At Job 40:17, is the "Behemoth" a Dinosaur or a Hippopotamus?

Not only does the context Job 40:17-23 describe the behemoth as similar to a hippopotamus, but a number of Bible translations (AT, La, Ro, NW, JB, RS) actually use the word “hippopotamus” in the main text or in footnotes to identify the creature referred to by God.

The tail of a hippopotamus is fairly short, measuring about 18 to 20 inches. But verse 17 says that it's the actions of its tail that are compared to a cedar, not that it looked like a cedar. This corresponds well to the hippopotamus because the animal has the ability to set its thick tail rigidly upright or swing it about like a tree.

Additional Reading:
Animal Creation Magnifies Jehovah (w06 1/15 pp. 13-16; "Behemoth Glorifies God")

BEHEMOTH (Insight-1 pp. 280-281; Watchtower Online Library)

Dinosaurs - When Did They Live? (Search For Bible Truths)