I have never heard that before. To me it sounds like a theory that was created out of a need to explain why the bones haven't been found. It is a
tad convenient if you ask me.

After the incineration is completed, the bone fragments are swept out of the retort, and the operator uses a pulverizer called a cremulator[3] (also known informally as a crembola[citation needed]) to process them into what are known as cremains which exhibit the appearance of grains of sand (note that this varies with the efficiency of the cremulator used, and recognizable chips of very dry bone may be seen in some final product cremated remains, depending on origin and facility). Cremulators usually use some kind of rotating or grinding mechanism to powder the bones, such as the heavy metal bearings on older models.[4]
Originally posted by sherpa
A long time ago in a galaxy far far away.......
No sorry, that is not what I was going to say but it was a long time ago that I read somewhere, and I can't remember where, that the reason dragons could breath fire and fly was that they produced a super lighter than air gas such as hydrogen.
The dragon was very lightly built like birds with hollow bones and the body having many cavities acted like a gas bag, the gas being flammable could produce fire, not sure what the ignition source was though.
Why the heck did I remember that.
That was the cartoon movie Flight of the Dragons. The dragons ate some rocks which released a very light gas when digested. They also had "honeycomb" bellies which stored the gas. Pretty sure that the hollow bones were in there too. Reading your description, the scene where they explain this immediately came to me. Must be a pretty memorable scene since we both remember it.
