Dinosaurs
are a group of
Archosaur
reptiles
of the
clade
Dinosauria
.
[1]
Dinosaurs eventually gave rise to
birds
.
Dinosaurs were the most powerful
land animals
of the
Mesozoic
era
. Over 500 different
genera
of dinosaurs are known.
[2]
Fossils
of dinosaurs have been found on every
continent
.
Dinosaurs began in the
Upper Triassic
, about 230 million years ago (mya).
[3]
The earliest date of a dinosaur fossil is that of
Eoraptor
and
Herrerasaurus
from
Argentina
, and
Saturnalia
from
Brazil
, 237 to 228 mya.
[4]
By the early
Jurassic
they were the top land
vertebrates
, and dominated most
environments
on land. They continued until the
K/T extinction event
66 million years ago.
[5]
From the
fossil record
, it is known that
birds
are living
feathered dinosaurs
.
[6]
They
evolved
from earlier
theropods
during the later
Jurassic
.
[7]
They were the only line of dinosaurs to survive to the
present day
.
[8]
Dinosaurs had
adaptations
that helped make them successful. The first known dinosaurs were small
predators
that
walked on two legs
.
[9]
[10]
All their
descendants
had an
upright
posture
, with the legs underneath the body. This transformed their whole life-style. There were other features. Most of the smaller dinosaurs had
feathers
, and were probably
warm-blooded
. This would make them active, with a higher
metabolism
than modern reptiles.
Social
interaction, with living in
herds
and co-operation, seems certain for some types. The existence of communal egg-laying sites is best understood if the adults travelled in herds, as herbivores do today.
The first fossils were recognised as dinosaurs in the early 19th century. Some of their bones were found much earlier, but were not understood.
William Buckland
,
Gideon Mantell
and
Richard Owen
saw these bones were a special group of animals.
Georges Cuvier
was also important in explaining what dinosaurs were. Dinosaurs are now major attractions at
museums
around the world. They have become part of
popular culture
. There have been best-sellng books and movies. New discoveries are reported in the
media
.
Dinosaurs are so varied that it is not easy to find what they all share. A reasonable list would include many features of the skeleton which are not familiar to the general reader.
[11]
Dinosaurs were, at the start, small and bipedal: they walked on their hind legs. They laid eggs in nests, and included both carnivores and herbivores. We now know that birds are their living descendents, and more about that later.
Changes in the basic set-up of dinosaurs happened because of
adaptations
to different
lifestyles
. From the start of their fossil record, there were both herbivores and carnivores.
Dinosaurs are united by at least 21
traits
in their skulls and skeletons.
[12]
These common characters (called '
synapomorphies
') are the reason
palaeontologists
are sure dinosaurs had a common origin.
However, when definite dinosaur
fossils
appear (early in the Upper Triassic), the group had already split into two great
orders
, the
Saurischia
, and the
Ornithischia
. The Saurischia keep the ancestral hip arrangement inherited from their
Archosaur
ancestors, and the Ornithischia have a modified hip structure.
A
.
Eoraptor
, an early
saurischian
,
B
Lesothosaurus
, a primitive
ornithischian
,
C
A saurischian pelvis (
Staurikosaurus
)
D
Lesothosaurus
pelvis
The following is a simplified list of dinosaur groups based on their
evolution
.
[8]
Groups with a dagger (†) next to them don't have any living members.
- Saurischia
("lizard-hipped"; includes Theropoda and Sauropodomorpha)
-
-
-
-
-
-
-
-
-
- †
Diplodocoidea
(skulls and tails elongated; teeth typically narrow and pencil-like)
- †
Macronaria
(boxy skulls; spoon- or pencil-shaped teeth)
- †
Brachiosauridae
(long-necked, long-armed macronarians)
- †
Titanosauria
(diverse; stocky, with wide hips; most common in the late Cretaceous of southern continents)
- †
Ornithischia
("bird-hipped"; diverse bipedal and quadrupedal herbivores)
-
-
The Archosaurs evolved into two main
clades
: those related to
crocodiles
, and those related to dinosaurs.
The first known dinosaurs were
bipedal
predators
that were one to two metres long.
[9]
[13]
The earliest confirmed dinosaur fossils include the
saurischian
('lizard-hipped') dinosaurs
Herrerasaurus
230?220 mya,
Staurikosaurus
possibly 230?225 mya,
Eoraptor
231.4 mya,
[14]
and
Alwalkeria
230?220 mya.
