The OP said "There's more time between the last Stegosaurus and the first T-Rex" which computes to 145-72 = 73 and "then (sic) there is between the last T-Rex and us right now." which computes to 66-0=66. Note that 7 million years is about 10% of the timescales involved, so perhaps not something to be dismissed as "scientific error".