Main Neocene

“The Last Ones”

These texts had been published first in Speculative Evolution group and saved later at the site Dyingearth.

Original text by Jordan Fryer.
Saved for all fans of speculative evolution by Nikolay Kilyachkov.
Translation into Russian by Pavel Volkov.

The last fish

735 million years from now

It is 735 million years into the future. Earth’s biosphere is now «terminally ill» as the Sun has grown brighter and increased heat on Earth. Most lifeforms died out over a hundred million years ago as most plants could no longer be sustained on their photosynthesis type. Within 110 million years all animal life will have been extinguished, and all lifeforms will follow between one and two billion years. Some Earth lifeforms may have been transported to other planets, but like an elderly parent, the planet is finally beginning to lose out.
Earth’s oceans have also been slowly evaporating for the past 50 million years or so. Their sheer size means they will take another few hundred million years or so to evaporate fully, but increasing salinity has already claimed one of the most well known groups to have ever swam in it.

Upon the beaches of salt of what used to be the Pacific Ocean, the recently deceased corpse of the last fish has washed up. For all intents and purposes it is very strange, but its form has remained conservative enough to ascertain its basic affinities. The cartilaginous skeleton, fin rays and extendable jaws of replaceable teeth give it away as the last known member of one of the most conservative vertebrate lines to have ever existed. The world’s last fish was a shark.

Descended from a species of carcharhiniformes (probably of the genus Mustelus which was one of the few shark genera to survive the Holocene extinction), the ancestors of this shark were the only cartilaginous fish to survive the mass extinction caused by the formation of Novapangaea. From then they became top apex predators of Earth’s oceans for the next several hundred million years and rediversified into filter-feeding, schooling and even amphibious forms. This particular species, only about half a meter long, was undoubtedly the ruler of the seas for the last couple of tens of millions of years leading up to now, and converged on primitive «sand tiger» type sharks that lived from the Cretaceous until the Postanthropocene, having a menacing appearance and being a predator of fungal reefs, feeding upon neo-cephalopod gastropods and pelagic crustaceans, the last ray-finned fish having died out as their eggs couldn’t cope with increased salinity. The sharks, giving live birth and already being well-adapted to saltwater, did not have this problem, and the gastropods evolved shelled eggs to cope with this.

But nonetheless, the heyday of the last shark did not last. Though the sharks could physically survive the hotter, saltier oceans, the stress from having to cope with extreme conditions slowly took their toll, and slowly but surely, a variety of pathogens such as bacteria and fungi slowly wiped out the shark population, and so death found the last surviving sharks, and fish as a whole, in the remnants of the Pacific Ocean. A lineage over a billion years old survived the Permian extinction, the K-Pg, the Holocene extinction and the Novapangea extinction only to be killed not by the Sun, a meteor, overfishing, or flood basalts, but by a disease brought on by stress in a hotter, saltier ocean. From now in, for the next several tens of millions of years, the only vertebrates left on the planet will be the hardened, distant descendants of skinks. Ironically, their extinction will have relatively little to do with heat, and instead be the result of a localized flood basalt similar to the Deccan Traps. A humiliating end to a great lineage.

The last vertebrates

767 million years from now

767 million years into the future, the last vertebrates on Earth survive in the rocky, secluded valleys of what was once the South Pole. Highly degenerate and barely recognizable, they look more like a graboid from the Tremors movie series than the skinks they descend from, most likely from Australian rainbow skinks but possibly also New Zealand Oligosoma skinks, which along with a few geckos and genetically modified tuatara gave rise to a variety of great Zealandian reptiles hundreds of millions of years before, including mosasaur-like marine skinks.

That era is long gone and forgotten, and now the last lizards live in rocky soil and feed on some of the last insects and arachnids, which are descended from beetles, midges and scorpions respectively. They are no more than twelve centimeters long, and have lost most of their bones and organs to conserve scarce resources. The only bones left are the bony jaws and spine, along with vestigial ribs, and they have completely lost their eyes, teeth, liver, nose, ears and have only degenerate brains and hearts just functional enough to keep them alive, and they detect prey via vibration detection. The kidneys are highly efficient and interlocking scales ensure that minimal water is lost, as fresh water only exists as rain, fog, or temporary water bodies which evaporate within hours or days, though they still relatively commonly form. Furthermore, they are nocturnal. For the past few tens of millions of years, these habits, along with increasing evolutionary sacrifices, have done these bizarre, degenerate lizards well in ongoing the solar apocalypse. But the temperature even here is 48 degrees Celsius on average, and rising. And there is a new threat burgeoning.

