Xenomorph, Space Jockey, identical body types, which came first?

Since Giger designed the Alien and the SJ,it looks like they are somehow related.While working on Alien,most of Giger's work consisted of bald humanoids with biomechanical skins and a large murial with those humanoids wearing the suits with the simmilar design of the xenomorphs (chest,arms,biceps etc).

But which came first,engineers or the xeno idk.I suppose the original idea that the xenos and SJ's were both connected.

Its nice to see they keep using Giger's old designs.

Looks like they used some of Giger's old Alien concepts to update the engineer design.

While Prometheus was still in development,the engineer architecture was more monolith than biomechanical in look,then they took everything the designed and infused it with biomechanical look to stay truthful to Giger.Somebody discovered some Russian 3D artist that was doing mechanical landscapes,I think his name is Gutalin.Ridley liked his artworks so they hired him from long distance and I think that he did the design of the Juggernaut.

if it is part of theyr anatomy then r they dead engineers standing outside the door that david enters? the last engineer clearly does not put anything on when he climbs up onto the pilots chair which suggests they wear them at all times during flight and in cryo but there is clearly, to me anyway, an empty flight suit next to the door when david first opens it. I wouldn't mind if im wrong and would def go along with the design similarities between the xeno and the engineer