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

Abstract

Abstract Urocordylids represent a group of the late Carboniferous–early Permian basal tetrapods, with short limbs, extremely elongated bodies and a deep and distinctive tail and vertebral architecture, which is indicative of an aquatic habitat. However, the important morphological structures that would indicate their ecological preferences unambiguously (e.g. hyobranchial apparatus, lateral line sulci) remain unknown. Moreover, the high degree of skeletal ossification present in urocordylids contrasts with the common pattern seen in most other basal tetrapods known to inhabit aquatic environments. Here, we describe an exceptionally well-preserved skull, with an associated mandible and a partial postcranial skeleton, of Sauropleura scalaris from the locality of Nýřany, Czech Republic, based on high-resolution micro-computed tomography. The labial surface of the mandible shows the first evidence of the lateral line system in Urocordylidae, which consists of both small pits and elongated grooves, and unambiguously supports the aquatic ecology of the group. The juvenile stage of the specimen provides new information on ontogeny of sauropleurines. The partly ossified opisthotic bone indicates that, unlike development in most other early tetrapods, the otic capsules were among the first neurocranial elements to ossify in nectrideans. Finally, an almost complete caudal region suggests that tails were much longer in sauropleurines than previously assumed.