Calm Before the Storm

At about 260 million years ago, this is the Guadalupian Epoch of the Permian Period. A piece of land that in the future will become part of the South African Western Cape province is now a semi-arid, fairly warm environment. Reasonably far from the coast, it is located on the south of the supercontinent Pangaea, which extends vertically across the globe, from the Northern Hemisphere all the way to the south pole. North of this gigantic landmass, both Siberia and Kazakhstania, now fused, can be encountered and, to the east, exists an aggregate composed of South China, Indochina, and Malaya. The ice age that started in the Late Devonian ended earlier in the Permian at last, with remaining glaciation in southeastern Pangaea continually decreasing, now almost over. Abandoning the world view, one can see this area is home to many rivers, flowing from the mountain belt that surrounds this plain, a product of tectonic processes which will continue to act in this region for the following millions of years. Owing to the abundance of such water resources, various creatures establish permanent residence or migrate here, especially in the dry season, which has extended for far more than usual.

One such migrant is a young male Tapinocephalus, a herbivorous creature 3 meters long. It is a synapsid, one of the two groups composing the amniotes (which originated during the previous period: the Carboniferous), the other being the sauropsids. Consequently, it shares a more recent common ancestor with us (remember that humans are of the class Mammalia, another component of Synapsida) than with reptiles (remaining sauropsids) and that certainly shows, as can be seen by the scaleless, glandular skin, the milk precursor its female counterparts produce (also present in some other egg-laying synapsids, this glandular skin secretion not only moisturizes their leathery eggs, but also delivers them important nutrients), and the tiny, sparse hairs distributed around its body. Despite these similarities, this creature and its relatives, the dinocephalians, are still very different from mammals, a reality evidenced by their ectothermy (a condition shared by most non-mammalian synapsids) and parietal eye, a photosensitive organ present in various vertebrates responsible, besides other important functions, for thermoregulation in ectotherms.

Anyhow, this individual was expelled from his herd due to complications with the alpha male a few days ago. His genus, like related ones such as Moschops, usually uses head-butting in order to settle disputes for mates, but he decided to try another strategy and, instead of competing traditionally, just copulated with the females while the others fought. Even though it worked out initially, he was eventually caught in the act and driven out. For some time, he encountered himself all alone, a dangerous affair in these expanses even for a creature his size. Finding water has been quite hard also. Normally, the many Tapinocephalus noses would quickly locate any sources of the fundamental substance, but he has only been able to find a few shallow puddles here and there, which, luckily for him, were accompanied by some Schizoneura horsetails he readily fed on. The flat leaves on such plants make them a peculiar bunch when compared to other horsetails and, in more optimal conditions, they can grow to 2 meters in height. 

Despite the apparent barrenness, much of the ground is covered by biocrust, a community of numerous lifeforms, like mosses, cyanobacteria, fungi, and lichens (themselves intimate associations between fungi and algae or cyanobacteria). Such carpets, held together by the secretion of structural carbohydrates, help stabilize the soil, protecting it against erosion, while also retaining some moisture, even in dire situations such as these. Mosses, a fairly new addition to the biosphere, having possibly originated in the Carboniferous, are, unlike the other Carboniferous plants we had the pleasure to explore, traditionally called non-vascular. This is not entirely true as a matter of fact, as some of these photosynthesizers may have conducting elements in the stem (from where leaves arise) and in the leaves proper. These, however, are usually not connected, unlike what occurs in vascular plants and, as such, mosses can have quite distinct ways of acquiring water. 

Most, consequently, rely on quickly absorbing water from the atmosphere, being unable to adequately store it. As such, they rapidly dry out. While this would seem to render mosses unable to survive in hostile habitats such as these, the majority can easily return to activity when wet once more, with only a few vascular plants from various groups (with the notable exception of gymnosperms) capable of surviving desiccation, normally ensuring they never completely dehydrate in the first place. Mosses adapted to these dry environments usually have thick cell walls with highly variable, hollow protuberances, which not only allow for efficient water transport (making rewetting a fast process) but also increase surface area for greater gas exchange. Factors to increase surface area are visible macroscopically too: when wet, the leaves become wide, but curl within minutes once water is lost (microscopically, cells detach from the cell walls, but remain alive, storing the products of photosynthesis in vesicles). 

