EBAD: The End-Binucleiozoic Atmospheric Disturbance


(End of an Era, illustrated by Nergali)

Summary

EBAD occurred at the end of Week 3, a severe crash in nitrogen and oxygen levels which caused a mass extinction. It wiped out all of Sagan 4's largest flora and fauna, disproportionately impacting large chitinous organisms such as crystal flora and arthrotheres. With a massive floral turnover and die-offs in many major clades, it is time for survivors to sally forth and take their place in a new era.

New Rules

Due to a reduced supply of nitrogen, there is now a permanent cap to the size of chitinous flora (i.e. crystal flora and cryoflora). Chitinous flora may not exceed one meter in size unless it has an alternative method for acquiring extra nitrogen (e.g. carnivory, symbiosis, etc.).

Oxygen levels remain low for the duration of Week 4. For this Week only, any new fauna over two meters in size must include respiratory and/or circulatory adaptations to low-oxygen conditions if they are to maintain a lifestyle with consistent high activity. A largely passive organism, such as one that drifts around or is sessile, does not require such adaptation, nor does one that is passive most of the time but has occasional bursts of activity, such as a trapping carnivore. Once an organism has established low-oxygen adaptation, its descendants do not need to add further adaptions as long as they retain the old one(s).
As a special exception, Dorite Island and the beaches and salt flat around Dorite Sea are exempt from the need for respiratory/circulatory adaptations for large fauna. This area is below sea level and has noticeably higher oxygen levels than the rest of Sagan 4's land.

Additionally, for Week 4 only, the entire abyss is anoxic. Aerobic species may not inhabit abyssal habitats unless they also inhabit habitats that do contain oxygen and are capable of storing oxygen for the duration of their visits to the abyss.

A History of EBAD

The last days of the Binucleiozoic began with flourishing, not death. New subduction zones and expanding rifts produced carbon dioxide in profusion. Moreover, the rising temperatures combined with tectonic movements increased the total area of rainforests. Under such conditions, flora thrived and proliferated in greater numbers than ever seen on Sagan 4.

Yet in this flourishing lay its own downfall. The largest trees on Sagan 4—especially in Hybarder—were crystal flora, which used chitin in its cell walls and to produce their tough crystal-like shell layer. Taking advantage of these conditions, some grew larger yet, producing at their pinnacle the Greatest Crystal Fortress; a single individual could grow to 480 meters wide and 240 meters tall, shadowing the land and sinking into craters of their own making.


(Greatest Crystal Forest by Disgustedorite)

As floral biomass soared, more and more nitrogen became sequestered in crystal flora, where it would take far too long to decompose and become available for new life to use. The nitrogen cycle, no longer able to keep up, strained until it broke down. Nitrogen availability crashed, making it difficult for any large flora to acquire the nitrates necessary to survive. Chitinous organisms were hit even worse, however, suffering great difficulty in producing their chitin, resulting in massive die-offs among all large organisms that used it, whether flora or fauna. This disruption to the food chain also spelled death for all fauna who relied on chitinous flora as part of their diet. Although many of the smaller species bounced back after the crash, their populations had dwindled during the worst of it, making specialists who ate them unable to sustain themselves. Phytoplankton dwindled as well, damaging the marine food web.

Meanwhile, oxygen levels had already undergone a gradual decline alongside the rise in carbon dioxide (the two being strongly correlated). The sudden death of swaths of flora only worsened this trend, as fewer and fewer photosynthesizers were available to produce oxygen. As a result, the decline accelerated and oxygen plummeted.

This was especially bad news for terrestrial fauna, which was still relatively new and not yet as well adapted to air-breathing. Still, even large water-breathers became sluggish and suffocated. Air-breathers that relied on passive diffusion suffered even worse; with no way to convey enough oxygen throughout their body tissues, the largest of the terraknights and terrestrial carpolantaians perished. Oxygen also could no longer penetrate the ocean's depths, leaving the abyss entirely anoxic and the midnight zones hypoxic. All aerobic life in the abyss died out, as did much of it in the midnight zone. In trenches and vents, aerobes only survived when oxygen-producing photosynthesizers were present, using volcanic light to power their photosynthesis.

