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Temporal range: Upper TriassicUpper Cretaceous
231 – 66 mya (except birds)
Clockwise from top-left are: Tyrannosaurus, Diplodocus, Parasaurolophus, Deinonychus, Protoceratops, and Stegosaurus
Scientific classification
Kingdom: Animalia
Class: Reptilia
(unranked): Archosauria
Superorder: Dinosauria
Orders & suborders
Tyrannosaurus and human size difference

Dinosaurs[1] were a type of very large reptiles. They were the most powerful land animals of the Mesozoic era (which happened 252.2 million years ago to 66 million years ago).

Scientists have found over 700 species of dinosaurs, and they estimate that at the end of the Mesozoic, up to 1,000 species might have been alive.[2] Scientists have found fossils of dinosaurs on every continent. On average, a new species of dinosaur is discovered every ten days.[2]

Dinosaurs were a kind of archosaur that appeared in the Upper Triassic, about 231 million years ago.[3] The first known dinosaurs were small predators that walked on two legs.[4][5]

By the early Jurassic, dinosaurs were the most powerful land vertebrates and controlled most environments on land.

Dinosaurs suddenly became extinct 66 million years ago, during the K/T extinction event.[6] That event killed all of the dinosaurs which walked on earth.[7]

Birds are the descendants of theropod dinosaurs.[7]

Types of dinosaurs[change | change source]

All dinosaurs share at least 21 traits in their skulls and skeletons.[8] Because all dinosaurs share these traits, paleontologists know all dinosaurs had a common origin. These common traits are called 'synapomorphies'.

Humans have only found definite dinosaur fossils as far back as the Upper Triassic. By that time, dinosaurs had already split into two great orders: the Saurischia and the Ornithischia. The Ornithischia began to develop a different hip structure. They developed bird-like hips.

Dino evol 1 modificated ES.svg
A. Eoraptor, an early saurischian, B Lesothosaurus, a primitive ornithischian,
C A saurischian pelvis (Staurikosaurus) D Lesothosaurus pelvis

Saurischian (lizard-hipped)[change | change source]

This order of dinosaurs did not develop a new hip structure.

There were two types of Saurischia:

Ornithischian (bird-hipped)[change | change source]

These were beaked, herbivorous dinosaurs with bird-like hips.

There were a few different types of Ornithischian:

Dinosaur origins and evolution[change | change source]

Archosaur evolution[change | change source]

The early archosaurs evolved into two main clades:

Earliest dinosaurs[change | change source]

The early forms Herrerasaurus (large), Eoraptor (small) and a Plateosaurus skull

The first known dinosaurs were meat-eaters that walked upright and were one to two metres long.[4][9]

The earliest confirmed dinosaur fossils include:

Saurischian (lizard-hipped) dinosaurs[change | change source]

Ornithischian (bird-hipped) dinosaurs[change | change source]

Pisanosaurus 230–220 mya

Lesothosaurus 199–189 mya

What were early dinosaurs like?[change | change source]

Early saurischians and early ornithischians looked alike. They did not look like modern crocodiles.

A major difference between saurischians and ornithischians was the shape of the bones in their pelvises. Another difference was in the skull. The ornithischian had a more solid upper skull. Also, the joint connecting the lower jaw was more flexible. This helped the ornithischian grind vegetable food.

Variations[change | change source]

Dinosaurs were a varied group. Over time, they were very good at adapting to allow them to live in many ecological niches. This is called adaptive radiation.

Paleontologists have identified over 500 different genera and 1,000 species of non-avian (non-flying) dinosaurs.[11] Today, there are over 9,000 living descendants of dinosaurs: the birds. These are the most diverse group of vertebrates on land.

Different dinosaurs evolved different adaptations to help them survive. For example, some plant-eaters, like Iguanodon, had special weapons to help them fight off the meat-eaters. Triceratops had three horns on its head shield, Ankylosaurus was covered in bony plates, and Stegosaurus had spikes on its tail.

The largest dinosaurs were Sauropod herbivores (plant-eaters), such as Apatosaurus and Brachiosaurus. They were the largest animals to ever walk on dry land.

The carnivores were bipedal (walked on their back legs), though not as humans do. Their body was tilted more towards the horizontal, balanced at the back by their tail. Some were very large, like Tyrannosaurus 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 a dinosaur.

Life style[change | change source]

Movement[change | change source]

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;[12] its traits suggest that the first dinosaurs were small, bipedal predators.[13] The discovery of primitive, pre-dinosaur,[14] types in Middle Triassic strata supports this view. Analysis of their fossils suggests that the animals were indeed small, bipedal predators.

Hip joints and hindlimb postures

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.[15]

Warm-blooded[change | change source]

A major change in outlook came in the 1960s, when it was realized that small theropods were probably warm-blooded.[16] 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.

Activity[change | change source]

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.[16]

Main-stream paleontologists have followed this view for small theropods, but not for larger herbivores.[17] 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.

