DINOSAUR
Dinosaurs are a diverse group of animals of the clade Dinosauria. They
first appeared during the Triassicperiod, 231.4 million years ago, and
were the dominant terrestrial vertebratesfor 135 million years, from
the beginning of the Jurassic (about 201 million years ago) until the
end of the Cretaceous(66 million years ago), when the Cretaceous–
Paleogene extinction eventled to the extinction of most dinosaur
groups at the close of the Mesozoic Era.
The fossilrecord indicates
that birdsevolved from theropoddinosaurs during the Jurassic Period
and, consequently, they are considered a subgroup of dinosaurs by many
paleontologists. [ 1 ]Some birds survived the extinction event that
occurred 66 million years ago, and their descendants continue the
dinosaur lineage to the present day. [ 2 ]
and ecological standpoints. Birds, at over 10,000 living species, [ 3
]are the most diverse group of vertebrates besides perciformfish. [ 4]
Using fossil evidence, paleontologistshave identified over 500
distinct genera [ 5 ]and more than 1,000 different species of
non-avian dinosaurs. [ 6 ]Dinosaurs are represented on every continent
by both extantspecies and fossil remains. [ 7 ]Some are herbivorous,
others carnivorous. While dinosaurs were ancestrally bipedal, many
extinct groups included quadrupedalspecies, and some were able to
shift between these stances. Elaborate display structures such as
horns or crests are common to all dinosaur groups, and some extinct
groups developed skeletal modifications such as bony armorand spines.
Evidence suggests that egg laying and nest building are additional
traits shared by all dinosaurs. While modern birds are generally small
due to the constraints of flight, many prehistoric dinosaurs were
large-bodied—the largest sauropoddinosaurs may have achieved lengths
of 58 meters (190 feet) and heights of 9.25 meters (30 feet 4 inches).
[ 8 ]Still, the idea that non-avian dinosaurs were uniformly gigantic
is a misconception based on preservation bias, as large, sturdy bones
are more likely to last until they are fossilized. Many dinosaurs were
quite small: Xixianykus, for example, was only about 50 cm (20 in)
long.
Although the word dinosaur means "terrible lizard", the name is
somewhat misleading, as dinosaurs are not lizards. Instead, they
represent a separate group of reptilesthat, like many extinct forms,
did not exhibit characteristics traditionally seen as reptilian, such
as a sprawling limb postureor ectothermy. Additionally, many
prehistoric animals, including mosasaurs, ichthyosaurs, pterosaurs,
plesiosaurs, and Dimetrodon, are popularly conceived of as dinosaurs,
but are not taxonomicallyclassified as dinosaurs. Through the first
half of the 20th century, before birds were recognized to be
dinosaurs, most of the scientific community believed dinosaurs to have
been sluggish and cold-blooded. Most research conducted since the
1970s, however, has indicated that all dinosaurs were active animals
with elevated metabolismsand numerous adaptations for social
interaction.
Since the first dinosaur fossilswere recognized in the early 19th
century, mounted fossil dinosaur skeletons have been major attractions
at museums around the world, and dinosaurs have become an enduring
part of world culture. The large sizes of some groups, as well as
their seemingly monstrous and fantastic nature, have ensured
dinosaurs' regular appearance in best-selling books and films, such as
Jurassic Park. Persistent public enthusiasm for the animals has
resulted in significant funding for dinosaur science, and new
discoveries are regularly covered by the media.
Source: en.wikipedia.org
No comments:
Post a Comment