Jurassic 200146 mya Defining Characteristics: "The Age of Dinosaurs": dinosaurs become very diverse,

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Jurassic 200-146 mya Defining
Characteristics - "The Age of Dinosaurs"
dinosaurs become very diverse, evolving into
stegosaurs, theropods, and huge sauropods
Secondary Characteristics - origin of birds -
origin of the parasitic feeding guilds in
terrestrial ecosystems-possibly replacing
predators as top insect carnivores - Pangea
continues breaking apart, and is better separated
toward the end of the Jurassic, with a lush, warm
tropical climate
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The name Jurassic comes from the Jura
Mountains, an extension of the Swiss Alps into
eastern France, where rocks of this age were
first studied by von Humboldt in 1799..
Jurassic rocks have now been found on every
continent.
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Jurassic Life
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Rising sea levels flooded many of the continental
interiors during the Jurassic, creating warm,
shallow-water environments where marine animals
and plants could thrive.
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These regions saw an increase in diversity of
microscopic phytoplankton such as
coccolithophores, dinoflagellates, and
foraminiferans.
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Reef ecosystems continued to flourish, thanks to
many species of corals and sponges.
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Among these sessile (stationary) organisms lived
gastropods (snails), along with the now-rarer
brachiopods and crinoids.
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In the waters above swam predatory cephalopods
such as ammonoids and belemnites.
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Sharks and bony fishes remained common and shared
the seas with ichthyosaurs, plesiosaurs, and
other marine reptiles.
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plesiosaur
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The first true marine crocodiles had appeared,
alongside the first true teleost fishes (which
today are the most diverse vertebrates on
Earth).
perch
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On land, herbivorous insects diversified, and we
see the first examples of many modern forms such
as leaf hoppers, snakeflies, and wasps.
Snake fly
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Beetles-the most diverse group of organisms on
Earth today-began their diversification during
the Jurassic as well. Some modern groups of
beetles had evolved by this time and fed on
conifers, cycads, and ferns just as their
descendents do today.
Jurassic Beetle
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All these animals lived in terrestrial
environments with abundant gymnosperm trees, but
flowering plants were still absent.
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The understory plants included ferns, horsetails,
and cycads, but grasses (a type of flowering
plant), had not yet evolved.
horsetail
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Diversity in the "Age of Dinosaurs"
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In the Early Jurassic, many dinosaurs were very
similar to their Triassic relatives. These
included prosauropods, early theropods, small
ornithischians, and early armored forms
(Scelidosaurus). Sauropods were present but
uncommon.
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By the Late Jurassic, however, these long-necked,
long-tailed herbivores ruled the land. Behemoths
such as Diplodocus, Apatosaurus, and
Brachiosaurus were among the largest animals to
ever walk on land. Some of the largest Jurassic
dinosaurs may have reached lengths of 120 feet
(35 meters) and weights of 60 tons.
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Because of their size, the biology of sauropods
is still subject to scientific debates. These
revolve around whether sauropods could lift their
heads high in the air or rear up on their hind
legs, how they mated, and what foods they ate.
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By the Late Jurassic nearly every major kind of
dinosaur had appeared, and they are found on
every continent.
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The world was now home to armored stegosaurs
(Stegosaurus) and ankylosaurs, herbivorous
ornithopods of all sizes (Camptosaurus), and
large (Allosaurus) and small (Ornitholestes)
predatory theropods.
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Many of these dinosaurs were collected from the
Morrison Formation, a thick formation of mud,
silt and sand that was deposited in western North
America about 150 million years ago by a large
braided river system running across much of the
central part of the continent..
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Flight and the Origin of Birds
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One of the most important paleontological finds
came in 1861, with the discovery of Archaeopteryx
in Late Jurassic (around 146 million years ago)
limestones near Solnhofen, Germany.
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Many other feathered dinosaurs have been found
in China, and future discoveries will help us
understand exactly how flight evolved in this
unique group of theropods.
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Although the first bird represents a remarkable
evolutionary event, the Jurassic skies truly
belonged to another group of vertebrates, the
pterosaurs.
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These flying reptiles, relatives of the
dinosaurs, had evolved in the Triassic but by now
were very diverse. Pterosaurs lived on nearly
every continent and were far more common than
birds throughout the Jurassic.
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They came in many shapes and sizes long-tailed
forms such as Rhamphorhynchus, huge-headed
Dimorphodon, and the sparrow-sized and
short-tailed Pterodactylus.
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Jurassic Climate and Tectonic Activity
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Pangea, which had begun forming in the Devonian
(400 million years ago) and lasted through the
Triassic, split apart in the Late Triassic.
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By the Middle and Late Jurassic, enough plate
movement had occurred to separate South America
from southern Africa. Laurasia (which consisted
of North America and Eurasia) also moved away
from Africa and South America, helping to create
the Atlantic Ocean and the Gulf of Mexico.
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Volcanic activity was common along these rifting
continental margins. At the same time, Eurasia
(Europe and Asia) moved to the south and started
to close off the Tethys Ocean.
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Sea level gradually rose during the Jurassic,
creating epicontinental seaways in North America
and Europe. The end result was a world with many
more separate land-masses, and a great deal more
coastline, than the world of the Triassic.
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Much of the Jurassic world was warm and moist,
with a greenhouse climate. Coal deposits formed
under forests in Australia and Antarctica.
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Although some arid regions remained, much of the
rest of Pangea was lush and green. Northern
(Laurasian) and southern (Gondwanan) biotas were
still distinct in many ways, but by the Jurassic,
faunas had acquired a more intercontinental
character. Some animals and plants were now found
nearly worldwide, instead of being restricted to
particular regions.
FINIS