Permian Earth – The Age of Amphibians

Permian Earth

298.9 to 252.17 Million Years Ago

Charles R. Knight

A late nineteenth-century painting by famous paleoartist Charles R. Knight depicting a dimetrodon with an edaphosaurus in the background.

With few large herbivorous animals to feed upon them, plants colonised just about every corner of the globe 300-million years ago, creating entirely new ecosystems for animal life to exploit. Land animals grew larger and more diverse than ever before, heralding in the Age of Amphibians and the rise of synapsid megafauna. In the ninth part of my “Journey through the History of Earth” series, we’ll be exploring this fascinating period of evolutionary diversity.

Part 1: Hadean Earth – The Violent Creation of Our World

Part 2: Archean Earth – Signs of Life

Part 3: Proterozoic Earth – The First Animals

Part 4: Cambrian Earth – An Explosion of Evolution

Part 5: Ordovician Earth – Colonising a Barren Land

Part 6: Silurian Earth – The First Breath of Air

Part 7: Devonian Earth – The Age of Fishes and Forests

Part 8: Carboniferous Earth – The Age Bugs

Part 9: Permian Earth – The Age of Amphibians

Part 10: Triassic Earth – The Rise of the Dinosaurs

Part 11: Jurassic Earth – The Land of Giants

Part 12: Cretaceous Earth – The Reign of Tyrants

Part 13: Paleogene Earth – The Rise of Mammals

Part 14: Neogene Earth – Human Ancestors

Part 15: Quaternary Earth – The Age of Man

298.9 million years ago, the volatile Carboniferous Period ended as the climate stabilised, glaciers receded and oxygen levels dropped. Amphibians were now well established, as were insects and the ancestors to modern fish. Lush primeval jungles spanned most of the Earth’s landmasses; ripe for exploitation by an ever-growing and diversifying ecosystem. The major continents of Pangaea and Siberia also grew enormously as sea levels dropped, transforming the face of our world.

First described in 1841 and named after the city of Perm near Russia’s Ural Mountains, the Permian Period is the last of the Palaeozoic Era. During this time, synapsids, a group of animals that includes all mammals, underwent extraordinary diversification, giving rise to the extremely successful and diverse group of iconic animals – the dimetrodons. However, the end of the Permian also saw the demise of almost all life on Earth in what was the most severe extinction event ever known.

Highlights of the Permian

• Great climate variation
• Ancestors of mammals evolve
• Rise of dimetrodons
• Formation of Pangaea
• Worst extinction event in Earth’s history
• Major drop in sea levels

Giant Lizards Roam a Warming Land

Dmitry Bogdanov

Contrary to popular belief, dimetrodons, such as the dimetrodon grandis depicted here, are not dinosaurs. Some 20 species of dimetrodon have been discovered, and they all lived between 272 and 295 million years ago, long before the dinosaurs.

Glaciations that started during the Late Carboniferous continued well into the Early Permian, an epoch also known as the Cisuralian. An icy tundra dominated the once temperate lands of what is now the Antarctic, spanning northward to about -40 degrees of latitude. In terms of climate diversity, the world was rather like what we know today, with distinct climactic belts forming a diverse range of ecosystems across the supercontinent of Pangea.

The Carboniferous Rainforest Collapse of the preceding period had served as both a destructive extinction event but also to put the brakes on evolution, thus preventing it from spiralling even further out of control. The enormously high oxygen levels, previously peaking at 35%, plummeted as vast swathes of swamp forest died out, reducing the global effects of photosynthesis. By the Permian period, the average oxygen level was only 23%, not much higher than it is today.

The Early Permian saw the glaciers recede markedly, giving space for the life-bearing swamp forests to expand once again. Early tetrapods, some reaching lengths of 10 feet (3 metres), dominated these humid biomes, ever increasing in their numbers and diversity. Among the most iconic animals of the time was the edaphosaurus, a large synapsid and a direct predecessor to the dimetrodons that would come to be the apex terrestrial predators later in the period.

As the Permian climate became warmer and drier, life continued to thrive mostly in lowland floodplains where semiaquatic animals were at the top of the food chain. Some 272-million years ago, the iconic mammal-like reptile dimetrodons evolved from earlier, more fish-like amphibians. These carnivorous creatures looked superficially like enormous iguanas or komodo dragons, albeit with the signature sails on their backs. The largest of the 14 species so far described was dimetrodon angelensis, a beast that grew to be 15 feet (4.6 metres) long.

Terrifying Predators Rise to the Top of the Food Chain

Dmitry Bogdanov

The ‘titanic murderer’ was one of the largest dinocephalians of all, and one of the most ferocious apex predators of its time.

Characterised by their large, bulky bodies, the gigantic lizard-like dinocephalians came in both herbivorous and carnivorous forms. The latter quickly rose to the top of the food chain, becoming one of the most terrifying predators to ever walk the Earth. Among them was the aptly named titanophoneus, which translates to ‘titanic murderer’. Added to that is the fact that the suborder it belongs to, dinocephalia, means ‘terrible head’. The skull alone was 2.6 feet (80 cm) long.

