Speculative Experiment - Land Colonists

 I decided recently to play around with the concept of fully aquatic and marine animals managing to colonize land, as some had many millions of years ago. Currently such a thing is unlikely because so many groups of animal dominate the land already, but what if some exclusively aquatic groups were presented with an opportunity to colonize an island or landmass, free of competition? Such a thing might happen after a major extinction event, or in a Panspermic setting.

So here we go:

Firstly, Cambrian invertebrates present an interesting potential for a completely different terrestrial colonization event.

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Sidneyia, a primitive Chelicerate, could become analogous to Insects.

The unique Opabinia may become a somewhat bizarre analogue to the centipede.

Anomalocaris may be the apex predator of this setting, with crab like legs and beartrap-like jaws.

Another Chelicerate, Sanctacaris, could become an active, Centipede like predator with grasping mouthparts.

The primitive Mollusk, Wiwaxia, being armored, may be better at conserving water than a typical slug, becoming analogous to land slugs eyes and all.

The most primitive shelled Cephalopoda, Plectronoceras, could evolve into a tentacled, predatory analogue of some of the more active kinds of snail.

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From Devonian stock, we may get unusual land colonists descended from primitive jawed and jawless fish.

Bothriolepis and similar Placoderms seem predisposed to colonize land, having jointed forelimbs and supportive body armor, here we see a large armored omnivorous descendant.

Armored jawless fish may evolve into sensitive, underground-tunneling predators of invertebrates, resembling legless Skinks or worm Lizards.

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The Mezosoic presents many marine creatures that may or may not colonize land, including various marine reptiles.

Placodonts like Cyamodus may colonize land and evolve into analogues of land tortoises.

A Plesiosaur like Rhomaleosaurus would have trouble colonizing land, but if it did, its limbs would need to become more flexible, and its digits would decrease in length, making it a sprawling predator.

Sea Crocodiles like Dakosaurus may have limbs which are better able to revert to a typical walking shape, and thus become a more conventional land-crocodile.

An Ichthyosaur like Platypterygius would probably not colonize land, but if it was forced to, maybe its elongate hyper-digited flippers would become part of its limb structure, and it would thus walk on the tips of its "toes".

Mosasaurs like Clidastes could revert to something more like a large, land-dwelling monitor lizard.

Plesiosaurs with hyper-elongate necks like Albertanectes would need a new shape in order to colonize land, perhaps they would become serpentine, with their necks still dominating their bodies.

Triassic Coelacanths such as Rebellatrix might re-enact the evolution of the first terrestrial Tetrapods, and become lizard-shaped, amphibian-like creatures.

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Tertiary kinds of ocean-dwelling fish may hold potential to colonize land, if the more conventional land-dwelling vertebrates went extinct.

Gurnards, who walk underwater on long fin-rays, may develop into insect-like land creatures, with jointed limbs.

Gobies like Mudskippers might devote both pairs of bodily fins, and their tail to becoming athletic, limbed predators

Eels may turn on one side and turn their fin rays into a myriad of Centipede-like legs.

Sharks like Dogfish or Epaulette Sharks, would start by crawling around on their fins like a primitive tetrapod, then would come better ossified skeletons, external supporting armor like a crocodile, and proper limbs.

With all fish that become terrestrial, there are a number of ways to breathe, well-sealed gills may be sufficient in humid conditions, or may develop into a labyrinth organ, or a structure analogous to lungs.

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Tertiary marine mammals may need to modify themselves heavily, if they were to colonize land, with Sirenians and Whales, the powerful tail may replace the long lost hindlimbs as a limb-like organ.

Given enough time, Dolphins may become fierce, hooved, upright terrestrial predators with fur.

Small Baleen whales would have a hard time colonizing land, but if they did they might be selective feeders. They would glean berries and seeds from bushes, or off the ground, as well as skimming shallow ponds and low growth for swarming insects, using tough, quill like baleen and a muscular tongue.

Dugongs may partly mimic Elephants and Arsinoitheres, in becoming heavy land grazers with muscular lips and horns.

Walrus or Sealions might have the best chance to colonize land, as they are still able to walk and run, perhaps they would be ferocious, saber-toothed apex predators the size of a bear.

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Flightless Water birds would not only need to sever ties with swimming, but also give up lying, in order to colonize the land.

Birds like Hesperornis would need to develop a posture to support walking on land again, but may become toothed, stork-like animals.

Penguins are already happy to run about and nest on land, they might lose their flippers and develop a more dynamic posture to hunt on land.

Annakacygna, the flightless sea-Swan, would possibly become a large, heavy grazer, but still use its specialized wings to carry and nurture its young.

Chendytes, the malacivorous, flightless sea goose, might come to resemble a Dodo in some ways, plucking large snails and fallen fruit from the ground, to be pulverized in its sizeable gizzard.

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Cephalopods are the least likely to colonize land, as fresh-water is poisonous to them, but seeing as snails managed it many millions of years ago, it remains a remote possibility.

The Reef Octopus may become a smallish, dexterous predator in humid forests, with stocky arms that have become supporting limbs for climbing and walking.

And Cuttlefish may save their arms for manipulation and capture of food, sequestering the muscular part of their mantle or fins, to become some kind o limb-like structure. The cuttlebone serves to provide the same function as a spine, and it has developed simple pouch-like lungs connected to its siphon.

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So there we have it, I think this was a valuable exercise in Speculative Evolution, with some fairly startling results.

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