Don't hate me, but at those speeds, it was likely blunt force or bones that did most of that damage, the flesh would have been nothing to the force of your car hitting the dog, poor thing would have been broken beyond repair... likely in pieces after being rolled over. It didn't feel much.
I know the pain tho, from both sides. My responsibility failed at 18 and I let my 2 yr old buddy out with me and he darted out the door and across the yard, he stopped by the road but when I called him to come back he turned and ran away... into traffic. Horror is watching your pup get ran over by a truck speeding at those speeds and knowing you have to go get him and put him into ground. I missed work that day, cried most of it (not proud but that was my best friend), but he deserved well. He was a good dog.
I have also been on the O NO end of the steering wheel watching it come out and knowing a swerve is endangering myself, my car, and my friends/girlfriend... poor dog, sorry.
It sux, but you did the right thing. Nothing else could have been done.