An Ankylosaurus with a siege tower on its back!
This is two models from the Autodesk 123D gallery, mashed up in Meshmixer. The dino is the Ankylosaurus and the siege tower is from the Siege Engine Chess set. I edited it in 123D Design online, adding brackets to reduce unsupported overhangs. That version is here.
Meshmixer works best with quite dense meshes, so the Siege Tower was imported into Meshlab and a subdivision remeshing filter applied. Exported from Meshlab as an OBJ file and combined with the dinosaur.