Systematic Palaeontology
Squamata Oppel, 1811 [99]
Lacertidae Oppel, 1811 [99]
Janosikia Čerňanský, Klembara, and Smith, 2016 [15]
Janosikia sp.
Figures 1, 2, 3, Additional File 1 and Additional File 2.
Material: Montaigu-le-Blin: a left dentary (PIMUZ A/III 4656).
Description: The left dentary PIMUZ A/III 4656 is incomplete, missing parts of its posterior, anteriormost, and ventral portions (Figs. 1, 2). It is slightly ventrally arched, while its posterodorsal portion is slightly inclined. The alveolar crest preserves 13 (partial or complete) teeth, but there are at least two other empty tooth positions. In medial view (Figs. 1B, 2B), the Meckel’s groove is deep and fully open; it is wider in the posterior and middle portions of the dentary but its width gradually diminishes towards its anterior edge. The symphyseal region is eroded. The subdental shelf is straight to slightly concave; it is thick in its anterior and mid-portions, being much narrower at its posterior part. Its anterior portion is not markedly elevated relative to the posterior portion of the shelf. A facet for the splenial is present in its ventral side. The alveolar foramen is relatively large, situated approximately at the level of the posteriormost preserved tooth. In labial view (Figs. 1A, 2A), the surface of the dentary is roughly smooth, alternated, however, with an array of irregular grooves and distinct ridges, which are most prominent at its mid-height and ventral portions. The labial surface of the dentary is pierced by at least five large labial foramina. Dentition is pleurodont and strongly heterodont, being amblyodont at the posterior portion of the dentary. Teeth are closely spaced. They gradually increase in size and robustness posteriorly. As such, teeth at the anterior portion of the dentary are small and slender, while the posteriormost ones preserved are considerably robust, forming blunt cylinders. The tooth crowns of all teeth bear distinct striations (Fig. 1D). Such tooth striation is more prominent at the medial side of the teeth. No clear accessory cusps are present on the preserved teeth.
Virtual microanatomy and histology: The micro-CT scan of the dentary PIMUZ A/III 4656 revealed a few internal structures, including the partially sediment-filled alveolar canal, the pulp cavities of each tooth, a fine branching neuro-vascular network of thin channels connecting the alveolar canal either with the pulp cavities or with foramina opening on the lateral bone surface, as well as a set of growth marks in the dentary bone (Fig. 3). The growth marks appear as brighter and darker colored triangular cones (different grey tones reflecting slightly different densities in the bone matrix and thus different growth periods; see [100]) at the posterior margin of the dentary and as gently curved parallel lines in the anterior part (Fig. 3). Seven growth marks could be counted in the dentary.
Comments: The dentary PIMUZ A/III 4656 can be referred to the lacertid genus Janosikia on the basis of its relatively low tooth count (around 15 preserved tooth positions), closely spaced teeth that are more slender anteriorly and become more robust posteriorly, presence of striation on the teeth, convex ventral margin of the bone, and the anterior, symphyseal region of the subdental shelf being not markedly elevated relative to the posterior portion of the shelf (see [15]). A more precise determination, i.e., whether it pertains to the type species, Janosikia ulmensis (Gerhardt, 1903) [12] from the early Miocene of southern Germany [15] or some different congeneric form, cannot be made as the dentary from Montaigu-le-Blin is incomplete. It therefore does not preserve important diagnostic features in its posterior portion, for example, in the coronoid and the shape/size of the posteriormost teeth. The distinct grooves and ridges present in the labial surface of the dentary from Montaigu-le-Blin seem to be rather prominent compared with other previously published specimens of Janosikia, where that surface appears to be smoother. Whether, however, this distinctly grooved pattern observed in the Montaigu-le-Blin specimen bears some taxonomic utility or is simply attributed to some taphonomical or preservational reasons, cannot be further evaluated.
Anguimorpha Fürbringer, 1900 [101]
Anguidae Gray, 1825 [102]
Anguinae Gray, 1825 [102]
Ophisaurus Daudin, 1803 [103]
Ophisaurus holeci Klembara, 2015 [104]
Figures 4, 5, 6, 7, Additional Files 3, 4, 5, 6.
