Which features suggest that some Osteostraci lived on the bottom?

The suggestion that some Osteostraci were bottom dwellers is primarily based on their physical morphology. Specifically, these organisms possessed a flattened head shield, which is a structural feature often associated with a benthic, or bottom-dwelling, lifestyle.1

While they were equipped with a powerful tail capable of swimming, their overall body form and the specific size and shape of their mouths indicate that they likely functioned as filter feeders along the bottom of their environment.1