Saturnalia
, 232?225 mya, may be a basal saurischian or a
prosauropod
. The others are basal saurischians.
Among the earliest
ornithischian
('bird-hipped') dinosaurs is
Pisanosaurus
230?220 mya. Although
Lesothosaurus
comes from 199 to 189 mya, skeletal features suggest that it branched from the main Ornithischia line at least as early as
Pisanosaurus
.
Early saurischians were similar to early ornithischians, but different from modern
crocodiles
. Saurischians differ from ornithischians by keeping the ancestral configuration of bones in the
pelvis
(shown in a diagram above). Another difference is in the skull: the upper skull of the Ornithischia is more solid, and the joint connecting the lower jaw is more flexible. These features are adaptations to
herbivory
; in other words, it helped them grind vegetable food.
Dinosaurs were a varied group of animals.
Adaptive radiation
happened. This let them live in many
ecological niches
.
Paleontologists
have identified over 500 different
genera
and 1,000
species
of non-avian dinosaurs.
[15]
Their descendants, the birds, number 9,000 living species, and are the most diverse group of land vertebrates.
The largest dinosaurs were
herbivores
(plant-eaters), such as
Apatosaurus
and
Brachiosaurus
. They were the largest
animals
to ever walk on dry land. Other plant-eaters, such as
Iguanodon
, had special weapons to help them fight off the meat-eaters. For example,
Triceratops
had three horns on its head shield,
Ankylosaurus
was covered in boney plates, and
Stegosaurus
had spikes on its tail.
The carnivores were
bipedal
(walked on their back legs), though not as we do. Their body was more towards the
horizontal
,
balanced
at the back by their
tail
. Some were very large, like
Tyrannosaurus
,
Allosaurus
and
Spinosaurus
, but some were small, like
Compsognathus
. It was the smaller sized meat-eaters that may have
evolved
into birds. The first
fossil
bird,
Archaeopteryx
, had a
skeleton
which looked much like that of the dinosaur
Compsognathus
, as
T.H. Huxley
commented.
Dinosaurs were primitively
bipedal
: their probable ancestors were small bipedal Archosaurs. The date of the early dinosaur
genus
Eoraptor
at 231.4 million years ago is important.
Eoraptor
probably resembles the common ancestor of all dinosaurs;
[16]
its
traits
suggest that the first dinosaurs were small, bipedal
predators
.
[17]
The discovery of primitive, pre-dinosaur,
[18]
types in Middle
Triassic
strata
supports this view. Analysis of their fossils suggests that the animals were indeed small, bipedal predators.
Those dinosaurs which returned to four-legged stance kept all four legs under their body. This is much more efficient than the sprawling legs of a
lizard
.
The big sauropods could never have reached so large a size without their pillar-like legs. A review surveys what we know about the mechanics of dinosaur movement.
[19]
A major change in outlook came in the 1960s, when it was realised that small theropods were probably warm-blooded.
[20]
The question of whether all theropods or even all dinosaurs were warm blooded is still undecided.
It is now certain (from fossils discovered in
China
: see
Jehol biota
) that small theropods had
feathers
. This fits well with the idea that they were warm-blooded, and that the
origin of birds
can be traced to a line of small theropods.
Warm blooded animals have a high metabolic rate (use up food faster). They can be more active, and for longer, than animals who depend on the
environment
for heating. Therefore, the idea of warm-blooded dinosaurs insulated by feathers led to the idea that they were more active, intelligent and faster runners than previously thought.
[20]
Main-stream palaeontologists have followed this view for small theropods, but not for larger herbivores.
[21]
Since we know that the size of a
Stegosaur
'
s brain was about the size of a
walnut
, there is good reason to think its
intelligence
was limited.
Despite their great success over a long period, there were life-styles which the dinosaurs never evolved. None ever evolved to live entirely in water, as many mammals do, though
Spinosaurus
was semi-aquatic. They never entirely dominated the small terrestrial
niche
. All through the
Mesozoic
most small vertebrates were mammals and
lizards
.
[22]
We have much to learn still about the smaller fauna of the Mesozoic.
The
extinctions
at the end of the Cretaceous were caused by a catastrophic event: a massive
meteorite
hit the Earth (the
Chicxulub
impact). We now know where it hit: in the
Yucantan peninsula
in what is now Mexico.
