Board Thread:Fan-made Monsters/@comment-26517142-20160614124848/@comment-27950421-20160701000415

Also, the similar appearance is due to the fossil originating from the same creature as the living mamono not due to having originated from the living mamono. Simply put, mamono haven't been around long enough to fossilize and an undead version of them would just be a zombie variant or skeleton variant not a fossil.