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

description: Lissotriton sp.
Figures 10–11
Material. Hambach 6C: one atlas (IPB-HaH 2118); three trunk vertebrae (IPB-HaH 2110, IPB-HaH 2115/2116). Hambach 11: two trunk vertebrae (IPB-HaR 2009, IPB-HaR 2011); two caudal vertebrae (IPB-HaR 2010, IPB-HaR 2012).
Description. The small atlas (Figure 10 A-E), missing most of the neural arch, has circular and flat occipital joints separated by a wide, thin and strongly gutter-like processus odontoideus. The articular surface of the latter is composed by two well-distinct separate areas facing ventrolaterally, medially contacting each other. The neural canal is roughly as wide as the processus odontoideus. The posterior cotyle is rather small and circular, being clearly narrower than the processus odontoideus. Ventrally, a longitudinal ridge runs in the middle of the centrum, flanked by two other ridges (one on each side). Some foramina are sparsely present on the ventral surface between the ridges. A lateral foramen is present on each processus lateralis, followed posteriorly by a ridge. These latter foramina are hosted in a concave area oriented anterolaterally, being visible on the lateral side of the occipital joints in anterior view. These concavities are defined by distinct lateral crests, which start from the occipital joints.
The trunk vertebrae from Hambach 6C are medium to very small sized. The centrum length is 3.5 mm in IPB-HaH 2115 (Figure 10 J-M), at least 2.5 mm in IPB-HaH 2116 (Figure 10 N-Q), and slightly less than 1.5 mm in IPB-HaH 2110 (Figure 10 F-I). The centrum of IPB-HaH 2116 is slightly eroded and it was therefore slightly longer in origin. They have an opisthocoelous centrum, with a distinct neck. In lateral view, the anterior condyle is anteriorly rounded and either straight or lightly ventrally inclined. The ventral surface of the centrum displays a number of more or less small foramina. Both the ventral and the zygapophyseal crests are well developed. The former originate a subtriangular ventral lamina. The zygapophyseal crests contact the dorsal part of the diapophyses. The neural arch is high; its posterior part is flat (IPB-HaH 2110) or somehow concave (other vertebrae). In dorsal view, IPB-HaH 2110 (Figure 10F) has a straight anterior margin of the arch, which is on the other hand slightly concave in IPB-HaH 2115 (Figure 10J) and IPB-HaH 2116 (Figure 10N). The deepest point of the margin is located close to the anterior end of the prezygapophyses. The neural arch does not show a clear hourglass shape between the prezygapophyses in dorsal view. The posterior margin has a wide and moderately shallow notch. The zygapophyses are subelliptical and either almost subhorizontal or slightly dorsally inclined. The neurapophysis is high. Its straight dorsal margin is only preserved in IPB-HaH 2110, even though with a large notch on it due to damage. The anterior end of the spine is broken off. The neurapophysis starts either by the posterior end of the prezygapophyses in the smallest vertebra, therefore being far from the anterior margin of the neural arch, or immediately posterior to the latter margin in the other specimens. Posteriorly, it expands in a triangular area that contacts the posterior margin. The posterior end of the postzygapophyses and the posterior margin of the neural arch, both preserved only in IPB-HaH 2110, are roughly aligned. The transverse processes of the vertebrae are slender, posterolaterally directed and provided with a foramen by their base.
The vertebrae from Hambach 11 (Figure 11) are opisthocoelous and very small (centrum length goes from 1.3 mm in IPB-HaR 2010 to 3 mm in IPB-HaR 2012). They have no developed neck. The anterior condyle of IPB-HaR 2009 is eroded, but it appears flattened in other specimens. It is vertical in IPB-HaR 2010 and IPB-HaR 2011 or slightly ventrally inclined in IPB-HaR 2012. Zygapophyseal crests are always well developed, whereas the ventral ones are moderately developed in IPB-HaR 2011 (Figure 11I) and IPB-HaR 2012 (Figure 11Q) or not developed in IPB-HaR 2009 (Figure 11E) and IPB-HaR 2010 (Figure 11N). The ventral surface is poorly preserved in all specimens, but the left side of IPB-HaR 2009 shows a moderately wide subcentral foramen and a number of small foramina are present ventrally in IPB-HaR 2011. Zygapophyses are narrow, almost horizontal and subelliptical. The neural arch is high and flattened posteriorly. The straight anterior margin of the neural arch reaches almost the anterior end of the prezygapophyses. Also in this case, the neural arch does not show a clear hourglass shape between the prezygapophyses in dorsal view. The neurapophysis is high and starts near the anterior margin of the arch; its dorsal half is broken in both specimens. A wide and deep V-shaped notch is present in the middle of the posterior end of the arch. The posterior margin of the neural arch does not extend posteriorly beyond the postzygapophyses. The latter are always broken off, but the base of the right one of IPB-HaR 2010 is preserved and extends beyond the margin. The portion of neural arch located by the sides of the posterior notch are almost vertically oriented.
Remarks. A small-sized salamandrid is also present in both Hambach 6C and 11. The atlas has sparse foramina on the ventral surface, a processus odontoideus that is wider than the posterior cotyle, and well-developed lateral crests (Ratnikov and Litvinchuk, 2009). The morphology of the vertebrae is generally alike that of both Ichthyosaura Sonnini de Manoncourt and Latreille, 1801, and Lissotriton, but few characters allow the attribution of the material to the latter. On the atlas, the articular facets of the processus odontoideus are in medial contact, thus differing from the condition showed by Ichthyosaura (whose surfaces are separated by a large or, rarely, narrow groove) and consistent with the variability seen in the extant species of Lissotriton. The neural arch does not show a clear hourglass shape between the prezygapophyses in dorsal view, further supporting affinities between the Hambach remains and Lissotriton. Attribution to Lissotriton boscai (Lataste in Tourneville, 1879) can be excluded because this species shows small lateral eversions of the neurapophysis. Caudal vertebrae (only found in Hambach 11) allow the exclusion of Lissotriton vulgaris (Linnaeus, 1758) and Lissotriton italicus (Peracca, 1898): in caudal vertebrae of these species, the posterior end of the neural arch is higher than the centrum in lateral view (Macaluso et al., 2023b), which is not the case in the Hambach remains (this can be clearly evaluated in IPB-HaR 2010). We were unable to observe the longitudinal ridge on the ventral surface of the atlas in any of the specimens of extant Lissotriton available to us for comparison. This may suggest that the Hambach vertebrae belong to a still unknown species, but given the high variability shown by urodele species we consider more cautious to herein refer all of the remains from Hambach (both 6C and 11) only at genus level.
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 14-16, DOI: 10.26879/1323, http://zenodo.org/record/10962296