Triturus

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 : 605-608

TRITURUS RAFINESQUE, 1815

Species: Triturus carnifex * (Laurenti, 1768) , Triturus cristatus * (Laurenti, 1768) , Triturus dobrogicus * (Kiritzescu, 1903) , Triturus ivanbureschi , Triturus karelini , Triturus macedonicus * (Karaman, 1922) , Triturus marmoratus * (Latreille, 1800) and Triturus pygmaeus * (Wolterstorff, 1905) .

Otic–occipitum complex ( Fig. 5G, H )

The prominentiae semicircularis anterioris and posterioris are clearly visible, whereas the prominentia semicircularis lateralis is generally covered by the parotic crest and process. The middle depression is smooth, but not deep. In lateral and posterior views, the circular or elliptical fenestra ovalis is visible ventral to the parotic process. Its anterior edge is in the middle of the complex or slightly posterior. The parietal crest is low, extending from the mid-length of the distal tectum synoticum to the anteriormost edge of the prominentia semicircularis anterioris, being lower anterior to the parotic crest. The parotic crest is variably developed, generally lower in its portion close to the parotic process. This crest is clearly visible in anterior view. Parotic and parietal crests meet slightly anterior to the mid-length of the prominentia semicircularis anterioris, and the parotic crest is laterally inclined close to the parietal crest and laterally concave close to the parotic process. The parotic process extends laterally, being rectangular in dorsal view and triangular in anterior and posterior views; in its ventral part, it is more laterally extended than in its dorsal part. In lateral view, the parotic process is almost horizontal, or the ventral tip extends anteriorly beyond the dorsal one. The anterior edge of the tectum synoticum is posterior to the mid-length of the complex. It extends medially almost as much as the hypochordal commissure and beyond the prefacial commissure, and a concavity is visible between the two commissures. The cylindrical otic process projects anteriorly on the prominentia semicircularis anterioris, bearing a circular articular surface. The foramen faciale is dorsolateral to the kidney-shaped articular surface of the processus basalis, which generally extends laterally into a sort of spine visible in ventral view, protruding beyond the main body of the complex. Between the processus basalis and the otic process, a sulcus petrosus is visible. The elliptical postoticum foramen is surrounded posteriorly by the cotyle, and its anterior margin is generally not connected with the prominentia semicircularis lateralis by a lamina. The foramen prooticum is almost completely surrounded by bone. The auditory cavity is well defined and deep. The basicapsular commissure is medially developed beyond the prefacial commissure and extends medially as the hypochordal commissure. The fenestra basicranialis is clearly visible between the basicapsular and hypochordal commissures. The ventral surface is variably perforated, with a medial crest. This crest runs from the posteriormost point of the basicapsular commissure to the posteriormost point of the hypochordal commissure and is crossed by the sulcus carotis.

Remarks: In MDHC 18, the parietal crest and the parotic crest and process are low or absent. In MDHC 145, the parotic crest is absent, and the parotic process is sub-triangular in dorsal view. In the two specimens of T. marmoratus , the parotic process is particularly elongate and rectangular in posterior view. In the two available specimens of T. marmoratus , the articular surface of the otic process is irregular (not circular), and the articular surface of the process basalis does not form a lateral spine. Moreover, in these specimens, the sulcus petrosus is hidden by a sharp process ventral to the prominentia semicircularis anterioris. In T. pygmaeus , a lamina connecting the posterior edge of the parotic process to the anterior margin of the postoticum foramen is present. In MDHC 38, this concavity is not present, but there is a bony connection between the tectum synoticum and the prefacial commissure.

Atlas ( Fig. 8E )

