Long ago nearly all animal life was in the sea. There were plants and arthropods on land, but no chordates (the big group including fish, amphibians, reptiles, mammals, and birds). At some point, perhaps both to escape predators and find new sources of food, some lobe-finned fish evolved stiffer limbs to briefly haul itself onto the beach, and eventually, evolved into amphibians (and later reptiles and mammals).
Let’s say that through some historical accident, chordates don’t happen. And let’s say the dominant medium-to-large life form in the sea are cephalopods. It could still be advantageous, for the same reasons as for those lobe-finned fish, for some species of cephalopod to evolve the ability to haul itself onto land. How might cephalopod evolution progress? What traits would/could these land pioneering cephalopods evolve? How would they stiffen and strengthen their bodies to counteract gravity? How would they keep from drying out? How would they breathe in the air?
This is all speculative, and just for fun, of course.
Although not cephalopods, slugs and snails are molluscs, and do OK on land, so it’s not impossible.
ETA: There was some speculative documentary show about future evolution that covered this - can’t remember what their putative future land cephalopods looked like though.
There is no inherent reason that cephalopds would have to emerge on land to develop technology and industry, and in fact there are good reasons that they would remain in the ocean. Of course, their technology would not be based on exothermic combustion and tin or iron metallurgy. Structures would likely be built from precipitates of carbonate salts, and energy would be from electrochemical interactions using the ambient seawater as the electrolyte. Advances technology would probably be biological in nature. The biggest limitation on cephalopods and the reason why molluscs are so limited in their niches on land is their use of the relatively inefficient hemocyanin for oxygen transport, which has required significant “engineering” (evolutional adaptation) to overcome for the more complex octopus and squid physiology.
In answer to the questions of the o.p.–adaptations to land dwelling–solutions would probably be analogous, if not identical to those made by vertebrates, e.g invaginating gill structures or oxygen transport interfaces into lungs, developing a relatively impermeable integument, creating pressure-stiffened hydraulic structures in lieu of a skeletal system, et cetera. We can’t make destail predictions because we lack any basis (land based molluscs are largely similar to their marine cousins) but there are many speculative solutions to these prronlems aside from the specific (and highly varied) paths adopted by vertebrates.
I want to say there was a Steven Baxter book that ended in a far-future world dominated by cephalopod descendents, too. Not “Evolution”…maybe one of the “Manifest:” series?
Manifold:Time. The squid (Sheena?) was genetically altered as being an idea candidate for a space-residing organism, but without spoiling the story, manages to subvert the plans of her human minders.
For one thing, I suspect that many cephalopods would probably take to the trees before they mastered the ground. It’s not a big reach (hah!) for an octopus to start swinging monkey-like through the trees. Being good at that would require fewer body changes than emulating terrestrial animals like a wolf or a cow. Perhaps they’d get their start in mangrove swamps.
Given the number of cephalopods with umbrella-like arms, it also seems like tree-dwelling varieties might adapt to short-distance gliding fairly easily.
For moving around on land, size would be very limited until they developed some sort of skeleton to support substantial weight. I suppose the existing internal bones (like a cuttle bone) could be the basis, but I don’t really know how that would work.
Seriously, octopuses can move around on land just fine now, as anyone who has tried to keep an octopus as a pet can verify. What it can’t do is carry a significant load. But clearly, their strength (which can be attested to by divers who have interacted with them) is quite impressive for their size, as is their incredible flexibilty and manipulation ability.
For the kind of technology base that we have, which is heavily dependent upon high temperature heat engines and metallurgy, sure. For a technology that is based upon and precipitated structures and organic “machinery”, it is much more viable. When you want to consider not the path that development did take (in our case) and consider other paths that intelligent life could develop an industrial technological base, you have to throw the preconception of ending up at our particular solution away and consider other alternatives which might not look like industry to us (e.g. it doesn’t give us iPhones and DeLoreons) but does provide a means for said creatures to create tools that allow them to manage and control their environment as well as expand their native physical and intellectual abilities, which is the very definition of technology.
I had this poster on my office wall for several months and you would not believe the number of people who commented in complete seriousness that they didn’t know octopuses could live in trees. I finally took it down after someone of corporate significant was making the rounds and made the same comment and I had the embarrassing task of explaining that it was actually a joke.
I think the problem is that it’s just so plausible. Nature is chock full of truly strange combinations, many of which are less weird than an octopus hanging out in a rain forest. It’s certainly no stranger than coconut crabs.
When you want to consider not the path that development did take (in our case) and consider other paths that intelligent life could develop an industrial technological base, you have to throw the preconception of ending up at our particular solution away and consider other alternatives which might not look like industry to us (e.g. it doesn’t give us iPhones and DeLoreons) but does provide a means for said creatures to create tools that allow them to manage and control their environment as well as expand their native physical and intellectual abilities, which is the very definition of technology.