Ophiomorus Duméril & Bibron, 1839

Georgalis, Georgios L., Villa, Andrea, Ivanov, Martin & Delfino, Massimo, 2024, New diverse amphibian and reptile assemblages from the late Neogene of northern Greece provide novel insights into the emergence of extant herpetofaunas of the southern Balkans, Swiss Journal of Palaeontology (34) 143 (1), pp. 1-91 : 38-39

publication ID	https://doi.org/10.1186/s13358-024-00332-7
persistent identifier	https://treatment.plazi.org/id/E86287BF-FFC8-FFDC-BA71-A5AEFA26FA04
treatment provided by	Felipe
scientific name	Ophiomorus Duméril & Bibron, 1839
status

Treatment

Ophiomorus Duméril & Bibron, 1839 View in CoL Ophiomorus sp.

Figure 34 View Fig

Material. Spilia 4: one right dentary ( UU SP4 605), 17 trunk vertebrae [ UU SP4 575, UU SP4 578, UU SP4 640, UU SP4 641, UU SP4 643, UU SP4 646 (10 elements), and UU SP4 709], one sacral vertebra ( UU SP4 625), and one osteoderm ( UU SP4 706).

Description.

Te small dentary (UU SP4 605) is rather well preserved, missing just the posterior processes ( Fig. 34a–c View Fig ). It is straight, rather slenderly built and rather short, having a complete length of the tooth row of 3.5 mm. Te medial side displays a well-developed subdental shelf with a sharp subdental ridge. Medial to the ridge, a deep sulcus dentalis is present. In medial view, the subdental self is rather high, but narrows posteriorly. By the anterior end, there is a narrow and horizontal mandibular symphysis. Te Meckelian fossa is wider posteriorly, but very narrow and ventrally exposed in the anterior two thirds of the bone. Due to a medial bending of the ventral margin that bring the latter almost in contact with the subdental shelf, the fossa is represented only by a very narrow groove at mid-length of the bone; no real closure of the fossa is however present. Te alveolar foramen is visible in ventral view, being located in correspondence with the second to last (13th) tooth. Te ventral margin is straight in medial view. Despite of the breakage, there seems not to be a dorsal bending of the posterior processes. Te dentary carries 14 tooth positions, most of them still bearing more or less preserved teeth. Te teeth are pleurodont, cylindrical and closely spaced. Tey are slightly smaller by the anterior and posterior ends of the tooth row, compared to those in the middle. Te largest teeth are the ones in positions 10th to 12th, but the size difference is very light. Te tooth base is not swollen. In the best-preserved teeth, the crown has both a labial and a lingual cusp. Tese are rather close, but the cristae originating from them (cristae mesialis and distalis and cristae lingualis anterior and posterior, respectively) are separated by a distinctly wide antrum intercristatum, which widens toward the tooth base. Te tip of the crown is somehow bent posteromedially. A moderately dense, but very light, striation is present on the lingual side, but not on the labial one. Te teeth are exposed laterally for either one third or one half of their height. Tey are blackish in colour, but the crown is brownish to yellowish. Te lateral surface of the dentary is smooth, with four mental foramina, the size of which is homogeneous.

Te trunk vertebrae are small sized and elongated

( Fig. 34d–f View Fig ). Te centrum length is around 2 mm in all of them. Tey have a slightly compressed centrum and rounded synapophyses. Te sacral vertebra (UU SP4 625; Fig. 34g –k View Fig ) shares with the trunk vertebrae both the size and general morphology.

UU SP4 706 is a very small and thin osteoderm that was located inside the neural canal of the sacral vertebra UU SP4 625 ( Fig. 34k View Fig ). Te osteoderm has an elongated subrectangular shape. Te internal surface is smooth, whereas the external one is composed by a smooth gliding surface in the anterior half and a poorly ornamented surface in the posterior one.

Remarks. Te scincid nature of the dentary is clearly evidenced by a set of features, among which (Villa & Delfino, 2019a): open and posteriorly-widening Meckelian fossa; subdental ridge present; straight ventral margin; pleurodont teeth provided with labial and lingual cusps, a slightly posteromedially bent crown, and a light striation on the lingual side. Te osteoderm (UU SP4 706) is strongly reminiscent in its morphology of one part of the compound osteoderms that are distinctive for skinks (Daza et al., 2024; Estes, 1983; Maliuk et al., 2024; Williams et al., 2022). Tis osteoderm was found inside the neural canal of the sacral vertebra UU SP4 625, possibly further supporting a scincid identity for this vertebra as well. Based on preliminary observations on the reference collection available to us, the morphology of all these vertebrae indeed recalls more a scincid condition, and in particular vertebrae of Ophiomorus (see also Camaiti et al., 2019, fig. 41). Among extant European skinks, moderately robust teeth without an enlarged crown are present in Ophiomorus punctatissimus (Bibron & Bory de Saint-Vincent, 1833) (see Camaiti et al., 2019; Čerňanský et al., 2020; Villa & Delfino, 2019a). A decreasing size in anteriormost and posteriormost teeth is also shared between this species and UU SP4 605, as are a rather high subdental shelf and the posterior position of the alveolar foramen, which is located by the second to last tooth position in the Spilia fossil and at the last position in O. punctatissimus (versus a more anteriorly located foramen in other European scincids; Villa & Delfino, 2019a). Te tooth count of UU SP4 605 also fits within the range of O. punctatissimus (Camaiti et al., 2019; Villa & Delfino, 2019a). UU SP4 605 is also very similar to an isolated dentary from the latest Early Pleistocene of Kaiafas referred to Ophiomorus sp. by Villa et. al. (2020), except for some minor differences (larger size, one more tooth, and one more mental foramen) and a distinct dorsal bending of the superior posterior process in the latter. Te same bending is present in O. punctatissimus (Camaiti et al., 2019; Villa & Delfino, 2019a), but it seems to be absent in at least one other representative of the genus ( Ophiomorus tridactylus [Blyth, 1853]; see Čerňanský et al., 2020, fig. 10A, B). Te fossils from Spilia may thus represent a species of Ophiomorus different from O. punctatissimus , whereas the Kaiafas occurrence might be suggested as a more derived form related to the latter. Tis could only be confirmed when more morphological information on the other extant Ophiomorus species, especially those from the western part of its distribution, are available, though.