ANSWER: There are three specific places where dinosaurs may be mentioned in Scripture. Two of these passages are in the book of Job, which some commentaries state is the only Old Testament writing that possibly mentions these large reptiles (Willmington's Complete Guide to Bible Knowledge – Old Testament Survey, etc.).
The first possible mention of dinosaurs is in Job 40, where God is directly quoted as stating the following about a mysterious beast known as Behemoth.
15. "Now behold the behemoth, which I made along with you; he eats grass like an ox; 16. See, now, his strength is in his loins, and his force is in the muscles of his belly. 17. He moves his tail like a cedar; the sinews of his thighs are knit together. 18. His bones are like tubes of bronze; his ribs are like bars of iron." (Job 40:15 - 18, see also verses 19 to 24)
The second reference is in Job 41 where God speaks of a creature referred to as Leviathan.
Many Scriptural scholars feel that these references are talking about the hippopotamus and the crocodile, respectively. Other scholars of a more scientific mind suggest that they are talking about dinosaurs.
1. "Can you draw out the leviathan with a hook, or hold down his tongue with a cord? 2. Can you put a ring into his nose, or pierce his jaw with a gaff hook? . . ." (41:1 - 2, also see rest of chapter)
The third possible reference to these reptiles is in Genesis 1:21 where it states that God created "great sea creatures." This may refer to large whales or very large marine creatures. The situation with these three references is not clear and either side may be correct.
The fossil record indicates that organisms existing thousands of years ago (before Noah's flood) grew large. Examples of these are, of course, dinosaurs, giant cave bears, giant sloths, giant dire wolves, etc. From a biological point of view, many reptiles also have the unusual proclivity of getting larger as they age.
Dinosaurs are simply large reptiles that have lived a long time. These reptiles existed before the flood and to a lesser extent after the flood. The record found in fossils indicates that the present planetary ecosystem is incapable of producing and supporting large bodied reptiles and mammals.
The word of God states that not only would mankind be destroyed but also the earth was to be wrecked (Genesis 6:13). Apparently, before the flood destroyed the antediluvian ecosystem, the earth could produce large bodied long living reptiles that we call dinosaurs (the word means fearful or monstrous lizards).
Will they return to earth?
Will dinosaurs exist again when God creates a new heaven and a new earth (Revelation 21)? If he recreates all extinct creatures, they will then return.
Some people have postulated that these large creatures will not be in the New Heavens and Earth because they are not mentioned as being alive during the Millennium (Jesus' reign on earth for 1,000 years). Those who make this argument forget that God's new creation will be first cleansed by fire.
12. Looking forward to and striving for the coming of the day of God, during which the heavens, being on fire, shall be destroyed, and the elements, burning with intense heat, shall melt? 13. But according to His promise, we look forward to a NEW HEAVEN and a NEW EARTH, in which righteousness dwells. (2Peter 3:12 - 13, HBFV)
All this means that if any creature exists after the new universe is created it would have to be recreated by the Eternal. There is nothing in the Bible to indicate that God could not repopulate the earth with some large reptiles like dinosaurs if he wanted to.