Limitations[change | change source]

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. And they never dominated the small terrestrial niche. All through the Mesozoic most small vertebrates were mammals and lizards.[18]

Extinction[change | change source]

Badlands near Drumheller, Alberta. Erosion has exposed the claystone K/T boundary

The extinctions at the end of the Cretaceous were caused by one or more catastrophic events, such as massive asteroid or meteorite impacts (like the Chicxulub impact), or increased volcanic activity.

Several impact craters and massive volcanic activity, such as that in the Deccan Traps in India, have been dated to the approximate time of the extinction event. These geological events may have reduced sunlight and hindered photosynthesis, leading to a massive disruption in Earth's ecology.[19]

Did any terrestrial dinosaurs survive the great extinction event? 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.[20] 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.

In popular culture[change | change source]

The first dinosaur fossils were found in the early 19th century. They are major attractions at museums around the world. Dinosaurs also became part of popular culture. There have been many best-selling books and movies about dinosaurs. The media widely covers new discoveries about dinosaurs.

"...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 when it was followed by the movie of the same name in 1993.

Related pages[change | change source]

References[change | change source]

  1. The word 'dinosaur' comes from Greek, meaning 'terrible lizard, ["Dinosaurs - What's in a name?". Children's BBC. http://news.bbc.co.uk/cbbcnews/hi/find_out/guides/animals/dinosaurs/newsid_1610000/1610428.stm. Retrieved 2009-10-03.] and was coined by English biologist Richard Owen in 1842. ["Richard Owen". Natural History Museum. http://www.nhm.ac.uk/nature-online/science-of-natural-history/biographies/richard-owen/index.html. Retrieved 2009-10-05.]
  2. 2.0 2.1 Longrich, Nick (December 13, 2016). "A new dinosaur species is described every 10 days. But how many were there altogether? Dinosaurs became extremely diverse for three main reasons: specialization, location, and speciation". Science: Archaeology. International Business Times. http://www.ibtimes.co.uk/new-dinosaur-species-described-every-10-days-how-many-were-there-altogether-1596281.
  3. They probably diverged from earlier Archosaurs in the late Middle Triassic. The earliest exact date of a dinosaur fossil is that of Eoraptor, 231.4 mya. It is dated by a layer of volcanic ash close beneath the fossil. [1]
  4. 4.0 4.1 Palaeos lists "probably habitually bipedal" among the characteristics of the Dinosauromorpha (that is, early proto-dinosaurs). [2]
  5. 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; Niedźwiedzki G. & Butler R.J. 2010. "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.
  6. "Dino Timeline". Natural History Museum. http://www.nhm.ac.uk/jdsml/nature-online/dino-directory/timeline.dsml?disp=gall&per_id=&sort=Genus. Retrieved 2009-10-05.
  7. 7.0 7.1 Norris, Scott. "T. rex protein "confirms" bird-dinosaur Link". National Geographic. http://news.nationalgeographic.com/news/2008/04/080424-trex-mastodon.html. Retrieved 2009-10-05.
  8. 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.
  9. 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. [3]; popular summary [4]
  10. 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. [5]
  11. Wang S.C. and Dodson P. (2006). "Estimating the diversity of dinosaurs". Proceedings of the National Academy of Sciences USA 103 (37): 13601–13605. doi:10.1073/pnas.0606028103. PMC 1564218. PMID 16954187.
  12. Sereno PC (1999). "The evolution of dinosaurs". Science 284 (5423): 2137–2147. doi:10.1126/science.284.5423.2137. PMID 10381873.
  13. 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: 64–66. doi:10.1038/361064a0.
  14. A clade of Archosaurs ancestral to all dinosaurs and pterosaurs.
  15. Alexander, R. McNeil 2006. Dinosaur biomechanics. Proceedings of the Royal Society B: Biological Sciences. 273 (1596): 1849–1855. [6] (full free access)
  16. 16.0 16.1 Bakker, Robert T. 1986. The dinosaur heresies: new theories unlocking the mystery of the dinosaurs and their extinction. Citadel N.Y.
  17. Benton M.J 2000. Walking with Dinosaurs: the facts. BBC, London, Chapter 6.
  18. Paleos introduction. [7]
  19. MacLeod N. et al. (1997). "The Cretaceous–Tertiary biotic transition". Journal of the Geological Society 154 (2): 265–292. doi:10.1144/gsjgs.154.2.0265. http://findarticles.com/p/articles/mi_qa3721/is_199703/ai_n8738406/print.
  20. Sullivan, RM (2003). "No Paleocene dinosaurs in the San Juan Basin, New Mexico". Geological Society of America Abstracts with Programs 35 (5): 15. http://gsa.confex.com/gsa/2003RM/finalprogram/abstract_47695.htm. Retrieved 2007-07-02.

Books[change | change source]

  • 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
  • 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 Osmólska, Halszka (eds) 2004. The Dinosauria. 2nd ed, Berkeley: University of California Press. ISBN 0-520-24209-2