On complex dermal elements in Loganellia species (Agnatha, Thelodonti) from the Upper Llandovery of Scotland (l.G.C.P. 328 Contribution)

Abstract

Two specialized squamation types from the Upper Llandovery of Scotland are described in detail for the first time. One type occurs mainly as fused structures here referred to as scale sets. They probably belonged to the thelodont gents Loganellia. Their morphology is discussed and ideas are put forward about their generation, function and topography. The second squamation type is here called denticulated plate, type A and denticulated plate, type B. The morphology of these plates is compared with that of the scale sets, with which they share some characteristics. The type A plates were discovered in the branchial area of a Loganellia specimen and are possibly fragments of an internal dermal cover interpreted as a complex of gill rakers.