Oceans
Sea
levels in the Permian remained generally
low, and near-shore environments were limited by the collection of almost
all major landmasses into a
single continent --
Pangaea. This could
have in part caused the widespread extinctions of marine species at the end
of the period by severely reducing shallow coastal areas preferred by many
marine organisms.
Paleogeography
During the Permian, all the Earth's major land masses except portions of East Asia were collected into a single supercontinent known as Pangaea. Pangaea straddled the equator and extended toward the poles, with a corresponding effect on ocean currents in the single great ocean ("Panthalassa", the "universal sea"), and the Paleo-Tethys Ocean, a large ocean that was between Asia and Gondwana. The Cimmeria continent rifted away from Gondwana and drifted north to Laurasia, causing the Paleo-Tethys to shrink. A new ocean was growing on its southern end, the Tethys Ocean, an ocean that would dominate much of the Mesozoic Era. Large continental landmasses create climates with extreme variations of heat and cold ("continental climate") and monsoon conditions with highly seasonal rainfall patterns. Deserts seem to have been widespread on Pangaea. Such dry conditions favored gymnosperms, plants with seeds enclosed in a protective cover, over plants such as ferns that disperse spores. The first modern trees (conifers, ginkgos and cycads) appeared in the Permian.
Three general areas are especially noted for their extensive Permian deposits - the Ural Mountains (where Perm itself is located), China, and the southwest of North America, where the Permian Basin in the U.S. state of Texas is so named because it has one of the thickest deposits of Permian rocks in the world.
Climate
The climate in the Permian was quite varied. At the start of the Permian, the Earth was still at the grip of an Ice Age from the Carboniferous. Oxygen levels decreased, wiping out plant life and the some of the giant insects from the Carboniferous.
Marine biota
Permian marine deposits are rich in fossil
mollusks,
echinoderms, and
brachiopods. Fossilized shells of two kinds
of invertebrates are
widely used to identify Permian strata and correlate them between sites:
fusulinids, a kind of
shelled amoeba-like
protist that is one of
the
foraminiferans, and
ammonoids, shelled
cephalopods that are distant relatives of
the modern
nautilus. By the close
of the Permian, trilobites and a host
of other marine groups became extinct.
Terrestrial Biota
Terrestrial life in the Permian included diverse plants, fungi, arthropods, and various types of tetrapods. The period saw a massive desert covering the interior of the Pangaea. The warm zone spread in the northern hemisphere, where extensive dry desert appeared. The rocks formed at that time were stained red by iron oxides, the result of intense heating by the sun of a surface devoid of vegetation cover. A number of older types of plants and animals died out or became marginal elements.
The Permian began with the Carboniferous flora still flourishing. About the middle of the Permian a major transition in vegetation began. The swamp-loving lycopod trees of the Carboniferous, such as Lepidodendron and Sigillaria, were progressively replaced in the continental interior by the more advanced seed ferns and early conifers. At the close of the Permian, lycopod and equicete swamps reminiscent of Carboniferous flora was relegated to a series of equatorial islands in the Paleotethys Sea that later would become the South China.
The Permian saw the radiation of many important conifer groups, including the ancestors of many present-day families. Rich forests were present in many areas, with a diverse mix of plant groups. The southern continent saw extensive seed fern forests of the Glossopteris flora. Oxygen levels were probably high there. The ginkgos and cycads also appeared during this period.
Insects of the Permian
By the Pennsylvanian and well
into the Permian, by far the most successful were primitive
relatives of cockroaches. Six fast legs, two
well developed folding wings, fairly good eyes, long, well developed
antennae (olfactory), an omnivorous digestive system, a receptacle for
storing sperm, a
chitin skeleton that
could support and protect, as well as form of gizzard and efficient mouth
parts, gave it formidable advantages over other herbivorous animals. About
90% of insects were cockroach-like insects ("Blattopterans").
The
dragonflies Odonata
were the dominant aerial predator and probably dominated terrestrial insect
predation as well. True Odonata appeared in the Permian
and all are amphibious. Their
prototypes are the oldest winged fossils,
go back to the Devonian, and are
different from other wings in every way.
Their prototypes may have had the beginnings of many modern attributes even
by late Carboniferous and it is
possible that they even captured small vertebrates, for some species had a
wing span of 71 cm.
A number of important new insect groups appeared at this time, including the
Coleoptera (beetles)
and
Diptera (flies).
Reptile and amphibian fauna
Early Permian terrestrial faunas were
dominated by
pelycosaurs and
amphibians, the middle Permian by primitive
therapsids such as the
dinocephalia, and the
late Permian by more advanced therapsids such as
gorgonopsians and
dicynodonts. Towards the very end of the
Permian the first
archosaurs appeared, a
group that would give rise to the
dinosaurs in the
following period. Also appearing at the end
of the Permian were the first
cynodonts, which would go on to evolve into
mammals during the Triassic. Another group
of therapsids, the
therocephalians (such as
Trochosaurus), arose in the Middle Permian.
There were no aerial vertebrates.
The Permian period saw the development of a fully terrestrial fauna and the
appearance of the first large
herbivores and
carnivores. It was the high tide of the
anapsides in the form of the massive
Pareiasaurs and host of smaller, generally
lizard-like groups. A group of small reptiles, the
diapsids started to abound. These were the
ancestors to most modern reptiles and the ruling dinosaurs as well as
pterosaurs and crocodiles.
Thriving also, were the early ancestors to mammals, the
synapsida, which included some large
reptiles such as Dimetrodon. Reptiles
grew to dominance among vertebrates, because their special adaptations
enabled them to flourish in the drier climate.
Permian amphibians consisted of
temnospondyli,
lepospondyli and
batrachosaurs.
Permian Extinction
The end of
the Permian is marked by the greatest extinction event in the geologic
record. The next two lessons will deal with the extinction event.
End of Reading
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Source Pages: Wikipedia - Permian, Permian Extinction