A Trilobite is an Alien creature created in a Med Lab on Prometheus. This creature grow from an alien removed from Shaw, created from some of the black liquid held in urns drank by Holloway and after he and Shaw spent a night together, the creature developed quickly into an Adult Trilobite and shared a resemblance with a Face Hugger.
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Appearances in the following;
This creature developed unchecked in a Med Lab aboard Prometheus and as Prometheus was set on a collision with the Derelict, the Trilobite was ejected along with the Escape Craft landing safely on the surface.
As the Escape Craft landed Shaw went to the landed Escape Craft and as she was there discovered the now Adult Trilobite still in the Med Lab. The Terraformer from the Derelict appeared having followed her aboard the craft, and as he did, Shaw opened the door of the Med Lab releasing the Trilobite. It grabbed and subdued the Terraformer impreganting it and shortly after an alien emerged.
A Trilobite only appears in the film Prometheus. The alien that emerged from the Terraformer is called a Deacon, and shares a resemblance with a xenomorph and a mural found in the Ampule Room from the Alien Temple.
Neville Page conceptual artist on Prometheus designed the small and adult Trilobites with Neal Scanlan studio creating the creatures on set with Richard Stammers visual effect supervisor for Prometheus.
Early concept designs by David Levy featured crustacean influences similiar to a Dicranurus, a genre of ancient arthropod. The creature designers were also influenced by artist Jean Giraud's (best known as Moebius) illustrations for a comic strip and The Long Tomorrow written by Dan O’Bannon and published in 1975.
Although cephalopods were the main influence for the Trilobite, Neville Page did not intend the tentacled monster to directly resemble an octopus.
The small Trilobite was sculpted by Ivan Manzella and built by Simon Williams, Andy Colquhoun and Joshua Lee, with puppeteer design by Matt Denton during it's extraction in the MedPod. It's movements were achieved with a multi-sectioned animatronic spine, the cables that controlled the creature were hidden in the arm and built by Neal Scanlan.
Scanlan’s team inserted the Trilobite animatronic in a silicon model of Shaw's torso and controlled it from below, the creatures extraction was then produced in CGI by Martin Hill from Weta Digital before Scanlan’s team animatronic model again appeared held in a clamp inside the MedPod.
In most digital Trilobites appeared in the final film by Weta Digital with both the 2' and the 18' animated models used for the more complex sequences by Mike Cozens’ team. Matthias Zeller creature’s supervisor at Weta creature animation used a 'layered deformer' approach to the muscle rig that would fire the muscles in tension and relax them in compression, this was then passed through to a 'solver', which would wrinkle skin where it was compressed more. These same tension and compression attributes were passed along to the shading system so that when the skin was taught and tense it would become lighter and shinier, in compression it would become rougher and darker in the folds and the wrinkles. A secondary peeling/flaking skin sat on top of the other deformers and was fixed in place at the base of the peeling skin of the underlying structure but didn’t stretch with the main tentacle motion.
Where the Terraformer is grabbed by the adult Trilobite a combination of CGI and large animated model was positioned so as to seem like the Terraformer was held by the Trilobite, a scene which required the actor to play the role with CGI taking over.