Eurypterygii caudal skeleton

Abstract

The osteology of the caudal skeleton in representatives of 41 genera in 39 families of eurypterygian fishes was studied. The caudal skeleton of eurypterygian fishes consists of five or six hypurals, a parhypural, one to three epurals, one or two pairs of uroneurals, ural centra 1 and 2, last preural centra and associated neural and haemal spines, and procurrent and principal rays. Eurypterygians like other teleosts have a diural caudal skeleton (two ural cen-tra). Primitively in basal Acanthomorpha and Acanthopterygii, the caudal elements are autog-enous and several intercaudal and postcaudal cartilages support these isolated elements. Basal groups usually have six autogenous hypurals, three epurals, two pairs of autogenous neurals, autogenous ural centrum 2, and autogenous haemal and neural spines on the last centra. In some basal groups such as Myctophidae, many of the caudal elements are fused, because of the presence of primitive conditions in related taxa, the fusion in such a groups should be re-garded as secondary and independent from that in higher taxa. In higher groups, there is a tendency for the elements to fuse together and to the centra and caudal cartilage are lost due to lack of function. In specialized groups