It's Not a Platypus

The theropod dinosaur Chilesaurus diegosuarezi was a temporal contemporary of the Morrison and Tendaguru dinosaur faunas, and in its own time may have seen flocks of Pterodaustro fly overhead on their way to their feeding/nesting grounds in ancient Patagonia, in what are now southern Chile and Argentina.

The dinosaur is an oddity by composition, with the hips and teeth of an ornithischian, and the jaws, legs, and arms of a sauropodomorph, but the neck -- and importantly, the ancestry -- of a theropod. Hidden in the strangeness is the most extreme anatomical development for processing vegetation in a theropod dinosaur shy of birds themselves, and possibly therizinosauroids.

Chilesaurus tells us that dinosaurs can still get odder and odder.