Chelotriton undetermined
Creators: name: Villa, Andrea
name: Macaluso, Loredana
name: Mörs, Thomas
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Amphibia
Caudata
Salamandridae
Chelotriton
Chelotriton undetermined

description: Chelotriton sp.
Figures 7–8
Material. Hambach 6C: one premaxilla (IPB-HaH 2005); two maxillae (IPB-HaH 2007, IPB-HaH 2046); three frontals (IPB-HaH 2000, IPB-HaH 2001, IPB-HaH 2337); four dentaries (IPB-HaH 2004, IPB-HaH 2039; IPB-HaH 2231/2232); one fragment of indeterminate tooth bearing bone (IPB-HaH 2008); one atlas (IPB-HaH 2022); 21 trunk vertebrae (IPB-HaH 2010/2011, IPB-HaH 2012/ 2021, IPB-HaH 2023, IPB-HaH 2038, IPB-HaH 2111/2112, IPB-HaH 2114, IPB-HaH 2177/2179; IPB-HaH 2386); one caudal vertebra (IPB-HaH 2113); 14 ribs (IPB-HaH 2024/2037); eight indeterminate bone fragments (IPB-HaH 2006, IPB-HaH 2041/2045, IPB-HaH 2048, IPB-HaH 2401).
Description. The premaxilla (Figure 7 A-E) is small. It was most likely paired and preserves mainly the pars palatina and the pars dentale. The base of the pars faciale is also preserved, showing a dense sculpturing made up by pits and ridges anterodorsally. The sculpturing extends on the anterior surface of the low crista lateralis, but it is less developed here. In posterior view, a wide and deep concavity is visible by the base of the pars faciale. The pars palatina is very expanded, being mediolaterally wider than anteroposteriorly long. The tooth row seems almost complete, even though rather poorly preserved. At least 23/24 closely spaced tooth positions can be counted.
The maxilla IPB-HaH 2046 is represented only by a very small fragment. It displays a strongly sculptured lateral surface, with numerous distinct tubercles. On the medial surface, a well-developed lamina horizontalis is present. Ventral to this, poorly preserved tooth positions are visible. IPB-HaH 2007 (Figure 7 F-G), on the other hand, preserves the posterior end of the maxilla. By the anterior breakage, it displays a medially-directed process, which most likely contacted the pterygoid in origin. This process is short and distally rounded. Ventral to the process, the posterior end of the tooth row is visible, showing at least seven closely spaced tooth positions. The tooth row does not extend posterior to the process and it is followed by a long toothless portion of the ventral margin. The lateral surface of the bone is covered by a dense dermal sculpturing made up by pits, ridges, and tubercles. The dorsal margin bends in medial direction and the sculpturing does not extend onto the bent part. The posterior end of the specimen expands into a robust structure for a strong contact with the quadratojugal, but its distal end is broken.
The frontals are moderately large and rather robustly built. IPB-HaH 2000 (Figure 7 H-I) and IPB-HaH 2337 (Figure 7 L-M) only preserve part of the lateral margin, whereas IPB-HaH 2001 (Figure 7 J-K) is relatively complete, preserving also the posterior margin of the orbital cavity. A wide and long processus postorbitalis is present in all of them, representing the posterolateral projection participating in the anterior part of the fronto-squamosal arch. Ventrally, part of the sharp crista orbitosphenoideum is visible in IPB-HaH 2000 (Figure 7H) and IPB-HaH 2001 (Figure 7J). The dorsal surface is covered by a very dense dermal sculpturing made up by isolated tubercles.
Dentaries (Figure 7 N-Q) are fragmentary, but they clearly show a well-developed dermal sculpturing made by pits, tubercles, and ridges on the lateral surface. IPB-HaH 2004 (Figure 7 N-O) preserves the anterior end of the bone, with the symphyseal region. The latter is high and roughly teardrop shaped, but with a straight lateral margin. On the medial surface, the sutura incisura dentalis is closed far posterior to the foramen alveolaris, which is located between the thirteenth and fourteenth tooth positions. Moreover, starting just posterior to the same foramen, a sharp ridge runs on the medial surface of the bone, defining a distinct sulcus dentalis. The sulcus is present anteriorly also, but it is shallower here.
The poorly preserved fragment of tooth bearing bone shows a dermal sculpturing made up by large pits and tubercles connected by sharp ridges.
The atlas has a posterior cotyle and is moderately large-sized, with a centrum length of 3.9 mm. It has large and roughly subelliptical occipital joints and a small and wedge-shaped odontoid process. The neural canal is drop-shaped in anterior view. The dorsal margin of the neural arch forms a dorsally flattened surface, which is triangular in dorsal view. This surface is dorsally eroded, and therefore the presence of sculpturing cannot be established.
Trunk vertebrae (Figure 8) are robust and large-sized (centrum length goes from 3 mm to 6 mm), provided with strong transverse processes. The vertebral centrum is opisthocoelous and has a flattened and very slightly anteroventrally inclined anterior condyle. There is no neck. On the ventral surface, the subcentral foramina are replaced by few smaller foramina. Anterior ventral and anterior zygapophyseal crests are lacking or poorly developed, whereas posterior ventral ones are moderately developed and posterior zygapophyseal ones are very well developed. Only in IPB-HaH 2114 (Figure 8 M-P), both ventral crests are well developed, clearly defining a triangular ventral lamina. Both pre- and postzygapophyses are subcircular to subelliptical; the latter extend behind the posterior margin of the neural arch. The neural arch is low and defines a small and subcircular neural canal; its anterior margin is straight in dorsal view and reaches the anterior margin of the prezygapophyses. There is no zygosphene/zyganthrum complex. The neurapophysis is very high and robust. In dorsal view, it forms a triangular and flattened surface provided with a dense sculpturing made by pits, tubercles, and ridges. This triangular surface can be notched posteriorly, as in e.g., IPB-HaH 2038 (Figure 8F). In such case, the notch is deep and narrow.
The caudal vertebra has similar morphology and proportions to the trunk vertebrae. However, the neurapophysis is mostly missing.
Ribs have a robust aspect and a moderately large size. All of them narrow distally. The proximal end is expanded and bears the articulation surfaces with the transverse process of the related vertebra. At least some of them clearly display a small spiny process.
The indeterminate bone fragments are characterized by the presence of a very dense sculpturing made by pits, ridges, and tubercles on their external surface.
Remarks. The vertebrae are clearly referrable to Chelotriton because of the large size and the tall neurapophysis with a large, triangular, and sculptured area at the apex (Colombero et al., 2017). Other elements agree with Chelotriton as well because of similar size, robustness, and sculpturing. The taxonomy of Chelotriton is currently not well understood. Schoch et al. (2015) only included Chelotriton paradoxus Pomel, 1853, within the genus, but few other species were described in the past. Due to these uncertainties, we here refer the Hambach material only to Chelotriton sp. pending a thorough revision and clarification of the Chelotriton taxonomy. Nevertheless, these fossils agree with the diagnosis of C. paradoxus given by Schoch et al. (2015) at least in the robustly-built elements and the extensive tubercular dermal sculpturing. Moreover, they differ from Chelotriton pliocenicus Bailon, 1989, because of the absence of zygosphene/zyganthrum.
description: Published as part of Villa, Andrea, Macaluso, Loredana & Mörs, Thomas, 2024, Miocene and Pliocene amphibians from Hambach (Germany): New evidence for a late Neogene refuge in northwestern Europe, pp. 1-56 in Palaeontologia Electronica (a 3) (a 3) 27 (1) on pages 10-13, DOI: 10.26879/1323, http://zenodo.org/record/10962296