In time, Sagan 4 recovered. The worst of the disturbance could not last long. As the greater amount of chitinous biomass died, demand for nitrogen slacked off, and the nitrogen cycle recovered. Flora that had become scarce and stunted recovered with the return of nitrogen, spreading out again over a landscape now more purple than green, bereft of trees. With it, oxygen began its gradual recovery, though it remained chokingly low by the standards of the previous era.

The Binucleiozoic was over: the time of hulking crystal trees at an end. What would come next?

EBAD's Rules

- Chitinous organisms (crystal flora, binucleid worms, Protodevoratori descendants, cryoflora) over 1 meter go extinct because they drained the environment of nitrogen faster than the nitrogen cycle or their own decomposition could restore it, leaving them without enough to sustain their chitinous parts. (compare to the end of the carboniferous period, when similar happened to carbon)
-- All other heavily chitinous organisms over 30 cm additionally have a 1/2 chance of going extinct, which may be tilted to 1/4 or 3/4 depending on existing features or adaptations.
--- Most crystal flora has a mix of photosynthesis and detrivory. Anything that lacks detrivory has extra trouble gaining nitrogen and is at a disadvantage. Anything that focuses on detrivory or that has an additional source of nitrogen is at an advantage. Species with multiple sizes in which some of the sizes are below 30 cm are also at an advantage.
--- Worm flora that lack roots are at a disadvantage.
- As a result of the above, herbivores and omnivores which depend on crystal flora, wormstems, and other chitinous flora as their only source of plant-based sustenance starve to death, even if some of their floral prey survives, due to shortage at the peak of the crash.
- Due to the crash in nitrogen, all other flora over 2 meters goes extinct, as the lack of bioavailable nitrogen means there is not enough nitrate or ammonium for them to assimilate to form their amino acids.
-- Remaining flora over 1 meter have a 1/2 chance to go extinct, which may be tipped to 1/4 or 3/4 depending on existing features or adaptations.
--- Flora with nodules that host nitrogen fixers are at an advantage.
- The crash in nitrogen leads to the extinction of all obligate planktivores over 1 meter
-- All other obligate planktivores over 50 cm have a 1/2 chance of going extinct, which may be tilted to 1/4 or 3/4 depending on existing features or adaptations, and being a planktivore puts species already in the rng range at an additional disadvantage.
--- Colonial planktivores are at an advantage.
-- Macroscopic phytoplankton have a 1/2 chance of going extinct, which may be tilted to 1/4 or 3/4 depending on existing features or adaptations.
--- Mixotrophic phytoplankton is at an advantage.
- Due to the crash in oxygen, active air-breathing fauna over 2 meters and other active fauna over 4 meters suffocate.
-- Remaining active air-breathing fauna over 1 meter and other remaining active fauna over 2 meters have a 1/2 chance to go extinct, which may be tipped to 1/4 or 3/4 depending on existing features or adaptations.
- Air-breathing fauna that uses passive respiration if over 10 centimeters suffocate. Species with photosynthesis are exempt.
-- Remaining air-breathing fauna with passive respiration if over 5 centimeters have a 1/2 chance to go extinct, which may be tipped to 1/4 or 3/4 depending on existing features or adaptations. Species with photosynthesis are exempt.
- All aerobic life in the abyssal zone and deeper suffocate, unless they are in a trench or vent where oxygen-producing photosynthesizers are present.
- Aerobic life in the midnight zone have a 1/2 chance of suffocating, which may be tipped to 1/4 or 3/4 depending on existing adaptations.
- Aerobic life in a trench or vent where oxygen-producing photosynthesizers are present have a 1/2 chance of suffocating, which may be tipped to 1/4 or 3/4 depending on existing adaptations.
-- Fauna within the rng zone due to the oxygen crash are at an advantages if they use low-oxygen specialized blood: hemerythrin or hemocyanin. They're also at an advantage if they have a particularly well-developed respiratory system. Those that lack mention of circulatory or respiratory systems at all are at a disadvantage.
- Lack of sexual genetic exchange is a disadvantage for any organisms in the rng zone.
- Organisms with large amounts of competition are generally at a disadvantage; those that lack competition are generally at a disadvantage. (Organisms that are unique in their niches have an easier time bouncing back after the crash, whereas those with competitors are more likely to get outcompeted by those, particularly species with non-chitinous competitors. If a species lacks competition only in a part of its diet that involves chitinous food, this does not count as an advantage.)