Material: Saint-Gérand-le-Puy: two parietals (PIMUZ A/III 4626 and PIMUZ A/III 4627).
Description: The two parietals are relatively well preserved. PIMUZ A/III 4626 is the most complete, lacking only small part of the left supratemporal process (Figs. 4A–B, 5). PIMUZ A/III 4627 is more incomplete, missing its anteriormost edge and the posteriormost tip of the left supratemporal process (Figs. 4C–D, 6). Their morphology is generally similar; however, PIMUZ A/III 4627 is relatively slenderer. The description is based on both specimens.
In dorsal view (Figs. 4A, C, 5A, 6A), the parietal table is covered by a prominent sculptured surface. The sculptured surface is slightly longer than wide (at the level of its mid-length and mid-width). The lateral margins of the sculptured surface almost coincide with the lateral margins of the parietal table. The ornamentation consists of distinct ridges and deep grooves and pits. The sculptured surface, which is divided by distinct sulci (i.e., interparietal and occipital sulci) into an interparietal shield, an occipital shield, and two lateral shields. The anterior end of the interparietal sulcus lies medial to the anterolateral corner of the sculptured surface. The parietal foramen is located at the posterior portion of the interparietal shield—it is proportionately larger in PIMUZ A/III 4627. The sulcus in the junction of the interparietal and occipital shields is extremely tiny and almost incipient. The occipital shield is triangular to slightly rhomboidal, as its posterior margin morphology is relatively concave. The anterolateral processes are preserved in PIMUZ A/III 4626, where they are well developed. The smooth area of the parietal table is larger in PIMUZ A/III 4627; in both specimens, its anteroposterior length in medial plane is larger than the anteroposterior length of the occipital shield. The supratemporal processes are almost straight. The arch-like arcuate edge is on the dorsal surface of the anterior halves of the supratemporal processes; it is straighter in PIMUZ A/III 4626, while it is more convex in PIMUZ A/III 4627.
In ventral view (Figs. 4B, D, 5B, 6B), the frontal tab is prominent in PIMUZ A/III 4626 (not preserved in PIMUZ A/III 4627). There is no muscular surface, as seen in species of Pseudopus Merrem, 1820 [105]. The parietal cranial crest lies almost at the level of the lateral margin of the parietal table. The parietal cranial crest is high and sharp especially in its mid-length, but becomes rather low in its anterior and posterior portions; the posterior portion of the parietal crest is lowest at its junction with the ventrolateral ridge of the supratemporal process. The postfoveal crest is short anteroposteriorly and low dorsoventrally—it is more prominent in PIMUZ A/III 4627. The supratemporal processes are straight—they mostly diverge posteriorly in PIMUZ A/III 4626 but not so in PIMUZ A/III 4627. The anterior end of the supratemporal process joins the posterior section of the parietal cranial crest at or slightly posterior to the posteromedian margin of the parietal fossa floor. The ventrolateral ridge of the supratemporal process is robust and coincides with the process’s lateral margin anterior to the supratemporal articulation.
Virtual microanatomy and histology: The two micro-CT scans of the parietals revealed a robust bone structure with a very similar internal microanatomy in terms of an extensive vascular network, whereas finer histological details (growth marks, cell lacunae, etc.) of the bone were not visible. Both parietals have the most extensive interconnecting vascular spaces just beneath the smooth area posterior to the parietal table (Fig. 7, Additional Files 4, 6). From here, a network of thinner interconnected channels extends posterolaterally into each supratemporal process, while two main vessels extend anterolaterally towards the anterior bone margin. These two main vessels connect dorsally with a fine regular meshwork of thin channels that perforate the ornamented parietal table and open up into numerous small dorsal foramina on the sculptured bone surface.
