THE FIRST ANIMALS...
...OR IS IT?
Diorama presenting the Ediacaran biota
On Earth, this point in time would be comparable to the Ediacaran Period of the Neoproterozoic - marked by the appearance of soft-body animals in fossil record.
On Earth, for a long period of time, we can just split animals into Fungi, Ichthyospores, Filastereans, and the metazoans that would split later on into the Choanoflagellates and Eumetazoans - these last two, along with the other creatures, were suppressed by the Cryogenian, and after the planet warmed up again, Metazoans spread and diversified, the Ediacaran period thus is of a few body plans as nature experiments with it's new environment, and by the start of the Cambrian, we see the rise of basically every other base body-plan we see today.
IT'S A SPONGE, IT'S A PLANT, IT'S A WORM, AND SOME TYPE OF WEIRD STRANGE WATER BUGS AND STRANGE FISH... - Bill Wurtz during the ~Caaaaambriaan Explosion~
On Paart however - we don't have a global freezing as in the Cryogenian to slow down evolution, and thus, is rather safe to assume things would have been way louder on Paart.
Modern Seapens (Ptilosarcus gurneyi) in the deep sea
One remarkable life form that ruled the Ediacaran were the Rangeomorphs, creatures with branches coming out of a semi-rigid stem or skeleton, pretty much like a feather. We know these are a kind of animal and not a plant, because the rocks from the sites were this fossil is found are dated to be under oceans that are over +1km thick, much deeper than the actual range of photosynthesis in water (about 200 meters deep), so they must not be plants but an actual kind animal (maybe and entire extinct kingdom), a simple filter feeding animal - an osmotrophic organism, passively absorbing organic particles into it's body, to be used as building blocks for it's cells - hence why they branched like pens, granting them a large surface area to absorb more nutrients from the water, also reproducing asexually like corals do today.
Rangeomorph reconstructions from fossil beds
At the moment I'm writing this post, and as far as my research for this went - there is an apparent gap between the sessile rangeomorph-like creatures and the mobile and arthropods we see at the dawn of the Cambrian period.
COMPARING EARTH'S EDIACARAN DEVELOPMENT
We can infer though, based on fossil record and on current animal reproduction cycles, that at one time, or several times over a certain period, a group of creatures native to Paart - that reproduced by spreading motile larvae suffered neoteny due an environmental trigger, could well be the drop in temperature of the water, maturing without becoming sessile, in this case - keeping motility, and thus as the cold waters persisted over 45 million years, those creatures developed new ways of living and interacting with the world.
For a long time in the Earth's fossil record, we are not able to see what these creatures looked like, but we can see burrows dug into the layer of bacteria and organic matter surrounding the sessile animals, and those burrows tell us that the larvae were probably benthic and slithered through the seafloor as they ate and grew until maturing into a sessile adult. However, as we dig into newer pre-cambrian rocks, we see those burrows go from aimless and disorganized burrows to non overlapping and patterned ones, what indicates that those benthic creatures are now gaining sensory organs and changing their strategy to better use their energy - not wasting it in already eaten areas.
Those creatures as larvae would be small at first, but once reaching and entirely new environment, with lots of niches to explore and a new ambient that required better ways to move around, they irradiated into new forms and sizes - ranging from millimeters to a couple centimeters, and giving rise to the creatures we see in the dawn of the Cambrian.
We can also see that this theory connects the existence of segments in animals with the pre-existing segments of stem animals that do have a very strong evidence and reason of why they are, and that will be carried along with them.
PAARTIAN STEM ANIMALS
The chemistry of the oceans at that time is likely to be rich in carbon compounds, as well other minerals washed out by the waves and storms from the continent to the sea by the hyper-canes and tsunamis that occurred regularly on Paart during this period.
This put seafloor sedimentation with regular thin layers or bacteria processed sediment and pure sediment brought from the land.
And we can infer that such a regular event in the environment's history would indeed influence the path evolution takes.
Early Paleopyrgian fauna would look pretty much like Earth's Ediacaran fauna, but as the animals are filtered by the subsequent underwater floods of sediments - one strategy that could arise is that during the early time of it's maturing stage, the creature would quickly develop a long vertical stem with a feeding surface on it's tip and after a certain age start building from this tip and beyond, this way, even when the foot of the animal becomes buried in the sediment, it can still feed and live, and I say after a certain age because despite this process happening regularly, it's rate could be by far outrun by the rate of growing of the creature, such as that by the point the sediment reaches the feeding surface of the animal, it would be already long dead or at the end of it's life cycle.
By the Neopyrgian, this leaves us with animals that would look a lot like peacock feathers instead, a rather dense stem at the foot to withstand the pressure from the sediment, with small less dense filaments through the stem and a large and dense surface for feeding on the top.
