▁those ▁used ▁by ▁sp iders ▁to ▁direct ▁and ▁manipulate ▁their ▁sil k . ▁ ▁Tr ig on ot ar b ids ▁are ▁not ▁true ▁sp iders , ▁and ▁most ▁Tr ig on ot ar bid ▁species ▁have ▁no ▁living ▁descend ants ▁today . ▁One ▁line age , ▁however , ▁led ▁eventually ▁to ▁the ▁earliest ▁t et rap ul mon ates , ▁which ▁then ▁evol ved ▁into ▁sp iders , ▁wh ip ▁sc orp ions , ▁and ▁close ▁relatives . ▁ ▁Emer gence ▁of ▁true ▁sp iders ▁ ▁At ▁one ▁stage ▁the ▁oldest ▁foss il ▁sp ider ▁was ▁believed ▁to ▁be ▁At ter cop us ▁which ▁lived ▁ ▁during ▁the ▁Dev onian . ▁At ter cop us ▁was ▁placed ▁as ▁the ▁sister - tax on ▁to ▁all ▁living ▁sp iders , ▁but ▁has ▁now ▁been ▁re inter pre ted ▁as ▁a ▁member ▁of ▁a ▁separate , ▁ext inct ▁order ▁Ur ar ane ida ▁which ▁could ▁produce ▁sil k , ▁but ▁did ▁not ▁have ▁true ▁sp inner ets . ▁ ▁The ▁oldest ▁true ▁sp iders ▁date ▁to ▁ ▁the ▁Car bon ifer ous ▁age , ▁or ▁about ▁ 3 0 0 ▁million ▁years ▁ago . ▁Most ▁of ▁these ▁early ▁segment ed ▁foss il ▁sp iders ▁from ▁the ▁Co al ▁Me asures ▁of ▁Europe ▁and ▁North ▁America ▁probably ▁belonged ▁to ▁the ▁Mes oth ela e , ▁or ▁something ▁very ▁similar , ▁a ▁group ▁of ▁primitive ▁sp iders ▁with ▁the ▁sp inner ets ▁placed ▁under ne ath ▁the ▁middle ▁of ▁the ▁ab d omen , ▁rather ▁than