Comments: The two parietals from Saint-Gérand-le-Puy can be assigned to Ophisaurus holeci on the basis of the following diagnostic features: (i) the anterior end of the interparietal sulcus lies medial to the anterolateral corner of the sculptured surface; (ii) the anterior end of the ventrolateral ridge of the supratemporal process joins the parietal cranial crest at or slightly posterior to the posteromedian margin of the floor of the parietal fossa; (iii) the posterior portion of the parietal cranial crest is rather low, particularly at its junction with the ventrolateral ridge of the supratemporal process; (iv) the supratemporal process is straight; (v) the base of the supratemporal process is mediolaterally narrow; (vi) the presence of a short postfoveal crest; (vii) a long anterior section of the parietal cranial crest is more or less distinctly concave (though this latter feature is not so prominent in the Saint-Gérand-le-Puy parietals) (features from [104, 106]). Differences among the French material and the holotype and previously referred parietals can be attributed to intraspecific variability. Accordingly, differences between the two parietals from Saint-Gérand-le-Puy can be attributed to intraspecific or ontogenetic variation, with the slenderer specimen (PIMUZ A/III 4627) pertaining probably to an earlier ontogenetic stage.
It is further worth noting that another anguine species has been previously described from the vicinity of Saint-Gérand-le-Puy. This is Ophisauromimus coderetensis (Augé, 2005) [61] from the latest Oligocene (MP 30) of Coderet, only a few (around 20) km away from Saint-Gérand-le-Puy [61]. This taxon was originally described as a species of the extant Asian genus Dopasia Gray, 1853 [107], by Augé [61], until it was eventually placed in its own genus, Ophisauromimus Čerňanský, Klembara, and Müller, 2016, by [108]. Ophisauromimus coderetensis was typified by a dentary from Coderet, with an additional fragmentary parietal from that locality referred to the same species [61]; other cranial remains (but not a parietal) have been referred to this species from the early Oligocene of France and the late Oligocene of Germany [61, 108]. This single described parietal from Coderet is too fragmentary to afford any reliable comparison with the new parietals from Saint-Gérand-le-Puy. In any case, although the dentary morphology of Ophisaurus holeci is not known with certainty, the dentary of Ophisauromimus coderetensis exhibits considerable differences with that of Ophisaurus spp. [108]. Therefore, we can exclude affinities of the Saint-Gérand-le-Puy parietals with Ophisauromimus coderetensis.
Ophisaurus sp.
Figures 8 and 9
Material: Saint-Gérand-le-Puy: ten presacral vertebrae (PIMUZ A/III 4637-PIMUZ A/III 4639, PIMUZ A/III 4641-PIMUZ A/III 4644, PIMUZ A/III 4655, PIMUZ A/III 4657, and PIMUZ A/III 4680) and ten caudal vertebrae (PIMUZ A/III 4640, PIMUZ A/III 4645-PIMUZ A/III 4652, and PIMUZ A/III 4658).
Description: The presacral vertebrae have centrum lengths ranging between 4.0 and 5.7 mm (Fig. 8). They are relatively dorsoventrally compressed. PIMUZ A/III 4657 is the only cervical vertebra—it bears a hypapophysis, however, this is rather damaged and therefore its shape and extent cannot be evaluated with certainty. All the rest of the presacral vertebrae lack hypapophyses, clearly therefore pertaining to the post-cervical region of the column. The ventral surface of the centrum in these vertebrae is relatively flat, occasionally with few subcentral foramina. There is no precondylar constriction. The lateral margins of the centrum are relatively concave (e.g., Fig. 8N, S), although in the largest vertebrae these appear to be more or less straight (Fig. 8D, I). The prezygapophyses are dorsally inclined in anterior view. The neural spine is incomplete in most specimens. Nevertheless, it is almost fully preserved in PIMUZ A/III 4655, where it is trapezoidal, being dorsoventrally low, anteroposteriorly long, and slightly posteriorly inclined (Fig. 8E). The neural spine is thicker in dorsal view at the posterior portion of the neural arch. The neural canal is large, with its height being larger to that of the cotyle (especially in PIMUZ A/III 4638 and PIMUZ A/III 4639; Fig. 8K, P); nevertheless, in the two largest specimens, PIMUZ A/III 4655 and PIMUZ A/III 4637, the height of the neural canal is smaller than that of the cotyle (Fig. 8A, F). The cotyle and condyle are markedly depressed. The synapophyses are elongated.
