Why did my dog get aggressive towards me when a new beef bone was 4 feet away from her?

My dog was aggressive and wanted to bite me when I petted her when she was 4 feet away from her new bone its a beef femur bone and actually too big for her to carry around why aggressive ?

Dogs get aggressive when trying to protect their meal. It is an instinct from when they were wolves because other animals, scavengers, would try to steal their meal. Dogs think that humans are dogs. Don't let the dog become aggressive over a bone. Take the bone away if he begins to growl, snarl, bite, or any negative behavior. Otherwise he could become a nasty dog and may become aggressive towards you. Show him you are the boss and you won't except that. If he shows any negative behavior because of a bone, treat, or toy immediately take it away unless you are playing. A dog has to listen to their master, the alpha of the pack. I have to dogs and they are very sweet but one is a black lab and loves chewing on anything. He is a food lover and has eaten anything from a rock to his own droppings, yeah.... Real nice isn't it?! He isn't aggressive though unless you are playing with him. He has never hurt any one of us badly on purpose. Ifound you don't watch your dog he might bite someone and you may have to put him down... : (