Behemoth has the following attributes according to Job 40:15-24 (Job was written approx. 1600 BC and is the oldest book of the bible. The very first dinosaur discovery was made in the late 1600 AD and then more discovery in the 1800s. Over 3000 years difference. Behemoth is believed to be a sauropod dinosaur.)
It eats grass like an ox.
It moves his tail like a cedar. (In Hebrew, this literally reads, he lets hang his tail like a cedar.)
Its bones are like beams of bronze, His ribs like bars of iron.
He is the first of the ways of God.
He lies under the lotus trees, In a covert of reeds and marsh.
Leviathan has the following attributes according to Job chapter 41, Psalm 104:25,26 and Isaiah 27:1. This is only a partial listing.
No one is so fierce that he would dare stir him up.
Who can open the doors of his face, with his terrible teeth all around?
His rows of scales are his pride, shut up tightly as with a seal; one is so near another that no air can come between them; they are joined one to another, they stick together and cannot be parted.
His sneezings flash forth light, and his eyes are like the eyelids of the morning. Out of his mouth go burning lights; sparks of fire shoot out. Smoke goes out of his nostrils, as from a boiling pot and burning rushes. His breath kindles coals, and a flame goes out of his mouth.
Though the sword reaches him, it cannot avail; nor does spear, dart, or javelin. He regards iron as straw, and bronze as rotten wood. The arrow cannot make him flee; slingstones become like stubble to him. Darts are regarded as straw; he laughs at the threat of javelins.
On earth there is nothing like him, which is made without fear.
Leviathan played in the great and wide sea (a paraphrase of Psalm 104 verses 25 and 26)
Leviathan is a reptile that is in the sea. (Isaiah 27:1)
Note: The word translated reptile here is the Hebrew word tanniyn. This shows that Leviathan was also a tanniyn (dragon).