Genesis: 6:1-7 
1 And it came to pass, when men began to multiply on the face of the earth, and daughters were born unto them,

2 That the sons of God saw the daughters of men that they were fair; and they took them wives of all which they chose.

3 And the LORD said, My spirit shall not always strive with man, for that he also is flesh: yet his days shall be an hundred and twenty years.

4 There were giants in the earth in those days; and also after that, when the sons of God came in unto the daughters of men, and they bare children to them, the same became mighty men which were of old, men of renown.

5 And God saw that the wickedness of man was great in the earth, and that every imagination of the thoughts of his heart was only evil continually.

6 And it repented the LORD that he had made man on the earth, and it grieved him at his heart.

7 And the LORD said, I will destroy man whom I have created from the face of the earth; both man, and beast, and the creeping thing, and the fowls of the air; for it repenteth me that I have made them.

Often the biases and presuppositions we bring into a matter prevent our understanding and acceptance of its face value and patient meaning. Modern Christians have often attempted to make this passage in Genesis more palatable intellectually by explaining the "sons of God" as Sethites and the "daughters of men" as Cainites, with their union representing the breaking down of the wall of separation between believers and unbelievers. Another interpretation which avoids the supernaturalistic implications is that the phrase "sons of God" referred to kings and nobles, in which case the commingling so described is merely an account of royalty marrying commoners. This passage is not the first to be met with a naturalistic attitude as such. The miraculous parting of the deep waters at the Red Sea, in which God provided a way of escape for the Israelites fleeing Egypt during the Exodus has been explained by liberals as an event whereby "a shallow swampy flood plain was drained during an unusually low tide accompanied by a particularly strong hot dry desert wind which dried off the land, thus permitting the Israelites to walk on dry ground at the shallow extremity of the Sea of Reeds."

 Yet the account in Exodus describes something startlingly different; a miraculous and dramatic division of waters where "the children of Israel went into the midst of the sea upon dry ground: and the waters were a wall unto them on their right hand, and on their left" (Exodus 14:21-22). In our present age the "scientifically impossible" is most often rejected outright anyway. In another case, unusually large and powerful animals, referred to as the behemoth and the leviathan, are described in Job 40:15-24 and 41:1-34. In the past they have been reckoned by Bible commentators to be descriptions of the hippopotamus or whale, yet neither of these creatures even closely fits the careful description of the beasts given in this passage of Scripture. It was only fairly recently realized that the behemoth and leviathan were large land animals, namely dinosaurs. Since the science of dinosaurs in our age is a fairly recent paleontological development, dating back only to the middle of the last century, most of the early writers of which our present commentaries are based had no knowledge of these creatures preserved in the fossil graveyards of the Earth. Had they taken God's word at face value and studied the descriptions of Job more carefully our knowledge and science of dinosaurs might very well have come at a much earlier time. Even the literal interpretation of the vast longevity of the antediluvians, who lived to such great age of nearly a thousand years instead of being cut off at three score and ten as in our age, is most often brought into question if not rejected outright by some theologians and Bible students. Regarding Genesis 6:1-4, none of the naturalistic interpretations, however, explain why the progeny of such unions would be "giants" or why they would lead to universal corruption and violence. Although Scripture does teach that believers should not wed unbelievers (II Corinthians 6:14; I Corinthians 7:39), there is no intimation that this particular sin is unforgivable or necessarily more productive of general moral deterioration than other sins. Regardless of intellectual difficulties, it is clear that something most remarkable, beyond the normal and natural, is described in Genesis 6:1-4.
Several of the Ancient text refer to man's  sexual encounters and altering states of animals. Remember these beings are part angel with knowledge of the Heavens. They were not just having sex with animals but knowingly maniplusting their genes.  Everything imaginable is done here. Another reason why God is sorry He made man. Can this offer an answer for the Dinosaurs and why they all died at the same time?