Species revival

A species revival is a type of retcon where a species that was once considered extinct is brought back to life.

Species may be revived for a variety of reasons, such as:
 * They were mistakenly assumed replaced when they were not / were only replaced locally
 * They were mistakenly never added to the ecosystem page
 * They were not added to all of their biomes on submission, resulting in them dying out when they should have survived in one of the excluded biomes
 * They were mistakenly removed from the ecosystem page while a neighboring species was also being removed
 * They were replaced or outcompeted, but the reasoning was deemed implausible and was thus undone
 * The parameters of an extinction event were retconned, resulting in a species getting through that didn't before
 * A biome was falsely flagged as extinct or was not succeeded correctly
 * They were mistakenly absorbed into a genus group that they did not belong in
 * A species was retconned into existence that saved them

Species revival may also refer to cases of species having their extinction date changed to be much later, even if they ultimately were not revived to the present day; this is the case for the vast majority of species found to have been killed by mistake. Some species that had their extinction date moved, such as the Desert Soriparasite, produced descendants afterwards as part of a separate retcon event; these are counted as revivals.

If you find a species that you believe should not be extinct, make sure to contact a staff member. They will investigate the extinction thoroughly, and in some cases the species may make it to the list of revivals.

Species that were at one point revived
These lists are incomplete, as revived species were not recorded with this much specificity before now.

Assumed replaced

 * Rainbow Marephasmatis

Never added to ecosystem page

 * Purple Poison Shrub

Not added to all biomes

 * Desert Soriparasite (cave was excluded)

Accidentally removed from ecosystem page

 * Uksip Marfinnus
 * This was the first major revival (second including Coolsteph Island's biota), which inspired investigations into more extinctions. Though its survival was overshadowed later by the more impressive Rainbow Marephasmatis, such an ancient species surviving through every single mass extinction event inspired hope that other ancient lineages that were lost to neglect or metagaming might be able to return.

Implausibly replaced

 * Fishing Grasper
 * Cave Rustmold and symbiotes
 * Species affected by burncumference
 * Dreidalbulb
 * Snohawkworm
 * Warf Gossalizard
 * Tundra Plyent
 * Burroskunik
 * Snow Puff
 * Xidhorchia
 * Windbulb
 * Pink Phlyer
 * Mini-Flower Ketter
 * Toxplage
 * Toxplage Ketter
 * Tundra Orbibom
 * Taloned Phlyer
 * Woollycoat
 * Polar Spade-Leaf

Extinction event parameters changed

 * Pre-ice age ocean biota
 * Sting Cell
 * Gomphioculum Microscopica
 * Megaorthoceros Segnoneustes
 * Funivenator Organuculus
 * Glirodlium Istaruthus
 * Crescoquin Scindestus
 * Wykraline
 * Macululuchia
 * Disturbed Infectoid
 * Sudline
 * Flashing Filtersquid
 * Symboather
 * Crastrum
 * Gilltail
 * Squarenet Crastrum
 * Featherbelly Foi
 * Cleaner Crastrum
 * Disorderly Gelatin
 * Hunting Darkswarmer
 * Sunlit Plagu
 * Oceanrorm
 * Cnidolium Simplistica
 * Megaorthoceros Circumorphos
 * Trikskirt
 * Doubent
 * Whorl Needler
 * Whorl
 * Pre-ice age vent biota
 * Vent Shrubite
 * Vent Urchip
 * Blind Foi
 * Necrotic Arrowhead
 * Ventrapper
 * Marfos
 * Xxeljet
 * Marocta
 * Rearing Swarmer
 * Vent Darkswarmer
 * Xxeltrapper
 * Swarmhunter
 * Martyr
 * Giant Pyavent
 * Sucker Foi

Accidental biome extinction

 * Artir beach biota
 * Thornshell
 * Polar Cellulosebane
 * Grubnub
 * Hornsniffer
 * Polarblades
 * Lickworm
 * Polar Ukback
 * Snowsculptor Janit
 * Flugwurm
 * Twinecoat
 * Purple Dotter
 * Raq coastal biota
 * Follower Gilltail
 * Broadleaf Calmstrum
 * Tethered Mine Layer
 * Double Bubblgea
 * Speckled Pumpgill
 * Raq Urpoi
 * Ovi Salt Lake biota
 * Globespot Gilltail‎
 * Golden Siever
 * Rhopa
 * Lacrimuck
 * Dartfin
 * Coolsteph beach biota
 * Boomsticks
 * Boomcracker
 * Hopketter
 * Fisticoat
 * Vermair
 * Shockscooter
 * Eeyore Stalks
 * Smoothcoat
 * Glacial beach biota
 * Polar Orbion
 * Bloodskin Skywatcher
 * Global glacier biota
 * Ice Teuthopin

Saved by retcon species

 * Many species saved by tlukvaequabora

Other

 * Genteel Tuskent - found to have been bred to be under the size threshold for the extinction event by sapient tripodicians

Requirements of Pre-Snowball Revivals
The vast majority of Sagan 4's biomes cannot trace their ancestry back forever, as there was a nearly complete biome turnover during weeks 21, 22, and 23 that wiped out more species than any other extinction event. The vast majority of ancient species found to have been falsely killed off ultimately die in the snowball event. However, there are a small handful of "sweet spots" where an ancient species is capable of surviving to the present day.

In order for a species to survive the snowball event and reach the modern day without assistance, it must meet all of these parameters:
 * Be in one or more of these biomes:
 * Any polar beach
 * Any hydrothermal vent
 * Any ancient volcano
 * Both sunlight and twilight zone of the open ocean
 * Darwin Tundra (became the modern Drake Tundra)
 * Any glacier
 * Some rivers (someone please add a list)
 * Be under 1 meter in size
 * If it is aquatic, be determined to be capable of surviving ancient polar seas
 * If it is terrestrial, be sufficiently adapted to life in a polar environment

If the species' date of incorrect extinction was before generation 100, it must also be able to survive the gamma ray burst, which requires at least one of the following adaptations:
 * Burrowing
 * Deep sea diving
 * Spelunking
 * Extremely high reproductive rate
 * If it is a plant, have a predator that stores its seeds or spores in burrows for later consumption

Exceptions
In rare cases, a species may make it through without meeting all requirements. This may happen if another species modifies it in some way which prevents it extinction. The gamma ray burst had many of these, mainly in the form of burrowers storing or farming food, though many of them may have been able to survive regardless; however, the most clear-cut example is the survival of the Genteel Tuskent, which was revived after it was found to have been literally altered by another species through domestication, which just happened to put it under the size threshold for survival at the end of the snowball event.

Another type of exception is one where a lineage is revived through a descendant being inserted into canon retroactively, usually in the case of species killed off by habitat loss. This happened to waxfaces, goutis, cheekhorns, goth trees, and several others.