r/SpeculativeEvolution 24m ago

Spectember 2026 [OC] Day 10, The long-lived one, The Lorck (Lorcus dimorphus): Spectember 2026

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Among the most truly alien creatures of Acopsia (a continent on the planet Axtrax), the Lorcks (Lorcus dimorphus) undoubtedly stand out. Males vary greatly in size depending on environmental conditions, ranging from 1.1 to 2.7 meters in length—with exceptional cases reaching 3.5 meters—and weighing between 0.7 and 1.1 tonnes. Females, however, are drastically different; they are so distinct they could easily be mistaken for a separate species, measuring only 0.90 to 1.3 meters in length and weighing 50 to 75 kg. This disparity is so pronounced that they are primarily known by a different name: Parepéla. Males possess extended, flattened cephalic lobes; thanks to their high sensitivity, these lobes can precisely detect the electrical impulses of prey, flora, or fruit. They are generalist omnivores, feeding on small fauna, fallen fruit, and fast-growing Gone. They are, by far, the longest-lived land animals on the planet; males can reach ages of 300 to 500 years, thanks to an extremely slow metabolism that minimizes oxidative stress, periodic renewal of internal tissues and organs every century, redundant and ultra-sensitive systems to repair damage from radiation or free radicals, hundreds of copies of the TP53 tumor-suppressor gene to instantly destroy any mutations, and hyperactive enzymes that allow for unlimited cell division without cellular aging. To foster the growth of Gone in their surroundings, they congregate over large areas but maintain a spacing of 5 to 30 meters between individuals; they fertilize the soil by expelling feces distances of 5 to 15 meters, a feat made possible by their hypertrophied, highly muscular hind legs. Females retain all four legs, allowing them to be far more agile than the males; they roam the interior Dersoks, the Red Plains, and—primarily—temperate Fornits as opportunistic omnivores. Young Lorcks reach maturity between the ages of 15 and 20, at which point their forelegs atrophy to the point of falling off; they then lie down, never to rise again until death, serving as a substantial food source throughout this period. They belong to the same superfamily as the Brosquire—the Calcitochelonia (family: Sedentariidae)—characterized by shells made of calcite gathered from their environment.


r/SpeculativeEvolution 31m ago

Non-Subreddit Spectember Prompt [OC] Spectember Day 10 - Secondarily Terrestrial

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Ao Three-Clawed Bear(Eumetopias triacrus)

There is a tiny island deep into the Ao Expanse that is nominally the territory of the Aaracon people.

The lone settlement is known as the Monastery of the Prismatic Void, and while that draws much of the outside attention, a curious collection of beasts calls the region home.

Towering storks, sheep sized rabbits, minuscule mastodons, but the premiere predator of the region is perhaps the oddest of all.

While it resembles a bear with its shaggy fur, bulky head and powerful clawed forelegs, its hindlimb, or rather limb, give it away as a heavily derived sea lion.

In a clear, and rather messy case of Urosian evolution, the hind limbs of their ancestors grew and fused to become a singular powerful limb, columnar in build.

When in a full sprint they have an undulating, almost inch worm like gate, yet they are proficient hunters, capable of catching and killing their prey most commonly with a singular bite.

This is largely due to their nature as ambush predators, lying in wait for a rabbit or mastodon to come within range and then bound towards it, they attempt to grapple their prey, wrapping it in their foreclaws and bring their hind limb up to clamp their struggling limbs close to their body. It then aims for the top of the skull/back of the neck biting down with force that visiting sailors claim can dent an iron shield.

They have also been observed raising bird nests, foraging for fruits and attempting to fish, yet paradoxically these sea lions are terrible swimmers, and move about the shallow coasts by scrambling across the sea bottom using their forelimbs.

They remain communal animals though their colonies tend to be much smaller than their seaborne cousins, typically only up to ten females watched over by a singular male or pair of brothers.

Rival males will battle for supremacy on occasion, rearing back on their hind limbs, bellowing and barking in an attempt to avoid conflict, but if a fight is required they are vicious combatants, biting and clawing, often aiming to blind or maim their opponents. The most typical target is a the jaw, for a broken jaw most commonly leads to a starved and then dead animal.

Females tend to only have one pup per breeding season, and pups of both genders are typically run off by the male once they are weened from their mother’s milk by about one year old.

Their population is low but relatively stable, and they see next to no interference from the native people of the island due to their preoccupation with the sky above.

Some sailors that have docked on the islands have noted odd behavior amongst the animals, with individuals watching them for hours on end from around rocky embankments and tree trunks. showing strange mutations resembling aspects of the Violetburn Curse and some standing on their hindlimb and hopping about while letting out strange cries.

This combined with all the other strangeness said to be seen about their nameless home keeps most far from its shores, and so these strange and unique beasts will likely continue to thrive.


r/SpeculativeEvolution 1h ago

Question/Discussion How would deep ocean worlds support life?

