Question: How do dinosaurs fit into God's plan?

The core of the problem is that the scriptures and the revelations simply don't talk about dinosaurs

My seminary class has questions regarding the dinosaurs. They seem to be stuck on "where" and "when." How do they fit into the creation story presented by the scriptures?

Your seminary students are probably hung up on the following issues:

Scientists say dinosaurs lived and died millions of years ago, and became extinct due to a cataclysmic event, probably an asteroid that struck the earth. This is what your students are taught in school, because it reflects the scientific consensus.
It is generally believed by many members of the Church that the fall of Adam and Eve took place around 4,000 B.C., and that before this there was no death in the world.
How do we square #1 with #2? How do we account for fossils that appear to be millions of years old, if we conclude there was no death before about 6,000 years ago?

The core of the problem is that the scriptures and the revelations simply don't talk about dinosaurs, and are inconclusive about whether there was physical death for other organisms before Adam and Eve's fall. This leaves each person to decide for themselves how the fossils we have discovered fit into the timeline of the plan of salvation. There generally two possible solutions that have been adopted by intelligent, faithful Latter-day Saints:

Some take the approach that the earth is very old, that there was death before the Fall, and that the dinosaurs lived and died in a era long before the story of Adam and Eve begins.
Some have reasoned that there was no death before the Fall, so the dinosaurs must have lived alongside Adam and the early patriarchs, perhaps dying in (maybe even after) the Flood. (See: Death before the fall main article FAIRWiki link.)
Some, based on the teachings of Joseph Smith that the earth was organized out of existing material rather than created from nothing, have even concluded that dinosaurs never existed on this world, and that the bones we've found are actually from the destroyed remains of other planets. This is not a popularly held notion today, and it contradicts the findings of modern paleontology. In fact, Brigham Young University has a paleontology museum.

The scriptures — especially the creation accounts in Genesis, Moses, Abraham, and the temple endowment — are not concerned with laying out a comprehensive history of the earth

The three important points to get across to your students are:

The scriptures — especially the creation accounts in Genesis, Moses, Abraham, and the temple endowment — are not concerned with laying out a comprehensive history of the earth. They are concerned with telling the story of God's covenant relationship with men, a covenant he first established with Adam and Eve. Anything outside this story is simply not relevant to the issue the scriptures are dealing with.
Latter-day Saints are ultimately interested in truth, whatever and wherever it may be. We should not be afraid of learning new things that may contradict our previous assumptions, and we should not be overly dogmatic about things that are peripheral to the gospel message (that message being Jesus is the Christ, Joseph Smith was a true prophet, the Book of Mormon was divinely revealed, the keys of the priesthood are on the earth). In other words, have an open mind, but not a gaping one.
Ultimately, our salvation does not depend on when we believed the dinosaurs lived, or even if we believe there was (or was not) death before the Fall. Our salvation lies in hearing the word the Lord and then doing it.

Notes

Question: How do dinosaurs fit into God's plan?