Cranial osteology and ontogenetic assessment of a partially articulated sub-adult Malpolon cf . monspessulanus (Serpentes: Psammophiidae) from the Early Pleistocene of Quibas (SE Spain)

Abstract Cranial remains of snakes are rarely preserved in the fossil record, which is dominated by isolated vertebrae, and this issue resticts reliable taxonomic and ontogenetic interpretations. Despite Malpolon representing one of the best-documented psammophiid genera in the European fossil record, most occurrences are based almost exclusively on vertebral material, limiting our knowledge about important morphological features related to the skull. Here we describe a partially articulated colubriform from the Early Pleistocene of Quibas (SE Spain) preserving a partially disarticulated portion of the skull and vertebrae, representing an exceptional occurrence for fossil colubriforms. The specimen is investigated through micro-computed tomography scanning, detailed osteological description, and comparative analysis with extant taxa. Quantitative analyses of trunk vertebrae are combined with an ontogenetic framework based on a developmental series of Malpolon monspessulanus. Although vertebral metrics fall slightly outside the typical range of adult Malpolon specimens, the integration of cranial morphology and ontogenetic data supports the interpretation of the Quibas specimen as a subadult individual of Malpolon cf. monspessulanus. This study highlights the importance of incorporating ontogenetic perspectives when interpreting fossil snakes and cautions against taxonomic overinterpretation based solely on isolated vertebral remains, especially when they belong to juvenile specimens.