Yes, HADROSAURS is a Scrabble word!

Letter values in Scrabble US: H 4, A 1, D 2, R 1, O 1, S 1, A 1, U 1, R 1, S 1.

Is it a valid word?

HADROSAURS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

any of numerous large bipedal ornithischian dinosaurs having a horny duck-like bill and webbed feet; may have been partly aquatic

Also: duck-billed dinosaur.

Not playable in Scrabble US: HADROSAURUS.