Several other impact craters, and massive volcanic activity in the
Deccan Traps
in
India
, have been dated to about the time of the extinction event. These geological events may have reduced sunlight and hindered
photosynthesis
, leading to a massive disruption in Earth's
ecology
.
[23]
Did any terrestrial dinosaurs survive the great extinction event? Yes they did, because we now know that birds are descended from dinosaurs. But dinosaurs as generally understood were eliminated. Several fossils have been found in the
Hell Creek Formation
about 40,000 years later than the
K/T extinction event
. Many scientists dismiss the "
Paleocene
dinosaurs" as re-worked, that is, washed out of their original places and then re-buried in much later sediments.
[24]
An associated skeleton (e.g. more than one bone from the same individual) found above the K/T boundary would be convincing, but no such finds have been reported.
- "...Dragons of the prime,
that tare each other in their slime".
Tennyson
,
In Memoriam
,1849.
Books about dinosaurs have been popular, especially with children, but adults have also enjoyed these kinds of books. In
Edwardian
times,
Arthur Conan Doyle
wrote a
novel
about a
plateau
filled with dinosaurs which he called
The Lost World
.
Jurassic Park
in 1990 started a new phase in dinosaur popular culture.
- ↑
The word 'dinosaur' comes from
Greek
, meaning 'terrible lizard, [
"Dinosaurs - What's in a name?"
. Children's BBC. 26 October 2001
. Retrieved
2009-10-03
.
] and was coined by English biologist Richard Owen in 1842. [
"Richard Owen"
. Natural History Museum
. Retrieved
2009-10-05
.
]
- ↑
That is, fossil dinosaurs and not modern
birds
.
- ↑
They may have began earlier:
Alcobar, Oscar A.; Martinez, Ricardo N. (19 October 2010).
"A new herrerasaurid (Dinosauria, Saurischia) from the Upper Triassic Ischigualasto Formation of northwestern Argentina"
.
ZooKeys
(63): 55?81.
doi
:
10.3897/zookeys.63.550
.
PMC
3088398
.
PMID
21594020
.
- ↑
Benton M.J. 2015.
Vertebrate palaeontology
. 4th ed, Wiley Blackwell, p205.
- ↑
"Dino Timeline"
. Natural History Museum
. Retrieved
2009-10-05
.
- ↑
6.0
6.1
St. Fleur, Nicholas (8 December 2016).
"That thing with feathers trapped in amber? It was a dinosaur tail"
.
New York Times
. Retrieved
8 December
2016
.
- ↑
"Sustained miniaturization and anatomical innovation in the dinosaurian ancestors of birds"
.
Science
.
345
(6196): 562?566. 1 August 2014.
Bibcode
:
2014Sci...345..562L
.
doi
:
10.1126/science.1252243
.
PMID
25082702
.
S2CID
37866029
. Retrieved
August 2,
2014
.
- ↑
8.0
8.1
Holtz, Thomas R. Jr. (2007).
Dinosaurs: the most complete, up-to-date encyclopedia for dinosaur lovers of all ages
. New York: Random House.
ISBN
978-0-375-82419-7
.
- ↑
9.0
9.1
Palaeos lists "probably habitually bipedal" among the characteristics of the
Dinosauromorpha
(that is, early proto-dinosaurs).
[1]
Archived
2015-03-15 at the
Wayback Machine
- ↑
Moderately large bipedal dinosauromorphs had appeared by 246 mya. Fossil tracks show that the dinosaur lineage appeared soon after the
Permian-Triassic extinction event
. Their age suggests that the rise of dinosaurs was slow and drawn out across much of the Triassic.
Brusatte S.L; Nied?wiedzki G. & Butler R.J. 2010 (2011).
"Footprints pull origin and diversification of dinosaur stem lineage deep into early Triassic"
.
Proceedings of the Royal Society B
.
278
(1708): 1107?1113.
doi
:
10.1098/rspb.2010.1746
.
PMC
3049033
.
PMID
20926435
.
{{
cite journal
}}
: CS1 maint: multiple names: authors list (
link
) CS1 maint: numeric names: authors list (
link
)
- ↑
Nesbitt, Sterling J. 2011. The early evolution of Archosaurs: relationships and the origin of major
clades
.