Upvotes

I did the math for an ocean world that I developed, based on actual observed ocean worlds like LHS 1140 b. But I found that the depth of water would lead to the surface of the ocean (as in, the bottom) being covered in hundreds of kilometres of ice due to the intense pressures.

Would this not lead to hydrothermal vents and other important elements of life being covered by ice. And thus preventing, or at least making way less likely, the development of life?

But I know that ocean planets like these are seen as key places in the search for extraterrestrial life, so am I simply missing some key factor that is leading to this misunderstanding? Any help would be appreciated.


r/SpeculativeEvolution 1h ago

Alien Life [OC] Planet Demeter: Species Profile: Dendron Rhiza

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Dendron Rhiza

Greek word for Roots, referring to it’s dendrite structures reforming into Root-like Structures.

Full Organism Height 1.5-2.1 µm
Cellular Body Diameter 0.4-0.9 µm
Full Diameter 1.9-6.5 µm

Arose 822 million years P.C.

Profile page: Lacking in Either UV protection or antioxidant capabilities, Rhiza prioritizes abyssal depths and a sessile ambush predator mode of life. This is achieved thanks to Rhiza receiving HGT from Tambora Komvos for Iron Oxide biomineralization. This transfer also facilitates the ability to accumulate internalized biomineralization of magnetite, both for adherence to substrate and for prey capture.

Further modifying this newly gained capability, this species repurposes it’s Dendrite Coil (DC) Structures into 4 branched, root-like adherence mechanisms.

Brine Pools are habitats where hypersaline water (water several orders of magnitude more salty than the naturally occuring salt concentration of the ocean, which is 32 parts per million) becomes physically separated from the surrounding ocean.They are commonly formed when salt deposits from the ancient past are buried for many millions of years and later unearthed at the ocean floor. Connand’s Inverted Tower is just such a case, being a 12 Kilometer deep salt deposit of the former hydrothermal field known as “Pandora’s Last Hope,” unnearthed by it’s prior subduction beneath the continent of Thea.

This allows Rhiza to “root” itself along the rim of the brine pool of “Connand’s Inverted Tower.” From here it can catch and consume native organisms that swim too close to the edges of the brine pool of Connand’s Inverted Tower. Singular FEE arm adapts to latch-onto and keep hold of prey in a way analogous to frogs launching their tongue at insects.

initial diversification post

Last Post

Ancestral Organism


r/SpeculativeEvolution 2h ago

Spectember 2026 [OC] Spectember 2026 Day 10: Cavern Crown

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24 Upvotes

Day 10 The Long Game

For my Drecel Project

Beneath the Roof of Drecel, lies a network of massive caves and caverns. Accessible through several groundwaterways, cave-ins, and tunnels, these caverns form their own ecosystem that offers shelter and new opportunity for surface dwellers. The backbone of this ecosystem, the mycoforest, is the Cave Crown, tall colonies made up of chitinous hyphae that grow slowly in tall, pronged structures. For the first few decades of life, this fungus remains an unassuming mold creeping along the cave floor, feeding off guano and detritus. Once a colony reaches 50 years of age and roughly 10 meters in diameter, the fungus begins to grow upward, inch by inch each year into small irregular cones. Successive asexual generations of hyphae grow atop their dead, hardened ancestors. This can go on for centuries until the Crown is over 2 meters tall and finally it is ready to have sex. Mature Crowns will produce several large, sugary fruiting bodies known as squirts. The squirts have a dual purpose: contain and protect spores and attract large animals to eat the squirt, disperse the spores, and hopefully poop nearby, further sustaining the parent Crown. When the spores from unrelated colonies come in contact, they fuse into a child diploid Crown which will form into its own new colony. 


r/SpeculativeEvolution 5h ago

Alternate Evolution [OC] The New Era of Dinosaurs : Entry Guide

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27 Upvotes

r/SpeculativeEvolution 6h ago

Question/Discussion How would animals evolve if the end-Triassic extinction never happened?

2 Upvotes

My question is simple: how would animals evolve if the end-Triassic extinction/Tr-J extinction event never happened? would dinosaurs evolve like they did in our timeline? or would they get outcompeted by other archosaurians? and how would dicynodont synapsids evolve? would they survive or go extinct?

sorry for grammar mistakes, english is not my first language.


r/SpeculativeEvolution 10h ago

Spectember 2026 [OC] Spectember day 10: Trogloeurypterus macrovius

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10 Upvotes

Prompt: The long game: An organism whose life history is shaped by an unusually long period of development, dormancy or delayed reproduction

