Not the ones in the U.S. in the last ~50 years[sup]1[/sup]. Not sure; maybe the practice of using steel, bronze or concrete vaults and bronze caskets (not all caskets are made of bronze, just the “best” ones) is older than I realize. But in order for an embalmed body to decay, it has to be buried in a container that is not impervious to Mother Nature.
And can you imagine the fuss people with the mores of the current U.S. culture WRT death at the idea of digging up their - or anyone else’s - “dearly beloved”?? Of course, if we don’t kill ourselves off (whether through war or stupidity), the culture is bound to change. However, IIRC, embalming, as practiced today, was first developed about 150 years ago.
In order for the body to be reprocessed by Mother Nature, the corpses hafta a) not be embalmed (The formalin embalming compound kills the bacteria; that’s entire purpose of its use. Of course, some bacteria survive, but they nearly always have some mutations. My friend (I’ve lost track of) Mohammad Sondossi did his Ph.D. proving that formalin induced mutations in common bacteria. If the formalin[sup]2[/sup] didn’t work quite as well, you wouldn’t be able to get in the same room with a body that had been kept at room temperature for several days (which is why both orthodox Jews and Muslims -and some other religions/cultures) practice burial within 24 hours), trust me.) and b) not interred with forty-leven barriers between the dead meat (yes, I’m being ugly, but until people think of it as what it is, rather than recognizing it as a rather useless thing,[sup]3[/sup] there will be no reversion to even the most minimal of ecological practices) and the environment.
Finally, the bodies of large animals don’t get turned into oil, or anything else. They are eaten by other animals, or they are broken down by appropriate saprophytes (bacteria and fungi which specialize in proteins and fats), which work on animals the same way that others, plus mushrooms and toadstools, work on decaying cellulose (plants).
<hijack>I’m experimenting with using a different font for my all-too-numerous looong parenthetical comments. I’d appreciate feedback on whether it makes it easier to read or harder. Otherwise I’ll hafta start footnoting everything. :eek: Y’see, the peripheral stuff just boils up when I try to discuss things. To write intelligibly without parenthetical expressions, I hafta rewrite ninety-leven times, instead of just forty-leven. 
Or maybe I could just use color changes (not bright ones)??
</hijack>
Footnotes
[sup]1[/sup]I’m not entirely sure of dates. I just know that when my mother died (1956), the funeral director showed caskets and a bronze vault to my father and me, and explained about the differences between vaults. I would suspect that vaults were available for the wealthy long before that. If I’m not mistaken, most cemeteries today require some kind of vault. I’m not sure that was true back in the 1950s.
[sup]2[/sup]Before formaldehyde was discovered and used for this, there were a variety of different ways that bodies could be preserved - just not as well. The ancient Egyptians used natron to dry out the body, although they had to remove parts that the natron couldn’t reach to desiccate before rot set in (parts which had to be removed were the brain and most of the insides - heart, stomach, intestines, etc.). Not sure of when it was first tried, but there was a Greek(?) general who died a long distance from home. They immersed his body in a large container filled with honey, which kept both bacteria and oxygen away from the body. Of course, the anaerobic (non-users of oxygen) microbes would still be doing their thing, so some decay was inevitable. Some centuries on, immersing a body in wine was also found to be fairly effective. However, it was the (relatively) modern practice of slitting one of the large veins in the neck, and another near one foot, draining out all the blood that could be extracted, and replacing the blood with formaldehyde (or some other sterilizing agent) which enabled the practice of “viewing the deceased.” However, the longer the body waits before treatment means that there is more blood which cannot be extracted - particularly from the hands and feet (and “innards”). This means that some decay will occur in the areas which still have blood in them.
[sup]3[/sup]Either you believe in a non-dying part of you, or you don’t. If you don’t, why would you want the dead meat preserved?
If you do believe in a resurrection, why do you doubt that the creator can rebuild your body? That seems to be a fairly trivial exercise for an omnipotent being. Think of the believers whose bodies have been destroyed. Do you suppose they will not be resurrected? I can understand people being unable to deal with such ideas when they have just lost someone dear to them. However, I cannot understand why people would not think about these things calmly at some other time, and think them all the way through.