Squamation in Andreolepis from the late Silurian of Sweden

Abstract:

The origin of osteichthyans (bony fishes and tetrapods) dates back to the Late Silurian, but theearly evolution of osteichthyans is poorly understood. Andreolepis is one of the oldest knownosteichthyans, but exclusively documented by detached and fragmented dermal microremains.Nevertheless, Andreolepis has unequivocally been attributed to the osteichthyan stem group.A variety of isolated scales of Andreolepis from Gotland, Sweden provides a large dataset,which would potentially improve our understanding of the acquisition of the osteichthyanbody plan. In the present study, various forms of Andreolepis scales were classified into tenmorphotypes by landmark-based geometric morphometrics. Based on comparative anatomyand functional morphology, each morphotype was assigned to a specific area of the body anda squamation model of Andreolepis was established. In this model, scales are allocated toanterior-mid lateral flank scales, posterior lateral flank scales, caudal peduncle scales, pectoralpeduncle scales, dorsal flank scales, dorsal fulcral scales, caudal fulcral scales, ventral flankscales, medioventral scales and cranial scales.