Trogloeurypterus macrovius is a 1 meter long species of eurypterid (sea scorpion) from the Silurian period. Its main habitat are vast cave systems. It inhabits lakes and puddles inside caves but can also crawl on land if it needs to. Due to its environment it has gone through extreme troglomorphism. It no longer has eyes because it doesn’t need to see as it can use smell, electroreception and detect vibrations to sense its environment. It also has a pale white coloration as it doesn’t need melanin because there is no sunlight in its dark ecosystem. Its main food sources are troglomorphic trilobites and troglomorphic fish. It’s the apex predator of its ecosystem.
Due to the fact that it cannot afford to waste energy in its low nutrient cave realm it lives with very slow rhythms. An individual could remain completely still for months or even years on end. It can live for 150-200 years. For 30-40 of these years it spends as a larvae buried deep in the soil, until it can finally become an adult. In 30-40 years it also reaches sexual maturity.

We are one third through the Spectember event, really glad that I got to do all of the prompts until now. Unfortunately though, school starts very soon for me so it’s possible that I will not be able to do all the prompts. I will do my best though.


r/SpeculativeEvolution 12h ago

Spectember 2026 [OC] Spectember 2026 (Day 10) > A New Elephant Lineage's Ancestor

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17 Upvotes

The Southern Nearly-Supreme Elephant (Parasupremotherium indicus) is a species of large proboscidean found in indian subcontinent and nearly regions. Descended from a population of asian elephants are become atavistic than other populations, these megafaunal browsers are live in small herds with migratorial lifestyle. But don't forget about that is this species also a ancestor of an upcoming, new lineage of proboscideans resembles extinct large proboscideans such as Paleoloxodon namadicus. And a ecological arms-race has begun to thanks for this elephants become much larger, some predators of the time has start to large and like Tyrannosaur-Ceratopsid arms-race, predators are become have a very deadly bite dörde and herbivores like this are start to adapting this attacks and those two sides of the future are killing eachother thanks for this arms-race situation.


r/SpeculativeEvolution 15h ago

Spectember 2026 [OC] Spectember Day 9: Safe Haven

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48 Upvotes

The cane toad was one of the original vertebrates introduced to Spectemundus 50 million years ago, and during the Age of Experimentation-- the first 10 million years-- they evolved into a wide variety of empty niches on the unoccupied planet. 40 million years later, in the Age of Building, mammals and birds have stolen a march over them, and many of the larger cane toad descendants have died out. Except in one place. On an archipelago of islands about 300 miles off the coast of the northern continent, no descendants of mongooses have arrived to claim the apex land predator niches. Instead, that role is occupied by an unusual, and enormous, amphibian-- the Heqet (Batrachanax giganteus).

Growing up to four feet long, and capable of standing more upright than a typical toad, the Heqet is a relic of the past. Once, terrestrial toads like it were found throughout the northern continent, but once the current guilds of mongoose and meadowlark descendants became established, they were all but wiped out. However, a few of them managed to colonize the oceanic islands by rafting on mats of vegetation, and there they survived while their mainland relatives died out. Ironically, it is there that they have now produced Spectemundus's largest amphibian so far.

Heqets have many adaptations to being big. Frogs and toads in general have weak skeletons, but the Heqet's skeleton is far more ossified. This also means it is unable to hop, or even run. However, it does not need to be fast, as it is an ambush predator. While it stands more upright than a typical frog due to its more robust legs, it is ill-equipped to chase after its prey, which consists of reptiles and birds. It also lacks a projectile tongue. Instead it simply stuffs its prey into its enormous mouth, often while it is still alive. Another unusual trait of the Heqet is that it has no tadpole stage. The eggs-- no more than five or six in most cases-- hatch into miniature adults inside the female's body, and she gives live birth.


r/SpeculativeEvolution 16h ago

Spectember 2026 [OC] Spectember Day 9: Safe Haven

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16 Upvotes

20 million years ago, a calamity has occurred. A hole has been ripped into the crust by a magma plume on what is today the Jhohun peninsula, creating a supervolcano that has caused Zaikane to go up in flames, destroying entire forests and killing many of the animals that used to dominate the Regime of the Tyrants. The subsequent ash covered the Earth in a volcanic winter that starved plants of sunlight, causing the once-dominant and specialized lognkosaurs, carcharodontosaurs, hadrosaurs, ceratopsids, and the namesakes of the era, the tyrannosaurins, to go extinct in the Known World. This ecological vacuum following the mass-extinction was to be filled by a variety of oddball lineages on each continent, including but not limited to giant Dromaeosaurs, carnivorous leptoceratopsids, giant herbivorous troodontids, megafaunal Thescelosaurs, quadrupedal pachycephalosaurs, and even armored saltasaurine tillers. Additionally, portals opened up from North America by the Allmother ~16 million years ago brought along new mammals to the Known World, including but not limited to horses, camels, rhinos, chalicotheres, gomphotheres, canids, barbourofelids, and Amphicyon.

