Well aliens are a term to refer to anything off this world. Otherwise if you want see aliens right on our planet look in the sea. Creatures that don't live in light, creatures that don't breath, etc... all kinds of cool weird stuff.
These 'nephelim' are a riddle in the bible. Some have tried to attribute them to 'angels' that 'fell' and some have attributed them to being beings like us or similar and then later demons if you read some descriptions of it.
In the qur'an God describes three creations, besides animals/the world. Three intelligent creatures that is. Humans made of the earth and water... with desires and intellect. Angels made of light and more like robots that serve God and obey God without disobedience, no desires. And Jinn, made of a smokeless fire and also with desires like humans.
Now most atheists will ridicule this.. however we know that in fact our body is composed largely of water... and of earth's elements. God speaking to us humans who would have not had all knowledge of the unseen, didn't have to talk to us about 'elements' or molecules.. but saying we are made of earth and water as enough to make later generations think.
The angels being made of light? Well.. again people may try to ridicule.. but it's not as far fetched. What does it mean yet we don't know. And likewise for the jinn. Today as far as light is concerned, we use it to transmit information, we use it for presentations, we are trying to make holograms. And there is SO MUCH that we don't see with the naked eye that happens in this very background of the universe.
Now reading about the nephelim makes me think of jinn somewhat.. as they have desires and their father Iblis, is the father of Jinns. Devils/demons/Satan. Iblis was in heaven, close to God, but he rebelled in arrogance and pride when asked to bow down to the first human created by God saying 'he is better' as he is made from fire while this thing is made from earth's mud lol. He was cast out of heaven and promised hellfire... and he vowed that until that day he will try to prove that humans are worse than him by leading them astray from God.
Similarly there is such an explanation in the bible that these demons will try to lead astray people until the day of judgment according to the bible.
Now as far as these elongated skulls go. These americas people used to have some bizzare traditions. Although they were 'intellegent' and advanced, they were idol worshippers, doing human sacrifices, doing weird rituals.
What some have attributed to aliens being worshipped, could very well be these humans creating idols out of angels who came to them and then worshipping them instead of God. And in some cases worshipping the demons.
Their culture seems to radiate with illustrations of serpents (usually culturally everywhere representative of evil.. except in china as 'blessing') and flying winged creatures also present in mesopotamia.
