P. pannonicus is a fossil species of legless lizard in the family Anguidae. It is distinct from the living Scheltopusik, Pseudopus apodus, although the two resemble one another closely in much of their skeletal anatomy. Previously estimated to have had a skull about 90–100 millimetres long, P. pannonicus was the largest known anguine. Its established temporal range extends from the Upper Miocene to the Lower Pleistocene, and its fossils have been reported from Spain, Ukraine and numerous sites in central and eastern Europe. The new material came from eight listed Ukrainian, Moldovan and Russian localities, spanning regional stages from MN 10 to MN 15, with Tatareshty tentatively placed near the beginning of MN 16a.

The reassessed collection comprises eight dentaries, five maxillae, four frontals, 11 parietals, one lacrimal, two fragmentary braincases, 133 osteoderms, 18 vertebrae and one rib. These are disarticulated fossils whose preservation ranges from poor to relatively complete. Most of the Ukrainian and Moldovan material was collected during expeditions in 1957–1965, while specimens from Gaverdovsky and Volchaya Balka were recovered in 2012. Researchers photographed the remains, used micro-computed tomography to inspect selected bones, produced three-dimensional visualizations and compared the anatomy with published specimens of P. pannonicus and P. apodus. Correlation analyses and Student’s t-tests, with a Bonferroni correction where required, assessed relationships among measurements and differences between taxa.

The largest individual element came from Khadzhi-Abdul in Moldova. Its right maxilla is nearly 37 millimetres long, bears 19 tooth positions and has eight labial foramina along its lateral surface. Earlier accounts had reported a maximum of 12 maxillary tooth positions for P. pannonicus, making the specimen important evidence that tooth number is more variable than those figures implied. The researchers therefore caution against treating maximum tooth counts as an absolute taxonomic test. Fused osteoderms cover much of the nasal process and form conspicuous ornamentation, one of the features they identify as characteristic of P. pannonicus. Statistical analysis of the available maxillae indicated that ornamentation dimensions were positively related to some measures of maxilla size, supporting an influence of growth on the expression of this feature.

The study proposes three principal features for distinguishing P. pannonicus from the living P. apodus. First, the nasal process of the maxilla bears more strongly developed dermal ornamentation. Second, the dentary has a splenial facet extending posterior to the anterior inferior alveolar foramen, a condition that excludes the coronoid from the foramen; in P. apodus, the coronoid normally forms its posterior margin. Third, P. pannonicus has short, compressed trunk vertebrae, whereas the trunk vertebrae of P. apodus are more elongated. The dentary condition is also visible in the newly designated lectotype, a left jaw from the Late Miocene locality of Polgárdi 2 in Hungary. This specimen was figured in the original description of the species and was subsequently called a neotype, but the study argues that the five original syntypes had never been reduced through a valid lectotype designation.

Not every apparent anatomical difference proved robust. The ventral muscular attachment surfaces of the parietals were broad in the fossil material, with a mean ratio of muscular-surface width to the distance between the parietal cranial crest and the bone’s median plane of 0.885. The corresponding mean for six P. apodus specimens was 0.534, and the difference was statistically significant. However, the analysis also found that the ratio was strongly influenced by body size, undermining its value as an independent diagnostic character. Maxillary ornamentation showed a similar relationship with growth, and the authors note that individual and ontogenetic variation must be considered when assessing fossil similarities or differences.

Trunk-vertebra proportions provided a stronger separation. The researchers measured elongation as centrum length divided by neural-arch width, so values near or above 1 represent relatively stout, compressed vertebrae, whereas lower values indicate greater elongation. The 27 available P. pannonicus trunk vertebrae had a mean ratio of 0.96, with a minimum of 0.79, a maximum of 1.37 and a standard deviation of 0.156. This differed significantly from an estimated mean of 0.62 for P. apodus, with a reported t value of 11.132 and p value of 1.4768 × 10⁻¹¹. The fossil centra were consequently proportionally shorter and wider than those of the living species.

