theropod vs saurischian

theropod and saurischian both are nouns.

Word	Noun	Adjective	Verb	Adverb
theropod	Yes	No	No	No
saurischian	Yes	No	No	No

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

theropod: any of numerous carnivorous dinosaurs of the Triassic to Cretaceous with short forelimbs that walked or ran on strong hind legs
saurischian: herbivorous or carnivorous dinosaur having a three-pronged pelvis like that of a crocodile

Other hypernyms of theropod include saurischian dinosaur.

theropod (noun)	saurischian (noun)
any of numerous carnivorous dinosaurs of the Triassic to Cretaceous with short forelimbs that walked or ran on strong hind legs	herbivorous or carnivorous dinosaur having a three-pronged pelvis like that of a crocodile