Job 40:15-17
15 Behold, Behemoth, which I made as I made you; he eats grass like an ox.
16 Behold, his strength in his loins, and his power in the muscles of his belly.
17 He moveth his tail like a cedar; the sinews of his thighs are knit together.
Just to clarify, as I have done a theological study on this exact subject for a talk I was invited to, the current consensus is that whatever it was described in the Book of Job was not necessarily an animal with a long tail. The phrase "he moveth his tail like a cedar" (sometimes "stiffens his tail") is translated from a Hebrew word which has an action verb. The Lebanese cedars known to the Hebrew audience at the time are very flexible trees so using them to compare to something bending makes sense. Whether the subject described had a tail that was big like a cedar tree is not clarified. But other passages describing it as having external genitalia ("his stones"), eating grass like an ox would (chewing), and ancient illustrations depicting it do support the entity described, real or mythic, as mammalian.
That's why the theological consensus, if this is not a mythical entity like the Greek Chimera, is that the description is of some kind of hoofed animal or elephant. So the idea that it has a huge tail like a cedar and that disqualifies a large mammal is not exact to the text.