The caudal vertebrae have centrum lengths ranging between 4.3 and 6.1 mm (Fig. 9). They are anteroposteriorly elongated and considerably narrow. In the most gracile of them (PIMUZ A/III 4651), this elongation is at its most extreme. In most of them, the transverse processes and haemal arches are broken, however, in few specimens, the former structures are complete (e.g., PIMUZ A/III 4648). The neural spine is also usually incomplete—when complete, it can be dorsoventrally high and anteroposteriorly thin; it is practically confined solely to the posteriormost portion of the neural arch and is inclined posteriorly (e.g., PIMUZ A/III 4648). The prezygapophyses and postzygapophyses are relatively small. The former are dorsally inclined in anterior view. Cotyle and condyle are rather depressed. The transverse processes are anteroventrally oriented—they are large and their bases are located in the anterior portion of the centrum. The chevron bones forming haemal arches are fused to the centrum, located at the posterior portion of the vertebra, relatively near the condyle. An autotomic plane can be present, being more visible in PIMUZ A/III 4645 (Fig. 9I).
Remarks: The presacral vertebrae can be referred to Ophisaurus on the basis of the lateral margins (subcentral ridges) of the centrum being concave instead of straight, the height of the neural canal being larger to that of the cotyle, and the neural spine being trapezoidal with the length of its basal portion being bigger than its height (characters from [109]). We nevertheless, have to highlight here that two among the largest vertebrae (PIMUZ A/III 4655 and PIMUZ A/III 4637) deviate from this typical Ophisaurus morphology, in respect to their neural canal height being smaller than that of the cotyle and the lateral margins of the centrum being more or less straight and not so concave. In fact, in these two latter features, PIMUZ A/III 4655 and PIMUZ A/III 4637 are more reminiscent of Pseudopus apodus (Pallas, 1775) [110] instead of Ophisaurus (characters from [109]); however, the shape of the neural spine of these two vertebrae is rather different from that of extant P. apodus. That being said, we would here refrain from considering these two largest vertebrae as pertaining to Pseudopus and instead regard them as being congeneric with the rest of the anguine material from Saint-Gérand-le-Puy. If our interpretation is correct, then these two vertebral features (i.e., the ratio of neural canal height to cotyle height and the concavity of the lateral margins of the centrum) may have been relatively more variable among earliest Miocene taxa of Ophisaurus and Pseudopus. More abundant anguine vertebral material from the locality may eventually confirm or refute this suggestion.
As for the caudal vertebrae, they display typical anguine features, i.e., the fused haemal arches and the presence of an autotomic plane (absent in Pseudopus). We tentatively refer them as well to Ophisaurus by the presence of an autotomic plane (at least in certain specimens) and the overall shape [109].
Although it remains possible that this vertebral material pertains to the same species as the above described parietals (i.e., Ophisaurus holeci), a more precise determination is not possible on the absence of species-level diagnostic features, as well as the fact that Ophisaurus was rather diverse during the early Miocene of Europe, with more than one congeneric species co-occurring in certain localities (e.g., [104, 106]). It is worth noting that so far published vertebrae which have been reliably referred to O. holeci based on articulated skeletons, show a typical Ophisaurus-like vertebral morphology [111]. On the other hand though, a recent phylogenetic analysis has recovered O. holeci as most closely related to the genus Ophisauriscus Kuhn, 1940 [13], from the Eocene of Germany instead of other Ophisaurus spp. [14]. Nevertheless, despite the fact that Ophisauriscus is known from several rather complete articulated skeletons from the Eocene fossil Lagerstätten localities of Geiseltal and Messel (see [13, 112]), certain of its vertebral features are not as yet adequately known.
