Quote Originally Posted by drone View Post
The facehugger "eggs" look manufactured, not laid, and the facehugger itself looks quite different. I wonder if this is the Mark I/Mod 0 version of the alien, or just the result of space jockey infestations.
Spoiler Alert, click show to read: 
there is some belief it's a space jockey thing that we mess with or have stolen.

If I remember correctly the cannon for the whole series is that the aliens take some of there structure/form from the host species therefore since we have only seen them infect mammals it folows the space jockey ones might be differ.