Returning to the biocrusts, they, due to their aforementioned properties, serve as habitats for a variety of minuscule animals. Living in water pockets are several nematodes. These worms, also discussed in the last chapter, occupy many ecological roles. Some, possessing a spear-like organ projecting from their mouths (called a stylet), pierce fungal and cyanobacterial cells, sucking away their cytoplasm and leaving only husks behind. Others have lips coming in a wide array of forms, including ones of smooth aspect or containing several elaborate processes, functioning either way to capture and consume bacteria. A few nematodes are even specialized in predating fellow animals, with a wide, open mouth counting with a single tooth-like structure or rows of such "teeth", though some stylet-bearers take to this lifestyle as well.

Too living in waterpockets or even plainly on the biocrust surface, are somewhat charismatic creatures known as tardigrades. Counting with a plump body and four pairs of stubby, clawed legs, these crawlers are, like the nematodes, fairly close arthropod relatives, but much closer. Also like the nematodes, they explore much of the same food items, with a pair of piercing stylets inside their mouths being essential for feeding. Although the nematodes themselves are quite hardy, able to endure desiccation and subsequently spring back to life (a process dependent on the conversion of storage sugars into smaller, cell-protecting carbohydrates named trehalose), tardigrades are even more exceptional in terms of environmental resistance. Instead of using such sugars, they mainly utilize specific proteins, which, when dried, enter a glass-like state (trehalose shows a similar response), protecting the cells until they are hydrated again. This does not always work and quick desiccation, without time for these proteins to be translated, culminates in tardigrade death. Additionally, they boast ways of defending themselves against UV and even ionizing radiation (the latter being a form of radiation with sufficient energy to dissociate electrons from atoms, thus ionizing them, instead of only promoting electronic excitation like other forms of radiation, with this being further discussed here). Such defenses range from proteins that bind to DNA-histone complexes to fluorescent pigments that absorb incident UV, not necessarily coexisting on the same tardigrade.

Already quite curious on their own, the ancestry of these critters is also noteworthy. They are descended from lobopodian worms, aquatic animals of roughly vermiform (despite having very varied formats) shape, characterized by their lobe-like, unarticulated legs. Very common in the Cambrian, such invertebrates were not seen during our visit however, but their legacy could not be more noticeable, even in the present day. While a few lobopodians retained most of their ancestral form and left no descendants, one of several branches led to the recognizable arthropods and another of those led to the Tardigrada phylum, which, since its origin, has seen a marked decrease in size, leading to these truly tiny animals, almost invisible to the naked eye. 

Despite all of this richness, the biocrusts are vulnerable to disturbance and take a long time to recover, possibly several years, making large herbivorous animals, such as Tapinocephalus, a considerable threat. Either way, the young male is now guided by a far more noticeable smell, which just keeps getting stronger. Not only that, but he has also found some company and protection in the form of four Jonkeria, which are also following the same pungent odor that signals hydration. Jonkeria are dinocephalians as well, equipped with rotund bodies and probably being the largest members of the clade, capable of reaching lengths up to 4 or 5 meters. They are omnivorous and will eat anything capable of fitting in their mouths, both animal and vegetal. 

Time goes by and the unusual group continues on its journey, getting closer and closer to its terminus. But not all will make it… One Jonkeria has strayed a little too far from the others while feasting on some vegetation that grows plenteously close to a narrow stream, already a signal that they are not far from lands of abundance. The wanderer does not notice that it is being watched. Behind a tall rock, stands motionless an imposing figure some 5 meters long, held up by four strong legs and dragging a long tail on the ground. Yet another dinocephalian, but carnivorous: the great predator Anteosaurus. The hunter focuses its eyes on its soon-to-be victim. The attack is imminent. After a few seconds, the carnivore lunges forward lightning-fast, ramming onto the Jonkeria and diving down its sharp teeth into the animal’s torso whilst pinning it with its front paws. Alerted by the guttural calls of despair, the other Jonkeria quickly move in to investigate, while the Tapinocephalus just stays alert, scanning the environment carefully.

