It's All in the Legs
One of the main differences between prehistoric reptiles and dinosaurs is the position of the legs. Moschops's front legs were splayed out to its sides, like a reptile. Its back legs were placed under the creature's hips, more like a dinosaur.
Semi-erect legsLater reptiles like this archosaur had legs more directly under the body, which could support more weight than those of its predecessor.
Lizard legsMoschops had bent, sprawling front legs like this lizard.
Dinosaur legsThe legs of this dinosaur were tucked under the body, fully supporting its enormous weight. The back legs of Moschops were well under the creature's hips, much like this dinosaur.