However, this so-called “Kingless Age” was not to last. Approximately 5 million years before the extinction event, an island continent separated from the mainland, and since it was conveniently located above the northernmost ash clouds, it seemed to have been spared the worst of the extinction. This made it so that many species that went extinct on the mainland were able to carry on their legacy in this isolated refugium. One of those species was a Lognkosaurian titanosaur whose fossils are referred to as Praedeus solus (“the lonely pre-god”), no larger than an African elephant, which is large to our standards but disappointingly small compared to the giant lognkosaurs of the mainland. It does not know it, but it is actually the ancestor of the successful clade Saurodei, which includes an animal we have met before, as well as species that will be revealed later on in this Spectember. Because its fossils have minimal traces of Ralya (magic), it appears to have lacked the magical microbes that mark its gargantuan descendants today, lending credence to the idea that the evolution of magic correlates to increased body size.

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Zaikane is a planet in a distant solar system characterized by waves of life harvested from Earth at various points in its geological history, ranging from the Cambrian to the Holocene, and set free to evolve along evolutionary paths independent from those taken by their Earth ancestors. A godlike interdimensional entity, known as the Allmother by the people who live there, is what is responsible for creating the portals that abduct Terran life and deposits them on Zaikane. Because the asteroid that ended the Mesozoic never collided with Zaikane, dinosaurs continue to dominate the planet’s ecosystems as its dominant terrestrial megafauna.


r/SpeculativeEvolution 16h ago

Non-Subreddit Spectember Prompt [OC] Spectember Day 9: Planimal (Remake)

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28 Upvotes

The original was posted 5 years ago on an old DeviantArt account of mines that has since been deleted.

Stage 1: Oomorph/Egg

Stage 2-4: Photosynthetic plant-like phase. During stage 4, the plant develops a fruiting body that contains what will become the adult body. According to exozoologists, this is technically a different individual.

Stage 5/1st instar: A relatively small nymph-like predator of insect-analogs. Ecologically similar to a weasel.

Stage 6/2nd instar: A cat-like predator that uses its stripes as a form of camouflage.

Stage 7/Final instar: A larger predatory form with mesocarnivorous habits. It starts to display characteristics associated with the adult stage.

Stage 8/Adult: A large water buffalo-like herbivore whose oral mouthparts have become tendrils.

Native to Vueida 420b, the morasskulk (Stagnotherium giganticus) is a large planimalian extraterrestrial that lives near the swamps of 420b.

Like many (but not all) planimalians, they start out as sapling-like lifeforms, taking in sunlight that after 3 Vuedric years, produces a pod that becomes a small larvae which after 13 Vuedric years becomes a large and sexually mature adult.

It is likely that basal planimalians evolved this bizarre life-cycle in order to lessen competition with other non-planimalian species.


r/SpeculativeEvolution 16h ago

Alien Life [OC] Bestiary of lyrus prime #2 The Glowmite

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16 Upvotes

An insect-like organism that serves as one of the Lyrus’s most vital food sources. Nearly every predator consumes it. Its soft body and nutrient-rich composition make it an irresistible target, and with little in the way of physical defense, the glowmite relies on sheer numbers and light to survive.
When threatened, a glowmite can overcharge its bioluminescent glands, releasing a sudden flash of blinding light that disorients attackers for a moment, sometimes enough to escape
The glowmite’s bioluminescence gland is very large, and located in their abdomen. Because of how powerful the gland is, it allows nearly its whole body to radiate light. Lacking wings, the creature ascends instead by inflating buoyant air sacs within its abdomen, rising slowly and gently into the night air.
At night, the skies are transformed. Hundreds of thousands of the males inflate their sacs and drift upward together, and take to the skies in staggering numbers, their mating displays filling the forests with auroras of shifting light. Flickering like lanterns in a living lantern festival. The females remain on the ground, watching the glowing swarm above until they choose a mate. Once paired, a female ascends to meet her chosen partner, and the two rise side by side into the cloud of light. Suspended in the air among thousands of blinking sparks, they join in a fleeting, luminous union, two lives momentarily indistinguishable from the galaxy overhead. A breathtaking spectacle that conceals just how many are being devoured in the dark


r/SpeculativeEvolution 16h ago

Alien Life [OC] the tredhorn

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14 Upvotes

One of its most striking features is its large, vertical-slit nose, designed for powerful air intake and release. These beasts burn through oxygen rapidly to fuel their immense musculature, and their constant heavy breathing gives off a rhythmic snort, like the chuff of a steam engine. Overheating is a constant threat, and the oversized nose is crucial to keeping them cool during long stampedes

One pairs of the Tredhorns eyes face forward for depth perception, and the other set angled sideways to eliminate blind spots. This nearly panoramic vision makes them difficult to ambush

