New Defender's Study Bible Notes
40:15 behemoth. The word “behemoth” means, simply, “huge beast,” and commentators commonly take it to be either an elephant or a hippopotamus. The subsequent description, however, fits neither of these, nor any other living animal. On the other hand, it seems to match the probable description of a great land dinosaur, such as the tyrannosaurus.
40:17 tail like a cedar. No elephant or hippo has a tail like a cedar! This description supports the theory mentioned above that a behemoth may have been a dinosaur (see notes on Job 40:19).