Sunfish do not have swim bladders, so how do they avoid sinking like a millstone? “..the most striking characteristic of the [Sunfish] skeleton is the great reduction of bony tissue. Ossification is so weak that the material […] resembles cartilage. The skeleton, when dry, for the most part shrinks into thin, delicate and fibrous or spongy pieces….”
Reference: Gregory & Raven, (1934).
As a consequence of these flimsy skeletones, few sunfish remains survive the test of time. We are consequently left with very few archaeological traces of these strange fish.