Board Thread:Warhammer 40k General Discussion/@comment-6589306-20130228113457/@comment-6078851-20130304165551

i also don't consider predator 2 to be 'official' lore, for aliens or predators (it's also a terrible film, in my opinion the novel 'predator: concrete jungle' is what pred 2 should have been). however the bleached xeno skull trophy is unquestionably endoskeletal. as we all know aliens do have a lip-like structure around the gum area, they also have visible, exterior tendon/ligament-like structures around the jaw. taking these into account i'm willing to accept that they may actually have an endoskeletal skull.

for the rest of the body, i'm still not convinced. every piece of information about xeno physiology repeatedly mentions their exoskeleton while making no mention of endoskeleton (excluding pred 2). also when their bodies are blown open they 'pop' like insects, and in the movies you can see organs but no endoskeletal structure.

legion - you're right about fluidity and subtlety of movement that only comes from an endoskeleton, but you're not totally right about reaction times. granted many insects aren't particularly quick creatures but when it comes to certain predatory insects - spiders in particular (and before anyone says anything i know they're arachnids not insects) can move at a speed that endoskeletal creatures can't match because of the positoining of the locomotive musculature. endoskeletal musculature directs locomotive force inwards which the skeleton then transmits outward, while exoskeletal musculature directs locomotive force outwards to the skeleton and so doesn't need further transmission, which allows for a faster reaction time between the nerve impulse and movement.

one final note on endo/exo - facehuggers. facehuggers are completely endoskeletal which is maybe the best pointer for an adult having an endoskeleton.

one final final note, lets not forget that an extraterrestrial lifeform doesn't have to play by terrestrial rules, for example xeno's are silicon based life.