DEX Media= Dex One plus Super media, hence Dex Media. Supermedia was GTE way back in time, then GTE merged with Bell Atlantic in 2000 to form, wait for it, yes they formed Verizon, Verizon then spun off its directories in 2006, they became Idearc. After a BK they became Supermedia and merged with Dex One and still remain HQ in Texas. Super media alot less debt than dex one when they merged. there you have it. Thats the media side , since you got the dex side already.
if you want to go back to the roots of bell telephone, that would be 1877. you could also go back to the beginning of rh donnelley, which goes back to 1886. i'm not sure what you would be able to trace back to 1841