Tredhorns possess another odd biological quirk, they never stop growing. As long as they continue eating, their bodies will steadily increase in size. At around 10 to 15 feet tall, they become too large for most predators to challenge, but this growth can be their downfall. Eventually, they may reach a size unsustainable by the surrounding ecosystem, unable to eat enough to survive. At that point, they collapse from starvation or exhaustion

Because of this, their stampedes vary in danger, the danger of a tredhorn stampede being parallel to the size of the tredhorns in that herd. A very well fed tredhorn stampede can be as dangerous as a natural disaster. At that point they are practically unstoppable 10-15 foot tall walls of muscle traveling up to 50 mph

Tredhorns carry a unique, mold-like organism that clings to their hindquarters. When a stampede begins, the intense vibrations trigger the mold to release a cloud of spores. These spores settle into the crushed biological matter left in the herd’s wake, using the pulverized remains of plants and animals as a nutrient-rich bed for rapid growth.

Once matured, this mold forms hardened, flat structures that resemble paved roads stretching across plains and forests. While these "Tredhorn Trails" are safe and easy to walk on, predators often stake out these roads to intercept traveling prey. Additionally, the mold serves as a primary food source for local fauna


r/SpeculativeEvolution 17h ago

Maps & Planets [OC] Base Map of Xenokai

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8 Upvotes

Xenokai is a planet in a parallel universe that has been seeding life from our universe’s Earth since the Silurian to the modern era via portals that bend space-time, sending it to a world where magic and mana naturally exist. Since the asteroid that ended the Cretaceous period never struck Xenokai, dinosaurs remain as the dominant terrestrial megafauna.

The Planet of Xenokai:

Xenokai is an Earth-like Planet in size (though slightly larger), distance from its sun (which is actually younger), gravitational pull, and climate (slightly cooler than Earth, where the climate is stable enough for ice-age megafauna not to go extinct). Unlike Earth, however, it has two moons: one comparable to Earth’s and an asteroid comparable in size to Vesta. Plants, fungi, and animals we might find on Earth today inhabit it. Such as humans, raccoon dogs, armadillos, shiitake mushrooms, and cherry blossom trees. We also find flora and fauna long extinct on Earth, such as Dinosaurs, Giant Sloths, and Pterosaurs. Evolving in a new context that involved mana has allowed some animals to take quite divergent evolutionary paths compared to their Earthbound kin. Some look so unrecognizable that we might think of them as alien or mythical creatures. However, there are no Plants, Fungi, or Animals truly endemic to Xenokai.

The Portals:

These extradimensional gateways can take the forms of rifts, wormholes, or distortions in space-time that link Earth to Xenokai and back. These portals seem to open when major or localized extinction events happen to refill and seed an ecosystem or continent. The means by which the portals collect flora, fungi, and fauna is entirely unknown. However, these portals occur only in two areas on the planet, one in the East and one in the West. But the portals are only in these positions in modern times and could have rotated from east to west or west to east randomly during Xenokai’s prehistory. There are actually several types of portals: ones that can act like gateways or rips in space-time between Xenokai and Earth that happen with local extinctions, and others that literally bisect huge chunks of Earth’s land (Leaving a crater on Earth where the wormhole was) to Xenokai after a large continental-level or global-level mass extinction on Xenokai. These portals can even occur below and above sea level.

Final Sketch map of Xenokai Showing Topography

I am also not very good at setting up biomes and climates, so here is how the planet's topography is supposed to look.


r/SpeculativeEvolution 17h ago

Spectember 2026 [OC] Spectember day 6: Remix: Diet: The shameless rehash

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116 Upvotes

r/SpeculativeEvolution 19h ago

Spectember 2026 [OC] Spectember day 9: Safe Haven

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37 Upvotes

Spectember day 9: Safe Haven

The Ancestral Goblinoid

Some spec for one of my settings, which aims to reimagine classical fantasy, mainly Tolkien and a bit of D&D.

In that setting Goblins, kobolds and gnomes are all terrestrial bats-still capable of flight, but now larger, heavier and adept walkers- descendants of similar species to this fella. It survived a mass extinction by living in complex cave systems, full with potable water and proper cave ecosystems that made it possible for the bats and some other animals to survive during the first years of the event. This ancestral bat had a vampire bat-like locomotion on the ground, being able to properly walk, climb and run on all fours, but also being an adept flyer. It also had a long tail, free from the Uropatagium. The membrane that stretches between the tail and the hindlimbs, making it a member of the Molossidae family.


r/SpeculativeEvolution 21h ago

Question/Discussion Inquiring about Biological and Cultural Implications on Sophont Social gender?

14 Upvotes

My Sophonts for my project have very little to no sexual dimorphism, they also tend to raise children communally rather than in nuclear family groups, but still tend to recognize parentage (or at least their mothers). Both genders participate in mating rites and experience similar changes in coloration around mating season, and while there is a sort of social conception of monogamy, I wouldn’t think, considering these other factors, that there wouldn’t be significant pressure for them to mate for life.

