About Dinosaurs

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When did the dinosaurs first appear on Earth?
The oldest dinosaur types are known from rocks in Argentina and Brazil and are about 230
million years old. The most primitive of these types, Eoraptor, was a small meat-eating
dinosaur. Because Eoraptor's skeleton shows some advanced skeletal features, older
dinosaurs may yet be found.

Are all fossil animals dinosaurs?
No.  Dinosaurs are a group of ancient reptiles that had a set of particular skeletal features. The
hips, hind legs, and ankles were specialized and allowed the legs to move directly under the
body, rather than extending out from the side of the body as in modern lizards. This
arrangement enabled dinosaurs to bring their knees and ankles directly below their hips and
provided the necessary attachments for very strong leg muscles.

Dinosaur skeletons were well designed for supporting a large body, for standing erect (upright),
and for running. The front legs were adapted for grasping prey, for supporting weight, or for
walking and running. The skulls of dinosaurs were designed for maximum strength, for
minimum weight, and (in some cases) for grasping, holding, or tearing at prey.

These skeletal features separated dinosaurs from other ancient reptiles such as Dimetrodon,
plesiosaurs, and pterosaurs. Fossil mammals, like mammoths and "sabre-toothed tigers"
(e.g., Smilodon), are also often incorrectly called "dinosaurs".

These ancient animals are NOT actually dinosaurs!

Did people and dinosaurs live at the same time?
No! After the dinosaurs died out, nearly 65 million years passed before people appeared on
Earth. However, small mammals (including shrew-sized primates) were alive at the time of the
dinosaurs. Many scientists who study dinosaurs (vertebrate palaeontologists) now think that
birds are direct descendants of one line of carnivorous dinosaurs, and some consider that they
in fact represent modern living dinosaurs. This theory  is still being debated and discussed with
and between the experts and it shows really that there is still so much that we do not know
about dinosaurs.

Where did dinosaurs live?
Palaeontologists now have evidence that dinosaurs lived on all of the continents. At the
beginning of the age of dinosaurs (during the Triassic Period, about 230 million years ago) the
continents we now know were arranged together as a single supercontinent called Pangaea.
During the 165 million years of dinosaur existence this supercontinent slowly broke apart. Its
pieces then spread across the globe into a nearly modern arrangement by a process called
plate tectonics.
Volcanoes, earthquakes, mountain building, and sea-floor spreading are all part
of plate tectonics, and this process is still changing our modern Earth.

Did all the dinosaurs live together, and at the same time?
Dinosaur communities were separated by both time and geography. The "age of dinosaurs"
(the Mesozoic Era) included three consecutive geologic time periods (the Triassic, Jurassic
(who saw Jurassic Park the movie?), and Cretaceous Periods). Different dinosaur species lived
during each of these three periods.

For example, the Jurassic dinosaur Stegosaurus already had been extinct for approximately 80
million years before the appearance of the Cretaceous dinosaur Tyrannosaurus. In fact, the
time separating
Stegosaurus and Tyrannosaurus is greater than the time separating
Tyrannosaurus and you. At the beginning of dinosaur history (the Triassic Period), there was
one supercontinent on Earth (Pangaea). Many dinosaur types were widespread across it.
However, as Pangaea broke apart, dinosaurs became scattered across the globe on separate
continents, and new types of dinosaurs evolved separately in each geographic area.

How are dinosaurs named?
Dinosaurs generally are named after a characteristic body feature, after the place where they
were found, or after a person involved in the discovery.

Usually the name consists of two Greek or Latin words (or combinations); in order, these are
the genus (plural, genera) and the species name. For example, the Greek and Latin
combination (binomen)
Tyrannosaurus Rex means "king of the tyrant lizards." Biologists name
modern animals exactly the same way. Some examples include humans (Homo sapiens),
domestic dogs (Canis familiaris), golden eagles (Aquila chrysaetos), box turtles (Terrapene
carolina), and rattlesnakes (Crotalus horridus).

What was the biggest dinosaur? What was the smallest?
The largest complete dinosaur we know of was Brachiosaurus ("arm lizard"); it reached 23m in
length and 12 m in height (about the length of two large school buses and the height of a
four-story building). Fragments of leg bones and vertebrae of even larger
dinosaur species are
known, but these skeletal remains are too incomplete to determine their exact size. Several of
these (Argentinasaurus and Amphicoelias) might have been one and a half to two times larger
than Brachiosaurus. The smallest dinosaurs were just slightly larger than a chicken;
Compsognathus ("pretty jaw") was 1 m (3 ft) long and probably weighed about 2.5 kg (about 6.5
lb). These three dinosaur types all lived during the Jurassic Period. Mussaurus ("mouse lizard")
was claimed as the smallest dinosaur, but it is now known to be the hatchling of a dinosaur
type that was much larger than Compsognaths when fully grown. If birds are advanced
dinosaurs then the smallest dinosaur would be the hummingbird!

How many types of dinosaurs are known?
Approximately 700 species have been named. However, a recent scientific review suggests that
only about half of these are based on fairly complete specimens that can be shown to be
unique and separate species.

These species are placed in about 300 valid dinosaur genera (
Stegosaurus, Diplodocus, etc.),
although about 540 have been named. Recent estimates suggest that about 700 to 900 more
dinosaur genera may remain to be discovered.

Most dinosaur genera presently contain only one species (for example, Deinonychus) but some
have more (for example,
Iguanodon). Even if all of the roughly 700 published species are valid,
their number is still less than one-tenth the number of currently known living bird species, less
than one-fifth the number of currently known mammal species, and less than one-third the
number of currently known spider species.

Were dinosaurs warm-blooded?
Scientists have different opinions on this subject.   

