Abstract
Specimens of two new fish species were collected from the Lower Devonian ichthyofauna of the Mackenzie Mountains, Northwest Territories, Canada. These two species are interesting in that they have monodontode scales, lack teeth, and have an unossified axial, visceral, and appendicular endoskeleton. These characteristics have been suggested to be primitive for jawed fishes. However, the new taxa have combinations of median and paired fin spines which are similar to those of acanthodian fishes. The new taxa show no obvious characteristics to suggest relationship to any particular group of acanthodians, and for the moment, we will not try to determine their relationships, but to use them as outgroups in an analyses of relationships within the class Acanthodii. Our cladistic analysis results suggest that climatiiform fishes are basal relative to acanthodiform and ischnacanthiform taxa. However, in contrast to previously published analyses, the order Climatiiformes appears paraphyletic relative to the other two acanthodian orders. Lupopsyrus pygmaeus is placed as the basal-most acanthodian species, Brochoadmones milesi, Euthacanthus macnicoli, and diplacanthids are relatively derived “climatiiform” fishes, and the heavily armored condition in Climatius reticulatus and Brachyacanthus scutiger appears as a uniquely derived state and not primitive for all acanthodians. In addition, Cassidiceps vermiculatus and Paucicanthus vanelsti seem to be related to acanthodiform fishes based on fin spine structures. Cassidiceps vermiculatus originally was placed with climatiiform fishes in the original description. Given our character coding, we identified several primitive characteristics which were retained in relatively derived acanthodian taxa.
