Mesacanthus mitchelli (renamed with Traquair 1888; Early Devonian, 410 mya; 3cm) is a basal acanthodian. Mesacanthus has open cheeks exposing the quadrate. Soft tissue preserves membranes posterior to all the spines.

Triazeugacanthus affinis (Miles 1966; Chevrinais, Sire and Cloutier 2017, Early Devonian; 380 mya; up to 5.2cm) is a small acanthodian basal to ray-fin fish not in the clade that produced tetrapods. That clade includes Prohalecites and Hulettia at its base.

Homalacanthus concinnus (Russell 1951; 30cm, Early Devonian, 380mya) was a little crustacean eater and prey for Eusthenopteron. In the LRT this taxon is a sister to Trachinocephalus, demonstrating that spiny sharks are a grade that convergently evolve ray fins.

Acanthodes bronni (Anonymous 1880; Davis, Finarelli and Coates 2012; Early Permian 290 mya; 20cm, other species 41cm) is the latest occurring acanthodian, the largest and has the best ossified braincase. It was derived from one of the most primtiive acanthodians, canthus (above). Davis et al. mislabeled the hyomandibular as a giant quadrate and the preopercular as the mislabeled hyomandibular. Acanthodes is toothless and presumed to be a filter feeder. No extra spines are present.

Here dermal skull bones are added based on phylogenetic bracketing and bony landmarks.

Reports that acanthodians are the last common ancestors of sharks and bony fish (Friedman and Brazeau 2010, Davis, Finarelli and Coates 2012) are not supported by the LRT. Rather various spiny sharks are basal to several bony fish clades and arise from a last common ancestor close to a Silurian sister to Gregorius.