The exceptionally well-preserved Sauropleura scalaris (Nectridea: Urocordylidae) from the late Carboniferous of the Czech Republic: new information on ontogeny, lateral line and tail.

This article focuses on the detailed description and analysis of an exceptionally well-preserved specimen of *Sauropleura scalaris* (a urocordylid basal tetrapod) from the late Carboniferous of Nýřany, Czech Republic, using high-resolution micro-computed tomography. The study provides new insights into the skull morphology, ontogeny, and palaeoecology of the species, notably documenting for the first time the presence of a lateral line system on the mandible, which unambiguously supports the aquatic lifestyle of urocordylids. Additionally, the juvenile specimen reveals early ossification of the otic capsules (opisthotic bone), a feature distinct from other early tetrapods, and indicates that the caudal (tail) region is longer than previously assumed, challenging prior distinctions between urocordylid subfamilies based on tail length. These findings refine the understanding of urocordylid anatomy, development, and ecological adaptations without relying on previously ambiguous or incomplete fossil evidence.