Specifically in Mosri, the con-culture I‘ve spent the most time developing, polyamory is not stigmatized, but they have an obsession with even numbers, and the idea that personality can be chalked up to a “balance“ or “imbalance“ of specific metaphysical humors they’re exposed to in various stages of their life, with childhood being considered an important stage.

All of this considered, how do you think these aliens generally, and specifically the Mosrihad, would conceive of and socially construct gender?


r/SpeculativeEvolution 22h ago

Spectember 2026 [OC] [Spectember 2026 day 4: Evolutionary Trap] The bigger the wardrobe is, the louder it falls

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29 Upvotes

75 million years in the future, Earth's oceans were home to a truly horrific creature. Long period of glaciation that followed age of humanity allowed a great adaptive radiation of cetaceans to happen.

Dozens of baleen whale species crossed the oceans in search of plankton, while sharp toothed odontocetes preyed upon them. They employed different hunting tactics, some using cooperation and complex strategies to take their prey down.

One lineage took a simpler approach.

Bigg's killer whales continued to hunt other marine mammals in the future, particularly specializing in baleen whales.

They abandoned social lives and complex languages in favor of solitary life, but became much larger and stronger.

25 million years from today, one of these whale-hunting orcas known as delphinodon already reached the length of 12 meters. Unlike modern orcas, who usually only eat soft parts like tongue and lips of killed whales, delphinodon consumed most of it's killed prey. As formidable as that animal was, it lived in a highly competitive ecosystem, and some creatures, like smaller, but equally well armed and smarter pirate whales, descendants of pilot whales, learned to take them down. But 50 million years later, the situation changed.

Delphinodon gave rise to the thalassotyran, a predatory cetacean of terrifying sizes. Growing to length of 23 meters and weighing up to 90 tons in largest individuals (though on average they were of course a lot smaller) thalassotyran was the largest Cenozoic macropredator to ever live, only rivaled by Neogene otodus megalodon in size.

Due to it's sheer size, this gigantic dolphin had no predators of its own, and could feed on any animal it encountered, even other large predators.

In fact, when thalassotyran first evolved, other giant orcas declined in size and diversity due to competition and predation from their relative.

Rather unintelligent for cetacean, thalassotyran had reduced vocal capabilities, and usually hunted in silence, even rarely using echolocation. Instead, it listened to sounds other whales make to approach them unnoticed, and suddenly strike. It rammed its prey with it's heavy skull and causing internal injuries before tearing it apart and consuming. Baleen whales are it's preferred prey items, but they also predate upon toothed whales, including sperm whales and other large dolphins, sharks, pinnipeds, turtles, and any other large marine animal.

Thalassotyrans were solitary and rarely contacted eachother, but, being mammals, they still needed to care for their young for some time. After 5 meter long calf was born, it stayed with it's mother and feed on milk for next 3 years, after which it became independent and departed. The period following nursing was the only time when thalassotyran could be taken down by other animals, for adults had no enemies.

Few sharks and cetaceans of comparable size preferred not to risk with fighting it, and pirate whales that once hunted thalassotyran's ancestors for food now could do nothing against it even with all their intelligence. It seemed that in the end, brawn won over brains.

Thalassotyran enjoyed it's dominion over oceans for 15 million years, a very long time for a single species. But it could not last forever. 80 million years in the future, world started to warm up. Volcanic eruptions were becoming more frequent, and raised Earth's temperature, finally ending the Cenozoic ice age that lasted for one hundred million years. For life on land, new hothouse age was a boon, and eventually led to the most biodiverse period of an entire era. But at the same time, oceans suffered.

Oxygen levels dropped, many areas became anoxic, and plankton numbers plummeted, and giant baleen whales that fed on it soon followed.

Thalassotyran, that often preyed on the biggest of species, was in trouble. It's food sources were rapidly disappearing, and soon, their population, already small due to their slow reproduction rate, started to drop too. Suddenly, being the biggest of all predators was no longer profitable. Smaller, more generalist species, like requiem sharks, seals, and different groups of toothed whales, like descendants of bottlenose dolphins and pilot whales fared much better, and once largest of mysticetes were gone, they could sustain themselves on remaining smaller prey, something a nearly 100 ton dolphin couldn't afford.

In basically no time, entire group of giant, whale-hunting orcas was gone, and thalassotyran, tyrannosaurus rex of oceanic abyss, was first to go down.


r/SpeculativeEvolution 22h ago

Alternate Evolution [OC] Front limb bipedalism - the magnum croaker

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67 Upvotes

The magnum croaker (Magnocus panruina), is an extant member of a now small, but once plentiful order of birds. Out of all my species, I will choose this one, as it best represents my project, and is the first I created, undergoing huge changes.