Caudal vertebrae proved much less informative and less secure to identify. Large anguine and varanid caudal vertebrae can look alike, and the available characters often permit identification only to an indeterminate anguine. In the new material, fused haemapophyses and posteriorly inclined, tube-like neural spines argued against varanid affinities, while the absence of an autotomic split supported assignment to Pseudopus rather than Anguis or Ophisaurus. The authors nevertheless stressed the difficulty of distinguishing among Pseudopus species from isolated caudal vertebrae. Their species-level attribution depended on morphology, size, stratigraphy, geography, the associated fauna and the presence of more securely identified Pseudopus remains, rather than on vertebral-column position alone.

The fossils came from a range of reconstructed environments. Gaverdovsky was associated with a densely forested shore under strong marine influence, whereas Volchaya Balka represented a freshwater basin with more open vegetation. Their age was constrained by stratigraphy, ostracod assemblages, palynology and mammalian assemblages to an estimated range of 8.1–7.6 million years ago, corresponding to the early Turolian or MN 11. Ukrainian material from Petroverovka came from Lower Maeotian deposits correlated with MN 11–12. Kalfa in Moldova was treated as early MN 10, while Etulia, Khadzhi-Abdul and Lucheshty were assigned to the late Ruscinian, around MN 15. At several of these sites, P. pannonicus was the most abundant or only known anguine.

One especially small fossil, a 20.73-millimetre-long dentary from Tatareshty, was interpreted as a juvenile. Its conical, slightly curved anterior teeth, broader spacing and more slender proportions suggest an immature individual, while its tooth morphology resembles juvenile P. apodus. It lacks the surangular spine regarded as diagnostic of P. ahnikoviensis and the expanded subdental shelf characteristic of P. laurillardi. Its late Ruscinian age is also younger than the known range of P. ahnikoviensis, while the splenial articulation resembles that of P. pannonicus and is consistent with the proposed diagnosis. The same locality produced a rare lacrimal bone, the first such element reported for P. pannonicus. Because lacrimals are uncommon in the European lizard fossil record and their morphological variation is poorly documented, the authors considered the species-level assignment of this isolated bone less secure than that of the associated dentary.

Overall, the fossils expand the geographic, chronological and osteological record of a remarkable giant anguine while showing why size alone cannot identify it. The North Caucasus material extends the confirmed distribution well east of the Hungarian type locality, and the Ukrainian and Moldovan specimens document the species across much of the late Miocene and Pliocene. The new comparisons also separate potentially useful anatomy from traits strongly entangled with growth. The strongest proposed distinctions lie in maxillary ornamentation, the arrangement of the dentary’s splenial and coronoid articulations, and the compressed proportions of the trunk vertebrae. The taxonomic position of Pleistocene material from Azerbaijan remains unresolved and could move the species’ confirmed eastern limit still farther.

Subject of Research: Fossil record and skeletal anatomy of the giant anguine lizard Pseudopus pannonicus

Article Title: The easternmost record of the largest anguine lizard that has ever lived – Pseudopus pannonicus ( Squamata , Anguidae ): new fossils from the late Neogene of Eastern Europe

Article References: Loréal, E., Syromyatnikova, E. V., Danilov, I. G., & Čerňanský, A. (2023). The easternmost record of the largest anguine lizard that has ever lived – Pseudopus pannonicus (Squamata, Anguidae): new fossils from the late Neogene of Eastern Europe. Fossil Record, 26(1), 51-84. https://doi.org/10.3897/fr.26.100059

Image Credits: AI Generated

DOI: 10.3897/fr.26.100059

Keywords: Pseudopus pannonicus, giant fossil lizard, Anguidae, Eastern Europe, North Caucasus, Moldova, Ukraine, Miocene, Pliocene, vertebrate palaeontology, easternmost, record