defining technological aliens as having:
- the ability to make and use fire, thus must operate on land
- the ability to make and use tools and carry them over large distances
- a large enough brain to understand and use technology
- a culture conducive to forming societies with technical specializations
one can then expect:
- carbon-based (silicon doesn't cut it), probably with water or ammonia as solvent and thalassogen
- bilateral symmetry quickly becomes advantageous in a chase-and-evade ecosystem
- a head with mouth, nostrils and a brain near forward-facing senses such as taste and vision are advantageous as well...
- lungs and an internal skeleton would be needed by any reasonably large land creature
- at least 4 limbs (2 for tools, 2 for locomotion)
- hands with 3-7 fingers and opposable thumb and forward-facing eyes (for depth perception), probably formed by
arboreal ancestry
- ability to communicate with others of its species quickly and easily
However, this doesn't mean they should look exactly like humans!
There are still plenty of options for variety:
1. biochemistry could be ammonia-based instead of water-based, on a planet with oceans and rivers also made of ammonia
2. aside from bilateral symmetry, general body shape could vary somewhat in terms of length, bulk, segmentation, etc
2. limbs: at least 2 hands and 2 feet, but possibly extra pairs, and maybe extras like wings, tail, ... feet and tail possibly prehensile... hands and feet could have claws so long as they don't get in the way
2.1. locomotion: comfortable on land, but could be partly amphibious or arboreal, maybe be able to switch easily between biped and quadruped, etc
3. skin could be slimy, smooth, leathery, thin or thick, and may be covered with hair, feathers or down, scales (pangolin), armored plates (armadillo), or even a shell (turtle)
4. head: should have forward-facing eyes, a mouth, and probably nostrils somewhere... other senses may be located elsewhere on the body... may have horns, tusks, antennas, eyestalks
4.1. mouth: jaw with teeth, mandibles, beak, straw-like appendage, no jaw (swallows food whole)
4.2. sensory organs: touch, taste, smell, vision, sound/vibration, other (infrared, ultraviolet, magnetic, etc)
4.2.1. vision could be colorblind, or cover different parts of EM spectrum such as infrared and/or ultraviolet
4.2.2. smell and sound/vibration are more flexible, and could be via antennas or distributed throughout the body
5. reproduction and lifecycle could vary a lot, with possibly very distinct phases not all of which have to be technologically capable or even sentient!
more to come
