| About Dinosaurs Back to Dinosaur Main |
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, the 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 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 remains under discussion and shows that there is still much we don't 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, 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
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 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 conflicting 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 flowering 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 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.
Did dinosaurs communicate?
Dinosaurs probably communicated both vocally and visually. The chambered
headcrests 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 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 thanks to:
U.S. Department of Education, Office of
Communications and Outreach,
Helping Your Child Learn Science,
Washington, D.C., 2005.
AND
http://edc2.usgs.gov
Wikipedia Junior
US Dept of Ed - School yard
Back to Dinosaur Main
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, the 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 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 remains under discussion and shows that there is still much we don't 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, 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
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 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 conflicting 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 flowering 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 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.
Did dinosaurs communicate?
Dinosaurs probably communicated both vocally and visually. The chambered
headcrests 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 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 thanks to:
U.S. Department of Education, Office of
Communications and Outreach,
Helping Your Child Learn Science,
Washington, D.C., 2005.
AND
http://edc2.usgs.gov
Wikipedia Junior
US Dept of Ed - School yard
Back to Dinosaur Main
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