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Dinosaur

From Wikipedia, the free encyclopedia.

? Dinosaur Conservation status: Fossil Fossil range: Triassic – Cretaceous
Replica of Tyrannosaurus rex at the Senckenberg Museum.
Scientific classification
Domain: {{{domain}}} Superkingdom: {{{superregnum}}} Kingdom: Animalia Subkingdom: {{{subregnum}}} Superdivision: {{{superdivisio}}} Superphylum: {{{superphylum}}} Division: {{{divisio}}} Phylum: Chordata Subdivision: {{{subdivisio}}} Subphylum: {{{subphylum}}} Infraphylum: {{{infraphylum}}} Microphylum: {{{microphylum}}} Nanophylum: {{{nanophylum}}} Superclass: {{{superclassis}}} Class: Reptilia Sublass: {{{subclassis}}} Infraclass: {{{infraclassis}}} Superorder: Dinosauria Owen, 1842 Order: {{{ordo}}} Suborder: {{{subordo}}} Infraorder: {{{infraordo}}} Superfamily: {{{superfamilia}}} Family: {{{familia}}} Subfamily: {{{subfamilia}}} Supertribe: {{{supertribus}}} Tribe: {{{tribus}}} Subtribe: {{{subtribus}}} Genus: {{{genus}}} Subgenus: {{{subgenus}}} Section: {{{sectio}}} Series: {{{series}}} Species: {{{species}}} Subspecies: {{{subspecies}}}
[[{{{diversity_link}}}|Diversity]]
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Binomial name
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Type Species
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Orders & Suborders
Saurischia Sauropodomorpha Theropoda Ornithischia
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Synonyms
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Dinosaurs are vertebrate animals that range from reptile-like to bird-like.^[1] Dinosaurs dominated the terrestrial ecosystem for over 160 million years, first appearing around 230 million years ago. 65 million years ago, at the end of the Cretaceous period, all non-avian dinosaurs became extinct. Dinosaurs still exist today in the line of birds (avian dinosaurs). Knowledge about dinosaurs is derived from both fossil and non-fossil records, including fossilized bones, feces, trackways, gastroliths, feathers, impressions of skin, internal organs and soft tissues.^[2][3] Dinosaur remains have been found on every continent on Earth, including Antarctica. Numerous fossils of the same dinosaur species have been found on completely different continents, corroborating the generally-accepted theory that all land masses were at one time connected in a super-continent called Pangaea. Pangaea began to break up during the Triassic period around 230 million years ago.^[4]

Since the first dinosaur was recognized in the 19th century, their mounted, fossilized skeletons have become major attractions at museums around the world. Dinosaurs have become a part of world culture and remain consistently popular, especially among children. They have been featured in best-selling books and blockbuster films such as Jurassic Park, and new discoveries are regularly covered by the media. The term dinosaur is also used informally to describe any prehistoric reptile, such as the pelycosaur Dimetrodon, the winged pterosaurs, and the aquatic ichthyosaurs, plesiosaurs, and mosasaurs, though none of these are dinosaurs.

The ongoing renaissance in the scientific understanding of dinosaurs began in the 1970s and was triggered, in part, by John Ostrom's discovery of Deinonychus, an active, vicious predator that may have been warm-blooded (homeothermic), in marked contrast to the prevailing image of dinosaurs as sluggish and cold-blooded. Vertebrate paleontology, arguably the primary scientific discipline involved in dinosaur research, has become a global science. Major new dinosaur discoveries have been made by paleontologists working in previously unexploited regions, including India, South America, Madagascar, Antarctica, and most significantly in China (the amazingly well-preserved feathered dinosaurs in China have further solidified the link between dinosaurs and their living descendants, modern birds). The widespread application of cladistics, which rigorously analyzes the relationships between biological organisms, has also proved tremendously useful in classifying dinosaurs. Cladistic analysis, among other modern techniques, helps to compensate for an often incomplete and fragmentary fossil record.

Contents [hide] 1 What is a dinosaur? 1.1 Definition 1.2 Size 1.3 Behavior 2 Study of dinosaurs 2.1 Classification 2.2 Order Saurischia 2.3 †Order Ornithischia 2.4 Evolution 3 Areas of debate 3.1 Warm-blooded? 3.2 Feathered dinosaurs and the bird connection 3.3 Evidence for Cenozoic dinosaurs 3.4 Bringing dinosaurs back to life 3.5 Discovery of probable soft tissue from dinosaur fossils 4 Extinction theories 4.1 Asteroid collision 4.2 The Oort cloud 4.3 Environment changes 5 History of discovery 6 In popular culture 7 See also 8 Notes 9 References 10 External links

What is a dinosaur?

