New Beginning

At about 233 million years ago, this is the Late Triassic Epoch. Part of what will become the future Brazilian state of Rio Grande do Sul is now a region of hot, semi-arid to arid climate, even though increased levels of rainfall will progressively heighten humidity levels in the next millions of years. Rather distant from the ocean and influenced by continentality, it is found in the southern reaches of interior Pangaea, the massive landmass which, like in the Permian, still goes all the way from the north to the south poles. Earth is in a greenhouse state, far from an ice age and, as such, significant amounts of vegetation extend to the highest latitudes, where, nevertheless, temperatures can still drop significantly. 

The biosphere has gradually recovered from the Permian-Triassic extinction event (explained in more detail in our previous trip) and new organisms have risen to prominence. A reptilian clade, in particular, is gaining the spotlight: Archosauria, part of the larger Archosauromorpha. These reptiles, the archosaurs, include many charismatic groups, such as dinosaurs, pterosaurs, and crocodilians (along with their myriad of relatives), have undergone a transition from a sprawling to an erect posture (enabling them to run and breathe simultaneously), exhibit an endothermic metabolism (it would be later lost in the aforementioned crocodilians due to changes in lifestyle), display air sacs along with post cranial pneumatic bones (traits later lost in several lineages, including in the crocodilians once again, though it has also been suggested that they are not common to archosaurs and evolved independently in different groups) and, overall, are showing signs of a bright future.

Glancing at the clearing before us, it is possible to notice a considerable presence of gymnosperms among the vegetation. Growing in dense aggregations along more shaded areas is the cycad Taeniopteris. Sometimes found in large gatherings under broad leaves such as the ones these plants sport are planthoppers of the family Derbidae, small insects belonging to the Hemiptera order, called the true bugs. While adults feed on sap, nymphs eat fungi, living in rotting logs and amid decomposing leaves. The nymphs secrete a small number of wax filaments possibly connected to a variety of functions, ranging from camouflage and defense all the way to cleaning (adults may or may not be covered in a powdery layer of wax). 

Two other plants, Nilssonia and Williamsonia, bear a striking resemblance to cycads, but are gymnosperms only distantly related to them, occupying much broader ranges up to near the poles. The Williamsonia forms big arrangements which consist of nothing more than seed cones in which bracts (like the modified leaves that may be found surrounding the flowers of the ornamental angiosperm Bougainvillea for example) cover said seeds and the scales distributed among them (pollen cones are also protected by bracts). Growing on the edge of a small elevation is the ginkgophyte Sphenobaiera (its clipped leaves being an adaptative mechanism against dehydration resulting from the elevated temperatures), with another genus of the same group, Ginkgoites, being found in the surrounding forest, the two living mostly on well-drained, higher grounds. Widespread during the Mesozoic, the ginkgophytes nowadays are restricted to a single species: Ginkgo biloba, and, curiously, they are one of the cycads' closer relatives, going to show how deceiving appearances alone can be. The conifer Podozamites can also be found, distinguished by its multi-veined, flat leaves capable of dropping, a defense against the many insects, such as the derbid planthoppers, that target it.

Apart from these, there is additionally the very plentiful seed fern Dicroidium, sporting a rather spindly trunk and widespread over meridional Pangaea as a whole, having been rather successful in filling the vacant niches left behind by the disappearance of the glossopterids shortly after the Great Dying. The actual fern Cladophlebis grows very close to the ground in humid soil, with the ongoing wet season allowing it to disperse significantly through spores and through rhizomes. Bearing the same method of breeding are horsetails (as discussed in our expedition to the Carboniferous), with a cluster of Neocalamites, possibly stretching to 10 meters tall, standing close to the river, where it is moist enough for their survival.

Close to these plants, three Proterochampsa bathe in the rays that filter from above, using the Sun to help regulate their body temperature in spite of having increased metabolic rates allowing for fast bone growth, possibly influenced, nonetheless, by external conditions, perhaps a way to more efficiently survive in this seasonal habitat. Reaching close to 1.7 meters in length, these are predatory archosauromorphs closely related to Archosauria (constituting a sister group), leading, to some degree, an amphibious lifestyle while still tied to terrestrial spaces. One of their telltale marks is the nodular protuberances adorning their heads, conferring them bumpy textures. Not far, another trio stands out. Also archosauromorph reptiles, they are Hyperodapedon, peculiar 1.3-meter-long herbivores known as rynchosaurs. Fairly stocky creatures, these animals use their beaks and teeth to make short work of plant material, grinding, for instance, the abundant large seeds originating from the Dicroidium and employing their well-muscled tongue to help manipulate food items. Do not be fooled by their arguably derpy appearance, as they can potentially deliver nasty bites. Predators thus act very carefully when attempting to hunt them, not wanting to get a painful or sometimes severe injury.

