Why can't dinosaur bones and teeth be directly radiometrically dated?

Answer 1

With the exception of Carbon dating, radiometric dating can only be used on igneous rocks, not sedimentary rocks or the actual fossils. Because fossils are found in sedimentary rock, paleontologists try to use radiometric dating information on igneous rocks found below and above the fossils in order to try and determine an age range for the sedimentary rocks.

The isotope concentrations can be measured very accurately, but isotope concentrations are not dates. To derive ages from such measurements, unprovable assumptions have to be made such as:
-The starting conditions are known (for example, that there was no daughter isotope present at the start, or that we know how much was there).
-Decay rates have always been constant.
-Systems were closed or isolated so that no parent or daughter isotopes were lost or added.

These dating methods are far from infallible—they are indirect methods based on quite a few assumptions, and evolutionary geologists themselves will often not accept a radiometric date unless they think it’s correct (i.e. it matches what they already believe). There are plenty of scientists who question their accuracy. For instance, the “RATE” project has discovered several striking examples of contradictions in these dating methods. If you want, you can get their book or movie called "Thousands...Not Billions" and learn about some of their remarkable results. If you do a bit of research, you will find that there is a lot of proof of radiometric dating not being accurate. The radioactive dating methods are often a classic example of self-deception and circular reasoning.

OK, since you mention dinosaurs, is there evidence of younger dates for dinosaur fossils?

In 1990 a sample of various dinosaur bones were sent to the University of Arizona for a “blind” Carbon-14 dating procedure. “Blind” in the sense that they didn’t tell them what the bones were. The oldest date they got was 16 thousand years; that’s a far cry from the millions of years evolutionists suggest. If dinosaurs became extinct more than 65 million years ago, there should be no carbon-14 left in their bones. Evolutionist of course say the samples must have been contaminated.

In 1981, scientists identified unfossilized dinosaur bones which had been found in Alaska 20 years earlier. Philip J. Currie (an evolutionist) wrote about this and some similar finds, “An even more spectacular example was found on the North Shore of Alaska, where many thousands of bones lack any significant degree of permineralization. The bones look and feel like old cow bones, and the discoverers of the site did not report it for twenty years because they assumed they were bison, not dinosaur, bones.” As Dr. Margaret Helder has said, “How these bones could have remained in fresh condition for 70 million years is a perplexing question. One thing is certain: they were not preserved by cold. Everyone recognizes that the climate in these regions was much warmer during the time when the dinosaurs lived.”

In 1990, Scientists from the University of Montana found T. rex bones that were not totally fossilized and even found what appeared to be blood cells in them. Dr. Mary Schweitzer said, “It was exactly like looking at a slice of modern bone. But, of course, I couldn’t believe it. … The bones, after all, are 65 million years old. How could blood cells survive that long?” How indeed?

And then in 2005, they found an even greater discovery. Science Daily website said (March 25, 2005): “Dr. Mary Schweitzer . . . has succeeded in isolating soft tissue from the femur of a 68-million-year-old dinosaur. Not only is the tissue largely intact, it’s still transparent and pliable, and microscopic interior structures resembling blood vessels and even cells are still present.” As Dr. David Menton said, “It certainly taxes one’s imagination to believe that soft tissue and cells could remain so relatively fresh in appearance for the tens of millions of years of supposed evolutionary history.” Wouldn’t that be a hit for the meat industry if we could figure out how to preserve meat for so long?

Answer 2

Because they contain rock - they are not the actual bones of the critters. They're fossils.
http://en.wikipedia.org/wiki/Fossil