Land
The brief age of insect dominion begins to wane as a growing diversity of birds begin to displace them.
Five million years after the first canary birds were freed upon a world of endless grassland and meadow, the world of Serina has already undergone several major transformations. It did not take long for the prairie grasses that initially covered the world to be pushed back by their distant relatives, the hard-wooded bamboo, as they rapidly spread and shaded the world of a world which offered them no competition. Among the fastest growing of all plants, they spread and filled in a world otherwise without trees at a phenomenal rate, by now growing in dense and often mono-cropped thickets from pole to pole wherever sufficient soil moisture allows, leaving expansive grasslands only where precipitation is too minimal for the growth of bamboo woodland. The domain of the leaf-cutter ant, innumerable billions of these insects still scurry in hordes throughout the forest, gathering leaves and shoots at a rate only surpassed by the incredible growth of the grass they feed on, with shoots rising from expansive rhizomes at up to four feet per day. Underground, colonies of the insects now extend hundreds of miles underground. Super-colonies have begun to form, combining their efforts to produce the largest single colonies of any insect ever documented with likely populations reaching into the trillions, each and every one of which is a member of a single cohesive colony providing food for a series of underground fungus gardens that might extend 100 feet bellow ground. Without moles or rodents, subterranean habitats are home instead to gigantic earthworms, crickets, and millipedes, while an ecosystem,still deficient in large predators experiences nutrient turnover instead through the actions of billions of burying beetles, which following the extinction of the empire ant are provided with an infinite and mostly untapped food source in the form of deceased birds, resulting now in their own population boom. By working to turn all carcasses they discover under the soil, they not only provide food for their own young but keep the surface environment clean and free of disease while also returning needed nutrients to the soil, where they will feed countless insects and micro-organisms before one day being returned to the plants themselves.
A world so far dominated by insects is slowly being taken over again by the vertebrates, as the birds - equally freed from empire ant predations - begin to diversify at their fastest rate yet. The age of the leaf-cutter ant is far from over, but the insects are no longer the sole rulers of their niche now as various forms, not only of birds but also of other invertebrates, begin to compete with, prey upon, or otherwise exploit the leaf-cutters. Five million years PE, the first truly herbivorous canaries, which feed predominately on leafy plant matter in favor of seeds or insect food, have begun to diverge. Several unique forms have simultaneously lost power of flight, or at least reduced it, and begun to develop an increasingly large, powerful bill to tear coarse foliage and a large gut to digest and make use of it. For another brief time, the world is largely free of predators, and flocks of increasingly squat, poor-flying and flightless birds are free to spread out far and wide. From plump, dove-like ancestors two million years ago have already emerged forms as large as chickens, turkeys, even geese, an exponential increase in size allowed by a total lack of predatory selection or competition for resources. The wings and often even legs of these birds have rarely grown in tandem with their immense bodies, and they are slow, awkward animals, nesting on the ground and out in the open and having few if any defenses - they still needn't worry about predators. Faced with this first major wave of avian diversity, the leaf-cutter ant empire begins to wane in both northern and southern temperate belts as the ants are slowly squeezed back to their ancestral tropical climes, unable to compete during cold winters with growing hordes of plant-eating birds that can remain active throughout the year, and ravaged during their seasonal hibernation by equally large flocks of increasingly specialized insect predators.
Five million years has been sufficient time for several independent lineages of ancestral seed-eaters to take almost completely to a diet of insects and arthropods, and quickly converge upon the warblers, the thrushes, and the wrens of their ancestral world. Among the most derived of such forms are the poor-flying Sprinter Serins, which are now among the most common of all the ground-feeding birds. With long, probing bills and lengthy, sturdy legs, some of these vaguely plover-like passerines have already largely given up flight - one of the first carnivorous lines to do so - and taken to a terrestrial habit, some dashing through the undergrowth of the bamboo forests and others scurrying through sandy savannahs and between sparse prairie grasses, with a few forms, such as the red-sided pond-diver, even beginning to feed from the water in riverine environments. All are in search of the insects and other invertebrates they now feed almost exclusively upon, but the diver may already include fishes in its catholic diet. With others favoring ants, others slugs, and others still crickets or beetles, this earliest wave of ground-predators shows great potential for long-term survival as still infinite food supplies fuel an incredible rate of evolution, as a world unnaturally barren continues to fill in its own gaps.
