Krypton is an ongoing seed world speculative evolution, and involves ONLY Pinnipeds, rather than being inhabited by any birds, reptiles, amphibians, nor even any invertebrates except krills and planktons. Krypton's only major inhabitors are Pinnipeds. Keplerner's environments are the most suitable for large animals to exist without food problems, and to make the animals to grow from the smallest to largest and largest to smallest and create the weirdest animals as possible as vertebrate evolution could get them to be to be to fill the niches invertibrates once held. At the same time, they also facilitates biodiverse environments with plants, bacterias, and fungi that are similar to earth's and ones completely unique to help pushes vertebrate evolution to its limit. The world will also follow the rules of realism pretty harshly.
Seed worlds are a branch in the genre of speculative biology. It is usually in a fictional setting, though most of them adheres to scientific realism.
In earth's ecosystem, invertebrates serve as background/maintenanced variables that decomposates rotten carcasses, Bioturbate the soil, and Pollinate which gives vertebrates a lot of luxury as many things are already done by theirs' spineless cousins, but what if we don't give vertebrates that luxury? Do they evolve to live underground to Bioturbate the Soil? Will small vertebrates help with decomposition of rotten carcasses? Will they evolve to help flowers pollinate? This is the main premise of Krypton.
Phoca vilutina (Harbor Seal)
Mirounga (Elephant Seal)
Zalophus californianus (California Sea Lion)
Pagophilus groenlandicus (Harp Seal)