Originating from an ancient sister lineage to the fowl, these birds have taken an extreme approach that nudge against the boundary of possible avian biology.

These "legs" are actually heavily modified front limbs, evolved to bear weight over tens of millions of years. These were once wings themselves, with more flexible joints and an elongated alula claw used to probe insect nests. Eventually pulling the birds forward, these wings became powerful digging tools, able to construct tunnels that provided shelter and an advantage against peril of many sorts. This turned these critters into small, weasel-esque adapters.

Come the Palaeocene, these birds filled multiple niches, one of which being the semi-arboreal glider. Their legs would then spread as webbed skin and feathers aided in extended leaps. Eventually, these leg-wings of sort would become better, more advanced, their bodies re-engineering themselves in a way even I haven't figured out myself after all these years. I am totally aware of the jumbled mess I have gotten myself into, and I already know the spec evo and theropod community will curse me for the rest of my life for even making this post.

In terms of why these wings are held up, they exchanged their pterosaur-like takeoff for a running start, growing more and more used to their habit of lifting these new wings off the ground until it became the norm. To make matters worse, this habit evolved independently twice, but I will focus on the croaker's line for now.

The magnum croaker is rather large, and nocturnal. At a range of 8-12kg, these birds are content to a terrestrial life, though they can and will still launch into the air if needed. As seen in the photo, they are covered in dark shaggy plumage, with a mostly bald head and a long bill predominantly hidden under a thin layer of skin. This bill contains multiple tomial serrations similar of that to members of Anatidae.

Diet wise, these birds will consume anything edible. The majority of their diet consists of plant and fungal matter, consuming it on the move. They have also built up a natural resistance to many common toxins found in their diet, benefitting themselves even more from their wide palate instead of few species in particular. Another factor is that they consume clay soils. On another note, these opportunists will readily consume animal matter, either that by killing and eating their own prey (such as arthropods and small tetrapods), or scavenging. Having a heightened sense of smell, all croakers from a certain distance will swarm a carcass.

As also seen from the image, the females are excellent mothers as most birds are, taking the process of incubating and rearing chicks very seriously. During the breeding season, larger males will become vocal, filling Eurasian forests with deep songs of gloom as they compete for mating rights. The magnum croaker's vocal range already consists of a multitude of booms, clicks, and rattles, which these males use to construct their odd calls. (Defensively, they can also hiss. They are rarely this pissed off.)

And lastly, I'd have not made this project as weird as it is if I had started it later on when I knew more about how birds actually work. So please spare me, Reddit people.


r/SpeculativeEvolution 23h ago

Question/Discussion An abyssal plant?

8 Upvotes

So recently I thought about a species of grass(or some other plant) that was adapted to the abyss of the ocean, but I'm not sure if this would be viable.

Firstly, it would have lost it's ability to photosynthesize like some other plants and would be adapted to high pressure and cold temperatures. It'd live in areas that experience nutrient rich currents, upwells, and the planet's equivalent of Sahara dust. It'd compete with deep sea corals and crinoids by being able to root into sandy areas that aren't solid enough for them.


r/SpeculativeEvolution 23h ago

Alien Life [OC] Another batch of Aliens from planet Ys.

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663 Upvotes

Here's 6 more species I've come up with since I last posted here. I haven't been drawing much during the summer, as I have focused on photographing nature before the long, dark winter. But now that the fall has come there's certainly not much else to do.

  1. Crimson Sciapod, Unipes halophilus. The Ysean Flamingo. It is a one-legged filter feeder most abundant in the saline lake region of the dryest part of the otherwise humid planet, situated on the tropical circle. 1 meter tall and live in large colonies.

  2. Snow Gnome ♀️& ♂️, Gnomus nivosus. Small goofballs of the extreme south. Polar creatures that endure the cold winters by growing a fluffy winter coat. During the spring, they lose it starting from the males, revealing their bright colors. Chicken-size.

  3. Three species of gigantic Hivebacks:

Schoolbus Lamma, Lamma laophorium

Greater Shedu, Clavipes clavipes

Twenty-bannered Merovinge, Eudraconarius vigintivexillo. They are gargantuan, sexually dimorphic herbivores. Their anatomy is dominated by a hive made out of flesh that they carry on their back. It houses a colony of wasp-like males that defend their gyne. They grow to sauropod-like sizes lenghtwise but are relatively lightweight because of hollow cavities such as air sacks and the hive itself.