When confronted with the horrific scene, two of the Jonkeria stay put, grunting and shaking their heads in a futile attempt to intimidate the Anteosaurus. One of them, though, decides to take a stand and walks as fast as it can in the predator’s direction. The carnivore does not notice the movement in time and is strongly hit, fumbling over to the ground. It manages to get up quickly and distances itself from the four other dinocephalians. Despite this, the animal has not given up and will bide its time: it is not worth it to confront all of the Jonkeria at once. The damage has already been done and the victim will not be able to keep up with the others. Its death is coming soon. As the group continues its migration, the Anteosaurus follows closely, occasionally dispatching destructive bites for as long as possible on the weakened Jonkeria and then running away, counting on its higher agility when compared to the ones of its victims. After only one hour, the creature is down and its corpse left abandoned for the bliss of this region’s most formidable killer.

The four that remain arrive at their destination on the same day, not long after the Anteosaurus finally made its kill. The trip was worth the wait, as water and food are plenty. The hydrous bodies allow for dense aggregations of trees, with Agathoxylon, a member of Cordaitales (although similar wood can be observed in seed ferns and conifers), forming forests responsible for creating shaded spaces apt for ferns and other ground plants while only being found sparsely in other areas. The also gymnosperm Glossopteris, for instance, is even more difficult to encounter than Agathoxylon, since it preferentially grows in habitats like swamps and river deltas. Consequently, it thrives here when water is more abundant, and, curiously, the glossopterids inhabiting high-latitude habitats like this one (where the duration of day and night are significantly affected over the course of the year) vary in their responses to these seasonal shifts in light availability, some shedding their leaves and others keeping them, the latter dominant in less stressful environments. 

Such leaves, emerging from trees able of growing to substantial 30 meters in height, are, even now in the dry season, subject to harassment by a variety of creatures, including by palaeodictyopteran insects, herbivorous four-winged fliers spousing mouthparts adapted for sucking, making them prolific piercers of plant tissue. Archostematan beetles, small and roughly rectangular shaped, too subsist on sap as adults (besides consuming pollen), with their larvae living in wet wood or tree roots where they feed on fungi. Due to this reliance on humid spaces at least during the start of their life, they are suffering during these trying times, but, nevertheless, will persist for much longer, still part of the modern-day biota.

The male Tapinocephalus dissociates from the Jonkeria just as fast as he joined them and directs himself into a new herd he hopefully will manage to get into. Unfortunately, things are not as easy as he had hoped for. As he approaches, the alpha male intercepts him. In all actuality, this was expected to happen, as no dominant male will let a potential competitor simply slip into his dominion. The current head of the group, though, is not in good shape: a result of a metastatic cancer that is gradually draining the life out of him. His emaciated body is a direct result of the rogue cells proliferating, seeing as they, which engage substantially in fermentation instead of the drastically more efficient aerobic respiration (this "choice" allows them to synthesize molecules and catalyze reactions necessary for continued divisions faster as a consequence of enabling the regeneration of larger quantities of the NAD+ cofactor, needed for these and many more processes), display a great uptake of glucose. The young male notices the poor physical condition of his rival but still backs off. The only time he ever came close to some sort of duel was during his expulsion, which he just half-heartedly resisted. Maybe he will try his chances on some other occasion, but, for now, a full belly shall have to compensate for his solitude.

While cancer is certainly very well-known in animals, plants also suffer from uncontrolled cell growth and the ones of this environment are no exception to this unfortunate rule that permeates multicellular organisms. However, in the photosynthetic organisms, tumors have, by essence, a decreased life-threatening potential and this is due to cell walls. Thanks to these scaffolds, vegetal cells cannot move around the larger whole they constitute and, consequently, the tumor, although perhaps destructive on its source of origin, stays restricted, without undergoing metastasis, a hallmark of cancer in the strict sense. Apart from this, plants appear to have less rates of spontaneous tumoriginesis in the first place (perhaps due to more controls in the cell division process and due to the importance of hormones in plant growth, requiring the action of various cells to promote tumors,  in contrast to animals, where a single cell can be much more disruptive on its own as it starts dividing), thus possessing a two grade system of protection against a malaise oh so disruptive in their heterotrophic counterparts. 

In this context, the main formers of tumors in these lifeforms are pathogenic microorganisms, for which a tumor may be a particularly suitable environment and perhaps even essential. Bacteria, for instance, can lay the groundwork for this dysfunction by sharing plasmid DNA, which, in the cells of the host, leads to dysregulation of hormone production and consequent tumor formation. Fungi, on the other hand, promote such events by sharing proteins, not genetic material, but which still dramatically affect and subvert once normal hormonal pathways. Some viruses exert their influence in an even more fundamental level: alterating the genetic controls of cell division, a few genes of which are shared with animals, also leaving the latter predisposed to tumors should those controls be affected (as some animal viruses can indeed do, such as the polyomaviruses previously mentioned).

