterior zygapophyseal crests are dorsally concave or descend towards the transverse processes. The posterior zygapophyseal crests contact the transverse processes distally and are more dorsal than the anterior zygapophyseal crests; as a result, the zygapophyseal crests along their entire length are sinusoidal. In lateral view, the anterior edge of the neural arch dorsal to the prezygapophyses is generally visible, and it is weakly inclined between them and the condyle. The incisura vertebralis caudalis is deep, usually reaches the vertebral centrum, and it is entirely covered by the transverse processes. Less than half of the postzygapophyses extends posteriorly beyond the cotyle. In dorsal view, the incisura dorsalis is formed by the forked neural crest, but it is not visible in posterior view (the dorsal edge of the neural arch is flat or rounded). In dorsal view, the anterior edge of the neural arch is concave, and the condyle and cotyle are both visible. The prezygapophyses are similar in size (quadrangular or circular), whereas the postzygapophyses are elliptical or ovoidal. The ventral lamina is not wide and is usually irregular in shape (triangular, trapezoidal or asymmetrically rhomboidal). The posterior ventral crests do not reach the cotyle. The ventral surface is variably perforated.

Caudal vertebrae ( Fig. 13A )

The caudal vertebrae are high (height/length ratio> 1.5). 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 in anterior view, laminar in lateral view, and posteriorly concave. The neural crest is high, similar to those on the precaudal vertebrae. The lateral surface is not smooth, because several crests and small foramina are present. There is no large foramen on the haemal arch, but a small foramen is present in some cases. The anterior ventral crests are low and are hidden by the transverse processes and the posterior ventral crests. The posterior ventral crests start from the mid-length of the posterior 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 concave (or posteriorly inclined) between the centrum and the anterior ventral crest, and convex (or anteriorly inclined) ventral to the ventral crest. The haemal crest is prominent, projects further anteriorly than the haemal arch and forms a rounded tip in lateral view. The haemal arch and crest are higher than the neural ones, with half of the height of the vertebra formed by them. The haemal arch and crest in lateral view are posteriorly convex and rounded, with neither having 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 10. Precaudal vertebrae of European urodeles. A, Mertensiella caucasica (MNCN 23821). B–D, Salamandra salamandra (MDHC 396): B, one of the first trunk vertebrae; C, trunk vertebra close to the pelvis; and D, sacral vertebra. E, Calotriton asper (MNCN 16122). From left to right: anterior, dorsal, lateral (right lateral for B, D; left lateral for A, C, E), 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.