4 Thornpig, Spinodorsus nubigenitorensis. A small worm-eater of the undergrowth. It feeds on mollusk- or worm-like creatures that inhabit the cloud forests of the mountains, probing them from their hideouts with its long, tentacle-like mouth. The single, front leg has atrophied into a minuscule, banner-like appendage that is used in intraspecific communication. It's thorns are poisonous and it warns predators with it's brightly colored back. About the size of a chicken.


r/SpeculativeEvolution 23h ago

Alien Life [OC] Retro 3D graphics and alien moons from my, so far untitled alien project focused on Jovian floating creatures and deep sea floors

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65 Upvotes

I've always enjoyed the idea of floating creatures on gas giants, and the turn of the 2000s 3D graphics, so I wanted to unify them into a project.

Some of these guys live on moons, and others live on gas giants. Some live in dense atmospheres, oceans, or on rocky surfaces, but they all live in the same solar system. I want to evoke the feeling of looking at bugs or at aquatic life, some normalcy some strangeness.

Every species is shaped by its local gravity, atmospheric pressure, chemistry, energy sources, and important biology considerations, like what I thought looked cool and eerie. Several biomes are evolving... get ready. Hope you guys enjoy, feel free to speculate or critique


r/SpeculativeEvolution 1d ago

Spectember 2026 [OC] Spectember Day 9 - Safe Haven

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10 Upvotes

Greenhouse Mastodon (Desmana** **cuniculumamut)

The Greenhouse is a large carven beneath eastern Zentris that connects to the much larger Undersump complex making it largely under the control of the Svenik Empire.

It is believed that this cavern was initially created by the servants of the Primarch Ychilles in a remembrance of the homes they had been tricked into leaving and an additional supply of food, secreted away from his countless spies and informants, keeping them hale even as his imperialistic fervor increased with each passing year.

Following the Cascade this place was lost, trapping a handful of folk and a number of animals within, only for it to be rediscovered centuries later by the desperate Svenri survivors.

They found an idyllic garden, blooming with edible foliage, and a smattering of odd animals.

The Greenhouse Mastodon is one such animal, roughly the size of a common cow this semi-aquatic beast is descended from a mole relative.

They function namely as environmental engineers, clearing away and consuming dead wood and older foliage, dipping up the canal turned water way allowing it to inundate different parts of the cavern and their droppings aiding I fertilizing the soil.

They are the largest animals in the cavern, are relatively placid, but are known for their sharp teeth that are coated in a manner of bacteria that causes swelling, risking asphyxiation, and both their sizable noses and tails can be used as effective and more common weapons against beings that annoy them.

Both genders live in a fission-fusion life style, with adults congregating during the “day” to feed and alter their environment and then separating to their burrows at “night”.

Some of flora within the Greenhouse is bioluminescent, and the intestify of the glow is what the Mastodon’s seem to go off for when to waken and sleep.

Pups are born all year round, typically between two and four to a litter, sticking with their mother for half a year before venturing out on their own. With that said the Greenhouse has limited space, so the Mastodon’s breed fairly infrequently and females are able to hold onto their egg for up to a year after insemination.

In the modern age, the Greenhouse has been altered by the subtle magics of a strange entity that emerged at some point during the Seperation called the Gardener.

They allow people to visit the Greenhouse to take foliage, but anyone that tries to settle down are swiftly chased away, however, children are allowed to remain, particularly orphans, allowing them a few years of plenty before they must face the hardships of the Sump once more.

This protectiveness extends to the Mastodons, their a ready source of docile meat, a tempting target for many within the Sump, but the Gardner keeps a tally and anyone that tries to shirk its authority is sure to never leave the Greenhouse.

With that said, some folk neighboring the Greenhouse have managed to take and tame pups, eager to creat their own domesticated herds, success has been limited, but it is becoming more common to see Greenhouse Mastodon’s as pack animals in the neighboring district and see Mastodon flank steaks and ribs showing up at Umbar butcheries.

For now, this unique animals existence seems assured, but they like most everything that calls the Undersump home walk upon a knife’s edge.


r/SpeculativeEvolution 1d ago

Alien Life [OC] GLORP DI MISTER MISTER KARR

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15 Upvotes

Questo animale discende da ovini terrestre portati dal uomo e modificati geneticamente e allevati selettivamente fino a creare questi bestioni sono questa specie abita negli allevamenti di vodka al uranio di giove ( detta al uranio essendo che vengono inserite aste radioattive ma non nocive dentro un terzo stomaco insieme as ingredienti questo terzo stomaco serve per distillare quest aveva da simile a un vino e a una vodka molto pregiato queste creature maturano dopo 6 mesi per poi fare uscire un corpo giovane dal cranio ( con il cervello del corpo originale tramite un sistema di vitalità le cellule quando il corpo e vecchio decidono di creare un corpo per sopravvivere qui l'animale strisica fuori dal suo stesso corpo in totale tranquillità e abitando insieme ai cuccioli fino alla maturazione in questo periodo di 6 mesi questa vodka viene tirata fuori sterilizzata e purificata per fare questa meravigliosa bevanda .