Excellent sci-fi/horror movie. What are the monsters?

Rating: 8/10 (7 April 2018)

A QUIET PLACE is an excellent, well-scripted and well acted science fiction/horror hybrid movie, in the vein of Alien. You don't see too many movies of that unique Hollywood niche too often.
I'm not going to rehash all the great things about this excellent sci-fi/horror hybrid movie that everyone mentioned. You can read it for yourself. I'll discuss more about the movie's monsters.
SPOILERS:
The movie begins after the creatures have wrought their world-wide destruction and virtually depopulated the planet. The movie never explains where the apex horrid monster predators originated. That was part of the storyline suspense theme. It's possible that in the movie the unfortunate citizens and their governments never discovered the creatures' origins.
For my money you can rule out, 1) supernatural origin, and, 2) earthly origin. There's nothing to indicate some supernatural or preternatural character of the monsters. They operate equally well in daylight and night. The creatures are shown late in the movie to be completely biological fiends. There's nothing to indicate the creatures originated from earth. It would have taken millions of years for such creatures to evolve but more, the biological structure of the creature has no evolutionary antecedent from whence it could have evolved. The physiology and biology of the creatures do not fit any earth lifeform biological architecture, meaning, it couldn't have evolved here. That leaves the last, logical explanation. The monster creatures are of extraterrestrial origin. But that is never confirmed in the movie because the premise is that it doesn't matter where the creature monsters originated; they're here on earth and they've killed off virtually all humans but also prey on animals as well.
As you're sitting in the theater, you can piece together the unexplained beginnings in your own mind, that predate the starting date of the movie, "89 days". Looking at all the missing people signs and scattered newspapers give you an idea of what happened over 89 days ago. That is when the monster creatures arrived/appeared on earth, perhaps accidentally introduced from a crashed alien cargo spaceship. The creatures are sightless and rely almost solely on their extreme keen hearing, as much as humans rely on eyesight. At first the creatures keep out of sight and stay low. People begin disappearing here and there and missing people signs go up. At some point in time the creatures are probably more numerous and more bold when they discover just how easy prey humans are. The creatures emerge from the shadows and openly attack people, day and night. The world's governments are caught totally by surprise. The creatures prove extremely difficult to kill, their exoskeleton is armored, they possess extreme speed and agility and their bodily limbs and structure are a whirling mass of sharp, knife-like claws and razor sharp teeth. Humankind has encountered an apex predator far above them. It's impossible for humans not to make sounds and in little time the cities and towns have been extinguished of people by these monsters.
I can't help but feel the same as another poster here. The concept of the blind, keen-hearing monster creatures seems very derivative of the creatures from the TREMORS movie series. The first creatures were subterranean and hunted by sound and vibration. The next evolved generation of those creatures emerged from underground and had developed two legs and hunted by opening the tops of their heads and detecting by heat signature. The monster creatures in A Quiet Place do the same and that shows the weak spot in their armored carapace. Not only do the monster creatures open the sides of their heads to expose their auditory organs for better hearing, they often open up their heads like a flower pedal for optimal detection, but it exposes the soft, vulnerable inner parts. I won't give away more but you can fathom the creatures' ultimate weakness and how it's finally used against them. My advice. Go watch the movie and find out for yourself.