100 million years post-establishment, Serina is now a world of rich and diverse ecosystems, home to a cast of characters both familiar and highly alien. Some creatures have changed remarkably little, if at all, over many hundreds of thousands of generations; many invertebrates such as earthworms, ants, and snails still remain virtually identical to their ancestors. Serina's freshwater streams still teem with drably colored live-bearing fishes which could still pass for the wild poecillids of the Holocene which gave rise to all of Serina's modern aquatic diversity, and even many seed-eating birds are scarcely changed fundamentally from the ancestral canary, except perhaps in their color.
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But that is not to say that nothing has changed. The land still teems with birdsong and the buzzing of crickets, but now there are forests in addition to Serina's primordial prairies. The descendants of small wild sunflowers and thicket-forming bamboo, they have spread across the world, growing taller and increasingly woody, filling what began as an ecological vacuum wherever rainfall allowed their growth. Browsers quickly evolved alongside to reach their heights to feed, small flighted birds transforming over the eons into enormous megafauna, larger than anything before them of their kind. To defend against them as well as their own plant competitors, some trees adopted armed artillery; defensive ant colonies which lived symbiotically within their tissues. For a time, these myrmecophyte plants - the descendants of bamboo - spread and dominated the planet. Made unpalatable to herbivores by the stings of their symbiotic partners and the space around them kept trimmed of any competitor's branches, they experienced a boom in diversity and greatly outnumbered their competitors by the end of the Tempuscene, 50 million years ago. By the middle Thermocene, these trees have become the dominant floral group across the planet, but success has come at a price.
Life is an arms race with very few true winners or losers; animals formerly unable to feed on myrmecophyte trees eventually developed immunity to the venom of the insects or simply developed longer beaks and tissues defended by skin too thick to be easily pierced by their attacks so that they could still feed on the plants' foliage. Additionally, the enormous increase in ant numbers resultant from the mymercophyte explosion of the Tempuscene was soon curbed by the appearance of highly successful animal lineages specialized specifically to consume ants. Soon, ants could not afford to be as bold and aggressive as they once could, lest they be rapidly seen, eaten, and their colonies eventually subject to collapse. On the floral front, some competing plant groups developed sticky protective coatings to guard their new growth against ants coming to prune them, catching the insects or gluing together their jaws so that they could cause no damage; once the stem was older and less vulnerable, it ceased to produce the substance. Others filled their sap with a thick latex to serve a similar function, covering the ants in a noxious glue as soon as they took a bite and broke the plant's tissues. Some sunflower trees also evolved which turned their competitor's armies against them. They began to host their own ants, producing their own enticing nectar or other food reserves and lodging in the form of hollows in their trunks, branches or leaves in return for protection against competing trees. By the Thermocene myrmecophyte trees remain the dominant floral group - though many others utilize sticky defensive sap or other adaptations to defend themselves instead - but these relationships are no longer groundbreaking simply because they have become so common; if every tree has ants to protect it, and herbivores have learned to deal with the ant's defenses, then effectively all of the adaptation is doing little overall to help any one individual ant or tree's survival compared to a forest where such symbiosis is totally absent. But the system has become so complex that in most cases, the relationship cannot simply dissolve, for because it has become so successful, any tree which stops providing for its partners - at least without developing an entirely new line of defense - will be the first to succumb when the ants living on the other trees or the browsing animals realize it lacks any defenses. This is why the relationship survives. Ants continue to guard their host trees as best they can without giving themselves away excessively to hungry ant-eating predators, whilst both the browsing animals and the trees simultaneously continue to develop new ways of protecting themselves and circumventing the ants' defenses. When an herbivore begins to feed on a bamboo tree, the ants on that tree will release pheromones, telling all of the ants living on trees downwind that a threat is approaching and to be on guard. All that a browser such as a serilope must then learn to do, however, is feed whilst moving upwind and it then will not alert the guardians of its food supply if it only spends a short time at each branch. It is so that life continues to be a battle among countless warriors with no end in sight. In the end, it may seem that all of the adaptation has almost become pointless. But in the even bigger scheme of things... isn't all life in the end?
Unless or until some new, groundbreaking adaptation appears to move the competitive arm's race back into the fast lane - something akin to the appearance of flowering plants on Earth or the original adaptation of ant symbiosis on a young Serina, it can be expected that Serina's forest communities, which had already reached this relatively stable state by the Cryocene, may remain relatively the same as they have been for many more millennia to come. Such stable conditions, so long as they last, will be beneficial for the continued survival of modern plant and animal groups, but will slow the appearance of new lineages in comparison to a younger Serina which was a much more unstable environment, where rapid change and new speciation was the recipe for survival. Serina will remain more volcanic throughout the Thermocene than ever before it, and will maintain its greenhouse climate and widespread tropical conditions for the next seventy five million years.