The first nonavian dinosaur discovered that is known to be capable of running and swimming is quite honestly bizarre looking. Researchers made a digital 3D image of the fossil with synchrotron radiation scanning while it was still embedded in stone. From the Mongolian fossil they were able to determine that the dinosaur has a long, swan like neck, flipper-like forelimbs, and amphibious ecomorphology. In other words, it looked like a duck. Halszkaraptor escuilliei, as it has been named, lived between 75 million and 71 million years ago, and used its sinuous neck to catch fish. Like the tyrannosaurs, H. escuilliei was a theropod – a group of carnivorous, bipedal dinosaurs.
https://sketchfab.com/models/c14b1ee2688d4406a9a0b16d223aff51/embed?autospin=0.2 Raptor by Royal Belgian Institute of Natural Sciences on Sketchfab
A 3D rendering of the fossil, still partially encased in stone.
(Cau, Beyrand, Voeten, Fernandez, Tafforeau, Stein, Barsbold, Tsogtbaatar, Currie, & Godefroit, 6 December 2017, Synchrotron scanning reveals amphibious ecomorphology in a new clade of bird-like dinosaurs, natureresearch journal)