Bulletin of the American Museum of Natural History
. New York: American Museum of Natural History. 2011 (352): 1?292. doi:10.1206/352.1. hdl:2246/6112. ISSN 0003-0090. S2CID 83493714.
- ↑
Nesbitt S.J. 2011. The early evolution of archosaurs : relationships and the origin of major clades.
Bulletin of the American Museum of Natural History
352
: 1?292.
- ↑
Allen, Vivian; Bates, Karl T; Li, Zhiheng and Hutchinson John R. 2013. Linking the evolution of body shape and locomotor biomechanics in bird-line archosaurs.
Nature
497
, 104?107.
[2]
; popular summary
[3]
- ↑
Alcober O.A & Martinez R.N. 2010. A new herrerasaurid (Dinosauria, Saurischia) from the Upper Triassic Ischigualasto Formation of northwestern Argentina.
Zookeys
.
63
, 55?81.
[4]
- ↑
Wang S.C. and Dodson P. (2006).
"Estimating the diversity of dinosaurs"
.
Proceedings of the National Academy of Sciences USA
.
103
(37): 13601?13605.
Bibcode
:
2006PNAS..10313601W
.
doi
:
10.1073/pnas.0606028103
.
PMC
1564218
.
PMID
16954187
.
- ↑
Sereno PC (1999). "The evolution of dinosaurs".
Science
.
284
(5423): 2137?2147.
doi
:
10.1126/science.284.5423.2137
.
PMID
10381873
.
- ↑
Sereno, P.C.; Forster, Catherine A.; Rogers, Raymond R.; Monetta, Alfredo M. (1993). "Primitive dinosaur skeleton from Argentina and the early evolution of Dinosauria".
Nature
.
361
(6407): 64?66.
Bibcode
:
1993Natur.361...64S
.
doi
:
10.1038/361064a0
.
S2CID
4270484
.
- ↑
A
clade
of Archosaurs ancestral to all dinosaurs and pterosaurs.
- ↑
Alexander, R. McNeil 2006. Dinosaur biomechanics.
Proceedings of the Royal Society B: Biological Sciences
.
273
(1596): 1849?1855.
[5]
(full free access)
- ↑
20.0
20.1
Bakker, Robert T. 1986.
The dinosaur heresies: new theories unlocking the mystery of the dinosaurs and their extinction
. Citadel N.Y.
- ↑
Benton M.J 2000.
Walking with dinosaurs: the facts
. BBC, London, Chapter 6.
- ↑
"Paleos introduction"
(PDF)
. Archived from
the original
(PDF)
on 2015-03-15
. Retrieved
2013-05-29
.
- ↑
MacLeod N.; et al. (1997).
"The Cretaceous?Tertiary biotic transition"
.
Journal of the Geological Society
.
154
(2): 265?292.
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:
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.
doi
:
10.1144/gsjgs.154.2.0265
.
S2CID
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.
- ↑
Sullivan, RM (2003).
"No Paleocene dinosaurs in the San Juan Basin, New Mexico"
.
Geological Society of America Abstracts with Programs
.
35
(5): 15. Archived from
the original
on 2011-04-08
. Retrieved
2007-07-02
.
Wikimedia Commons has media related to
Dinosauria
.
- Bakker, Robert T. 1986.
The Dinosaur Heresies: new theories unlocking the mystery of the dinosaurs and their extinction
. New York: Morrow.
ISBN
0-688-04287-2
- Farlow J.O. and Brett-Surman M.K. (eds) 1997.
The Complete Dinosaur
. Indiana University Press.
ISBN
0-253-33349-0
- Holtz, Thomas R. Jr. 2007.
Dinosaurs: the most complete, up-to-date encyclopedia for dinosaur lovers of all ages
. New York: Random House.
ISBN
978-0-375-82419-7
- Iggulden, Hal; Iggulden, Conn (2007). "Dinosaurs".
The Dangerous Book for Boys
. New York: HarperCollins. pp. 30?34.
ISBN
978-0061243585
.
- Paul, Gregory S. 2000.
The Scientific American book of dinosaurs
. New York: St. Martin's Press.
ISBN
0-312-26226-4
- Weishampel, David B; Dodson, Peter and Osmolska, Halszka (eds) 2004.
The Dinosauria
. 2nd ed. Berkeley: University of California Press.
ISBN
0-520-24209-2
- National Geographic:
Dinosaurs: a new look at the prehistoric icons
. Good account of discoveries at American sites.