The core of this question is this: Given what we believe we know about the requirements for a tool-using, space-faring race to evolve, how viable would a species that has a hybrid exo/endoskeleton be?
Believed requirements for a tool-using, space-faring intelligent species:
- Dextrous manipulator appendages, at least two (i.e. hands)
- Upright structure to keep manipulator appendages free for use (or some other means of keeping the 'hands' free)
- Centralized nervous system (for more efficient processing)
- Terrestrial: Need controllable heat sources to make advanced materials. i.e. fire
- Varied sensory suite located near brain, focused on vision or vision-like sense
- 'Head' likely located high above ground to allow greater field of vision
- Medium-Monkey-sized or larger (need to be big enough to allow for complex brain)
- Capable of withstanding gravity-escaping accelerations
- Evolutionary need to develop tool-use (apex predators and 'tank' animals have no need to be clever to survive, their physical structure is enough)
I am aware of the limitations and restrictions facing the use of a pure Exoskeleton, including but not limited to: temperature regulation, ability to self-repair, thickness/weight constraints as something gets bigger, and materials concerns. So a pure exoskeletal creature would probably not reach a size great enough to develop intelligence. So, my thought moved to a hybrid: a creature with a mixed endo-/exo- skeleton (like a turtle).
The basic design in my head is this: exoskeletal armoring covering much of the body, particularly the vital organs. I'm not thinking of an 'upright giant turtle' with a shell it can retract into. I'm looking at a creature that has an exoskeletal primary body that is thick enough to withstand day to day abuse, which is fused to an endoskeletal structure that is used within the dextrous manipulator appendages, mobility appendages, and any other 'jointed' location that needs freedom of movement. Those appendages are likely covered in a form of flesh or scales that allow a freedom of movement not permitted by a thick exoskeleton. The basic image in my head is similar to that of plate armor. (note: I'm not talking about an endoskeletal creature with natural armor. Anywhere there is armor, there is no endoskeleton apart from where it connects.)
My mental concept of them seems sound...like something that could actually function and survive, though I have concerns about whether or not a creature with such effective natural armor would even need to develop tool use.
So, reality-check time. Am I missing anything? Is this design for intelligent life sound according to what we currently know of biology, evolution, and physics? Could such a creature survive, and then make it to space?