Chelotriton sp.
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publication ID |
https://dx.doi.org/10.3897/fr.25.83781 |
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publication LSID |
lsid:zoobank.org:pub:7A16698D-4F18-48D2-9D96-51A6E0CC15AC |
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persistent identifier |
https://treatment.plazi.org/id/14130CC9-9D4F-5FC3-8573-A8624152D9BF |
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treatment provided by |
by Pensoft |
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scientific name |
Chelotriton sp. |
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Figs 5G-5 View Figure 5 , 6M View Figure 6
Material.
Four frontals HLMD-Ez 2070-2073, four prefrontals HLMD-Ez 2068-2069, one nasal HLMD-Ez 2058, seven maxillae HLMD-Ez 2063-2065, two squamosals HLMD-Ez 2066-2067, one dentary HLMD-Ez 2057, five trunk vertebrae HLMD-Ez 2059-2061, ten ribs HLMD-Ez 2053-2056.
Description.
Frontal: All four frontals are fragmentarily preserved. They represent individuals of different sizes. The frontal is widest at its most complete posterior portion. Its dorsal surface is covered by dermal ornamentation (Fig. 5G, I, K View Figure 5 ). The bone is slightly bent along its midline between the fronto-squamosal arch (sensu Ivanov 2008) and the rest of the bone. The fronto-squamosal arch projects posteriorly behind the main part of the bone. In ventral view, the partes contactae are reduced and run parallel along the anteroposterior axis of the bone. The braincase roof, located medially from the pars contacta, is delimited by a low crest of a semilunar outline (Fig. 5H, J, L View Figure 5 ).
Prefrontal: The prefrontals are wing-shaped bones, anteriorly broad and posteriorly narrowing to a sharp tip (Fig. 5M-N View Figure 5 ). The lateral margin (margo orbitalis) of the bone forms the anterodorsal wall of the orbit. The anterior corner of the margo orbitalis is pierced by the foramina of the V nerve. In ventral view, the ventral vertical wall separates the margo orbitalis from the rest of the bone. The articulation surface with the frontal bone, located at the posterolateral margin of the bone, is massive and more strongly developed than any other margin of the bone.
Nasal: The nasal bone has a nearly rectangular outline (Fig. 5O-P View Figure 5 ). All its margins are flat, without any concave outlines. Its dorsal surface is slightly rounded and possesses dermal ornamentation. In ventral view, parallel to the medial margin of the bone a ridge for articulation with the premaxillae is present.
Maxilla: only the posterior portions of the bone without dentition are present in the material. In dorsal view, the bone is narrow and a thin-walled horizontal pterygoid process projects lingually (Fig. 5S, U View Figure 5 ). In lateral view, the bone surface is covered by dermal ornamentation made of a dense network of small pits and pustules. Posteriorly the bone increase in height. In lingual view, the bone surface is smooth (Fig. 5R, T View Figure 5 ). The articulation surface with the quadratojugal bone is located on the posterodorsal surface of the bone. The size and dimensions of the articulation surface vary among available maxillae.
Squamosal: Two squamosals are partially preserved. In dorsal view, the HLMD-Ez 2066 is nearly semilunar in outline (Fig. 5V View Figure 5 ). The frontal process is curved slightly medially and possesses a vertical and almost flat articulation surface with the frontal. The lateral margin of the bone is rounded. The dorsal surface of the bone is somewhat horizontal and is covered by dermal ornamentation similar to other skull bones. The parietal process (in HLMD-Ez 2067, Fig. 5X View Figure 5 ) has a horizontal surface. It is slightly shorter but broader than the frontal process. In ventral view, a medioposteriorly oriented ridge, corresponding to the base of the ventral process of the bone, is visible. Posteriorly from the ridge, the bone surface is moderately concave.
Dentary: The fragmentary-preserved dentary is 1.7 mm in height. In lingual view, it shows a very low dental shelf with traces of the tooth pedicles. The preserved portion of the Meckelian groove is narrow and rather shallow (Fig. 5Z View Figure 5 ). Another but smaller groove is observable below the posterior half of the Meckelian groove, resembling most probably the articulation surface with the coronoid. In lateral view, the dentary is heavily ornamented by pits and pustules (Fig. 5Y View Figure 5 ). A remarkable concave surface separates the portion of the dental shelf from the rest of the bone.