The neural canal is circular in anterior view and is as high as each occipital joint. In posterior view, the neural canal is usually slightly wider than the circular cotyle (see Remarks). The occipital joints are circular or elliptical, with the major axis being horizontal (or sub-horizontal). Generally, the articular facets of the odontoid process are separated by a narrow groove on the ventral surface (see Remarks). In ventral view, the width of the base of the odontoid process is similar to that of each occipital joint or larger. 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. They can reach or not reach the posterior end of the neural arch. The neural spine is generally present and low. The lateral surface of the atlas is variably perforated by foramina. The incisura vertebralis cranialis is small or wide. In lateral view, the dorsal edge of the neural arch is sub-horizontal (inclination of 10–40° above the horizontal). The posterior margin of the lateral wall of the neural arch ventral to the wide incisura caudalis in lateral view is concave, inclined or sub-vertical. The maximum concavity of the incisura vertebralis caudalis is dorsal to the horizontal plane that comprises the maximum concavity of the incisura cranialis. The well-developed lateral crests reach the postzygapophyses posteriorly, or the incisura vertebralis caudalis. The inferior crests are low or marked (see Remarks). In posterior view, the neural arch is dorsally convex (inverted U-shaped). Less than one-third of the postzygapophyses extend 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 variably visible, formed by the forked neural crest or by the neural arch. The cotyle is not visible in dorsal view. The ventral surface is smooth or bears more than two foramina.

Remarks: In MDHC 145, there are two secondary crests per side. In T. marmoratus and T. pygmaeus , the neural canal is 2 or 2.5 times higher than the condyles in anterior view. In T. dobrogicus , the two odontoid facets form a low angle relative to the horizontal (30–40°), whereas the angle is higher in T. carnifex , T. cristatus , T. marmoratus , T. pygmaeus and T. macedonicus . Secondary crests are equally distant from the dorsal edge of the neural arch and postzygapophyses in T. dobrogicus and T. macedonicus , whereas these crests are closer to the dorsal edge of the neural arch than to postzygapophyses in T. marmoratus , T. carnifex and T. cristatus . In T. pygmaeus , this character is variable. The convexity of the neural arch between the cotyle and the incisura caudalis is particularly strong in T. macedonicus and T. carnifex . In these species, the incisura caudalis is covered, in part, by the lateral crests, which are generally developed posterolaterally, where the posterior tips of these crests form a right angle. This character is almost never present in T. dobrogicus , T. pygmaeus and T. marmoratus , in which the lateral crests are generally less developed posteriorly. In T. cristatus , this character is variable depending on the specimen. In T. marmoratus MNHN 1938 _146, the part of the neural arch between the postzygapophyses and the cotyle is vertical, and the incisura vertebralis caudalis is weakly developed. In this specimen, the lateral crests are low, starting from slightly dorsal to the mid-height of the condyle. The lateral crests raise rapidly until they reach the postzygapophyses, and dorsal to the first spinal nerve foramen (anterodorsal to the crest on the right side and posteroventral on the left side) the crests become less evident, being present only as a slight convexity. In the other specimens of T. marmoratus and T. pygmaeus , the lateral crests are high and start ventral to the mid-height of the occipital joints, showing the same outline as MNHN 1938_146, being higher close to the first spinal nerve foramen and reduced close to the postzygapophyses. This is not true for the other species of Triturus based on the material from HNHM, in which the lateral crests are not evident around the foramen of the first spinal nerve, although they are more evident anterior to the incisura vertebralis caudalis. Different from MNHN 1938_146, the lateral crests begin from the dorsal edge of the condyles, slightly lateral to its mid-length, and the foramen for the first spinal nerve is usually ventral to it. Similar to MNHN 1938_146, they rise rapidly until they reach the postzygapophyses, being inclined at ~60°. In T. marmoratus MNCN 16067, the lateral crest is posteriorly reinforced by a thick crest, clearly visible in posterior view. The inferior crests are not present in T. marmoratus or in T. cristatus (but visible in BSPGM 4099 and HNHM 2002.143.6), whereas they are clearly visible in T. carnifex and T. dobrogicus . They can be present or absent in T. macedonicus , thereby documenting its high intraspecific variability. In T. pygmaeus , the inferior crests are low. In posterior view, the cotyle is smaller than the neural canal in the French specimen of T. marmoratus (MNHN 1938_146), in which the cotyle diameter could fit at least four times into the cross-section of the neural canal. In T. pygmaeus , the cotyle diameter could fit almost three times into the cross-section of the neural canal. In T. cristatus and T. carnifex and in Spanish specimens of T. marmoratus , the cotyle diameter could fit at least two times into the cross-section of the neural canal. In T. dobrogicus and T. macedonicus , the neural canal is only slightly larger than the cotyle. In ventral view, the odontoid process is more anteriorly extended in T. cristatus , T. marmoratus , T. dobrogicus and T. carnifex than in T. macedonicus , such that the two articular facets do not contact the condyles. In T. macedonicus , the articular facets of the odontoid process contact the condyles. In T. marmoratus and in MNCN 42552 ( T. pygmaeus ), the articular facets of the odontoid process are separated by a groove. In T. marmoratus MNHN 1938 -146, the ventral surface is generally not smooth, bearing several small crests and tubercula.

