In his Doctrines of Salvation, President Joseph Fielding Smith makes it pretty clear that the ONLY way for death to enter the world is through a broken law—transgression: “Is it true that millions of years before Adam came into this world death was here? If so, I want to know who brought it. Who was the transgressor? And who atoned for the beings who died before Adam’s fall?” Joseph Fielding Smith, Doctrines of Salvation, Vol.1, p.116 – p.117. Given this position, is there any way to avoid the conclusion that the dinosaurs lived after Adam fell?
Your question contains several implications which you undoubtedly believe to be true. The question you ask is something like the well-known, “When did you stop beating your wife?” Implicit in that question is the assumption that person being asked had been beating his wife.
Implicit in your question is the concept that Adam was not the first person living on the earth, and so there must have been a pre-Adamic Savior for the pre-Adamic beings living on the earth.
Then you ask the apparently rhetorical question is death was on the earth millions of years before the advent of Adam. That presupposes the proposition that life was present on the earth millions of years before the advent of Adam.
From all of the presumptions implicit in your question I can only conclude that archeologists and anthropologists are in possession of absolute truth, and man must rationalize God’s creative process with what is “known” to be true in science.
Further, you seem to go along with the interpretation of many of the conventional bible scholars that date Adam’s transgression and his expulsion from the Garden of Eden was in the year 4004 B.C. This concept is taken from the conventional interpretation of Genesis 2:17
But of the tree of the knowledge of good and evil, thou shalt not eat of it: for in the day that thou eatest thereof thou shalt surely die.
…Now let’s see if we can sort things out a bit.
The above instruction given to Adam was given before the fact. It undoubtedly was given to Adam before the present 24-hour day began. Further, it was the Lord talking, and a day from the Lord’s perspective is as a thousand years from man’s perspective. As recorded in 2 Peter 3:8
But, beloved, be not ignorant of this one thing, that one day is with the Lord as a thousand years, and a thousand years as one day.
In addition to Peter’s declaration, there is a Latter-day Prophet by the name of Brigham Young who made the following inspired statement–
“Though we have it in history that our Father Adam was made of the dust of this earth and that he knew nothing about his God previous to being made here, yet it is not so; and when we learn the truth we shall see and understand that he helped to make this world and was the chief manager in that operation.
He was the person who brought the animals and the seeds from other planets to this world and brought a wife with him and stayed here. You may read and believe what you please as to what is found written in the Bible. Adam was made from the dust of an earth, but not from the dust of this earth. He was made as you and I are made, and no person was ever made upon any other principle”. Daniel H. Ludlow, ed., Latter-day Prophets Speak: Selections from the Sermons and Writings of Church Presidents, p.266-267
So my suggestion to you is that you take the word of God and of his authorized servants to be the absolute truth and judge the words of the scientists by how well they concur with the words of God and his authorized servants, rather than the other way around.