Oxymor is a speculative evolution/worldbuilding project set as a sort of spiritual successor to Sheatheria. It's not the same, but it borrows a lot. The setting is more down to earth and less fantastical. If you like this, I take commissions for maps!
Life is not rare in the universe. It has evolved countless times on countless worlds that man has not discovered, the vast majority of which he will never know. But not all life scattered across the cosmos originated where it now occurs on its own. In many cases, set here and there, it has been given a lift from one world to another by a mysterious force - a god-like intelligence nicknamed the Old Ones. They are hypothesized to be an artificial intelligence set loose by an ancient, long-lost empire, intended to build new worlds for colonization by a race long since extinct - though exactly what the old ones are is still only conjecture. All we really can be sure of is that they are ancient beyond human comprehension, that they are totally benign and mean no harm, and that they have just one goal in mind: panspermia - the transport of plants and animals from one planet across the universe. They seeded barren but promising worlds with the seeds of life and sowed whole new worlds from the tiniest fragments of others. Their means and methods must be left to the imagination, though their power is great; they can cross not only space but time itself in their efforts to put together just the right building blocks to a new ecosystem for their projects.
There is no telling how many worlds the Old Ones have established from the stock of life present on Earth. The people of Earth would only ever know for sure of one, discovered in some ten thousand years by the distant, enlightened descendants of modern man. By this time having evolved beyond aggression and selfishness, these posthumans lived as a peaceable, space-fairing, post-scarcity society. Several truly alien worlds had already been documented, and so the idea of life outside Earth was no longer anything but to be expected. This world, however, immediately struck them as unusual. In a small solar system of rocky planets circling a bright yellow sun, the second one out closely resembled Earth from a distance, a brilliant marble of green vegetation and bright blue seas, but it was quite a bit larger and supported almost three times the surface area. An apparently lighter composition however meant its gravitational pull was very similar despite - actually just a hair less than Earth at about 0.9 G's - and so suitable for the survival of a similar range of life as Earth. Most surprising though was the life that would be found there.The planet was inhabited by animals that, though distinct from any known, could be grouped for the most part into the same categories of vertebrates, reptiles, even mammals. It was as if the plants and animals of all epochs of their home world had been tossed and turned together into strange new combinations and left to evolve there together into new ecosystems over tens of millions of years. And this is exactly what this second Earth was; a planet artificially planted with terran lifeforms from seemingly any and all time periods.
Fortunately for this world it would be spared the ecological destruction that faced the first Earth, which had only just begun to recover from thousands of years of intensive exploitation by the ancestors of these people. These humans were not here to colonize and conquer. They had no need for its resources. They would establish no permanent ground bases - there was no need, for all they needed was up in the cosmos. But they would visit, and study, and learn as they did on all the life-bearing worlds they came across - and they would slowly but surely unravel the mystery of how this place came to be.
They have now studied the planet intensively over the course of three hundred years, all the while making sure not to disturb the native life any more than absolutely necessary. In this time almost all of the world has been mapped and explored. Enough of a fossil record has been obtained to establish a history and piece together the family tree of the world's life. All plants and animals here could trace ancestry back to a prolonged panspermia event lasting around one million years that occurred approximately 110 million years ago, during which time first simple algae and bacteria were established and gradually increasingly more advanced plant and animal life as the ecosystem and atmosphere apparently matured to a state able to support them. Introduced species apparently included a bewildering mixture of nearly-modern life - including grasses and flowering plants as well as animals like the brown rat (Rattus norvegicus) and common frog (Rana temporaria) - and lifeforms known only from fossils tens or even hundreds of millions of years old, such as the small, lightly-built early dinosaur relative known as Scleromochlus and multiple extremely primitive mammal relatives known as cynodonts, some of which had probably not yet evolved either external ears or lactation. The unearthed fossil remains of such animals stood out markedly in comparison to those of the clearly modern rats that had somehow been sent back through time 110 million years to coexist with their distant ancestors which were in turn moved forward at least the same amount.
Mankind had never invented backwards time travel which could take oneself further back in the time than the date upon which the first looping wormhole was stabilized, allowing them only a few thousand years of travel back now at most, and so could only hypothesize how whoever had brought these creatures here had done so at such a vastly grander scale. Regardless the evidence was clear; however they got there, all of the creatures had been introduced from Earth at once and left to evolve together until the world was discovered 110 million years later. By tracing fossil records and observing as they became increasingly changed from these ancestors a history could be put together for all the world's strange and unusual plants and animals that had been left to adapt and evolve into forms that would never have occurred on their native world. Everything found here had evolved from a form originally native to Earth. Humble rats, lacking competition, evolved into fearsome apex predators. Frogs speciated dramatically into bizarre and alien forms, evolving a warm-blooded metabolism and upright gait. Some species reached similar conclusions to their counterparts on Earth despite circumstance; Scleromochlus took the skies, but in a different form than the pterosaurs. Other animals meanwhile produced descendants so remarkably unlike anything on Earth that virtually no superficial similarity remained.
