megalosaur vs theropod dinosaur

megalosaur and theropod dinosaur both are nouns.

Word	Noun	Adjective	Verb	Adverb
megalosaur	Yes	No	No	No
theropod dinosaur	Yes	No	No	No

As nouns, theropod dinosaur is a hypernym of megalosaur; that is, theropod dinosaur is a word with a broader meaning than megalosaur:

megalosaur: gigantic carnivorous bipedal dinosaur of the Jurassic or early Cretaceous in Europe
theropod dinosaur: any of numerous carnivorous dinosaurs of the Triassic to Cretaceous with short forelimbs that walked or ran on strong hind legs

Other hypernyms of megalosaur include bird-footed dinosaur, theropod.

megalosaur (noun)	theropod dinosaur (noun)
gigantic carnivorous bipedal dinosaur of the Jurassic or early Cretaceous in Europe	any of numerous carnivorous dinosaurs of the Triassic to Cretaceous with short forelimbs that walked or ran on strong hind legs