Dinocephalia were, for the 12-million years they existed, among the most successful of all Palaeozoic orders of terrestrial mammals. Perhaps the best known of them all was moschops, Greek for ‘calf face’, a hulking herbivore with an enormously thick skull that may have been used for head-butting its contemporaries as part of mating rituals. Another bizarre creature belonging to the order was the ‘antlered’ estemmenosuchus, the ‘crowned crocodile’, which is believed to have been omnivorous. Despite being the dominant terrestrial animal of their time, the entire dinocephalian suborder died out around 260-million years ago, leaving no descendants. Their sudden disappearance remains a mystery, although various factors, such as climate change and disease, may have been partially responsible.

James St. John

This photo of a public display from Field Museum of Natural History in Chicago shows the bizarre dental arrangement of a Permian helicoprion.

While dinocephalians and dimetrodons ruled over the Permian swamplands, something perhaps even more formidable terrorised the ancient Panthalassic Ocean. These titanic marine monstrosities are known as helicoprions, a type of prehistoric shark that thrived between 290- and 250-million years ago. While enormous sharks are disconcerting enough, helicoprion also had a circular saw in place of its teeth. A discovery published by Idaho State University described remains of a 1.8-foot-long (56 cm) tooth whorl, which suggests that the largest among these ocean predators grew around 40 feet (12 metres) long.

Ancestors to Mammals Evolve

Nobu Tamura

The ferocious inostrancevia was the largest of the carnivorous gorgonopsids. It grew up to 11.5 feet (3.5 metres) long and likely preyed upon the slightly larger scutosaurus, a reptile with which it shared its habitat.

Synapsids were already well-established by the Late Permian, an epoch also known as the Lopingian. However, they continued to evolve and diversify, with some species starting to slightly resemble today’s mammals, although it would still be tens of millions of years before true mammals would appear. Some of these orders managed to survive the Permian Mass Extinction, forming the foundation of evolution that started the Cenozoic Era, that which saw the dinosaurs rise to fame.

Two main orders of synapsid dominated terrestrial ecosystems during the Late Permian: the carnivorous gorgonopsids and the herbivorous dicynodonts. Both taxons were extremely successful, colonising vast swathes of land spanning the supercontinent of Pangaea. They thrived in a diverse range of habitats, ranging from coastal shallows to inland swamp forests to drier, fully terrestrial regions. Among the most common and successful was lystrosaurus, a piglet-sized dicynodont that survived well into the Triassic.

Gorgonopsids were the largest terrestrial carnivores during the Late Permian, with inostrancevia being the size of a large grizzly bear. Many of these ferocious beasts are mistakenly referred to as dinosaurs, but they were not in fact closely related. Dozens of gorgonopsids species have been discovered, ranging from the agile-looking lycaenops to the dog-sized sycosaurus. Among the smallest was the aloposaurus, which grew no larger than a cat.

The Great Dying Transforms the Face of the Earth

Lystrosaurus

Lystrosaurus, meaning ‘shovel lizard’, was one of the few families of animals to survive the Permian-Triassic Extinction and live well into the Triassic period.

Steadily decreasing biodiversity, likely caused in part by climate change and volcanic activity, culminated some 252-million years ago in the most severe extinction event in the history of our planet. Marine ecosystems in particular were left truly devastated by the Permian-Triassic extinction event, with as many as 96% of all species disappearing off the face of the Earth forever. Terrestrial ecosystems also underwent a devastating series of mass extinctions, with over two thirds of all land vertebrates vanishing. Even insects took a major hit in what was the only mass dying of their kind. Trilobites, having thrived for 300-million years, also died out, though they had already been in steep decline since the Carboniferous.

Quite what caused the Permian Extinction Event remains shrouded in mystery, but it was almost certainly down to a culmination of events. There is no doubt, however, that climate change and transformation of the Earth’s atmosphere played a major role. For a start, the rapid decrease in oxygen-producing forests led to plummeting oxygen levels which, by the beginning of the Triassic, were less than half what they were during the Carboniferous. As a side-effect, the oceans suffered a deadly anoxic event, whereby greatly decreased oxygen levels in the water literally choked almost all maritime life to death. At the same time, rising global temperatures, due in part to increasing prevalence of CO2 in the atmosphere, also made for a stressful environment for many terrestrial Permian organisms.

Ultimately, the Late Permian extinction was the result of a combination of causes, perhaps even including an impact event like that which is believed to have wiped out the non-avian dinosaurs some 186-million years later.

Owing to the profound changes to the Earth’s biosphere and the devastatingly high loss of species diversity, life took an exceedingly long time to recover after The Great Dying. The intensity of the crisis lead to a recovery period of some 10-million years, during which time the climate continued to change, further strangling the course of evolution.

Conclusion

The Permian-Triassic Extinction event marked the end of the Phanerozoic Era, which had spanned 289-million years. However, despite the profound transformation of our world, and despite suffering unimaginably heavy losses, some important groups did manage to survive, including the dicynodonts, which survived well into the Late Triassic. Next week, we’ll be exploring the beginning of a whole new part of our planet’s history, the Triassic Period of the Cenozoic Era, the time when the first dinosaurs roamed the Earth.

Part 10: Triassic Earth – The Rise of the Dinosaurs