The people who discovered this grand new world, a mixed and muddled but nonetheless beautifully unique twin to our own home planet, categorized it and its life with a combination of their own derived language and the archaic one known as "English". As a result, names may feature components derived from either or from both languages. For the world itself, on account of its intricately woven, opposing attributes of familiarity and fantasy, they decided on the name Oxymor, from the English oxymoron, meaning "a figure of speech in which apparently contradictory terms appear in conjunction".
It was a beautiful world with much to discover. Though the fundamental basis of its ecology was familiar, it had undergone enough change over time to be, at times, completely alien to its observers. A new era of exploration had been ushered in, and Oxymor had many secrets to tell.
Life and Land
Over the past three centuries Oxymor has been extensively mapped and named. Most of the planet's land is divided predominately into two major supercontinents that broadly stretch from the north pole to the south known as Aenvarna and Andromere. Rainfall across most of Oxymor is high and so most continents across the world harbor abundant coastal rainforest intermixed with grasslands and arid interior regions, with jungles giving way to temperate forests toward the poles. Both continents support all biomes that occur on the planet, however broadly speaking Aenvarna is more heavily forested and Andromere more arid, particularly in its far north. The coastlines around the land are highly varied with many bays, inlets and peninsular lands allowing for a high diversity of shallow coastal environments and offshore insular habitats. Aenvarna and Andromere are currently coming together, the tectonic plates upon which they rest having already met along the planet's equator, producing a large expanse of very shallow, fertile sea called the Ocean of Tranquility that is less than ten thousand feet deep at its extreme. Oceans elsewhere, however, are very deep indeed; the lowest measurement on the planet so far surveyed, found on the seafloor within the Hell's Gate Trench in the middle of the deepest Unfathomable Ocean, was 48,500 feet below sea level.
Paleontologists studying the ways the first life on Oxymor dispersed immediately following their introduction have determined that while vegetation, decomposers, and other imicrofauna vital to the ecosystem, like springtails and isopods, were very widespread from the start, the different vertebrate species were seemingly introduced at first to different regions, sometimes with several together and sometimes with just one as the sole inhabitant. Rat fossils are extremely numerous across Andromere, where they seem to have originated, but do not begin to show up on Aenvarna for some fifty million years and then only in considerably derived forms. Likewise Aenvarna seems to have been the original home of the common frog and also the tiger salamander, Ambystoma tigrinum, creatures that would not colonize other continents for many millions of years as a result of their sensitivity to saltwater effectively marooning them there in the beginning. The majority of vertebrates introduced to Oxymor are from the Quaternary, but three identified species are known that originate from the Triassic. These are Scleromochlus, a small, early dinosaur and pterosaur relative with a hopping upright gait; Oxymortherium, a squirrel-like species of tritheledontid cynodont (a very near relative of mammals) from the middle Triassic that had not been previously classified on Earth, which seemed to be adapted to a more omnivorous diet than other members of its clade; and Lystrosaurus, an herbivorous, beaked therapsid (a more distant mammal relative). At around the size of a pig, this latter animal was by far the largest animal introduced to Oxymor, and also one of the least successful long-term. Apparently introduced to Andromere, they are today represented only by a single surviving lineage of semi-aquatic sea creatures, having otherwise apparently been heavily outcompeted by the descendants of rats. Other animals introduced included the diamondback terrapin (Malaclemys terrapin), introduced to coastal Aenvarna, which as a result of its adaptations to brackish water was the first land animal to colonize the oceans, and the land hermit crab Coenobita perlatus that was destined to be the largest land animal present on the island continent of Decapaeus for tens of millions of years.
It is surmised that Aenvarna and Andromere were once much more distant than they are today, situated on the equator at opposite ends of the Earth and separated by a vast expanse of open sea. Aenvarna has since drifted south and Andromere north, finally beginning to come together some thirty million years ago via a land bridge called the transcontinental passage and allowing major ecological interchange from both continents into the other for the first time in the planet's history, with waves of amphibians moving north and mammals into the south. This bridge today is fractured by higher sea levels - a result of the loss of the planet's ice caps due to a runaway greenhouse effect - and the two opposing continents are now connected only by isolated islands each a few dozen to a hundred or so miles apart.
One major continent also worthy of note right now is Wumbus, an isolated landmass approximately three times the size of Australia, which has apparently never been part of any other continent. Originally just off the shore of Aenvarna, it has now drifted far out to sea. No land animals seem to have been introduced to Wumbus when the planet was colonized, with all of its life having found their way to there later on via newly-evolved wings, fins, or rafting. Turtles, it seems, arrived first, and today still exist there in their greatest variety of form.
One thing lacking on all of Oxymor's lands are the insects; they were apparently never found here, and all of Oxymor's ecosystems have adapted to live without them. The only invertebrates left to fill their place have been annelids (earthworms predominately), isopods (both terrestrial, like woodlice, and aquatic) and springtails (closely related to insects, but wingless), all of which must have been introduced to perform the role of decomposition in Oxymor's earliest days and to feed its more carnivorous colonists. The oceans and rivers received one other group of crustaceans to fulfill needed niches; several species of small eurypterids - also known as seascorpions, which hailed from Earth's Permian, making them Oxymor's most ancient colonist. In seas without fish, they prospered and remain widely successful today, though very early on had to adapt to competition from increasingly large amphibian larvae that soon began both to compete with and prey upon them, an evolutionary arms race that continues today.