Another herbivore, a very frequently encountered one for the record, is the big cynodont Exaeretodon (up to maximum sizes of 2 meters long), belonging to one of the few synapsid groups that managed to survive the Permian-Triassic extinction. In the end, the cynodonts would be the only ones to continue on beyond the Triassic in the form of mammals and their closest kin. The Exaeretodon wander about in a lumbering gait, communicating by a squeak-like, yet rather lower pitched, sound. While preferring the more easily accessible plants, these amniotes often dig briefly, unearthing only the most superficial of rhizomes. They also not rarely bury their excrements, making a shallow hole with their front paws before relieving themselves. This is in order to quickly cover any odor that might attract unwanted attention from predators. Here in this clearing however, they are not so worried. The two main dangers, still to be mentioned, are much more preoccupied with one another. 

Exaeretodon, somewhat like various preceding synapsids, already has very mammalian traits, like hair, a complete secondary palate (allowing breathing and eating at the same time), and even milk, a cocktail of ancient origin (as previously brought up) serving as the newborns' nourishment source. These newborns do not suckle, with their mothers lacking nipples and the milk simply being licked from specific skin patches, a condition also seen in extant monotremes, having lost this likely ancestral mammalian condition due to specific dietary habits (read about the phylogeny of mammals in a little more detail in the next chapter). Even when getting older their eating preferences do not completely match the ones of fully-grown individuals, with the young Exaeretodon being generalists, to the point of consuming other animals.

Even more closely related to Mammalia is the other cynodont Trucidocynodon, resting on a fallen Dicroidium. This creature, while not very large, at about 1.2 meters from head to tail, is an active predator and runs down its prey (various small vertebrates), that, when captured, get promptly dispatched with the help of its long, quite noticeable canines. Counting with a more upright posture, it also sports the diaphragm muscle, which evolved earlier in the synapsid lineage, making its respiration more efficient and thus assisting it in achieving the higher speeds necessary to reach its equivalently fast-footed quarry. Despite its ferociousness when on the hunt, it is not free from other dangers, including autoimmune diseases and, as a consequence of one, it has lost quite a lot of its fluffy covering, developing bald spots around its body as a result of its hair follicles being attacked by leukocytes. In contrast with such role as a larger-ish predator, some of its relatives have undergone a miniaturization process associated with the development of endothermy in mammaliamorphs, members of which include but are not restricted to mammals.

Occasional victims of Trucidocynodon are Ixalerpeton, frail and delicate reptiles. Covered with a layer of fuzz-like feathers, they are quite agile and skittish. These critters are lagerpetids, relatives of pterosaurs, which form with them the grouping Pterosauromorpha. Communicating between themselves with high-pitched quick chirps in rapid succession, a gang of Ixalerpeton swiftly covers ground, always paying close attention to any potential threats. Coming their way is a Saturnalia, a dinosaur. Both are archosaurs and part of the clade Avemetatarsalia, which includes Aphanosauria (a group of quadrupedal, long-necked carnivorous reptiles), Dinosauromorpha, and the aforementioned Pterosauromorpha, the latter two likely sharing, apart from all the archosaur characteristics listed before, feathers as an ancestral trait of their own clade: Ornithodira.

Dwelling into dinosaur classification, Saturnalia in specific is part of Sauropodomorpha, one of the two lots making up the Saurischia division, also composed of Theropoda and probably of basal members that do not fit into any of the two established groupings. The other division inside Dinosauria (located inside Dinosauromorpha) is Ornithischia, which includes many subdivisions that will be explored in the subsequent chapters. Now moving away from phylogenetic matters, this mainly carnivorous animal, about 1.5 meters in length, is looking for some tiny prey, lowering its head to the ground in an attempt to simply see anything that might interest it or pick up some scent: if anything catches its attention, the slightly elongated neck provides better access to crevices or other spaces difficult to reach where its targets may be hiding.

On top of the mound harboring the ginkgophyte Sphenobaiera, two more dinosaurs can be seen: a pair of Staurikosaurus, carnivores a little longer than 2 meters with particularly extended tails. They are, like Saturnalia, saurischians, but conceivably fall into the basal members' category, neither theropods nor sauropodomorphs, belonging to the family Herrerasauridae, which contains other less gracile predators, with one such example, Gnathovorax, being found here as well. This couple, which uses their dewlaps for display purposes, has been on the look for some prey items for their young, sufficiently grown to make their first kills. Luckily for them, a Clevosaurus was found bathing on the trunk of the tree and captured soon after, the poor animal's efforts to look as intimidating as possible via raising its head and exposing its tusk-like tooth going unnoticed. The hapless lizard-like being is a rhynchocephalian (the only reptile not belonging to Archosauromorpha we will encounter, instead being part of Lepidosauromorpha, a grouping that also includes squamates), an order that, despite its success during the Mesozoic, today is represented only by the tuatara, endemic to New Zealand, a case uncannily similar to that of the ginkgophytes. Since the little spiny amniote is reserved for their chicks, they are eyeing up a larger meal.

