The beast had qualities of a bear and a boar and moaned like the creature in the book, while also providing a visual terror not present in the novel.
The bear moaned in horrific fashion and cried out with the voices of its victims as it terrorized the expedition and thinned its ranks.
It is kind of funny that Jeff VanderMeer is so fearful of wild boars that, like Batman, he wanted others to share his dread by including a boar in Annihilation.
So clearly Alex Garland took some of these disparate elements and came up with the bear-like creature in the film.