New volcanoes have begun forming around this sanctuary within the past few thousand years. Alone, a single volcano is not much of a threat, but slowly and surely the eruptions have become larger and more frequent. Just two thousand years ago, this hostile region was still covered in grasslands, now the toxic, acidic soil has killed off all plants of significant size and only the smallest, toughest spots of green and lichens now remain on higher, non-volcanic ground. The few surviving small beetles, midges and scorpions are the handful of macroscopic remnants of an invertebrate fauna that also included millipedes, cockroaches, spiders, ants and termites, and even then they can only support a population of less than a hundred lizards at any one time. Half a million years ago, they could reach a foot in length, now the maximum length is twelve centimeters and usually less. Very soon into the future, it would seem likely that inbreeding depression would spell the doom of one of the world’s last two terrestrial ecosystems (the other being in the North Pole, conveniently enough), and the last vertebrates. But such a vice will not get the chance.

One of the skinks is overwhelmed by a massive flow of vibrations. Another, then another, until many start rolling and crawling on the rocks and sand, having no higher awareness of what is going on. A quick burning sensation is followed by death, and outside, the mountains and valleys are filled with ash and lava, within less than a minute.

A massive flood basalt fills the former sanctuary of the South Pole with lava and ash within seconds, quickly killing off the last vertebrates, arachnids and surface-dwelling insects. The end of the squamate lineage comes with a bang so loud, but so short it may as well have been a desperate whimper. Within a few million years, the North Pole’s terrestrial ecosystem will follow, and at the Mortassic-Mortaceous boundary the destruction of photosynthesis will wipe out all multicellular life left in the caves and evaporating saline oceans, except for two hydrogen-breathing animal species, giving rise to the short post-oxygen animal era.

The last land-dwellers

769 million years from now

769 million years into the future, the increasing luminosity of the Sun has pushed animal life to the brink of extinction. Vertebrates and arachnids have been extinguished from the planet entirely due to increased volcanism in the South Pole, insects only survive in the form of tiny cave beetles and spiralians have been extinct for a few million years as well. Five phyla of animals now remain, those being the tardigrada, arthropoda, nematoda, loricifera and placozoa respectively in order of numbers, adding up to about 80 animal species. Now, only one relict terrestrial ecosystem remains in the North Pole, now concentrated into a single tiny valley surrounded by mountains. Despite having temperatures of 50 degrees Celsius on average, there is actually slightly more water in the environment as the valley is located above a system of large aquifers, which during winter months is able to supply exceedingly rare surface water to the valley, forming a large but temporal stream which lasts less than a week per year, though large fogs and rains continue a few weeks afterwards. The last true plants and lichens store this precious water in large amounts below the surface. By day, these would seem to be the only macroscopic lifeforms left in this ephermal ecosystem, but by night, it’s a different story.

At night, the rocks and sand of the valley at the end of the world are crawling with arthropods. These are not the cave beetles, nor are they the arachnids which died out in the South Pole. Volcanic activity may have killed the last of the South Pole’s myriapods, but not the small millipedes and centipedes which make up the last macroscopic terrestrial animals. A single millipede and a single centipede, each growing no larger than a baby’s finger, make up a predator-prey duo in this last refuge. They are not even the last myriapods, as even tinier aquatic centipedes are the top predators in the aquifers, but in this dying world they may as well be megafauna. The millipedes feed on lichens and plants and are more abundant than the centipedes, which feed on the millipedes, but also suck water from plants and lichen. During the summer months they aestivate, usually in deep rock crevices and burrows where precious dew can form as their only form of sustenance during this period of drought. Spring and autumn nights are their main, and only, time of significant activity. Centipedes only need a little food to survive per year, and in fact eating too much will kill them by using up precious water. It’s a shoestring existence, but it’s the only lifestyle that has gotten them this far.

Nevertheless, the Sun is still becoming brighter, and temperatures are still rising. Aquifers are either disappearing or eroding rock and receding deeper underground as a result, making the winter floods slowly become smaller and less frequent, along with the corresponding fogs and rains. A deep canyon forms and gives the lifeforms of the North Pole some more time, but within another million years the last floods occur. Without water, the last terrestrial ecosystem dies out within a figurative instant. The aquatic centipedes within the aquifer, however, will last until the disappearance of virtually all multicellular life at the Mortassic-Mortaceous boundary, 800 million years from now.

The last oxygen-breathing beings

795 million years from now

It is 795 million years from now. Animal life on the terrestrial surface has ceased to exist for millions of years due to the rising heat. The surface temperature of the Earth reaches 50 degrees Celsius and beyond. The oceans have been boiling away to the point where you could see the distant shore of a mid-sized ocean body from the other side of it, if it weren’t for the fact that the heat and overwhelming glint of salt crystals reflecting the oppressive sunlight would blind you. But even in hot water that reaches 40 degrees Celsius and is almost 30% salt, life survives.

