Epoch 4
Biodiversity reaches a new peak, while the average climate continues to steadily cool, and a new supercontinent begins to take shape.
The family tree of tetrapods in particular becomes impossibly complicated during this era, with air-breathing fish again evolving to crawl on land in several regions, all while descendents of the amniotes that had survived the Great Dying were swapping their legs again for fins or - by the end of this era - wings. Still other species of amphibians and lizards were losing their limbs to crawl around with snake-like bodies. The end result is a near-global distribution of amniotes for the first time, although with a very confusing evolutionary tree, and many features having been repeatedly evolved in parallel.
Still, these new vertebrate creatures do not have it all their own way. Much of the world’s landmass is still the domain of highly-evolved invertebrates that have been able to take hold since the Great Dying, and the evolutionary arms race continues...
First to the continent of Otope, isolated and straddling the tropics, with a mix of forest, alpine and arid regions. Beginning with a diverse population of large lizard-like creatures, this era saw the rise of faster, higher-metabolism creatures, some with a more upright way of walking and running - some even becoming semi-bipedal. These pseudo-archosaurs went through a rapid evolution, with an early branch of small, fast insectivores taking to the trees and rapidly evolving through gliding stages into full powered flight by the end of the era, at which point these pseudo-pterosaurs were visiting every major landmass.
Back on land, these pseudo-archosaurs compete for many niches, but struggle to overcome the inertia of some of their more primitive relatives; herds of large herbivorous lizards, built like tanks with thick skins and sprawling gaits, still plod their way through the plains and forests. Some of the archosaurs evolve complex pack-hunting behaviours in order to work together to tackle these behemoths.
In the sheltered coastal bays of Otope, a separate clade of archosaurs evolved to swim and hunt for small sea creatures in shallow waters. While some settle for a crocodilian lifestyle, others evolve further, becoming fully seagoing creatures by the end of this era, with their legs evolving back into large flippers. Evolution occured rapidly in the seas between Otope and the Ailean archipelago; vivipary (live birth) also became a feature of this clade, allowing some species to live permanently at sea without ever coming ashore to nest. While these sea-going archosaurs were rarely top of the food chain, this vivipary combined with increasingly large body sizes allowed them to carve out a niche between some of the monstrous sharks, squid-like creatures and giant predatory fish that now stalked the oceans; these pseudo-plesiosaurs were soon visiting the coasts of every continent.
While Otope was serving as a launch pad for new kinds of tetrapods to spread around the world, the inhabitants of Altica were not so outgoing. As the continent steadily drifted over the north pole, it did in fact reach a crisis point of maximum glaciation (coinciding with global dips in temperature); some of the native pseudo-mammals and unique cold-adapted plant species were driven into genetic bottlenecks, as for millions of years only a few coastal regions remained habitable - if not for a burst of volcanic activity raising greenhouse gasses, the global cooling trend may have been too much for them to survive. But Altica eventually drifted away from the pole, with much of the continent basking in the relative warmth of a temperate climate towards the end of this era, bringing a return of shrublands and forest where once had been thick glaciers. Winters are still fierce however, getting increasingly cold as the era progresses; hardy tuber-like plants remain common, providing vital food source to the burrowing mammals.
While this was happening, Altica was also colliding with the volcanic microcontinent of Moddier, raising a large new mountainous plateau out of the seabed, and leading to dramatic, tortured landscapes were former volcanic flows had been steadily tilted and uplifted by tectonic forces. Behind the land bridges formed an isolated inland sea, complete with its own unique set of fish, squid, trilobite and shark species. There was also a partial revival of volcanic activity in the area, with new volcanoes erupting close to ancient extinct brethren.
The new continent of Almod had now formed, although weakly held together with a chaotic series of fault lines outlining the old coastline of Moddier, and an extensive system of geothermal springs - hosting unique microbial life and providing warmth for larger creatures; a network of ‘hot smokers’ in the seafloor around Moddier also became a stronghold for chematroph reefs, tended by special species of heat-resistant trilobites.
The pseudo-mammals of Altica rebounded and diversified to exploit the new terrain, colonising the former Moddier continent as soon as land bridges formed - finding no large animals to hold them back, they diversified into many niches. The existence of social behaviours, partially warm blood, a partial coating of fine, feathery growths, sensory whiskers, glands producing a milky substance used to nurture their partially-soft eggs, and prominent teeth such as tusks were all common features of these species. Some also had upright gait evolved in parallel to the archosaurs of Otope, and some also had the breakthrough of giving birth to live young. The mammals were joined by pterosaurs and plesiosaurs towards the end of this era, thriving especially in the steep rocky fjords of former Moddier. It is notable that species of amphibious trilobites persist here, breeding en-mass on certain beaches and using weight of numbers as a response to the new predators.
None of the mammal species were able to venture beyond Almod, but tectonic forces were steadily narrowing the distance to other continents beyond..
Nessperia is a continent with a very different story. Of the native tetrapods, only one clade manages to push beyond the rainforests of the east coast - descendents of frog-like amphibians that now evolve lizard-like features in parallel to their cousins elsewhere, complete with tough scaly skin and shelled eggs. Some relatives remain in the rainforest and become adapted for climbing and gliding between trees, partly to escape the vast array of invertebrate predators. But this experimentation in flight is halted by the arrival of their distant cousins - roaming pterosaurs begin to colonise the treetops towards the end of this era, not hesitating to prey upon these gliding-frogs in turn. The appearance of gliding squid-like creatures adds to the commotion in the forests by this era’s end.