Definition

The superorder or clade "Dinosauria" was formally named by the English scientist Richard Owen in 1842. The term is a combination of the Greek words deinos ("terrible" or "fearfully great" or "formidable") and sauros ("lizard" or "reptile"). The name was chosen to express Owen's awe at the size and majesty of the extinct animals, not out of fear or trepidation at their size and often-formidable arsenal of teeth and claws. Dinosaurs are extremely varied. Some were herbivorous, others carnivorous. Some dinosaurs were bipedal, others quadrupedal, while others could walk easily on two or four legs, such as the dinosaur Ammosaurus.

Under phylogenetic taxonomy, dinosaurs are defined as all descendants of the most recent common ancestor of Triceratops and modern birds. Ornithischia is defined as all taxa sharing a more recent common ancestor with Triceratops than with Saurischia. Saurischia is defined as all taxa sharing a more recent common ancestor with birds than with Ornithischia. It has also been suggested that Dinosauria be defined as all the descendants of the most recent common ancestor of Megalosaurus and Iguanodon

There is an almost universal consensus among paleontologists that birds are the descendants of theropod dinosaurs. Using the strict cladistical definition that all descendants of a single common ancestor are related, modern birds are dinosaurs and dinosaurs are, therefore, not extinct. Modern birds are classified by most paleontologists as belonging to the subgroup Maniraptora, which are coelurosaurs, which are theropods, which are saurischians, which are dinosaurs.

However, referring to birds as "avian dinosaurs" and to all other dinosaurs as "non-avian dinosaurs" is clumsy. Birds are still birds, at least in popular usage and among ornithologists. It is also technically correct to refer to birds as a distinct group under the older Linnaean classification system, which accepts taxa that exclude some descendants of a single common ancestor (paraphyletic taxa). Paleontologists mostly use cladistics, which classifies birds as dinosaurs, to construct their taxonomies, but many other scientists do not.

For clarity, this article will use "dinosaur" as a synonym for "non-avian dinosaur", and "bird" as a synonym for "avian dinosaur" (meaning any animal that evolved from the common ancestor of Archaeopteryx and modern birds). It should be noted, however, that this article's definition of "bird" differs from common usage. To most people, a "bird" is a two-legged animal with wings and feathers. Under this more general colloquial definition, animals like Velociraptor and Oviraptor (in fact, all maniraptorans) are not dinosaurs, but birds. "For those that have actually seen the relevant specimens and considered all of the relevant data (which is a basic procedure for any scientist), it is becoming increasingly difficult to draw the line between 'bird' and 'non-avian dinosaur'." [5]

Size

Only a tiny percentage of animals ever fossilize, and most of these remain buried in the earth. As a result, the smallest and largest dinosaurs will probably never be discovered. Even among those specimens that are recovered, few are known from complete skeletons, and impressions of skin and soft tissue are rare. Rebuilding a complete skeleton by comparing the size and morphology of bones to those of similar, better-known species is inexact, and reconstructing the muscles and other organs of the living animal is, at best, a process of educated guesswork.

Largest and smallest dinosaurs

While the largest and smallest dinosaurs will probably remain unknown, and comparisons involving existing specimens are imprecise, it is clear that, as a group, dinosaurs were large. By dinosaur standards the sauropods were gigantic. The smallest sauropods were larger than anything else in their habitat, and the largest were an order of magnitude more massive than anything else that has ever walked the Earth.

The tallest and heaviest dinosaur known from a complete skeleton is the Brachiosaurus, which was discovered in Tanzania between 1907–12. It is now mounted in the Humboldt Museum of Berlin and is 12 m (38 ft) tall and probably weighed between 30,000–60,000 kg (33–66 short tons). The longest dinosaur is the 27 m (89 ft) long Diplodocus, which was discovered in Wyoming and mounted in Pittsburgh's Carnegie Natural History Museum in 1907.

