Formidable fauna

Dinocephalians appeared in the early Permian and became the largest animals of this period, some...
Dinocephalians appeared in the early Permian and became the largest animals of this period, some possibly weighing up to 2 tons. The dinocephalians mysteriously became extinct at the end of the middle Permian. Images: Gondwana Studios
Unlike the small amphibians of today, such as frogs, toads and salamanders, Permian amphibians...
Unlike the small amphibians of today, such as frogs, toads and salamanders, Permian amphibians achieved monstrous sizes, and some featured massive, tooth-studded jaws and strong legs.
Pareiasaur ("cheek lizard'') was a medium to large herbivore possibly related to modern turtles.
Pareiasaur ("cheek lizard'') was a medium to large herbivore possibly related to modern turtles.
The sail-backed Dimetrodon was among the pelycosaurs ("basin lizard''), which evolved into a...
The sail-backed Dimetrodon was among the pelycosaurs ("basin lizard''), which evolved into a range of herbivores and carnivores but did not survive the Permian-Triassic extinction.
Cynodonts ("dog teeth'') appeared towards the end of the Permian and are believed to be among the...
Cynodonts ("dog teeth'') appeared towards the end of the Permian and are believed to be among the therapsid group, the direct ancestors of all mammals.

A new exhibition looming at Otago Museum is a matter of life and death, writes Shane Gilchrist.

Once upon a time, more than 250 million years ago, Earth was home to a wondrous menagerie, possibly weirder even than the film-friendly and occasionally fanged fauna that were to follow in the form of dinosaurs.

 Small collection of Permian fossils at Otago Museum

On the subject of teeth, some had a formidable array, such as the giant saber-toothed gorgonopsid Inostrancevia; other apex predators included Dimetrodon, an animal with a lizard-like body and a sail-like fin on its back believed to help regulate its internal temperature. There was also Lystrosaurus, a metre-long herbivore which, with a flattened face, two tusks and a reptilian stance, was a cross between a lizard and a hippopotamus.

Lasting from 299 million to 251 million years ago, the Permian is regarded as pivotal in the story of Earth's evolution: it's when the vertebrate organisms - that is, animals with backbones - lived on the planet. These ancestors of both mammals and dinosaurs are being brought to life in a forthcoming exhibition at Otago Museum, ''Permian Monsters: Life Before The Dinosaurs'', which opens on August 26 and runs until early next year.

Created by Australian group Gondwana Studios, which specialises in scientifically accurate fossil reproductions, the exhibition mixes fossilised skeletons and reconstructed models, including several animatronic replicas.

Hamish Campbell, a geologist and paleontologist at Crown Research Institute GNS Science, has spent a ''fair whack'' of his career collecting and studying the Permian fossils of New Zealand. He describes the period as fascinating.

''The world is pretty familiar with dinosaurs, but the organisms of the Permian predated both dinosaurs and mammals.''

During the Permian, the two supercontinents of Euramerica (in the north) and Gondwana (in the south) were connected, part of an enormous landmass called Pangaea.

Shaped roughly like a capital ''C'', it included landmasses towards the top that later became modern Europe and Asia. Africa was inside the curve, North and South America on its outside; Australia, New Zealand, India and Antarctica were included at the lower part of the curve.

Given its massive size, Pangaea had climatic extremes: much of the south was frozen under ice caps, whereas more northern areas had wet and dry seasons; the interior regions were also  much cooler and drier than the more separate landmasses of the previous period, the Carboniferous.

As time passed, the icecaps melted and the Earth slowly warmed up, becoming a lush green planet, where both animals and plants thrived.

Permian flora comprised ferns, conifers and small shrubs. Animals included fish, arthropods, amphibians and reptiles, which developed mammal-like characteristics, although the first true mammals would not appear until the next geological period, the Triassic.

The Permian period was the end of an era called the Paleozoic, meaning ''ancient life''. During the Paleozoic the sea - specifically, an enormous ocean called Panthalassa -  teemed with all sorts of life, from tiny single-celled organisms to marine arthropods and large fish, including bizarre-looking sharks.

There were also many invertebrate life-forms, such as sponges, ammonites, nautiloids, crinoids, gastropods, brachiopods and trilobites. Corals also formed in the Paleozoic; after their near-extinction at the end of the Devonian period, they began to regenerate during the Permian period, producing huge reefs.

Like today's amphibians, Permian amphibians were cold-blooded creatures that metamorphosed from a juvenile water-breathing form to an air-breathing adult; they laid their eggs in water, as did their fish ancestors.Unlike the small amphibians of today, such as frogs, toads and salamanders, amphibians were the dominant land animals of the early Permian. They achieved monstrous sizes, some featuring  massive, tooth-studded jaws and strong legs. Several groups evolved strong, robust limbs and vertebrae and became adapted to life on land, while others developed into heavy-bodied semi-aquatic predators.

Towards the end of the Permian, amphibians were pushed back into the swamps by the newly-evolved mammal-like large reptiles, which first appeared at the end of the Carboniferous, the period immediately before the Permian.

For the first time in the history of the Earth, reptiles dominated the land, evolving into many forms, from saber-toothed flesh-eaters to large herbivores and small, probably warm-blooded reptiles that would eventually give rise to mammals.

Yet not only did the Permian document life in all its varied glory, it also experienced the greatest extinction in the history of the Earth.

