The Permian Period was the final period of the Paleozoic Era. Lasting
from 299 million to 251 million years ago, it followed the Carboniferous Period
and preceded the Triassic Period. By the early Permian, the two great
continents of the Paleozoic, Gondwana and Euramerica, had collided to form the
supercontinent Pangaea. Pangaea was shaped like a thickened letter “C.” The top
curve of the “C” consisted of landmasses that would later become modern Europe
and Asia. North and South America formed the curved back of the “C” with Africa
inside the curve. India, Australia and Antarctica made up the low curve. Inside
the “C” was the Tethys Ocean, and most of the rest of Earth was the
Panthalassic Ocean. Because Pangaea was so immense, the interior portions of
the continent had a much cooler, drier climate than had existed in the
Carboniferous.
Marine life
Little is known about the huge Panthalassic Ocean, as there is little
exposed fossil evidence available. Fossils of the shallower coastal waters
around the Pangaea continental shelf indicate that reefs were large and diverse
ecosystems with numerous sponge and coral species. Ammonites, similar to the
modern nautilus, were common, as were brachiopods. The lobe-finned and spiny
fishes that gave rise to the amphibians of the Carboniferous were being
replaced by true bony fish. Sharks and rays continued in abundance.
Plants
On land, the giant swamp forests of the Carboniferous began to dry out.
The mossy plants that depended on spores for reproduction were being replaced
by the first seed-bearing plants, the gymnosperms. Gymnosperms are vascular
plants, able to transport water internally. Gymnosperms have exposed seeds that
develop on the scales of cones and are fertilized when pollen sifts down and
lands directly on the seed. Today’s conifers are gymnosperms, as are the short
palm like cycads and the gingko.
Insects
Arthropods continued to diversify during the Permian Period to fill the
niches opened up by the more variable climate. True bugs, with mouthparts
modified for piercing and sucking plant materials, evolved during the Permian.
Other new groups included the cicadas and beetles.
Land animals
Two important groups of animals dominated the Permian landscape:
Synapsids and Sauropsids. Synapsids had skulls with a single temporal opening
and are thought to be the lineage that eventually led to mammals. Sauropsids
had two skull openings and were the ancestors of the reptiles, including
dinosaurs and birds.
In the early Permian, it appeared that the Synapsids were to be the
dominant group of land animals. The group was highly diversified. The earliest,
most primitive Synapsids were the Pelycosaurs, which included an apex predator,
a genus known as Dimetrodon. This animal had a lizard-like body and
a large bony “sail” fin on its back that was probably used for
thermoregulation. Despite its lizard-like appearance, recent discoveries have
concluded that Dimetrodon skulls, jaws and teeth are closer to
mammal skulls than to reptiles. Another genus of Synapsids, Lystrosaurus, was
a small herbivore — about 3 feet long (almost 1 meter) — that looked something
like a cross between a lizard and a hippopotamus. It had a flat face with two
tusks and the typical reptilian stance with legs angled away from the body.
In the late Permian, Pelycosaurs were succeeded by a new lineage known
as Therapsids. These animals were much closer to mammals. Their legs were under
their bodies, giving them the more upright stance typical of quadruped mammals.
They had more powerful jaws and more tooth differentiation. Fossil skulls show
evidence of whiskers, which indicates that some species had fur and were
endothermic. The Cynodont (“dog-toothed”) group included species that hunted in
organized packs. Cynodonts are considered to be the ancestors of all modern
mammals.
At the end of the Permian, the largest Synapsids became extinct, leaving
many ecological niches open. The second group of land animals, the Sauropsid
group, weathered the Permian Extinction more successfully and rapidly
diversified to fill them. The Sauropsid lineage gave rise to the dinosaurs that
would dominate the Mesozoic Era.
The Great Dying
The Permian Period ended with the greatest mass extinction event in
Earth’s history. In a blink of Geologic Time — in as little as 100,000 years —
the majority of living species on the planet were wiped out of existence.
Scientists estimate that more than 95 percent of marine species became extinct
and more than 70 percent of land animals. Fossil beds in the Italian Alps show
that plants were hit just as hard as animal species. Fossils from the late
Permian show that huge conifer forests blanketed the region. These strata are
followed by early Triassic fossils that show few signs of plants being present
but instead are filled with fossil remnants of fungi that probably proliferated
on a glut of decaying trees.
Scientists are unclear about what caused the mass extinction. Some point
to evidence of catastrophic volcanic activity in Siberia and China (areas in
the northern part of the “C” shaped Pangaea). This series of massive eruptions
would have initially caused a rapid cooling of global temperatures leading to
increased glaciations. This “nuclear winter” would have led to the demise of
photosynthetic organisms, the basis of most food chains. Lowered sea levels and
volcanic fallout would account for the evidence of much higher levels of carbon
dioxide in the oceans, which may have led to the collapse of marine ecosystems.
Other scientists point to indications of a massive asteroid impacting the
southernmost tip of the “C” in what is now Australia. Whatever the cause, the
Great Dying closed the Paleozoic Era.
