presented his version of the Late Devonian ptyctodontid placoderm, Campbellodus (Fig. 1, Miles and Young 1977).
Based on phylogenetic bracketing,
using Cheirodus (Fig. 2) as a guide, I moved the originally disarticulated elements of Campbellodus from the Long 1997 diagram into a reconstruction (Fig. 2) not far from its phylogenetic sister (Fig. 1). It helps to have a blueprint when working with roadkill.
Campbellodus decipiens (Miles and Young 1977; Late Devonian) The posterior mandible parts in the diagram are re-identified here as internal jaw elements + a hyomandibular. Other elements are colorized using tetrapod homologs. Currently (Fig. 3) traditional placoderms are diphyletic, with ptyctodontids apart from the rest of the placoderms.
As a reminder,
fish experts do not yet recognize the similarities in traits shared by Campbellodus and Cheirodus. Hopefully, that will change someday, because the two are quite similar.
We’re going to have to homologize fish skull bones
with tetrapod skull bones someday. Sooner would be better than later. Many bones, like the frontals, quadrate and premaxilla are already homologized. Just a few remain.
Long JA 1997. Ptyctodontid fishes from the Late Devonian Gogo Formation, Western Australia, with a revision of the German genus Ctenurella Orvig 1960. Geodiversitas 19: 515-555.
Miles RS and Young GC 1977. Placoderm interrelationships reconsidered in the light of new ptyctodontids from Gogo Western Australia. Linn. Soc. Symp. Series 4: 123-198.