Referred to as ''The Great Dying'' or the more scientific ''Permian-Triassic Boundary'',  the majority of living species on the planet were wiped out 251 millions years ago.In less than 500,000 years - almost a blip on the radar in geologic timeframes - more than 70% of land animals were wiped out. Significantly, plant life, too, withered.

Marine life was the most affected. By the end of the Permian 96% of all marine life had disappeared.

Some groups that had dominated the ocean, such as ammonites, nautiloids, brachiopods and crinoids, did survive but their species were greatly diminished in number and they never held ecological dominance again.

Sharks and bony fishes suffered a major reduction in species but survived. Many corals did not, the horn corals and tabulate corals that had built many reefs disappeared. And trilobites, a dominant lifeform in the ocean for 290 million years, became extinct.

Scientists are unclear about what caused the mass extinction. Some point to evidence of catastrophic volcanic activity in Siberia in an area known as the Siberian Traps, where a series of massive eruptions initiated a rapid global cooling.

According to recent scientific climate modelling of Earth's atmosphere during the Siberian Trap eruptions, more than 1200 billion tons of methane and 4000 billion tons of sulfur dioxide could have emerged from the area over a timeframe spanning 500,000  years.

Glaciation, too, would have reduced the volume of water in the ocean. That lowering of sea level would have killed marine life in the shallows, reducing diversity while also releasing methane.

Dr Campbell acknowledges there are various theories about what precipatated this event (and other mass extinctions in Earth's history).

''We still don't know for certain. Personally, I believe it was caused by a comet that struck the Earth.''

I think the comet literally acted like a bullet striking the Earth, creating a massive shockwave  and breaching the Earth's crust, which led to a depressurisation of the Earth's mantle.

''One of the consequences was the widespread volcanism that produced the Siberian Traps.''

The reason I think it was a comet is because they are largely comprised of carbon dioxide and water and have no tell-tale heavy metals, unlike a meteorite, such as the one that struck where Mexico now is, and prompted the Cretaceous-Tertiary boundary event.

''We know a lot more about that because it was solid rock and left a tell-tale signature'' Dr Campbell says in regards the popular theory as to what precipitated the mass extinction around 65 million years ago that wiped out, among other species, dinosaurs.

Yet some species did cross the biological dividing line from the Permian to the Triassic, although it took 30 million years for surviving species to recover.

Among the groups of animals that survived was a mammal-like reptile family known as therapsids. One genus, Lystrosaurus, has been described as the Permian/Triassic ''Noah'', because there is fossil evidence that it existed before and after the extinction. Notably, however, most of therapsids had become extinct by the mid-Triassic.

Cynodonts are one of the few groups of therapsids or mammal-like reptiles that survived the Permian-Triassic extinction. It is believed that they are the ancestors of modern mammals.

Another small group were the diapsids, the ancestors of snakes, lizards, crocodiles, birds and dinosaurs.

During the Permian, diapsids were far less abundant than mammal-like reptiles, but after the extinction diapsids began to displace the surviving mammal-like reptiles, forcing them to evolve into small nocturnal insect eaters. This night-time lifestyle probably assisted their evolution towards becoming true mammals, requiring them to develop fur and higher metabolic rates.

Although fossils from the Triassic Period reveal fish of a very uniform shape, indicating relatively few families survived the extinction, what might be regarded as modern stony corals could be found in the mid- to late-Triassic.

''All sorts of organisms were wiped out, but the extinction event created opportunities for other organisms to accelerate their evolution and adaptation,'' Dr Campbell says.

''What remained filtered through to the Triassic and gave rise to what we know as dinosaurs and mammals. We know from the fossil record that there was a profound change.''

 

The talk

Hamish Campbell, senior scientist at GNS Science, will describe the nature of New Zealand's Permian rocks and what they tell us about our geological history. Hutton Theatre, 2pm, Sunday, September 10 (free, bookings essential).

Image: Gondwana Studios
Image: Gondwana Studios

Permian reptiles

Paleontologists classify Permian reptiles into three main groups - synapsids, anapsids and diapsids - based on the number of holes in their skull.

• Permian synapsids were the dominant group of reptiles during the Permian. They are also commonly known as mammal-like reptiles because they showed characteristics of mammals, which had not yet evolved. These include a single hole in the skull behind each eye, and, in some species, the presence of hair. They also had different types of teeth: frontal incisors, big lateral canines for tearing and molars for chewing; a characteristic shared by modern mammals. Synapsids are further divided into two main groups: Pelycosaurs dominated the early Permian, and they include the wellknown sail-backed Dimetrodon.

Therapsids evolved into many different groups, and became the dominant terrestrial carnivores and herbivores of the late Permian. They include the gorgonopsid Inostrancevia which became a top predator in the late-Permian.

Therapsids are believed to be the ancestors of all mammals, and therefore our own ancestors.

Dinocephalians were therapsids that appeared in the early Permian and became the largest animals of this period, some possibly weighing up to 2 tons. Some were carnivores, while others were herbivores or omnivores.

The dinocephalians mysteriously became extinct at the end of the middle Permian, leaving no descendants.

• Permian anapsids are distinguished by the absence of a hole in the skull behind each eye.

• Permian diapsids are distinguished by two holes in the skull behind each eye.

Despite their small size and little dominance during the Permian, they are believed to be the ancestors of snakes, lizards, crocodiles, birds and dinosaurs.

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