Are there any official CR 8 beasts that are not dinosaurs, for the purpose of the Polymorph spell?

Although the party wizard has had a wand of polymorph since finding it in a hand-converted U3: The Final Enemy (before the release of Ghosts of Saltmarsh), she has typically used it defensively, turning enemies into slugs and such. Only recently has she begun to use it offensively. After fighting some carnivorous apes, she turned the 7th-level barbarian in the party into a CR 7 Giant Ape when he was low on HP.

Per the description of the polymorph spell:

The new form can be any beast whose challenge rating is equal to or less than the target’s (or the target’s level, if it doesn’t have a challenge rating).

As a result of that battle, the party has leveled up, and the wizard can now polymorph the barbarian into a beast of CR 8.

Unfortunately, I know of only one CR 8 creature that is a beast – the Tyrannosaurus rex. While RAW there is no restriction on using polymorph to achieve forms that the character has not seen before, it would harm the verisimilitude of my game, in which none of the characters have even heard of dinosaurs.

Do any official published products include CR 8 beasts that are not dinosaurs?