The general body plan of Neoproterozoic creatures over time, sorted left to right, from older to newer
Over
time, some orders will eventually out-compete others, and phylums will
be replaced by ones with better versions of the same strategies, that's probably
what happened to the Ediacaran biota once Metazoans have arisen.
ATMOSPHERE, OCEAN CHEMISTRY AND LIFE
The southern ocean would cast several hypercanes and tsunamis over the equatorial part of the supercontinent
The Ediacaran
biota were very intimate of the bacterial mat on the seafloor, which
consumed the oxygen and other nutrients from the oceans, one strategy
that helped the nutrients to cycle through the trophic levels was to eat
the microbial mat. Over time, animals begun to get more and more
effective at eating the microbial mat, exposing the immature planetary
soil, the exposure of regolith to erosion led to the release of
chemicals such as calcium and phosphates, the phosphates were rather very useful to life, but calcium were not so much, to avoid calcium toxicity, animals begun to build shells of calcium compounds to both protect their bodies from the environment and to secret the toxic calcium excess in their bodies. The biomineralization, the end of the microbial mat, and the arise of swimming animals, let to the positive feedback loop of rising biodiversity - and unfortunately, this process may ended up destroying the specific environment the Ediacarans were so well adapted to live on.
Whereas on Earth, the oceans would be of a reducing character, the oceans of Paart would be pretty oxidizing.
The solubility of oxygen in water is dependent on temperature and pressure. Increase the pressure (using gravity or water column) and the amount of oxygen water can potentially store increases - though that would probably mean this deep waters would have less contact with the atmosphere and are closer to oxygen consuming bacteria. Increase the temperature and the oxygen levels will decrease, as the water molecules are further away from each other, allowing free oxygen to escape more easily.
The temperature of Paart at this time is rather cold, about 10 degrees Celsius - at Earth parameters, this would mean an equilibrium between 10 and 11,5mg/L.
But Paart has a weaker gravity than Earth (0.71g of gravity), a less dense atmosphere (0.97atm of pressure), and it's atmospheric oxygen is about 14% by the late Paleopyrgian.
But since we have to consider that at 14% O², the actual equilibrium ceiling goes down to 6,5mg/L.
For perspective, under the same temperature conditions, the Ediacaran oceans would bear only 1,8mg/L.
With 3,6x more oxygen than Earth's oceans, creatures would have the potential to grow 1,5x larger than on Earth (square cube law), that of course wouldn't last longer, as the microbial mat and exposed regolith would slowly deplete the oxygen content of the water.
As the sediment oxidizes in the water, it creates several compounds such as calcium carbonate and calcium sulfate, and other earthly oxides.
Carbon dioxide and some metals like bismuth and aluminum are way more common than other substances dissolved in water, and are way more likely to be used to build protective shells - against what? you may ask...
Aside from the sediment's pressure, Elpidomorphs (Greek for hope shaped, like a sinking hand asking for help) would like to defend themselves against their neighbors pesky kids, as they would easily eat through their stems if they weren't thick enough, and later - if they weren't properly armored with a layer of calcium carbonate, and for the ones able to, a shiny dark shell of bismuth and silicon carbide, leaving the only food source available for them at the moment to be the bacterial mat at the seafloor.
Medusas go through a young Polyp phase before the adult motile phase
Some of Paart's animals may also suffer double neoteny, having the polyp-like / sessile part of their lives as young and turning motile as they mature
CLIMATE AND ORIGIN OF STEM ANIMALS
And from that, we get larvae that now prey on each other instead, and subsequently they now can establish an ecosystem of their own, this strategy of changing diet as the organism matures is particularly efficient as it grants the adults will not out-compete their brood for resources - and can be well observed in insect life cycles, and while some may preserve this strategy, others on the far south regions of the planet where the waters are colder and not so turbulent as on the north, neoteny may kick in most of species, and we would now have several hundreds of genera, dozens of orders that had converged into similar-looking body-plans and strategies, despite their last common ancestor lived about 50 or 70 million years prior to their existence.
So, while on Earth, the Ediacaran fauna managed to persist for about only 40 or so million years, and Rangeomorphs in particular - only about 25 million years, but here the gradual evolution and existence of different habitats along different latitudes and temperatures, allowed this type of animal to be more successful, already expanding through the 45 million years of the Mesofrigian, and the 110 million years of the next epoch, the Albanian (after latim for "striped", referring to the alternate layering of organic and sediment substrates), making it through 155 million years, leaving a huge mark in the fossil record, as the rapid sedimentation of the seafloor would allow organisms to preserve nicely.
CLADISTICS
Let's organize these first animals, at the moment, they all live in rather similar looking environments (banded nutrient rich seafloor), and do share a major characteristic in common (being segmented), and as well, are simple soft-bodied organisms - I then name this phylum, Albazoa (Striped Animals) - as I'm writing this, the term Kingdom in cladistics has fallen in disuse, and I could not find further substitute term, so I will try not bother with kingdom naming so far, as we pretty much can discern what a plant or animal is.