There were larger dinosaurs, but knowledge of them is based entirely on a small number of incomplete fossil samples. The largest specimens on record were all discovered in the 1970s or later, and include the massive Argentinosaurus, which may have weighed 80,000–100,000 kg (88–121 tons); the longest, the 40 m (130 ft) long Supersaurus; and the tallest, the 18 m (60 ft) Sauroposeidon, which could have reached a sixth-floor window.

Dinosaurs were the largest of all terrestrial animals. The largest elephant on record weighed 12,000 kg (13.2 tons), while the tallest giraffe was 6 m (20 ft) tall. Even giant prehistoric mammals such as the Indricotherium and the Columbian mammoth were dwarfed by the giant sauropods. Only a handful of modern aquatic animals approach them in size, most notably the blue whale (which reaches up to 190,000 kg (209 tons) and 33.5 m (110 ft) in length).

Not including modern birds like the bee hummingbird, the smallest dinosaurs known were about the size of a crow or a chicken. The Microraptor, Parvicursor, and Saltopus were all under 60 cm (2 ft) in length.

Average size

The meaning of "dinosaur average size" is not only debatable but it varies in time (Triassic versus early Jurassic versus late Jurassic versus Cretaceous) ^[6]. According to Bill Erickson, "Estimates of median dinosaur mass range from 500 kg to 5 metric tons [...] Eighty percent of the biomass from the Late Jurassic Morrison formation of the western United States consisted of stegosaurs and sauropods; the latter average 20 tons. [...] The typically large size of the dinosaurs, and the comparatively small size of modern mammals, has been quantified by Nicholas Hotton. Based on 63 dinosaur genera, Hotton's data yield an average generic mass in excess of 850 kg (about the size of a grizzly bear) and a median generic mass of nearly 2 tons (comparable to a giraffe). This contrasts sharply with extant mammals (788 genera) whose average generic mass is 863 grams (a large rodent) and a median mass of 631 grams (a smaller rodent). The smallest dinosaur was bigger than two-thirds of all living mammals; the majority of dinosaurs were bigger than all but 2% of living mammals." ^[7]

Behavior

Interpretations of behavior based on the pose of body fossils and their habitat, computer simulations of their biomechanics, and comparisons with modern animals in similar ecological niches rely on speculation, and promise to generate controversy for the foreseeable future. However, it is likely that some behaviors common in both of their closest living relatives, crocodiles and birds, were also common among dinosaurs. It should be noted that nearly all interpretations of evidence are subject to change, as theories surrounding dinosaurs evolve continuously.

The first evidence of herding behavior was the 1878 discovery of 31 Iguanodon dinosaurs that perished together in Bernissart, Belgium, after they fell into a deep, flooded ravine and drowned. Similar mass deaths and trackways suggest that herd or pack behavior was common in many dinosaur groups. Trackways of hundreds or even thousands of herbivores indicate that duck-bills (hadrosaurids) may have moved in great herds, like the American Bison or the African Springbok. Sauropod tracks document that these animals traveled in groups composed of several different species, at least in Oxford, England,^[8] and others kept their young in the middle of the herd for defense according to trackways at Davenport Ranch, Texas. Dinosaurs may have congregated in herds for defense, migration, or to care for their young.

Jack Horner's 1978 discovery of a Maiasaura ("good mother dinosaur") nesting ground in Montana demonstrated parental care long after birth among the ornithopods^[9][10]. There is also evidence that other Cretaceous-era dinosaurs, like the Patagonian sauropod Saltasaurus (1997 discovery), had similar nesting behaviors, and that the animals congregated in huge nesting colonies like those of penguins. The Mongolian maniraptoran Oviraptor was discovered in a chicken-like brooding position in 1993, which may mean it was covered with an insulating layer of feathers that kept the eggs warm.^[11] Trackways have also confirmed parental behavior among sauropods and ornithopods from the Isle of Skye in the United Kingdom.^[12] Nests and eggs are known from most major groups of dinosaurs, and it appears likely that dinosaurs communicated with their young, like modern birds and crocodiles.

The crests and frills of some dinosaurs, like the marginocephalians, theropods and lambeosaurines, may have been too fragile for active defense, so they were probably used for sexual or aggressive displays, though little is known about dinosaur mating and territorialism. Communication is also an enigma, but the hollow crests of the lambeosaurines may have been resonance chambers used for a wide range of vocalizations.