The following day, many animals have congregated around a river. The three Jonkeria are about to get a drink, their reflections mirroring their placid faces on the still water: such reflections being no more than a product of the light's electric field interacting with the liquid's molecules, changing their positions (for more regarding the relation about moving charges and the creation of electromagnetic waves, go to our Jurassic voyage, with it being important to note that a water molecule, despite being neutral overall, has regions of positive and negative charge) and giving rise to more electromagnetic waves, the light that truly forms the reflection. In no time, they are interrupted by a particularly territorial Rhinesuchus, a temnospondyl amphibian that consumes fish and has a maximum length of about 3 meters. Displaying seasonal growth, this tetrapod is, nonetheless, quite resistant to troubled periods and, as its large size indicates, it has already survived through a lot, currently being in its thirties. An infestation of several leeches on its underside, however, is not helping its life expectancy, with the parasitic annelid worms secreting anticoagulants that ensure a steady flow of blood while they hold on using their anterior and posterior suckers, the former being also responsible for ingesting the fluids. 

On the other side, an Anteosaurus yawns lazily and moves in a groggy manner to the water. This individual is not the same from before, as can be seen by its bigger size, and has just woken up from a long nap under the Permian Sun. Trying to take refuge from the blistering rays are four Bradysaurus, a 2.5 to 3-meter-long genus of early pareiasaur, a group of herbivorous reptiles characterized by their body armor and cranial ornamentation, their barrel-shaped bodies being ideal for housing an extensive digestive tract in accordance with a diet high in fiber. Bradysaurus in specific can be considered lightly armored when compared to some later forms, covered in far more bony knobs, with dwarf pareiasaurs even more heavily protected. 

They are all part of the Parareptilia clade, a diverse set of sauropsid amniotes that has a very controversial phylogenetic placement, being either recovered as a sister group to "traditional" reptiles (Eureptilia) all the way to being interpreted as a paraphyletic grouping containing various evolutionary radiations, with some representatives actually sharing a more recent common ancestor with members of Eureptilia, which is itself another target of considerable discussion. Be that as it may, for some time, it was believed that pareiasaurs, due to some similar features, were the ancestors of turtles, but it is probable that these similarities were only due to convergent evolution (when matching traits not present in the organisms' common ancestor evolve due to equivalent evolutionary pressures), turtles probably being "true" reptiles more closely related to archosaurs (a group discussed in more detail in the next chapter) and, as such, only distantly related to Pareiasaura.

As a matter of fact, there is a possible closer turtle relative right in this habitat. Sunbathing on the top of a rock is an Eunotosaurus, a critter able of growing only to 30 centimeters in length, easily discernible by its wide belly, which, in the future, will perhaps culminate in the trademark shell seen in Testudines (turtles) or maybe not, perhaps this animal only constituting a dead end branch of the reptilian tree. Whatever it may be, the unusual body type, along with powerful forelimbs and large claws, is an adaptation for a burrowing lifestyle, which allows for protection both against predators and the elements. 

Popping up from the ground nearby is a very different organism adopting the same strategy when in dire conditions such as now: the synapsid Diictodon, around 50 centimeters long. It is a representative of the dicynodonts, which share a herbivorous diet and keratinous beaks, other traits being less universal. Diictodon, for example, bear tusks, or, more appropriately, males do, females being tuskless. Thus, it is sexually dimorphic, with males, like the Tapinocephalus, occasionally fighting for breeding rights, the tusks being used mostly in intimidation and, rarely, in active combat if the former fails to dissuade rivals. The enemies may resort to head shoving as well, their vulnerable parietal eye protected by a boss, present only in males too, with a comparison being drawn once again to Tapinocephalus, which also show traits to safeguard the "third eye". In spite of these confrontations, they are quite social and many individuals occupy together different spiral or more horizontal burrows dug close to each other, constructed preferentially in humid soil. Furthermore, the young can also be raised underground, in a less severe, more hospitable, and controlled environment, sheltered not only from the day's heat, but from the night's cold additionally. 