Serpentes Linnaeus, 1758 [46]
Constrictores Oppel, 1811 [113] (sensu [114]).
“erycines” (sensu [115]).
Bransateryx Hoffstetter and Rage, 1972 [3]
Bransateryx sp.
Figure 10
Material: Saint-Gérand-le-Puy: two trunk vertebrae (PIMUZ A/III 4653 and PIMUZ A/III 4654); Gannat: a trunk vertebra (PIMUZ A/III 4681).
Description: All three vertebrae are rather small, with centrum lengths ranging between 3.0 and 3.8 mm (Fig. 10). In anterior view (Fig. 10A, F, K), the zygosphene is rather thin, with its dorsal level being almost straight, with the exception of PIMUZ A/III 4681, where this is slightly convex. The neural canal is large. The prezygapophyses are dorsally tilted. The cotyle is circular to slightly elliptical. In posterior view (Fig. 10B, G, L), the neural arch is rather depressed. The condyle is circular to slightly elliptical. In dorsal view (Fig. 10C, H, M), the neural spine is thicker towards the posterior portion of the neural arch. The zygosphene bears two prominent lateral lobes along with a less distinct medial one (which is more prominent in PIMUZ A/III 4681). The posterior median notch of the neural arch and the interzygapophyseal constriction are considerably deep. The prezygapophyses extend anterolaterally. The prezygapophyseal articular facets are large and oval. In ventral view (Fig. 10D, I, N), the haemal keel is crossing almost the whole mid-line length of the centrum, commencing anteriorly at the ventral level of the cotyle and terminating posteriorly prior to the condyle. The haemal keel is moderately thick in PIMUZ A/III 4653 and PIMUZ A/III 4681 but is considerably thinner in PIMUZ A/III 4654. The subcentral grooves are deep. The paradiapophyses are massive and are not clearly divided into diapophyseal and parapophyseal parts. The postzygapophyseal articular facets are large. In lateral view (Fig. 10E, J, O), the neural spine is rather short and its anteroposterior length is developed mostly towards the posterior half of the neural arch; it commences well below the level of the zygosphene and gradually increases in height. Lateral foramina are present below the level of the interzygapophyseal ridge. The subcentral ridges are convex. The haemal keel projects ventrally. All three vertebrae pertain to the posterior trunk portion of the column, judging from the width of the haemal keel (particularly in PIMUZ A/III 4653 and PIMUZ A/III 4681) and the depressed neural arch.
Remarks: As in all “erycines” (and unlike most other snakes), the main diagnostic vertebral features of Bransateryx lie in the caudal vertebrae [3, 116], elements which are absent from the Saint-Gérand-le-Puy collection. Nevertheless, the material described herein bears strong resemblance to trunk vertebrae previously referred to Bransateryx; these include trunk vertebrae of the only valid species, Bransateryx vireti Hoffstetter and Rage, 1972 [3], from its type locality (Coderet [MP 30], which is very near to Saint-Gérand-le-Puy), as well as a single trunk vertebra from the area of Saint-Gérand-le-Puy itself, described previously [3].
Bransateryx has been considered to pertain to erycine boids [3, 8, 59, 116]. However, it is now known, based on molecular data, that the traditional concept of erycines is paraphyletic, i.e., with the Old World erycines pertaining to a different group (Erycidae) than the New World ones (Charinainae). The latter group forms, together with Ungaliophiinae, the Charinaidae [115, 117, 118]. The most characteristic feature shared among Erycidae and Charinainae is the peculiar complex nature of the caudal vertebrae, which is nevertheless absent in the latter’s group closest relatives, i.e., the Ungaliophiinae [115, 118]. It is now known that charinaines were present in the European Eocene (i.e., Rageryx Smith and Scanferla, 2021 [118], from Messel) [115, 117, 118]; as such, it is currently not possible to assess the exact affinities of certain European Paleogene and early Neogene taxa that possess this kind of caudal vertebrae [115]. Accordingly, we follow the scheme of Smith and Georgalis [115], under which Bransateryx is placed into the informal group “erycines”.