Another overlooked human ancestor
enters the large reptile tree (LRT, 1793+ taxa) and with it, new light is shed on the history of how we came to be.
Note: these are both late survivors of a Middle Silurian radiation based on phylogenetic and chronological bracketing. That gives both taxa plenty of time to evolve individual traits that appear, but do not remove both taxa from their phylogenetic order in the LRT.
The mandible of Orodus is massive
(probably a newly evolved trait). The cranium is narrow. The fins are larger than those illustrated by Zangrel 1981. The FMNH specimen preserves skin and gill slits.
Note: the distance between the pectoral fins and skull shrinks in Prohalecites, one way to make five gill opercula shrink to just one.
The FMNH (Field Museum) specimen of Orodus
would make a wonderful project for a PhD candidate. Not much has been written about it. It might be a good idea to run it through an x-ray machine to see the now covered coronoid process.
Earlier we looked at
Prohalecites (Fig. 2) a tiny descendent of Orodus also nesting in the LRT between sharks and bony fish and discussed the increasingly common instances of phylogenetic miniaturization at the genesis of major clades.
Agassiz L 1838. Recherches Sur Les Poissons Fossiles. Tome III (livr. 11). Imprimérie de Petitpierre, Neuchatel 73-140.