Okay , going away from the main idea again.
It just looks too much like some animals were killed just for the antlers.As it appears to me. Sometimes you find bodies with no heads, sometimes you find heads with no antlers.
Here yes, on private land do as you wish ,dump where you want.Our landfill has specific area for animal waste and carcasses.For a price of course. I believe and I could be wrong, that if it is a public place it wouldn't be any different than an old washing machine , hamburger wrappers, or animals parts.
The coyotes and the birds will process the remains very efficiently, the thing that bothers me is the means and possible motives that happened previous to the dumping.
As for the same as road kill, that is unintentional. What do you think a LEO or CO what have to say if they witnessed you throwing bones and hides and heads into the ditch? Doubt the same as roadkill statement would help much.
Yes I am assuming here, but others are also assuming that they were taken legally.