Overall, however, it is the arachnids that are now dominant across the continent - having diversified to fill many niches, from the ancient lines of larger free-hunting predators into tiny herbivorous mites, and thriving in both rainforest and desert. Many species remain carnivores; a new clade of arachnids evolves to dominate predatory niches across the spectrum, from trap-laying insectivores (some using rudimentary silk webs) through to large free-hunting carnivores, reaching up to a metre in width and climbing firmly to the top of the food chain in drier regions. Many have venomous bites to subdue their prey, and some carry their developing eggs with them in special abdominal pouches.
These arachnids hunt land trilobites, descended from Panzernan ancestors (somewhat resembling giant cockroaches) that are now extremely well-adapted for desert survival and meagre diets. Some of these evolve thick armoured carapaces and the ability to roll up in a ball for defence, while others remain small, evolving sharp senses and quick reflexes.
Terrestrial squid-like cephalopods of Nessperia split into distinct clades; one is made up of climbing ambush hunters, lurking in branches to drop down on prey and grapple with their tentacles; another are almost snake-like species with elongated bodies and short, folded tentacles, most often found prowling through swamps and undergrowth. Both types share potent camouflage abilities thanks to the chromatophores in their skin. Some of the climbing ambush hunters also evolve the ability to glide between trees, and although they lag behind the flying abilities of pterosaurs which arrive at the end of this era, they are still sometimes able to ambush and prey upon them. Still another clade of land-cephalopds are peaceful herbivores, evolving ever thicker and stronger tentacles to haul around on land, and thicker skins for defence.
While successful, these cephalopods are still unable to survive in drier climates and where vegetation cover is lacking. Even in the rainforests they are not technically top of the food chain; that crown is taken by monstrous, anaconda-sized, harpoon-spitting species of velvet-worms; a clade which continues to diversify, some species evolving thicker skins and venturing into drier parts of the continent. Others take to a burrowing lifestyle, again shrinking in size but becoming effective ambush predators and scavengers. These burrowing velvet worms are also notable for evolving cooperative social behaviour somewhat similar to the pseudo-mammals of Almod, and thrive in the dry plains of the west, offering the strongest competition to the arachnids.
The diversity of animals in Nessperia is mirrored by the diversity of plants and other organisms; the continent remains a stronghold of unique species of fungii large and small - some trap and consume insects with sticky secretions, attracting them with bioluminescent growths; others have a parasitic nature, with their spores able to grow inside insects and other small creatures, consuming them from the inside out - some more specialised forms are even able to alter the behaviour of their host species to aid in spreading their spores. Other fungii are vital symbionts for the rainforest trees and merely have passive defences in the form of poisons and other chemicals that act on the nervous systems of animals.
Nessperia at this time is also home to regular outbreaks of deadly pathogens - virus, bacteria and unicellular parasites - which actually helps diversity over time, as they tend to cause greatest harm to species with the most densely-packed populations, allowing other species to rebound. But velvet worms, particularly the smaller burrowing/scavenger species, are notable for evolving the greatest immunity to these diseases and may even use them as a kind of passive defensive weapon against predators.
In the Panzerna islands, there are still very few tetrapods or amniotes living permanently on land. Those plesiosaurus that adapt to cold southern waters do not advance far from the shores, and most pterosaurs are seasonal visitors. Specially-adapted land trilobites still dominate here - as the climate steadily cools, some evolve antifreeze proteins in their blood, and are able to hibernate through extreme cold winters in alpine regions. Panzerna also still has the world’s largest terrestrial trilobites, armed with tree-shredder mouthparts, though these are in steady decline as the islands drift slowly southwards and glaciers continue to spread from the mountaintops. Partly as a response to this, some of the larger trilobites are returning to the waters as aquatic air-breathing herbivores with turtle-like lifestyle, though for now they remain limited to kelp beds off the shores of the larger islands.
Finally to the Ailean archipelago, were plesiosaurs and pterosaurs are able to run riot - some evolving back into fully terrestrial forms. The only resistance is from native species of more primitive lizard-like forms, and from land trilobites - most of these are amphibious or otherwise peaceful herbivores. As a response to the predators, some of the island trilobites evolve poisons and spikes, and advertise this with an assortment of colourful patterns and bright metallic hues in their carapace.
Coral reefs flourish in the waters between the Ailean islands and the shores of Otope, with sparkles of bioluminescence at night; these are prime hunting grounds for the most advanced squid-like creatures, which have evolved pack hunting strategies to gain an edge over the larger sharks and coelacanths; chromatophores and bioluminescent patches are now used equally for communication as for camouflage. There are no easy comparisons between the cephalopod brain and those of tetrapod lineage, as both have evolved on very different paths, but there is no doubting the increasing intelligence of these cephalopods; as well as complex social behaviours, tool use can also be seen - reusing discarded shells and plant material either for nest sites or for camolague.
As the continent of Otope continues to head eastwards, and Nessperia and Almod edge towards each other, a new super-continent may soon be forming. The exception is Panzerna, which remains on a slow southern drift. While the tropical regions are still warm, globally a cooling trend continues, likely only to increase as new mountains are raised from continental collisions.
From what I read about arachnids I would say they do have Pedipalps, and some also produce silk but are using it for wrapping up their eggs. Most are carnivores, ambushing insects or catching them on the run. A few larger species prey on the land trilobites and velvet worms, I imagine some would have poison bites.
