Late Triassic

Time-Span: 237 – 201 million years ago

Overview: Geologists date the start of the Triassic Period, the first of the Mesozoic Era’s three major divisions, to around 252 million years ago. It began after the end of the Permian Period, the last period of the Paleozoic Era, punctuated by the Permian-Triassic extinction event – the most catastrophic mass extinction in earth’s history. At the dawn of the Early Triassic, only around ten percent of the world’s animal species had made it through, with the oceans being particularly devastated (even the trilobites, which had thrived for over 250 million years before, were wiped out). Studies suggest the Permian-Triassic event was likely caused by cataclysmic volcanic fissures that opened up in what is now Siberia, slowly flooding the region with lava fields. Gases released by this event probably altered the climate, leading to the so-called “Great Dying” at the end of the Permian. Dominant groups from the end of the Paleozoic, such as the therapsids (which included the saber-toothed gorgonopsians), among others, would mostly die out, leaving many niches open to exploit. Therapsids were a group closely related to the ancestors of mammals. Said ancestors would make it through the Permian-Triassic event.

Life on earth would take a long time to recover, only returning to normal during the Middle to Late Triassic. Notable animal lineages on land included mammal relatives like the dicynodonts and cynodonts, crocodile-like phytosaurs, and the prehensile-tailed drepanosaurs. In the oceans, turtle-like creatures called placodonts had evolved, as well as numerous other marine reptiles. This included long-necked carnivores like Nothosaurus and the fish or dolphin-like ichthyosaurs, some of which grew to be enormous. Among the land vertebrate groups, the Archosauria was probably the most successful at this point. This was an advanced and dynamic group of reptiles, which included many famous lineages – one of which was the Dinosauria. Dinosaurs may’ve dated back to the Middle Triassic, but the most solid fossil evidence for them dates to the Late Triassic, around 230 million years ago. Most of such dinosaur genera, including Eoraptor and Herrerasaurus, lived in South America. They were generally small, carnivorous or omnivorous animals, though some Herrerasaurus specimens were decently large. They largely lived in the shadow of larger animals, including some crocodile relatives in the Pseudosuchia.

Some pseudosuchians, such as Saurosuchus and Postosuchus, grew to be decently large, exceeding six meters in length. Such “proto-crocs” undoubtedly fed upon early dinosaurs, as they were easily the top predators of most regions in the Late Triassic. Herbivorous “proto-crocs” also flourished, including the slender-bodied Shuvosaurus and the heavily armored aetosaurs, which included the tank-like Desmatosuchus. Many of these pseudosuchians occupied niches that dinosaurs would later come to dominate. Towards the end of the Triassic, some dinosaurs would reach larger sizes and compete with such animals. Carnivorous examples of which included Germany’s Liliensternus, while herbivores included numerous sauropodomorphs – so-called “prosauropods” – like Plateosaurus and the much larger, four-legged Lessemsaurus. Dinosaurs and pseudosuchians weren’t the only archosaurs to thrive at that time, with the skies being populated by small early pterosaurs like Peteinosaurus and Eudimorphodon, which preyed on smaller animals or insects. By the end of the Triassic Period, the dinosaurs had diversified into a few major lineages, including some early potential ornithischians.

The planet was a very different place at the start of the Triassic Period, with most of the world’s landmass being gathered together in a single massive supercontinent – Pangaea. By the end of the Triassic, Pangaea had begun to split apart, however. The existence of Pangaea played a big role in the Triassic’s rather severe climate and weather patterns. Within the vast continent’s interior, water was scarce, with large swathes of it being covered by nearly uninhabitable desert. Along the coasts, major storms and monsoons would develop, caused by the enormous continuous ocean Panthalassa. Modern types of vegetation like flowering plants and grasses had yet to evolve at this time. Herbivorous animals mainly subsisted on conifers, gingkoes, cycads, seed ferns, true ferns, and horsetails. While the breaking up of the Pangaean landmass would see the end of certain climatic conditions, it would also lead to its own negative effects. Another major extinction event occurred at the end of the Late Triassic, without which dinosaurs may not have overcome the pseudosuchians as the world’s dominant group of land-dwelling vertebrates (though many “proto-crocs” would survive this event, among other animals).

Notable Late Triassic Dinosaurs: Staurikosaurus, Herrerasaurus, Eoraptor, Guaibasaurus, Unaysaurus, Zupaysaurus, Procompsognathus, Plateosaurus, Liliensternus, Melanorosaurus, Ingentia, Lessemsaurus, Coelophysis, Thecodontosaurus, etc.

Notable Late Triassic Formations: Santa Maria (Brazil), Ischigualasto (Argentina), Caturitta (Brazil), Los Colorados (Argentina), Lower Elliot (South Africa), Trossingen (Germany), Löwenstein (Germany), Chinle (United States), Magnesian Conglomerate (United Kingdom), etc.