Mesacanthus pusillus (Agassiz)
This tiny acanthodian must have been the main food for most of the fishes. In the Sandwick Fish Bed laminites it can be found in certain layers by the hundreds on a surface of a square metre.
In literature two different species have been described, M. pusilles and M. peachi. Since the author was not able after long research to distinguish between the two both were lumped in the species M. pusillus (the first species named by Agassiz).