Ancient Dinosaur Discovery Or Thunderbird?

This bird-like/dinosaur-like skeleton was found in a Western US cave in 2006.  It was about a half mile into the cave within a very small crawlspace opening. They had some cans and bottles with them that they put out and proceeded to take photos. There was no way they were leaving the cave with this item. It had mineralized, part of the trachea was there and very brittle, some hide on it appears to still be on it. The finders did not really understand what they had found, but shared it with someone who recognized it was very unusual, MK Davis. MK was kind enough to share this with me to put out there for the public to puzzle over and see if anyone can identify what this was.

It was a large - what at the time looked like an ostrich sitting on its haunches, head missing, tail missing, upper arms missing (notice the cross bone over the ribs where a velociraptor would have attachment of the forearms) and lower part of the hind leg articulation is missing. When compared to a velociraptor skeleton (below) it looks pretty damn close.

This is one of those mysteries that we hope to settle and I would seriously appreciate any input into what this was.

Thank you Jim Heater, host of Paranormal Geeks Radio, for cleaning up the pics with this clearer version above.

A thank you to Bruce Hoch, who mentioned the lower legs and skull might have been taken by a shaman or tribe member long ago as trophies for the skull and claws or for powerful symbols. Very good. Keep the theories coming --

In fact, this might be an explanation for the legend of Thunderbirds and the kernel of truth it could be based upon if such finds as these talons and skulls were found and sought after, they might make stories of what the origins of these strange things were. Hmmmm 

One more possibility


Update #2
Update #3 - see him standing erect 
Update #4 - Expedition planned
Update #5 - More on Expedition