ARCTOLEPIS

extinct genus of Early Devonian fishlike animals (408 to 387 million years ago), considered to be an early and primitive member of a group known as the arthrodires, or jointed-neck fishes. Arctolepis had a bony head and trunk shield but was unarmoured behind the trunk region; the body tapered to a pointed tail; a tail fin was developed only on the lower margin of the tail. Arctolepis was a small animal, less than 30 cm (12 inches) in length but with enormously developed pectoral spines that must have been some aid to swimming but could hardly have been very efficient.