Precaudal vertebrae ( Fig. 11F, G )

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 neural arch between the condyle and the elliptical prezygapophyses is inclined. Diapophyses and parapophyses are distinguishable, connected by a smooth lamina that reaches their distal ends and is distally concave. They are posteriorly oriented, entirely or partly covering the posterior edge of the neural arch between the postzygapophyses and centrum. In lateral view, the neural arch dorsal to the prezygapophyses is generally visible. Most of the height of the vertebra is formed by the centrum and neural arch ventral to the postzygapophyses (only one-fifth of the height of the vertebra is formed by the neural arch dorsal to the postzygapophyses). The neural crest, when present, is blade-like, starts posterior to the anterior edge of the neural arch and is posteriorly slightly broadened, not always reaching the posterior edge of the neural arch, which is gently concave in dorsal view. 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 or slightly ventrally concave, contacting the diapophyses in a variety of locations. Anterior and posterior ventral crests are low and form an asymmetrically or symmetrically rhomboidal 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 or horizontal. The incisura vertebralis caudalis is deep and contacts the centrum. 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 in lateral view is sigmoid or vertical. Less than half of the postzygapophyses extend posteriorly beyond the cotyle in lateral view. In dorsal view, the neural arch is anteriorly concave (U-shaped) or flat. The condyle is visible in dorsal view, whereas the cotyle is not visible (or, rarely, it is slightly visible through the incisura dorsalis). The ventral surface is generally perforated.

Remarks: In T. pygmaeus and T. marmoratus , the neural crest is high and dorsally horizontal, similar to T. karelinii figured by Ratnikov & Litvinchuk (2007). In T. pygmaeus , the neural crest starts from the posterior edge of the prezygapophyses, whereas in T. marmoratus , the neural crest starts from the posterior third of the prezygapophyses.

Caudal vertebrae ( Fig. 14D, E )

The caudal vertebrae are not particularly high (height/ length ratio <1.25). The neural canal is pentagonal or circular, and the haemal canal is elliptical or U-shaped. The neural canal is wider than or as wide as and as high as the haemal canal. The transverse processes are triangular or rectangular (with the longest side vertical) in anterior view; they are subvertical in lateral view and triangular in dorsal view. The neural and haemal crests are high and posteriorly enlarged or forked; if they are enlarged, the dorsal surface is smooth. The lateral surface is not smooth, because of the presence of several crests and small foramina, and a large foramen on the haemal arch. The zygapophyseal crests are marked and horizontal. They are poorly connected with the transverse processes. The anterior ventral crests are marked and reach the anterior edge of the haemal arch, sometimes projecting more anteriorly than the haemal arch. The posterior ventral crests start from the posteriormost tip of the haemal arch. 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 between the centrum and the anterior ventral crest. Ventral to the anterior ventral crest, the anterior margin of the haemal arch forms another concavity (or is posteriorly inclined); therefore, the anterior edge of the haemal arch in lateral view is convex close to the anterior ventral crests. The haemal crest projects anteriorly beyond the haemal arch, forming a sharp or rounded tip in lateral view. The haemal arch and crest in lateral view form a sharp tip posteriorly. The neural arch is usually more developed dorsally than the haemal arch ventrally, meaning that the haemal crest is usually lower than the neural crest.

Remarks: In T. macedonicus and T. cristatus , the posterior zygapophyseal crest contacts the transverse processes distally or medially, forming a ventral and posterior concavity; in T. carnifex and T. dobrogicus , the posterior zygapophyseal crest generally contacts the transverse processes more proximally, and the concavity is not evident or absent. In T. macedonicus , the ventral edge of the haemal arch is horizontal, and the haemal crest is low. In T. marmoratus MNCN 16089, the ventral tip of the haemal arch is only slightly visible or absent, and there is no posterior tip, although the posterior edge of the haemal arch/crest is rounded.

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.