Con ot rach el us ▁eleg ans ) ▁is ▁a ▁true ▁we ev il ▁species ▁also ▁found ▁feed ing ▁on ▁g alls ▁of ▁the ▁h ick ory ▁leaf ▁stem ▁gall ▁ph yl lo x era . ▁ ▁The ▁band ed ▁h ick ory ▁b orer ▁( K n ul li ana ▁cin ct a ) ▁is ▁also ▁found ▁on ▁h ick ories . ▁ ▁E volution ary ▁history ▁ ▁The ▁earliest ▁ancest ors ▁of ▁h ick ories ▁are ▁identified ▁from ▁C ret ace ous ▁pol len ▁gra ins . ▁The ▁C ary a ▁as ▁we ▁know ▁it ▁first ▁appears ▁in ▁O lig oc ene ▁str ata ▁ 3 4 ▁million ▁years ▁ago . ▁F oss ils ▁of ▁early ▁h ick ory ▁n uts ▁show ▁simpler , ▁th inner ▁shell s ▁than ▁modern ▁species ▁with ▁the ▁exception ▁of ▁pec ans , ▁suggesting ▁that ▁the ▁trees ▁gradually ▁developed ▁def enses ▁to ▁rod ent ▁seed ▁pred ation . ▁During ▁this ▁time , ▁the ▁genus ▁had ▁a ▁distribution ▁across ▁the ▁Northern ▁Hem is phere , ▁but ▁the ▁Ple ist oc ene ▁Ice ▁Age ▁beginning ▁ 2 ▁million ▁years ▁ago ▁completely ▁ob liter ated ▁it ▁from ▁Europe . ▁The ▁distribution ▁of ▁C ary a ▁in ▁North ▁America ▁also ▁contract ed ▁and ▁it ▁completely ▁disappeared ▁from ▁the ▁continent ▁west ▁of ▁the ▁Rock y ▁Mountains . ▁Since ▁foss il ▁records ▁show ▁North ▁America ▁as ▁having ▁the ▁largest ▁number ▁of ▁Jug land aceae ▁species , ▁it ▁is ▁likely ▁that ▁the ▁genus ▁origin ated ▁there ▁and ▁later ▁spread ▁to ▁Europe ▁and ▁Asia