Board Thread:Questions and Answers/@comment-174.55.84.86-20130814204753/@comment-10941901-20130815212051

Okay, for this I've found that you need to shoot these parts until something breaks off (look hard enough, you should see it):

Head horns

Back spines / spikes

Red poison sacks (at the base of the stinger)

Tail

You'll need to do this for each Gear Rex mission. Keep trying, you'll get them.