 Only the beaks are robust and distinctive enough to allow for good taxonomic delimitation, and even these are usually found as broken pieces.For example, "Argilliornis" and "Neptuniavis" were recently found to be arm and leg bones, respectively, of "Dasornis", which until then was only known from skull bones.Size is generally regarded as reliable marker for generic diversity, but care just be taken to ascertain whether smallish specimens are not from young birds.