▁established ▁the ▁details ▁of ▁pla cod erm ▁an atom y ▁and ▁identified ▁them ▁as ▁true ▁j aw ed ▁fish es ▁related ▁to ▁sh arks . ▁He ▁took ▁foss il ▁spec im ens ▁with ▁well - pres erved ▁sk ull s ▁and ▁ground ▁them ▁away , ▁one ▁t enth ▁of ▁a ▁millimeter ▁at ▁a ▁time . ▁Between ▁each ▁gr inding , ▁he ▁made ▁an ▁im print ▁in ▁w ax . ▁Once ▁the ▁spec im ens ▁had ▁been ▁completely ▁ground ▁away ▁( and ▁so ▁destroyed ), ▁he ▁made ▁en larg ed , ▁three - dimensional ▁models ▁of ▁the ▁sk ull s ▁to ▁examine ▁the ▁an atom ical ▁details ▁more ▁thoroughly . ▁Many ▁other ▁pla cod erm ▁special ists ▁thought ▁that ▁St ens i ö ▁was ▁trying ▁to ▁sh oe horn ▁pla cod erm s ▁into ▁a ▁relationship ▁with ▁sh arks ; ▁however , ▁as ▁more ▁foss ils ▁were ▁found , ▁pla cod erm s ▁were ▁accepted ▁as ▁a ▁sister ▁group ▁of ▁ch ond rich thy ians . ▁ ▁Much ▁later , ▁the ▁ex quis it ely ▁preserved ▁pla cod erm ▁foss ils ▁from ▁G ogo ▁re ef ▁changed ▁the ▁picture ▁again . ▁They ▁showed ▁that ▁pla cod erm s ▁shared ▁an atom ical ▁features ▁not ▁only ▁with ▁ch ond rich thy ians ▁but ▁with ▁other ▁g n ath ost ome ▁groups ▁as ▁well . ▁For ▁example , ▁G ogo ▁pla cod erm s ▁show ▁separate ▁b ones ▁for ▁the ▁nas al ▁caps ules ▁as ▁in ▁g n ath ost om es ; ▁in ▁both ▁sh