The chart shows a Xenorangeans organized left to right by latitude, and bottom to top by cladistics
Names shown are the Orders of animals inside the Classes Ptosimorpha and Elpidomorpha
Early related to the Xenorangeans, another Albazoan group are the ones which use the sediment as protection.
Polyps that let themselves to be buried in organic matter, and buds up as sediment falls off covering it's feeding surface, and some that deliberately build up sediment as protection - Chalea (SHA-LEH-AH) (derived from carpet in Greek).
The chart shows Chaleans organized left to right by latitude, and bottom to top by cladistics
Names shown are the main Orders of animals inside the Classes of Chaleans
We can also expect several families - like sea-slugs do, to enter temporary or long term symbiotic relationship with photosynthetic algae in shallower regions of 200m or less for when conventional food (the microbial mat) is scarce - and oh boy it will be scarce over time.
SYMMETRY AND RISE OF METAZOA
The exact origin of Metazoans (animals like sponges, crabs, you, your dog/cat) on Earth still quite a mystery, over time, we have proposed that all Metazoans had originated in a core original group or colony of single celled organisms - that, regardless of their original configuration, developed into specialized cells or tissues with specific functions like, respiration and digestion of food. Others have suggested that this didn't happen only once, but several times over the course of history, and that all Metazoan groups are not related at all, but evolved independently from different protist ancestors.
In any case, and whatever type of simple animal the Ediacarans were (because they are multicellular, but lack specified tissues - still, they're not sponges because they don't look alike sponges, and doesn't seem to have any other specific structures for feeding or reproduction, as said before, they could well be composed of slightly differentiated cells but being like a balloon of tissue feeding through osmosis), protists were already around by that time, living as bottom feeders.
Whatever led to the Ediacaran success, be it the particularly chill environment or the richness of food, it was so particular that the mere removal of one piece made their entire reign fall. I like to assume something similar to the rise of dinosaurs happened in the Ediacaran-Cambrian period - dinosaurs weren't the strongest, or more resilient of animals around, they were generalists, and when the climate changed, leading to the fall of the environment where the saurosuchians lived, they were just the ones with more tools at their disposal, quickly taking over the empty niches.
As well, protists and eventually Metazoans, were just the more prompted to adapt to the new environment, and then we could say that, like it would later happen several times in Earth's history, the success of a species may be the exact key of their downfall.
Radial symmetry or lack of any symmetry at all is a rather efficient way to catch food, when all you need to do is sit on the bottom of the ocean and wait for the food to come to you.
However, when you have motility, disposing of several filaments or surfaces may be a disadvantage (depending on your scale), perhaps, the key to the downfall of the Ediacaran biota, is that they had long lost their evolutionary potential to overcome future disasters.
See, insects as we know them, don't have the evolutionary potential to take over the world and become a technological civilization, because the process that allow that exist in macroscopic scales, and their own body structure and respiratory system, doesn't allow for an individual to reach larger sizes without collapsing or suffocating (lobsters suffocate and die after they reach a certain size because their body becomes larger than their gills can provide oxygen to).
As well, Ediacarans would be so well adapted to a low oxygen environment, rich in organic matter, and as well, grown sessile, adapted to these specific niches, that evolution couldn't work it's way back on the majority of creatures to give them any chance against Metazoans, which not only occupied several orders of magnitude, but probably slingshot their way up the trophic levels through the success of Ediacarans - which gathered lots of nutrients in their bodies and lived in large clumped numbers all over the Earth's oceans, creating ecumenical cradles of bottom-feeders, the abundance of dead Ediacarans to prey on led to the appearance of active scavengers, and after that, active predators on the abundance of other Metazoans, which later on became more adapted to the new substrate, climate and trophic relationships.
The Ediacaran substrate were firm, layered, anoxic, with a sulphidic substrate, whereas Cambrian substrate were, loose, with an oxygenated upper substrate with burrowing animals
The little critters (Illaboreans, Erpaeans, and Metazoans) that have arisen by the Late Albanian, will over time - eat away the microbial mat, but as there is more oxygen available in the water, rapid grow back is rather a given, spanning the time required to the destruction of the Albazoan environment plus the ever pressuring environment will not let them settle down with one or a couple specific body-plans, on Paart's Neoproterozoic oceans, Albazoans had the time, and pushes into motility through neoteny, they will persist and directly compete with Metazoans for the oceans of Paart.
Albazoans crowding the Early Albanian seafloor, the thick bacterial mat gives the soil a light appearance
This
starting evolutionary arms race, between Albazoans and several Metazoan
factions, will be the fuse leading to Paart's Cambrian Explosion event...
- M.O. Valent, 07/04/2020