Overview of Extinctions

Cladogram before EBAD


Cladogram after EBAD (note the great increase in crosses)


Binucleids were among the worst hit, due to the presence of chitin in all crystal flora and binucleid worms, groups which also included many of Sagan 4's largest organisms.

The loss of all of Sagan 4's largest crystal flora was one of the most stunning changes, transforming, as it did, much of the view of Sagan 4 from space from green to purple. Several entire clades were wiped out: every form of krelp, crystalmat, crystalblight, octocrystals, and both tudeeps. The formerly dominant petrolignopsids, from gazebos to groves to staggering fortresses, survived only in the form of dwarf gazebos. All the 'trops survived, though.

Not only were binucleid worms chitinous themselves, but many of them depended on crystal flora, often as part of their diet, but also often for their life cycle, as happened to the lesser and even lesser knightworms could no longer nest. Aquatic knightworms came through in severely reduced numbers: two ikoslites, a few arthrotheres including euryptiles and carrkins, one shovelface, greim and common naelk, deep sea species, and the common knightworm itself. On land, terraknights were mostly fine, though their losses included their largest members, on the island of Snow. Terrestrial arthrotheres, however, were hit particularly hard, leaving some of their smaller members, just a few lineages left on each continent they inhabited after having completely dominated the megafaunal niches of Barlowe, Glicker, and Darwin. A new contrast developed in Darwin, as well, as an expanded inlet separated western and eastern biomes; the hoppok, catbug, and pumbug died out in the west while remaining in the east, the first divergence between these newly separated habitats.

Worm flora, by contrast, had far fewer deaths than their knightworm relatives or the similarly chitinous crystal flora, owing to being, by and large, quite little. As such, it was the great communal worm flora who were reduced to just wormotheon, alongside the loss of the largest individuals: wormbracken and all of the slimestalk lineage bar the hardy patroclimas. Stickymoss died too, its crystal flora hosts gone, but not before giving rise to descendants that had made it to Glicker and Barlowe.

Purple flora, mostly on the smaller side and entirely without chitin, mostly made it through with few losses. Violet flora was much more afflicted, with the loss of the vast majority of violetfringe descendants and with the violetpalm lineage reduced to only drylicad and violetpalm itself. There would be opportunities aplenty for whatever flora reclaimed the vacant tree niches across the world.

As devastated as the binucleids were, lituslugs perhaps fared the worst. There were few to begin with; in the end, the group was transformed, as litusgrexes were the sole survivors.

Among luceremundaria, the small class of suckers (comprising only two species) was entirely wiped out. Devoratorians only barely clung through, survived only by the minidevorators and the twilight neodevorator. There were few deaths among the siluros, with their bony exoskeletons and lack of megafauna, though a few died due to dietary reasons. Carpolantaians also largely fared well, though some of the terrestrial ones had difficulty with their passive respiratory systems; glassbelly died out, and goblati became restricted to Barlowe, while a few other species perished due to over-reliance on crystal flora. All 'lixos survived but the namnoboros, which relied on krelp.