From a behavioral standpoint, one of the most valuable dinosaur fossils was discovered in the Gobi Desert in 1971. It included a Velociraptor attacking a Protoceratops^[13], proving that dinosaurs did indeed attack and eat each other. While cannibalistic behavior among theropods is no surprise^[14], this too was confirmed by tooth marks from Madagascar in 2003.^[15]

There seem to have been no burrowing and few climbing dinosaurs. This is surprising when compared to the later mammalian radiation in the Cenozoic, which included many species of these types. As to how the animals moved, biomechanics has provided significant insight. For example, studies of the forces exerted by muscles and gravity on dinosaurs' skeletal structure have demonstrated how fast dinosaurs could run,^[16][17] whether diplodocids could create sonic booms via whip-like tail snapping,^[18] whether giant theropods had to slow down when rushing for food to avoid fatal injuries,^[19] and if sauropods could float.^[20]

Study of dinosaurs

Information on dinosaurs is obtained from a variety of fields of study including Physics, Chemistry, Biology, and the Earth Sciences (which includes Paleontology). Activities include the discovery, reconstruction and conservation of dinosaur fossils and the interpretation of those fossils to better understand the evolution, classification and behavior of dinosaurs.

Classification

Main article: Dinosaur classification

Dinosaurs (including birds) are archosaurs, like modern crocodilians. Archosaurs' diapsid skulls have two holes where jaw muscles attach, called temporal fenestrae. Most reptiles (including birds) are diapsids; mammals, with only one temporal fenestra, are called synapsids; and turtles, with no temporal fenestra, are anapsids. Dinosaurs have teeth that grow from sockets (an archosaur characteristic) rather than as direct extensions of the jaw bones, as well as various other archosaur characteristics. Within the archosaur group, the dinosaurs are differentiated most noticeably by their gait. Instead of legs that sprawl out to the side, as found in lizards and crocodylians, they have legs held directly under their body. All dinosaurs were land animals.

Many other types of reptiles lived at the same time as the dinosaurs. Some of these are commonly, but incorrectly, thought of as dinosaurs, including plesiosaurs (which are not closely related to the dinosaurs) and pterosaurs, which developed separately from reptilian ancestors in the late Triassic.

Dinosaurs are divided into two orders, the Saurischia and the Ornithischia, on the basis of hip structure. Saurischians (from the Greek meaning "lizard hip") are dinosaurs that originally retained the hip structure of their ancestors. They include all the theropods (bipedal carnivores) and sauropods (long-necked herbivores). Ornithischians (from the Greek meaning "bird-hip") is the other dinosaurian order, most of which were quadrupedal herbivores.

Saurischian pelvis structure.

Ornithischian pelvis structure.

The following is a simplified classification of dinosaurs. A more detailed version can be found at List of dinosaur classifications.

The dagger (†) is used to indicate taxa with no living members.

Order Saurischia

• †Family Herrerasauridae
• Suborder Theropoda
  • †Superfamily Coelophysoidea
  • †Superfamily Ceratosauria
    • †Family Abelisauridae
  • (unranked) Tetanurae
    • †Family Spinosauridae
    • †(unranked) Carnosauria
    • (unranked) Coelurosauria
      • †Family Coeluridae
      • †Superfamily Tyrannosauroidea
      • †Superfamily Ornithomimosauria
        • †Family Alvarezsauridae
      • (unranked) Maniraptora
        • †(unranked) Oviraptorosauria
          • †Superfamily Therizinosauria
        • †Superfamily Deinonychosauria
          • †Family Troodontidae
          • †Family Dromaeosauridae
          • †Family Microraptoria
        • Class Aves (birds)
• †Suborder Sauropodomorpha
  • †Thecodontosaurus
  • †Family Plateosauridae
  • †Riojasaurus
  • †(unranked) Sauropoda
    • †Family Diplodocidae
    • †(unranked) Macronaria
      • †(unranked) Titanosauriformes
        • †Family Brachiosauridae
        • †Family Titanosauridae

†Order Ornithischia

• †Suborder Thyreophora
  • †Superfamily Stegosauria
  • †Superfamily Ankylosauria
• †Suborder Cerapoda
  • †Family Heterodontosauridae
  • †Superfamily Pachycephalosauria
  • †Superfamily Ceratopsia
    • †Family Psittacosauridae
    • †Family Protoceratopsidae
    • †Family Ceratopsidae
  • †Superfamily Ornithopoda
    • †Family Hypsilophodontidae
    • †Family Iguanodontidae
    • †Family Hadrosauridae

~blackmamba