A good chunk of the cast of "Black Panther" got together to ring in one of their co-stars' 40th birthday ... but they probably had more reason to celebrate than just that.
Danai Gurira -- who plays Okoye in the upcoming film -- turns the big 4-0 Wednesday, but she and her cast members rang in her fab 40s on Monday night in NYC instead.
They were partying it up at the Boom Boom Room atop of The Standard, High Line hotel -- and from the looks of these shots ... it appears most of the major "Black Panther" actors were there, sans Michael B. Jordan.
Danai and co. certainly seemed chummy in celebration, and why shouldn't they? Their new Marvel superhero flick is expected to have a massive box office opening, with projections of up to $165 million domestically for its debut weekend.