Asterzoan fates were diverse, as befits so large a clade. Asterstreida had few extinctions, most of them the result of living in poorly oxygenated depths. The original stinzerstar went extinct due to its reliance on crystal flora, and its descendants' fates mostly depended on whether they had kept that dietary specialization or changed it, along with the death of all arboreal spardis. Still, representatives of ranasterids, kugards, and 'zors all survived. Other asterzalians experienced a few scattered extinctions. A strong majority of asterfolians survived, the floral representatives being mostly on the smaller side and lacking the hindrance of chitin. One asterfolian extinction was matleaf, such an expanse of phytoplankton unable to sustain itself during the worst of the nitrogen crash; its loss brought with it the fractalgill, the scoopmaw flutterworm, and the only web to go extinct, the subweb.

Uniquely, the doomzor met three different thresholds for guaranteed extinction, and the mailclad devorator met three different thresholds for luck-based extinction.

EBAD's Victims

Habitat Loss, Suffocation from Large Size Due to Oxygen Crash, Malnutrition Due to Nitrogen Crash
Doomzor

Bad Luck: Difficulty Growing Properly Due to Being Chitinous in Nitrogen Crash, Lack of Phytoplankton Due to Nitrogen Crash, Lack of Oxygen in the Deep Sea
Mailclad Devorator

Habitat Loss and Inability to Grow Properly Due to Being Chitinous in Nitrogen Crash
Trifold Bristlestalk
Northern Stiltrok

Habitat Loss and Malnutrition Due to Nitrogen Crash
Wedgenose

Inability to Grow Properly Due to Being Chitinous in Nitrogen Crash and Lack of Phytoplankton Due to Nitrogen Crash
Decanaut

Inability to Grow Properly Due to Being Chitinous in Nitrogen Crash and Malnutrition Due to Nitrogen Crash
Gigantaurok
Centaurok
Reaching Whitejaw
Bumbler
Forest Centaurok

Inability to Grow Properly Due to Being Chitinous in Nitrogen Crash and Lack of Phytoplankton Due to Nitrogen Crash
Filterclad
Filter Chad
Filter Lad

Habitat Loss
Purple Cushion
Tundra Kralptus
Digmite
Austrostalk

Inability to Grow Properly Due to Being Chitinous During Nitrogen Crash
Greatest Crystal Fortress
Crystal Bush
Crystal Tower
Landfall Grove
Crystalmat
Darwin Octocrystal
Krelp
Wormreef
Crystal Gazebo
Terra Grove
Crystal Fortress
Crystal Dome
Rupee Tree
Thanos' Shrub
Treecrystal
Crystal Pagoda
Armored Krelp
Perfectogon Crystalmat
Hydro Gazebo
Rupine
Kralstalk
Crystal Gondola
Kraltree
Tritessellate Crystalmat
Kramboo
Drake's Diamond Crystalmat
Giant Kraltree
Darwinian Shadow Fortress
Steepine
Hercules Stalk
Clouded Kramboo
Clouded Treecrystal
Taiga Kralptus
Wormosseum
Giant Gazebulb
Beastpalm
Emerald Column
Swooping Euryptile
Barlowe Tuitrok
Acropard
Glicker Stiltrok
Greathorn Sentrok
Cursorithere
Tabbypard
Mitted Gnaw
Ebony Crestbuck
Harenotaur
Noctithere
Red-footed Clubhog
Dwarf Harenotaur

Bad Luck: Difficulty Growing Properly Due to Being Chitinous in Nitrogen Crash
Colony Crystal
Southern Colony Crystal
Tentacle Crystal
Thorny Tudeep
Tigris Dagger
Rupee Cluster
Freshwater Chandelier
Soilpod
Aquamarine Pentacrystal
Bonsai Pagoda
Slimestalk
Hydro Peridot
Wormbracken
Iolastalk
Wormocropolis
Gharion
Swinetrok
Slender Catbug
False Hogtrok
Mottleback
Shrugg

