The majority of you guys are morons. There is no way that bone under the jaw is a bone that it choked on. That would imply that it died while eating, so where is the rest of the animal that is being eaten? Also, the animal is clearly very well articulated so the chances are low that it is a disarticulated limb bone. Especially, when all of the limb bones are accounted for. Also, the bone under the base of the tail is the ischium stupid.
To answer the question of why more specimens aren't found so complete is simple. There are too many variables. Everything needs to be perfect to get a specimen like this one. I've seen many dinosaur skeletons and few had an intact hyoid bone or sclerotic ring. This makes the present specimen very valuable.