Dolichophis sp.

Čerňanský, Andrej, 2024, The first lacertid and partly articulated snake from the Middle Miocene of the Devínska Kobyla Hill in Slovakia, from the type locality of the earliest known seal, Comptes Rendus Palevol 23 (24), pp. 385-399 : 390

cf. Dolichophis sp.

( Figs 2-5)

MATERIAL EXAMINED. — Slovakia • Bratislava, Devínska Nová Ves, Bonanza site ; Middle Miocene (MN 6b); SNM Z 29222, articulated portion of the vertebral column together with ribs in firm tabular limestone .

LOCALITY AND HORIZON. — Slovakia, Bratislava, Devínska Nová Ves, Bonanza site; Middle Miocene ( MN 6b).

DESCRIPTION

Skeleton

The postcranial skeleton is mostly articulated ( Fig. 2), although weathered. It represents a small snake, the maximum anteroposterior length of the best preserved vertebra being 4.4 mm. The whole specimen is embedded in limestone – unfortunately, the computed tomography reconstructions show that the rock density value is similar to that of the fossil. Even so, the exposed portions and CT revealed, at least partly, the morphology of these vertebrae. Eight and half vertebrae are preserved in the upper part of the slab, whereas nine and half are preserved in the lower part of the slab. The latter ones are larger, but only four have preserved the neural arch. The neural arch is moderately vaulted. The dorsal region of the neural arch is more-or-less flattened and bears the neural spine along its central section. The neural spine appears to be more-or-less trapezoidal in lateral view, but markedly low – in the fourth vertebra (counted from posterior) with fairly complete neural spine, its anteroposterior length (2.2 mm; Fig. 3) is approximatelly four times larger than its height. Its anterior and posterior margins are almost vertical, although note that the base of the anterior margin is slightly concave. Anteriorly, the neural spine starts to rise dorsally in the first quarter of its length and thus leaves a short, flat area of the neural arch anterior to the base of the neural spine. Here, at the anterior end, the zygosphenal lip is well developed. It is slightly convex, having two small lateral lobes. In the vertebrae, in which it is preserved, there is no indication of the presence of a median notch. The zygosphenal articular facets are steep and markedly dorsally inclined to agle of around 50° from a horizontal plane ( Fig. 3C, C 1). In anterior view, the zygosphene is distinctly wider than the cotyle. The neural canal is large, tunnel like, its width is more-or-less equal to its height (mostly observed in cross-section µCT slices of this region). The zygantral area is poorly preserved in this section. A potential presence of a paracotylar foramen cannot be properly observed. The interzygapophyseal constriction is well developed as well as interzygapophyseal ridges. Prezygapophyses are anterolaterally oriented and the prezygapophyseal accessory processes are well-developed, narrow and pointed distally. Their length can be estimated to reach almost the length of the prezygapophyseal articulations. The prezygapophyseal articulations are almost horizontal, inclined in an angle of only 10° from the horizontal plane. Paradiapophyses are not well preserved. Note, however, that the parapophyses are damaged in most of the vertebrae and their shape is unknown. One exception is the third vertebra in the larger column ( Fig. 4). They are moderately developed. A division into diapophyses and parapophyses can be recognized, being well developed ( Fig. 4D). The ventral margin of the parapophyses extend ventrally, being located below the cotylar rim. The diapophysis in this vertebra appears to be located posteriorly relative to the parapophysis. The vertebral condyle and cotyle are moderately large, rounded. The condyle is connected to the centrum by a short “neck”. The centrum is anteroposteriorly elongated. The haemal keel is well developed, but ventrally short. It is narrow. The remaining vertebrae of this column located in the anterior section have damaged neural arches. Thus, the neural canal is exposed, being filled in by the calcite which forms an internal core of the canal. Here, prezygapophyses are well visible, having rounded articular surfaces. The postzygapophyses are distictly expanded laterally. The cotyles and condyles are more-or-less rounded here as well.

The smaller vertebrae located in the second column are basically identical in morphology. They represent a distal portion of the vertebral column. The low neural spine can be observed in the posteriormost preserved complete vertebra ( Fig. 5A, C-H). Here, the postzygapophyses are fairly complete, being posterolaterally oriented. Compared to the larger vertebrae, they have smaller articular areas relative to the prezygapophyses. Between the right and left postzygapophyses, a V-shaped notch is present ( Fig. 5D). The zygantrum is well-developed.

Several ribs are still attached to the precaudal vertebrae and remain articulated with synapophyses. In some places, they are preserved only as imprints ( Fig. 2).

COMMENTS

Note that computed tomography reconstructions show that the rock density value is very similar to that of the fossil. The rock block with its tiny bones is relatively thick, and unfortunately CT is unable to provide a usable 3D model with all features clearly visible. On the basis of vertebrae alone (without cranial bones), determination of fossil colubrids is very difficult, even more so at the generic level. This specimen is provisionally allocated to Colubridae based on the combination of an elongated centrum, vaulted neural arch, short parapophyses with ventral border situated close below the cotylar rim and presence of a haemal keel. See Discussion below regarding areas of uncertainty.