Diaries of a Speculative Biologist

The idea of land-dwelling cephalopods was most popularized by the television program The Future is Wild. The show introduced the world to several species: the swampus, an octopus descendant; the squibbon, a small arboreal squid with high intellect; and the megasquid, a massive multiton creature dwelling the future's northern forests. These future finned molluscs are all fantastic and unusual, but are not very likely to evolve, as will be detailed further on in this article.

The walking-squid (or ambuloteuthid)

The background behind the walking-squid is rather elaborate. As with most land-squid concepts, such a creature would require at least 200 million years or so for the cephalopods to come on land with at least one, if not more, extinction events having occurred between that time and modern day.

It has made several major adaptations to a terrestrial lifestyle. First, the mantle has vascularized and become roughly equivalent to lungs with the gills becoming (originally I had designed it so that the gills entered and exited the body, taking in oxygen with every flicker, but such a behavior would cause the gills to dry and stick together and outweigh the benefits of the increased exposure to air). Three pairs of legs have been re-purposed for walking on land with a rigid muscular/cartilaginous system and powerful suckers at the tips of the legs for more support. A fourth pair of legs has been adapted for the manipulation of food and other objects. The rostrum (molluscan beak) has been enlarged severely and is attached to a long proboscis that aids in feeding. Even the siphon has been modified, now used for vocalization rather than for propelling in water. Although having made all these adaptations to land, the ambuloteuthids still spend a good deal of their lives in the water as larve and adolescents as these cephalopods live an amphibian-like lifestyle.

Now, this concept still has a number of problems. First, for such a muscular system to develop, it would require a complete restructuring of the squid's muscles and cartilage. And even after that there would be no guarantee that the structure of the legs would be rigid enough to support the body. Second, there are countless other species that would venture on land long before the cephalopods (the strangest of molluscs) would take that evolutionary leap. Finally, the gills and mantle may not be suitable for the derivation of lung-like structures, so the land-squids might find themselves about of breathe after they climb onto shore.

Denizen of the canopy, the slothsquid

The concept of the slothsquid is basically an alternative to TFIW's elegant squibbon. This cephalopod has taken on a slow, arboreal lifestyle. Rather than being an active hunter like its marine ancestors, the slothsquid is a herbivore that uses its tentacles to grasp fruits and vegetation. The slothsquid has a few advantages over the ambuloteuthid. First of all, it doesn't need nearly as strong limbs; the rigidity needed for a terrestrial lifestyle is not nearly as necessary for an arboreal species. The highly adhesive suckers on its legs allow it to cling to branches and tree trunks. Also, the slothsquid lives in a humid, tropical environment where it would be easier for a creature with a combined gill-lung breathing system to acquire air to breathe. Still, the evolutionary probability of such a squid is not very high.

The best bet

The most likely terrestrial specialization for cephalopods is not large walking squids or climbing slothsquids. Instead, it is for small, slow-crawling octopi. Such octopi would not need to make major adaptations for terrestrial life. They would likely only need small, primitive lungs in order to breathe on land. The advantages for coming on land could vary: a way to escape predators, a way to catch terrestrial prey, or even an extra route to reach fresh breeding or feeding grounds. Such mollusc species could evolve as soon as only several million years in the future if they are to be residents of island environments. Otherwise, the horizon does not seem too bright for terrestrial squids and octopi.