Carnivory is also beginning in the skies as the ancestral egg-eater canaries have given rise to increasingly bold and opportunistic forms, the Shriekers. Relatively large birds, these boisterous and social species have taken their egg-eating tendencies well past hatching and have become particularly suited to the killing and eating of nestlings, fledgelings, and even weak adult birds with their increasingly sharp, sometimes hooked beaks. The jays of the canary world, though they remain highly generalistic - indeed still consuming a fare amount of green food, seeds, and insects - they are already beginning to show increasing adaptations of both form and habit to a predatory ideal. Forest birds can no longer leave their nests unattended without worry as the shriekers, having been watching from a distance, may now descend immediately to savage their young, one member of a mated pair distracting the mother hen and the other going in to slaughter the chicks.
Among the first mutations that developed in the Serinan bird population was an incredible diversity of color, evolved for lack of carnivorous concern, but in recent times rising predator worries means many small birds now exhibit increased selection for camouflage, particularly of hens on the nest. So too reappear formerly relaxed, atrophied instincts of parental care, lost during several eons of safety, in all small bird species, while for the large ground birds size, for now, leaves their otherwise defenseless young unmolested by Serina's first small but specializing predators.
Sea
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Though riverine habitats now teem with life, Serina's seas have lagged behind the land in developing ecological stability.
The seas of Serina, from a modest initial stock, quickly became rich with life. Billions of fishes soon flocked and shoaled its waters, as a food chain beginning to form in earnest as increasingly large and specialized hunters, mainly in the form of swordtails, pursued unfathomably immense shoals of smaller pelagic live-bearers, fed by copious planktonic algae and copepods. Forests of kelp and algae colonize all sunny seashores, feeding shoals of beautifully-colored, otherworldly grazers - sea slugs - which may grow as large as dogs - and immense herbivorous sea snails with shells over five feet long (a last remnant of a brief time of mollusc domination long since ended on land), taking the niches of sea cows in early Serina's waters. Of all Serina's earliest freshwater stock - the three live-bearers, the crayfishes, the shrimps, the snails - only the platyfish, a creature which had lead far greater success in the niches of riverine cyprinids, has not successfully infiltrated marine environments by this time, though remnant genes resulting from early swordtail hybridization likely still remain within the sea's new apex predator's genomes.
From the sunlit shoreline environments, the Serinan sea often looks completely pristine, with beautiful fishes, great colorful sea slugs, and large, brightly-colored crabs abounding in clear waters. However, as one moves several hundred miles out to sea, the oceans of 5 million PE have slowly become a slowly-ticking time bomb. Gone is the era of unbridled peace of past millennia. As a result of no significant organisms moving through different levels of water as they do on Earth, distributing nutrients and oxygen, and nearly all life existing within one hundred feet of the surface, Serina's benthic zones have become stagnant and anoxic. Blooms of anaerobic bacteria which, in death, release highly toxic substances into the water now occur regularly, inducing large-scale die offs of marine life, which in turn release enough nutrients to produce even larger red tides - toxic algal blooms - which may be carried via currents for thousands of miles, causing harm to all life they come across. Serina's open oceans are in constant flux and lifeforms struggle to establish themselves as great swaths of waters are periodically cleansed of virtually all advanced life, often becoming breeding grounds for fleeting population explosions of jellyfishes and little else. Though rapidly-breeding and highly adaptable live-bearing fishes, shrimps, and copepods are among the best-suited of creatures to rebound following such a calamity, their very ability of rapid reproduction becomes their downfall. Smaller