If I had to guess at two things that are wrong, I'd go with the Predatory behaviour and the 12 foot height. Predatory behaviour might have just been a simple overlook on your part, and there might be multiple different height estimates. Am I correct in my elimination choices?
Not being a predator would explain the uselessness of the claw, so I'll assume that's right. But if 12 ft tall is right, then that means that it isn't from the Cenozoic... Which would mean... A Pterosaur, perhaps? Or maybe one of the early Aves?