Some thought Behemoth is amphibious.
But some later and very learned men take the leviathan to be the crocodile, and the behemoth to be a creature called the hippopotamus, or river-horse, which may seem to be fitly joined with the crocodile, both being very well known to Job and his friends, as being frequent in the adjacent places, both amphibious, living and preying both in the water and upon the land, and both being creatures of great bulk and strength.
behemoth—The description in part agrees with the hippopotamus, in part with the elephant, but exactly in all details with neither. It is rather a poetical personification of the great Pachydermata, or Herbivora (so "he eateth grass"), the idea of the hippopotamus being predominant. In Job 40:17, "the tail like a cedar," hardly applies to the latter (so also Job 40:20, 23, "Jordan," a river which elephants alone could reach, but see on Job 40:23). On the other hand, Job 40:21, 22 are characteristic of the amphibious river horse. So leviathan (the twisting animal), Job 41:1, is a generalized term for cetacea, pythons, saurians of the neighboring seas and rivers, including the crocodile, which is the most prominent, and is often associated with the river horse by old writers. "Behemoth" seems to be the Egyptian Pehemout, "water-ox," Hebraized, so-called as being like an ox, whence the Italian bombarino.
Barnes also agrees:
It is an amphibious animal, or an animal whose usual resort is the river, though he is occasionally on land. This is evident, because he is mentioned as lying under the covert of the reed and the fens; as abiding in marshy places, or among the willows of the brook, Job 40:21-22, while at other times he is on the mountains, or among other animals, and feeds on grass like the ox, Job 40:15, Job 40:20. This account would not agree well with the elephant, whose residence is not among marshes and fens, but on solid ground.
After the description of Behemoth in Job 40, it is immediately followed by the description of Leviathan in Job 41.
"Look at Behemoth, which I made along with you and which feeds on grass like an ox.
1“Can you pull in Leviathan with a fishhook
or tie down its tongue with a rope?
Crocodile and hippopotamus are often paired together by ancient writers. Then perhaps Leviathan is a crocodile and Behemoth is hippopotamus.
As they are here grouped together in the argument, it is probable that they belong to the same class; and if by the leviathan is meant the "crocodile," then the presumption is that the river-horse, or the hippopotamus, is here intended. These two animals, as being Egyptian wonders, are everywhere mentioned together by ancient writers; see Herodotus, ii.-69-71; Diod. Sic. i. 35; and Pliny, "Hist. Nat." xxviii. 8.