Trunk vertebrae: the vertebrae are robust. The opistocoelous vertebra centrum is massive and slightly dorsoventrally flattened. The neural crest is nearly as high as the vertebra centrum (Fig. 6B, I View Figure 6 ). In dorsal view, its dorsal surface possesses a flat and (elongate) triangular in outline plate, which is covered by a dermal ornamentation made of deep pits and low pustules (Fig. 5A, H View Figure 5 ). This place can be well developed and projects over the neural arch. Anteriorly, the neural crest does not reach the anterior tip of the neural arch (Fig. 6D, F View Figure 6 ). The pre- and postzygapophyses are round or elongated and project (latero-)anteriorly. The neural arch between the anterior half of the prezygapophyses has a smooth and convex surface. In anterior view, the neural canal is rounded or nearly triangular in outline (Fig. 6F View Figure 6 ). The condyle has a dorsoventrally flattened oval shape.
Small subprezygapophyseal foramina (sensu Vasilyan et al. 2017) can be present at the basis of the prezygapophyses. In lateral view, the transverse process is connected with the postzygapophysis by a clearly visible dorsal lamina (Fig. 6B, I View Figure 6 ). The posterior alar process connecting the parapophysis with the cotyle is smaller than the dorsal lamina. The prezygapophysis is connected with the parapophysis by a well-developed accessory alar process. A very thin anterior alar process connects the base of the prezygapophysis with the parapophysis of the transverse process. In ventral view, rather large-sized subcentral foramina and rather smaller foramina are visible on the ventral surface of vertebrae. The transverse process consists of para- and diapophysis, which, though located close to each other, are separated by a thin lamina (Fig. 6B View Figure 6 ). In posterior view, the pterygapophysis possesses two distinct notches.
Ribs: All ribs are fragmentarily preserved. The articulation joints with the transverse process of the vertebrae are bicapitate. Both articulation heads are rounded and connected with a thin bone lamina (HLMD-Ez 2053, Fig. 6L View Figure 6 ). The dorsal surface of all ribs possesses two (HLMD-Ez 2054, Fig. 6K View Figure 6 ) to five (HLMD-Ez 2055, Fig. 6M View Figure 6 ) spines of different sizes and orientations.
Remarks.
Based on the combination of the following characters, the described fossil remains can be attributed to the genus Chelotriton , broadly known from the Cenozoic deposits of Europe: 1) the presence of the characteristic dorsal ornamentation on skull bones and the horizontal plate of the neural spine of vertebrae; 2) the pterygoid process of the maxillae connected with the pterygoid; 3) the presence of spines on the ribs and 4) general morphology and dimensions of the bones ( Ivanov 2008; Schoch et al. 2015; Vasilyan 2020). The remains cannot be clearly assigned to any known species of the genus due to the lack of a comprehensive understanding of the taxonomic diversity within the Chelotriton genus. However, some comparative remarks can be given below. The described skull bones differ significantly from all so far known Chelotriton records. For example, the frontal shows an intermediate morphology observable in Chelotriton sp 1. and sp. 2 from Mokrá-Western Quarry, Czech Republic, early Miocene ( Ivanov 2008) and Chelotriton paradoxus from the Enspel Maar, Germany, late Oligocene, and Randecker Maar, Germany, early Miocene ( Schoch et al. 2015). The shape of the squamosal in the Echzell material can be found only in Chelotriton sp. from Orsberg, Germany, late Oligocene ( Marjanović and Witzmann 2015), where a bone of a similar shape is named as a quadratojugal-quadrate bone. The nasal from Echzell (nearly rectangular in outline) can be clearly distinguished from that of all known forms in which the form varies from irregular-shaped one (e.g. in Chelotriton paradoxus from Enspel, Roček and Wuttke 2010) to trapezoid-shaped in Chelotriton sp. form Orsberg ( Marjanović and Witzmann 2015). Most probable, the suggested high variability of the skull bone ( Schoch et al. 2015) can be explained by uncovered high specific diversity of Chelotriton . Thus, at this stage of knowledge, we describe the fossil remains of Chelotriton with an open nomenclature.
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