Many commentaries about "behemoth" from the Book of Job (Job 40:15-24), believe it was a "hippopotamus". A animal that inhabits rivers and lakes in Africa. But is this the creature that God was showing Job.
Creationists have long believed Job's behemoth was some type of extinct creature. The revealing part of Job's account is the implied size, diet, habitat, and then the exceptional statement, "He moveth his tail like a cedar" (Job 40:17a). This description tells us that its tail was a lot different from the hippopotamus. The hippopotamus has a tail but it does not even come close to that of a cedar (a tall evergreen tree). The hippopotamus has a stubby tail about 22 inches in length.
It was not until very recently that modern science discovered that many of the dinosaurs would walk holding their tails parallel, stiff as a beam. They did this, most likely, for balance. These creatures needed a counterbalance when they walked so that would not topple over. Just go to your local natural history museum and look at some of the dinosaur fossil specimens. Carnegie Museum of Natural History in Pittsburgh has an excellent collection of dinosaur fossils.
For the Book of Job to record that this gigantic herbivore, which was one of the largest of God's creations according to this description, had the ability to make its tail stiff like a cedar is remarkable.
Job recorded only what he saw and his eyewitness account of this living creature does not fit a hippopotamus description. Read Job 40:15-24, for yourself. Whatever this creature was, it is extinct now. But its description fits a creature that could possibly be a dinosaur.
In the book, 'Biblical Cryptozoology: Revealed Cryptids of the Bible' (ISBN : 978-1-4415-2267-2) it has a chapter about behemoth, "Behemoth : Those Terrible Lizards", pages 11-17. The chapter gives a possibility what behemoth could be. Whatever the creature was God said that the creature was "chief of the ways of God" (Job 40:19a), meaning it was a creature that God wanted Job to know that it was different from all other creatures in the animal kingdom. That is why God said, "Behold now behemoth, which I made with thee, he eateth grass as an ox" (Job 40:15).