Why are there not millions/billions of fossils showing the failed animals of the evolutionary theory of natural selection?

Species don't really 'fail' in an evolutionary sense, and individual animals certainly don't, unless they are the result of mutation. Dinosaurs have been mentioned in another answer, whereas in fact the dinosaurs were one of the most 'successful' types of animal ever. They lived about a hundred times longer than human beings have managed so far. But they died out when their environment changed.

What happens is that species fit their environment - when that environment changes, the species will either adapt or die out. There are many fossils representing species that died out, just as there are many fossils showing how species adapted.

If you read up on natural selection you will get a greater understanding of how it all works.

The chances of finding any particular individual's fossilised skeleton is very slim indeed. Out of the millions of individual T-Rex's that ever existed, we only found a few skeletons. So, if there was a mutation that failed to take hold and only produced a handful of individuals, the chances of coming across such a skeleton are microscopic.
On the other hand if you mean a failed species (ie, a species that went extinct), that's what all dinos are.

I think you would agree that the dinosaurs failed to evolve, and there are countless dinosaur fossils.

There are. 99.9% of all know species are extinct. How many trilobites, ammonites, dinosaurs do you see today? And those are the well know ones. If someone digs up a fossil, it is almost certainly of an extinct species. And nearly as certainly one without modern descendants.

Failure and the idea that there are fossils aren't in the same category.

There are millions of fossils,billions even,who's to say this one or that one was a failure or not,or even not a failure but a simple adaptation.

You must remember that dinosaurs were here for some 650 MILLION years,that's a very long time to adapt and change to differing conditions,time for bones to dissolve,for new species to come into being.Man hasn't been here for all that long and we have more than a few means to preserve our bones,animals didn't have this(like opposing thumbs/chemical means.etc)

The only way I can see to prove your theory would to find a specific species dating to it's origin,adaptations over millions of years,and the final modern adaptations,,like the fish that finally walked on land.

Over 99% of all species of animals that have existed are extinct. Fossilization itself is a very rare process. Conditions have to be just right. The vast majority of animals die and decompose right to their bones and we never see 'em.
Then, the fossilized animal must survive plate tectonics, earthquakes, volcanic eruptions and so on and so forth.
Then, the fossil must remain in a place on the earth's crust where we CAN get at it.
Then, it has to be found.

That is why it is very, very safe to assume that if we find x number of fossils, many many many many times x animals have actually been around and vanished leaving little trace.

"Failed" is a human concept. And I'm not sure how you happen to mean it.

Any creature that happened to leave a fossil must have lived - so one might say it succeeded.

And by that logic any creature that didn't exist could be seen to have failed - but would obviously be unable to leave one.

What other criteria would one have for evolutionary failure?
* Extinction? Almost all fossils are of extinct creatures.
* Not being clever enough to have died in such a place that their reminds get discovered a few mil years later?
* Not making the Evolutionary Top of the Pops? :-)

There are.

It would help if the Creationistic ninnies paid attention to them.

Others have answered well here so there is not much I can add. "Failed" is a bit of a broad brush to describe the process by which, over 100s of millions of years, entire groups of species thrive until circumstances change.
It appears you do not live in an area rich in limestone deposits. The legacy of trilobites, which thrived for almost 300 million years, is in nearly every flagstone.

All fossils are of dead animals, so they all failed.

you mean the ones that died at birth?