What is a dinosaur, exactly?
were large land animals that roamed the earth millions of
years ago during the Mesozoic Era. The best known dinosaur to
date is the Tyrannosaurus rex. The exact cause of the
extinction is still unknown. However it has been theorized
that a sudden asteroid impact was what led to a catastrophic
temperature change on earth doomed those giant creatures.
When did the first dinosaurs appear on
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.
all fossil animals dinosaurs?
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, the plesiosaurs, and pterosaurs.
Fossil mammals, like mammoths and "saber-toothed tigers"
(e.g., Smilodon), are also often incorrectly called dinosaurs.
Did people and dinosaurs live at the same
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
paleontologists) 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
remains under discussion and shows that there is still much we
don't know about dinosaurs.
Where did dinosaurs
Paleontologists 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 Pangea. 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
communities were separated by both time and geography. The
"age of dinosaurs" (the Mesozoic Era) included three
consecutive geologic time periods (the Triassic, Jurassic, 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 (Pangea). Many dinosaur types were
widespread across it. However, as Pangea 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
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
largest complete dinosaur we know of was Brachiosaurus ("arm
lizard"); it reached 23 m in length and 12 m in height (about
the length of two large school buses and the height of a
four-story building). Fragmentary 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 Compsognathus when fully grown. If birds are
advanced dinosaurs, then the smallest dinosaur would be the
How many types of dinosaurs are
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
have conflicting opinions on this subject. Some
paleontologists 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?
lifespans relate in part to their body size and in part to
their type of metabolism. Dinosaur lifespans probably varied
in length from tens of years to hundreds of years. Their
possible maximum age can be estimated from the maximum
lifespans 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 lifespans of cold-blooded animals,
would be too long if dinosaurs had metabolisms more similar to
modern birds and mammals.
What did dinosaurs eat?
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 flowering plants is still uncertain, the last of
the dinosaurs certainly had fruit available to eat.
How fast could dinosaurs walk or
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 to outrun an adult
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 measuring distances between fossil
footprints in a trackway and using these distances to
calculate 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.
probably communicated both vocally and visually. The chambered
headcrests on some dinosaurs such as Corythosaurus and
Parasaurolophus might haved been used to amplify grunts or
bellows. Defensive posturing, courtship behavior, 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
Why did some dinosaurs grow so
Paleontologists don't know for certain, but perhaps a
large body size protected them from most predators, helped to
regulate internal body temperature, or 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, paleontologists
think that the dinosaurs' world was much different from the
world today and that climate and food supplies must have been
favorable for reaching great size.
Which was the smartest
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.
What colors were
fossil evidence for dinosaur skin color is unknown.
Paleontologists think that some dinosaurs likely had
protective coloration, such as pale undersides to reduce
shadows, irregular color patterns ("camouflage") to make them
less visible in vegetation, and so on. Those dinosaurs that
had enough armor, such as the stegosaurs and ceratopsians, may
not have needed protective coloration but may have been
brightly colored as a warning to predators or as a display for
finding a mate. Most dinosaurs probably were as brightly
colored as modern lizards, snakes, or birds.
Were dinosaurs social
dinosaurs were social creatures. Recently discovered evidence
indicates that they travelled together and that some may even
have migrated (because dinosaur fossils have been found above
the Arctic Circle, where food supply would have been
seasonal). Grouped hadrosaur nest sites have been found with
badly crushed eggshells and skeletons of baby dinosaurs (with
slightly worn teeth) still in the nests, suggesting that some
babies stayed in their nests after hatching and probably were
fed by parents.
When did dinosaurs become
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
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.