Messelophis variatus Baszio, 2004

Venczel, Márton, Codrea, Vlad A., Solomon, Alexandru A., Fărcaș, Cristina & Bordeianu, Marian, 2025, Late Eocene-early Oligocene snakes from the Transylvanian Basin (Romania), Comptes Rendus Palevol 24 (13), pp. 229-240 : 234-236

Species Messelophis variatus Baszio, 2004

cf. Messelophis variatus

( Figs 3 A-K; 4A-I)

MATERIAL. — CetăŢuia Hill : one anterior trunk vertebra ( UBB V 1045 ), four trunk vertebrae ( UBB V 1046 /1-4 ); Suceag 1: eight trunk vertebrae ( UBB V 1047 /1-8 ), one caudal vertebra ( UBB V 1044 ) .

DESCRIPTION

The specimen UBB V 1045 represents a partial anterior trunk vertebra with the roof of its neural arch broken off ( Fig. 3A, B). The centrum is slightly longer than wide and features a salient and posteroventrally projecting hypapophysis.Two small subcentral foramina are present and the paradiapophyses appear robust and undifferentiated, however their surfaces are strongly eroded. One of the best preserved mid-trunk vertebrae from the CetăŢuia Hill locality is represented by UBB V 1046 /1( Fig. 3 C-F); however, in the specimen the right prezygapophysis and the left postzygapophysis are completely broken off, whereas the lateral margin of the left prezygapophysis, the ventral margin of the cotylar lip and the posterior tip of the condyle are also missing. The estimated centrum length of the UBB V 1046 / 1 specimen approaches 2.42 mm, whereas its centrum width approaches 2.39 mm; in the UBB V 1047 / 1 specimen from Suceag 1 locality ( Fig. 4 A-C) the centrum length reaches 2.64 mm, whereas its centrum width equals 2.46 mm. In dorsal view, the most striking feature is that the neural spine is extremely short and point-like, positioned on the upraised dorsoposterior border of the neural arch, whereas the area in front of the neural spine is flat ( Figs 3C, G, H; 4A, D, E); however, in all the specimens the distal tip of the neural spine is broken off ( Figs 3G, H; 4H). The interzygapophyseal constriction is moderate and a well-defined posterior notch is present on the neural arch. The anterior margin of the zygosphene is provided with two lateral lobes and with a less developed median lobe ( Figs 3C; 4A). In ventral view, the haemal keel is well-defined, more salient in the specimens from CetăŢuia Hill ( Figs 3D, I; 4F), whereas in those from Suceag 1, it is somewhat widened and flattened ( Fig. 4B). The subcentral foramina are present and of variable size, the subcentral grooves are weakly defined, whereas the paradiapophyses project strongly laterally; the prezygapophyseal process is vestigial ( Fig. 3I, J). In lateral view, the vertebrae appear moderately flattened with the neural arch elevated near the neural spine ( Fig. 4C, D). The paradiapophyses are undifferentiated and robustly built, as seen in specimen UBB V 1046 /3 ( Fig. 3J). In anterior view, the neural arch is slightly flattened, the neural spine is relatively low, whereas the cotyle is circular and the paracotylar foramina are lacking; the zygosphenal roof is almost horizontal ( Fig. 3E, H). In posterior view, the neural arch appears slightly convex, the condyle is rounded, whereas the parazygantral foramina are lacking ( Fig. 3F, K).

A single caudal vertebra (UBB V 1044), representing a small sized individual (however,about five lines of the arrested growths are observed on its prezygapophysis indicating that it was an adult snake), possesses a low neural spine extending from the base of the zygosphene to the posterior notch of the neural arch ( Fig. 4G). The centrum is longer than wide, whereas the neural arch is depressed possessing a weak interzygapophyseal constriction ( Fig. 4H); below the right prezygapophysis, a tiny prezygapophyseal accessory process is preserved, and the prezygapophysis itself is elongated. In ventral view, the pleurapophyses are broken off; however, the remnants of the paired haemapophyses are partially preserved ( Fig. 4H, I).

REMARKS

Some of the phenotypical features of the vertebrae described above closely resemble those of Messelophis variatus (e.g. presence of an extremely short “point-like” neural spine, developed near the posterior border of the neural arch and the paracotylar foramina absent). Similar to the specimens of our study, the vertebrae of M. variatus are elongated, with extremely short neural spines developed at the posterior border of the neural arch, the paracotylar foramina are absent and the prezygapophyseal accessory processes are weakly developed ( Baszio 2004; Schaal & Baszio 2004; Scanferla et al. 2016: fig. 1B). Moreover, in the holotype of M. variatus (SMF-ME 1828 A-B), exposing a short portion of the ventral side of its vertebral column (MV pers. obs.), and in the recently referred specimen SMF-ME 513a from the early middle Eocene of Messel, Germany, exposing the ventral side of its vertebral column ( Scanferla & Smith 2020b: fig. 1B), the trunk vertebrae possess prominent haemal keels of variable shape (i.e., of gladiate or spatulate-shape, sensu Auffenberg 1963). The caudal vertebra UBB V 1044, similarly to M. variatus , possesses a low neural spine and provided with paired haemapophyses ( Scanferla et al. 2016: fig. 18A); however, in M. variatus the haemapophyses appear laminar, whereas in UBB V 1044 the remnants of the latter structure comparatively are less elongated anteroposteriorly.

A number of comparable attributes of the studied specimens should be noted also in the fossil genus Dunnophis Hecht in McGrew et al., 1959, which was originally designated based on isolated vertebrae as an incertae sedis snake from the late early Eocene of North America ( Hecht 1959), and recorded later from the Eocene of Western Europe (e.g. Rage 1973, 1974, 1984, 2006; Rage & Ford 1980; Rage & Augé 2003, 2010; see Smith & Georgalis 2022), and even from the late Palaeocene of Morocco ( Augé & Rage 2006). Among the peculiar features of Dunnophis , as noted by the above authors, are the following: the centrum is depressed, narrow and longer than wide; the extremely short neural spine is developed near the margin of the deep posterior notch of the neural arch; the prezygapophyseal processes are absent or vestigial; and the caudal vertebrae, rarely present in the fossil material, likely possessed haemapophyses, as seen in the North American type species of the genus, Dunnophis microechinis Hecht in McGrew et al., 1959 (see Hecht 1959: plate 56: 7-10). Resemblance between Dunnophis and Ungaliophis Müller, 1880 was already noted by Bogert (1968), while similarity between Dunnophis and Messelophis was mentioned by Baszio (2004). Rage & Augé (2010) suggested that Messelophis might be considered a junior synonym of Dunnophis . On the other hand, the specimens from the early Oligocene of Romania described herein, share with the two recent genera of ungaliophiids (i.e., Exiliboa Bogert, 1968 , and Ungaliophis ) a number of phenotypic features, as follows: lightly built vertebrae with their centrum longer than wide, the presence of a prominent haemal keel in the trunk vertebrae (according to Szyndlar & Georgalis, 2023, the haemal keel is less developed in Ungaliophis ), the absence of paracotylar foramina, and weakly developed or vestigial prezygapophyseal accessory processes. Some of these characters (e.g. elongation of the trunk vertebrae and presence of haemal keel in the caudal vertebrae) have been considered synapomorphies of Ungaliophiidae within the clade of Constrictores ( Smith 2013).