Patches of spherulitic calcified cartilage are described inside the paired fins of the osteostracan Escuminaspis laticeps from the Upper Devonian of Miguasha, Canada, thereby confirming Belles-Isles interpretation of these patches as evidence for paired fin endoskeleton. The distribution of these calcified cartilage patches suggests that the osteostracan paired fin endoskeleton was a single cartilaginous plate located in the lateral half of the fin, and was thus not made up of separate radials. This morphology resembles that of the endoskeletal disc of the embryonic and larval pectoral fin of piscine gnathostomes, prior to its decomposition into radials, and may mirror the general condition for the clade that includes osteostracans and gnathostomes.