Archaeocoleostraca (lit. "ancient Coleostracans") are an extinct branch of Coleostraca. They were the first macropredators to have ever existed.
Emerging around 4185ma, the Archaeocoleostracans were the first clade of terrestrial macropredators, feeding upon other clades of Diplostomes. Archaeocoleostracans measured around 50cm in length, and possessed short, barbed oral tentacles. Their gladius helped them obtain speeds greater than other Diplostomes. The evolution of the Archaeocoleostracans led to the emergence of the Desmostraca clade, and led Placostracans to evolve thicker armor.
The Archaeocoleostracans persisted for over 15 million years after the emergence of the Osteopods. However, they were eventually driven to extinction by the first Dromaeopods, whose greater speed made them superior hunters.