Malnutrition Due to Nitrogen Crash
Tudeep Sucker
Southern Knightworm
Shovelface
Arthrothere
Thornant
Beach Arthrothere
Migratory Arthrothere
Boring Mudworm
Carapacer
Nightgrazer
Red-Tailed Shovelface
Prying Horrorstar
Sayceback
Crimson Saddlebug
Freshwater Shovelface
Stinzerstar
Clubscythe
Grindgill
Arsnoot
Lituslug
Swiftshell
Linzor
Mudslider
Grovestalker
Petro-Boring Knightworms
Vinagime
Teal-Tailed Shovelface
Beach Shield
Kronosid
Squid Island Longjaw
Pulpolanta
Cryomower
Coolelerd Shovelface
Linzantor-of-Paradise
Crystaltrok
Crystal-Crushing Locrint
Arborgopob
Hogtrok
Chunky Knightworm
Carpet Spardi
Wormsnout
Beach Knightworm
Maroon Knightworm

Inability to Synthesize Sufficient Amino Acids Due to Nitrogen Crash
Notchpalm
Bowpalm
Gnarlpalm
Yokto Palmstem
Purpine
Termite Island Foliostrum
Tetrovi Tasselweed
Missixon Tasselweed
Tuscaloosa Fringeweed
Valdosta Fringeweed
Homosaraetes
Skynotch
Purpole
Busrota
Montane Asterplent
Medamaude Gnarlpalm
Scalebab
Ribbon Willow
Trident Cushio
Notchtower
Busromble

Bad Luck: Difficulty Synthesizing Sufficient Amino Acids Due to Nitrogen Crash
Raleigh Fringeweed
Annual Tasselweed
Perennial Tasselweed
Purplevine
Barlowe Foliostrum
Vylicad
Bemissidya Fringeweed
Purpacera

Large Phytoplankton Unable to Survive Nitrogen Crash
Southern Leafstar
Matleaf
Jester's Helm

Lack of Phytoplankton Due to Nitrogen Crash
Brain Shev
Shevalcyon
Reefstar

Suffocation from Insufficient Passive Respiration Due to Oxygen Crash
Maroon Snowworm
Paarl Snowworm

Bad Luck: Difficulty Breathing with Passive Respiration Due to Oxygen Crash
Glassbelly

Suffocation Due to Lack of Oxygen in Deep Sea
Vailnoff Abyssal Mosshroom
Trawler Nautstar
Hellworm Sucker
Armored Lituslug
Lituswush
Tudeep

Bad Luck: Suffocation Due to Lack of Oxygen in Deep Sea
Midnight star
Polentatesta
Scytheworm
Spectrestar
Daggerback
Polentling
Nightlady Nautstar
Darkoth Nautstar
Nyxoth Nautstar
Abyssal Clumpstar
Giant Charnlit
Winged Litusfoi

Loss of Food and Nesting Sites
Fractalgill

Loss of Food
Scoopmaw Flutterworm

Loss of Nesting Sites
Lesser Knightworm
Even Lesser Knightworm

Loss of Hosts
Saprobe Protomancer
Subweb
Five-Fingered Crystalblight
Carpotestan Thermaparasitica
Crown-of-Thorns Crystalblight
Star-of-Bethlehem Crystalblight
Mosshroom Saprobe
Colony Grappler

Dependent on Extinct Trees
Fluttering Spardi
Monket
Sheet Spardi
Arborithere
Windcrystals
Pale Mycostrum
Sagan ivy
Grey Crystalbane
Stickymoss
Upshroom
Mycoss
Mychen
Palmcap

Dependent on Extinct Wormreef
Reef Gillstar

Dependent on Extinct Wormosseum
Reef Ribbon

Dependent on Extinct Nightgrazer
Bubble Siliconium

Dependent on Extinct Krelp
Namnoboros

Dependent on Extinct Purple Cushion
Tundraknight

Outcompetition
Nitromoeba
Violetshoot