All of the observed synapsids, besides the characteristics mentioned earlier regarding Tapinocephalus and its dinocephalian relatives, share another curious trait: a small opening on the lower jaw, this actually being their ears! As said in the previous chapter, tympanic hearing evolved independently in multiple tetrapods and it has developed in these also. Mammals, though, have derived this ability further by the formation of a jaw joint that permitted the decoupling of certain bones from the feeding apparatus, allowing them to associate with hearing and ultimately giving representatives of Mammalia two more ear ossicles apart from the stapes (homologous between amniotes). This bone "recruitment" made mammalian ears unique when compared to those of other tetrapods, which only have, despite their independent origins, one ossicle.

Returning to the Permian, not far from the Diictodon hole, the young Tapinocephalus has made his way to the herd once again. The urge to pass on his genes is stronger than his fear and inexperience: he will fight. The alpha male lowers his head and both share their first blows, combining both head butting and pushing. The females, all the while, mind their own business, not really interested in the confrontation. At first, the fight is a stalemate, with no side managing to edge out the other. However, in a few minutes, the tides turn and the young male drives the alpha all the way to the edge of the water and lands a final blow, finally winning against his adversary, now fallen to the ground and trying to regain his breath. This has been the sick male’s final fight. He will now wander aimlessly through this landscape until the end of his days. On the horizon, dark clouds signal the arrival of a storm: the dry season is drawing to a close and, with its conclusion, the barren landscapes witnessed through the course of this chapter will be radically altered.

Unfortunately for the dinocephalians, their end as a whole is also creeping closer. In what will one day become southwestern China, severe volcanic eruptions are happening, releasing several greenhouse gases into the atmosphere that are promoting significant global warming and other effects. This is the Capitanian mass extinction event, which, despite not being considered one of the “Big Five” mass extinctions, had an extremely significant impact on the planet’s lifeforms. In the aftermath, shallow marine ecosystems would be severely harmed and, on land, large pareiasaurs like Bradysaurus would also mostly disappear, being replaced by their aforementioned smaller and more heavily armored relatives, with only a few still retaining more considerable dimensions. Dicynodonts and other synapsids would take over former dinocephalian ecological niches, with Diictodon not only surviving but thriving through the extinction likely due to their burrowing habits.

This, however, would not be the only mass extinction in the Permian, as the period ended with the most catastrophic extinction of the Phanerozoic: the Permian-Triassic extinction event, known as the Great Dying. Volcanism also played a major part in this cataclysm, but, in this case, the eruptions were much more intense than in the Capitanian (age of the Guadalupian Epoch) and took place in Siberia. The disruptions were similar but elevated to a far grander scale, with different cascade effects resulting in the release of ever more greenhouse gases. As a direct result, there were higher levels of acid rain, temperature increase was more considerable, and, thus, the habitability of low-latitude areas was severely compromised. Warming waters led to anoxia and acidification, resulting mainly from the dissolution of gases like carbon dioxide, further affected the hydrous bodies. As a consequence, the oceans were the hardest hit: the rugose and tabulate corals, which had already suffered through the Late Devonian extinction, were completely wiped out, as were trilobites. The marine fish fauna, until then dominated by cartilaginous fishes, would transition into bony fish domination during the aftermath, a scenario that holds up to the present. Away from saltwater, the remaining eurypterids (freshwater forms such as Hibbertopterus) were also decimated, along with various insects (including the palaeodictyopterans cited earlier). 

In regards to plants, they were not as harmed as animals (likely a product of their distinct physiology and lifestyles when compared to the metazoan ones), with it being argued these disturbances could not even be considered a mass extinction for the photoautotrophs, but some, like the glossopterids, for example, while managing to eke out to the very start of the next period in polar refugia, ended up succumbing all the same. The pareiasaurs would not manage to escape this time and many of the synapsids from after the Capitanian extinction would also perish, but dicynodonts and cynodonts (which eventually gave rise to mammals) would be examples of synapsid survivors. Various reptiles endured as well and were poised to take advantage of the many opportunities made available by the environmental collapse. And it would be like this that the second era of the Phanerozoic, the Mesozoic, would begin.

***

1-Agathoxylon

2-Glossopteris

3-Schizoneura

4-Eunotosaurus

5-Diictodon

6-Anteosaurus

7-Bradysaurus

8-Rhinesuchus

9-Jonkeria

10-Tapinocephalus