Red algae, bacteria and archaea thrive in these hot, salty waters. Black yeast are present as well, as are tardigrades and loriciferans. And feeding upon the red algae are tiny crustaceans no more than half an inch long. They resemble shrimp larvae, and neotenic shrimp larvae is indeed what they are. The last crustaceans, they do not vary much in physical morphology but several different species exist with varying biological quirks. One species acts much like a photosynthetic sea slug in that it uses red pigments and chloroplasts from red algae it eats to photosynthesize, while other deeper-dwelling species live in symbiosis with chemosynthetic bacteria from which they derive food. Another species acts as a meso-predator upon tardigrades.

All of these in turn are prey for the last oceanic apex predator. This last predator is pathetic compared to oceanic leviathans of past ages such as sharks, orca whales, mosasaurs and even anomalocarids, but is a true tyrant in these ephemeral seas. At only 1.5 inches long, it is a tiny shrimp with pincers and mandibles which it uses to catch and eat prey respectively, and is very rare with a low population, as not to hunt its only prey into extinction. These «scorpion shrimp» evolved hundreds of millions of years before, but have not played a major ecological role until now. But this rule will not last long.

In five million years or so, multicellular photosynthesis will become impossible. This will cause free oxygen to disappear from the atmosphere, and suffocate all multicellular life apart from two species of hydrogen-breathing animal, a loriciferan and placozoan respectively. Life shall last another two billion years after that, but will spend the vast majority of that time as nothing more than lowly bacteria and later archaea. Back to square one, a kind of «book end» for life on Earth.

The last multicellular animals

845 million years from now

The Mortaceous, or post-oxygen animal era, starting 800 million years hence and ending 845 million years hence, was the final period of multicellular life on Earth.

It started when 200 million years of dropping carbon dioxide levels, starting 600 MYH when the aging of the Sun caused Earth to heat up and disrupt the carbon-silicate cycle, finally reached the level where photosynthesis, responsible for Earth’s oxygenated atmosphere for billions of years, was no longer possible. Within a few years, all plant and very likely algae species died out, and over the next few thousand years, oxygen was depleted from the atmosphere until it was only present at trace levels, spelling doom for almost all multicellular organisms, which by this point were reduced a few invertebrates and fungi in the disappearing seas and underground aquifers, as surface temperatures of over 80 degrees Celsius became the norm. After a few thousand years, all of these species were now extinct, with exactly two animal species being the exception, the final legacy of multicellular life on Earth. Formerly the underdogs of the animal world, they had now become the dominant species on Earth for the first, and only time.

The first species had its earliest known relatives in the Holocene Mediterranean. A species of loriciferan, several of its Holocene relatives had evolved the ability to breathe hydrogen rather than oxygen in deep ocean sediments, feeding on bacteria. These sediments were also saline, like Mortaceous oceans were, except the latter were far more so, comparable to the Dead Sea. Here, these hydrogen-breathing loriciferans, feeding on halophilic bacteria, live in hot, salty, slowly evaporating oceans, still physically massive but a fraction of the size and depth of the oceans of old, surrounded by massive mountains, canyons and inhospitable deserts of rock and salt, covered in the salt-encrusted, «fossil» remains of long-extinct marine fungal reefs, crustaceans and the last fish, descended from marine sharks which did not have to lay eggs which would perish in the salty water. The oceans are tainted red by halophilic bacteria, which is only fitting because the hot temperature of the surface and burning salt would remind one of lava, although it is of course not nearly that hot.

The other species was even more of an underdog than the loriciferans. Also an independent adopter of hydrogen breathing, the oxygen-breathing ancestors of the final placozoans were regarded by humans as mere biological curiosities. Now, in the red, hot, saline oceans slowly boiling off in the Mortaceous, the hydrogen-breathing placozoans formed what could generously be described as tiny «reefs», building finger-sized, sponge-like towers feeding on bacteria and particles in the hot water. They did not compete with loriciferans despite having similar food sources, as placozoans inhabited waters closer to the halite beaches while loriciferans lived in deep sea sediments. Radiotrophic stromatolites also lived along the shoreline.

Overall, the last 45 million years of multicellular life on Earth, though depressing, were also arguably beautiful. It was a reminder of both early Precambrian seas and seas before the Oxygen Crisis billions of years before, with hydrogen-breathing tiny invertebrates living in anoxic oceans. Archaea actually became more diverse than bacteria in the Late Mortaceous, already able to handle many extreme environmental conditions.

Alas, the Mortaceous was not to last. 838 MYH, the last placozoans became extinct as the oceans evaporated to the point that they were too salty even for these extremophilic pseudo-sponges. Seven million years later, the energetic expense of fending against both extreme salinity and extreme heat became too much to bear for the loriciferans as hydrogen respiration alone could not afford it. Animal life, and indeed multicellular life on planet Earth, was finished.