Below them, a not fully grown Aetosauroides, a genus of aetosaur (armored quadrupeds with contrasting feeding habits, some being more adapted to herbivorous diets, while others display a preference for softer foodstuffs, including plants and unhardened insects, such as larvae), lays dead, which, though having achieved sexual maturity, never managed to contribute to the next generation. Its killer is close: a Dynamosuchus. Both are pseudosuchians, an archosaur sister group to Avemetatarsalia containing crocodilians among many more representatives. The latter is more specifically an ornithosuchid, a family constituted by unique predators of downturned snouts and capable of moving bipedally in fast strides. Albeit normally a scavenger, this carnivore is able to hunt, using its strong bite and large teeth to inflict fatal wounds. Its meal, however, is being contested by yet another pseudosuchian: the rauisuchian Rauisuchus. Unlike what a superficial overview may suggest, the Aetosauroides and the Dynamosuchus are possibly more closely related between themselves than to the Rauisuchus (sharing a more recent common ancestor with crocodilians, which are likely part of Rauisuchia if such group is to become monophyletic). Either way, the ornithosuchid, regardless of its fierce aspect, is at a clear disadvantage, being smaller than its rival, which stretches to 3 meters. After exchanging hisses and bellows for a brief couple of minutes, the original “owner” of the carcass gives up and the Rauisuchus secures the prize. The winner takes it all for now.

Concomitantly, the Staurikosaurus return to their lair, producing low growls to signal their arrival. Three babies emerge from a tight cluster of Cladophlebis ferns and get agitated when they see the writhing Clevosaurus. As the small injured reptile is thrown to the ground, it gets no chance to escape, with the scraggly young pouncing onto it, rapidly tearing the unfortunate tetrapod to shreds. Soon, the chicks will abandon the nest and go on to fend off for themselves, with this first kill being an important step at that. Even though Staurikosaurus are precocial (meaning the newborns are already quite mature and mobile), it is noticeable that the parents provide care and protection, with the chances of the infants surviving alone increasing the longer they stay with their progenitors. At the same time, the higher the possibility of a predator, such as a Trucidocynodon, finding their hiding spot and murdering them all in one go. Such a possibility is by no means far-fetched, which can be concluded from the fact the nest has changed locations in a short period and from the current number of offspring, originally much greater. As the feeding time ends, the Staurikosaurus head out once again with the goal of getting some pieces from the Aetosauroides corpse, counting on their agility and nimbleness to outmaneuver the dangerous Rauisuchus.

In the end, dinosaurs, along with their pterosaur relatives, would come out on top in terrestrial habitats as the Triassic ended. A string of extinctions connected to greenhouse emissions possibly emanating from volcanic activity would permeate near the end of the period, ultimately resulting in the demise of creatures like much of the large temnospondyls, rynchosaurs, cynodonts closely related to Exaeretodon and the dicynodonts, beings that had managed to, millions of years earlier, survive the greatest mass extinction of the Phanerozoic. 

Not so much later in terms of geological time, further large-scale volcanic eruptions would, like before in life's history, cause severe disruptions in Earth’s ecosystems through the intense release of even more greenhouse gases, contributing to the recurring themes of ocean acidification, ocean anoxia, global warming, etc. This, the Triassic-Jurassic extinction event, hit marine ecosystems hard once more, with conodonts and mollusks such as ammonoids and bivalves dropping significantly in numbers, all of them having already suffered decreases in the preceding Triassic extinction just cited. However, on land, the increase in temperatures, while long term, did not come immediately and, instead, the release of sulfur aerosols would promote several cold pulses that led to the extinction of various non-insulated animals, not able to cope with the temporary cooler conditions. Consequently, the way for the rise of those which had some sort of covering in conjunction with endothermic metabolisms, the earlier stated ornithodirans (dinosaurs and pterosaurs) and the mammaliamorphs (encompassing mammals), was paved. With many ecological opportunities now open, dinosaurs specifically, many once restricted to higher latitudes, would now spread more significantly over the whole planet, ushering in the start of their golden age.

***

1-Dicroidium

2-Williamsonia

3-Taeniopteris

4-Ginkgoites

5-Podozamites

6-Neocalamites

7-Sphenobaiera

8-Nilssonia

9-Cladophlebis

10-Ixalerpeton

11-Saturnalia

12-Trucidocynodon

13-Exaeretodon

14-Proterochampsa

15-Hyperodapedon

16-Staurikosaurus

17-Clevosaurus

18-Rauisuchus

19-Aetosauroides

20-Dynamosuchus