Some palaeontologists think that all dinosaurs were "warm-blooded" in the same sense that
modern birds and mammals are: that is, they had rapid metabolic rates. Other scientists think it
unlikely that any
dinosaur could have had a rapid metabolic rate. Some scientists think that very
big dinosaurs could have had warm bodies because of their large body size, just as some sea
turtles do today. It may be that some dinosaurs were warm-blooded. The problem is that it is
hard to find evidence that unquestionably shows what dinosaur metabolisms were like.

How long could a dinosaur live?
Animal lifespan relate in part to their body size and in part to their type of metabolism. Dinosaur
lifespan probably varied in length from tens of years to hundreds of years.  Their possible
maximum age can be estimated from the maximum lifespan of modern reptiles, such as the
66-year lifespan of the common alligator (Alligator mississippiensis) and the impressive
lifespan of a Black Seychelles Tortoise (Geochelone (Aldabrachelys) sumeirei).   One specimen
of this now-extinct species, which was an adult when captured, lived a record 152 years in
captivity (1766-1918) and had an accidental death.   These estimates, based on lifespan of
cold-blooded animals, would be too long if dinosaurs had metabolisms more similar to
modern birds and mammals.

What did dinosaurs eat?
Some dinosaurs ate lizards, turtles, eggs, or early mammals. Some hunted other dinosaurs or
scavenged dead animals.  Most, however, ate plants (but not grass, which hadn't evolved yet).   
Rocks that contains dinosaur bones also contain fossil pollen and spores that indicate
hundreds to thousands of types of plants existed during the Mesozoic Era.   Many of these
plants had edible leaves, including evergreen conifers (pine trees, redwoods, and their
relatives), ferns, mosses, horsetail rushes, cycads, ginkos, and in the latter part of the dinosaur
age flowering (fruiting) plants. Although the exact time of origin for flowerin plants is still
uncertain, the last of the dinosaurs certainly had fruit available to eat.

How fast could dinosaurs walk or run?
Estimates of dinosaur speeds vary because several different methods are used to calculate
them.  One recent estimate suggests that an average person might have been able to outrun an
Tyrannosaurus (although you probably would not volunteer to try).  The two basic
approaches for estimating dinosaur speed are comparing to recorded speeds of modern
animals of similar body size and build, and also measuring the distances between fossil
footprints in a track way and using these distances to calculate the estimated speed.
Walking-speed estimates for medium-sized bipedal (two-legged) dinosaurs vary from 4 kph to
6 kph, and peak running-speed estimates vary from 37 kph to 88 kph.   The highest figure (88.6
kph) is the same as the peak speed of the currently fastest land animals, such as the North
American pronghorn "antelope" (Antilocapra Americana), and very probably is too high.

Did dinosaurs communicate?
Dinosaurs probably communicated both vocally and visually.  The chambered head-crests on
some dinosaurs such as Corythosaurus and Parasaurolophus might have been used to
amplify grunts or bellows. Defensive posturing, courtship behaviour, and territory fights probably
involved both vocal and visual displays.   

An angry
Triceratops bull shaking his head at you, even silently, would have made himself very
clearly understood!

Why did some dinosaurs grow so big?
Palaeontologists don't know for certain, but perhaps a large body size protected them from most
predators, helped to regulate internal body temperature, or maybe let them reach new sources
of food (some probably browsed treetops, as giraffes do today).  No modern animals except
whales are even close in size to the largest dinosaurs; therefore, palaeontologists think that the
dinosaurs' world was much different from the world today and that climate and food supplies
must have been favourable for reaching great size.

Which was the smartest dinosaur?
Although there is no direct way to measure a dinosaur's intelligence, one of the few possible
measures of intelligence might be a large brain in a small body.   The genus that perhaps fits
this description best was the Cretaceous bird-like dinosaur Troodon, which also may have had
binocular vision (depth perception) and excellent eyesight and was built for speed. Even so, this
dinosaur was probably not as "intelligent" as most modern birds and mammals.

When did dinosaurs become extinct?
Dinosaurs went extinct about 65 million years ago (at the end of the Cretaceous Period),  after
living on Earth for about 165 million years. If all of Earth time from the very beginning of the
dinosaurs to today were compressed into 365 days (1 calendar year), the dinosaurs appeared
January 1 and became extinct the third week of September.  (Using this same time scale, the
Earth would have formed approximately 18.5 years earlier.) By comparison, people (Homo
sapiens) have been on earth only since December 31 (New Year's eve). The dinosaurs' long
period of dominance certainly makes them unqualified successes in the history of life on Earth.

Why did the dinosaurs die out?
There are dozens of theories to explain a probable cause or causes.  Throughout the Mesozoic
Era, individual dinosaur species were evolving and becoming extinct for various reasons.   The
unusually massive extinction at the end of the Cretaceous exterminated the last of the
dinosaurs, the flying reptiles, and the large swimming reptiles, as well as many other marine
animals. There is now widespread evidence that a meteorite impact was at least the partial
cause for this extinction. Impact craters are visible on most planets in our solar system.

A spectacular example of this was witnessed in 1994, when Jupiter was struck by a series of
cometary fragments. Some of these impact blasts were larger than the Earth's diameter. Other
factors such as extensive release of volcanic gases, climatic cooling (with related changes in
ocean currents and weather patterns), sea-level change, low reproduction rates, poison gases
from a comet, or changes in the Earth's orbit or magnetic field may have contributed to this
extinction event.

Special acknowledgements and thanks to:
U.S. Department of Education, Office of
Communications and Outreach,
Helping Your Child Learn Science,
Washington, D.C., 2005.
Wikipedia Junior
US Dept of Ed - School yard

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