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Dinosaurs (useful notes): Difference between revisions
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{{Useful Notes}}
[[Blatant Lies|A brief summary]] of [[Tropesaurus Index|dinosaurs]], for those of us who wish to address a few problems where [[Somewhere a Palaeontologist Is Crying]].
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* [http://albertonykus.deviantart.com/art/Why-Birds-are-Dinosaurs-193639479 Birds are dinosaurs.] Because there are still birds alive today, dinosaurs are [[Science Marches On|technically not exinct]]!
All clear? Right. On to the next topic.
== The Dinosaur Family Tree ==
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The mammal-like "reptiles", which had ruled in waves during the Permian period, were the first to spread on the planet, and it looked like they were set to rule it all again. There were two groups of these, mostly the herbivorous dicynodonts and the cynodonts. Mammals evolved from the latter set; the former died out without leaving any descendants.
However, both groups quickly found themselves under stiff competition against the first archosaur reptiles, from which the dinosaurs would emerge. The archosaurs were particularly effective thanks to their water-conserving adaptations, which were typical of most reptiles. Quickly, the archosaurs divided into several groups, such as rauisuchians, aetosaurs, phytosaurs and proterosuchids, and by seizing control they reduced the variety of the mammal-like reptiles, which survived only through their smaller species. Later, cynodonts evolved many special features that are typical of modern mammals today, humans included.
In the midst of this inter-group conflict, roughly 230 million years ago, the early dinosaurs appeared. They were descended from tiny archosaurs such as the 1 ft-long ''[[Prehistoric Life/Non Dinosaurian Reptiles|Lagosuchus]]'', but they did not make their impact felt until ten million years later, when they grew from small, unassuming bipeds to impressively large forms. The three main lineages were forged at this crucial time: the meat-eating theropods, the long-necked sauropodomorphs, and the plant-eating ornithischians, although at this stage they all looked like variations of the thin, elegant Theropods like ''[[Stock Dinosaurs True Dinosaurs|Coelophysis]]'' and its relatives, and it's quite possible that all of them were omnivorous initially.
They were notable for taking the bipedal stance, which was also adopted by some triassic archosaurs related to modern crocodilians, such as ''[[Prehistoric Life/Non Dinosaurian Reptiles|Ornithosuchus]]'' and the deceptively-dinosaurian ''[[Prehistoric Life/Non Dinosaurian Reptiles|Effigia]]''. Indeed, some of these were mistaken for dinosaurs when they were first discovered. To walk in the upright stance, early dinosaurs developed a horizontal backbone but vertical joints to the pelvis, which meant that their legs were tucked underneath their body to support their weight. This also permitted them an exceptionally good turn of speed, and with their long tails to serve as counterbalances, the dinosaurs had hit upon a good design feature which would serve them well again and again.
Even with all the similarly-adapted archosaurs, Dinosaurs were notably successful at this early stage, and by the end of the Triassic period they had diversified into some of the largest animals ever to appear on the land. Early sauropodomorphs in particular (traditionally called "prosauropods", which means "before the sauropods") reached lengths and heights never seen before, like ''[[Stock Dinosaurs True Dinosaurs|Plateosaurus]]'', which could grow up to twenty feet long, and the even larger ''[[Prehistoric Life/Dinosaurs|Riojasaurus]]'' and ''[[Prehistoric Life/Dinosaurs|Melanorosaurus]]'', both elephant-sized and thirty feet long. On the other hand, predatory theropods remained generally small in the Triassic, with some exceptions such as ''[[Godzilla|Gojira]][[Prehistoric Life/Dinosaurs|saurus]]'' (whoever said that paleontologists had no sense of humour?), which could reach 15 ft in length.
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The purpose of these plates is unclear, but the purpose of their tail spikes and shoulder spikes was arguably for self-defence against any animal that tried to hurt or kill the animal. Their cousins, the ankylosaurs, took the scutes and developed them into stronger armour all along their backs and even, in some cases, along their undersides. The species ''Ankylosaurus'' even had armour-plated eyelids, and a thickened block of bony tissue at the end of their tails to act as clubs in case the armour wasn't a good enough hint for some carnivores. They came into greater prominence during the Cretaceous period, when the stegosaurs died out.
Besides the thyreophorans, there were the cerapods - the collective name for both the ornithopods and the marginocephalians. Ornithopods became more diverse during the Jurassic (''[[Prehistoric Life/Dinosaurs|Dryosaurus]]'' and ''[[Prehistoric Life/Dinosaurs|Camptosaurus]]'' were widespread at that time), but they really came into their own during the Cretaceous period, possibly because of the spread of the newly-evolved flowering plants which had appeared not long before, or because they coped better with the changing climate as sea levels rose worldwide. The marginocephalians possibly had Late Jurassic roots, but like the ornithopods they are better known for their Cretaceous forms, and originally evolved from very small ornithopod-like forms such as ''[[Prehistoric Life/Dinosaurs|Yinlong]]''.
Main points:
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During their time on Earth, the dinosaurs thrived in diverse terrestrial habitats, from swampy terrain and dense forests to open prairies and the driest of deserts. Some even weathered the harsh winter conditions of Antarctica and Australia (which were near the South Pole at the time). However, the dinosaurs did not survive the Cretaceous-Paleogene (formerly known as the Cretaceous-Tertiary) mass extinction event which wiped out roughly 65% of all living things, at least according to the fossil record. This is that eponymous event which underscores the trope [[Phlebotinum Killed the Dinosaurs]], and if you read some of the hypotheses about how they died, they often run a lot like that trope.
There have been several hypotheses in the past about this event, but most of them are bunk and the rest are on shaky ground at best. In the early days of palaeontology, when snobbery of the past was widespread and extinction more or less meant you were an inferior species, it was believed that the dinosaurs simply became [[Too Dumb to Live]], or to put it more scientifically, their craniums housed brains which were inefficient by dint of being too small, and so they were outwitted by the smaller but much cleverer mammals. Some have suggested that egg-devouring mammals were responsible, but there is no evidence that the mammals consumed eggs, at least not in bulk. Some suggested that the dinosaurs found it harder to supply their large bodies with oxygen, ignoring the fact that Late Cretaceous dinosaurs were pretty tame compared with the giganic sauropods which had dominated in the Jurassic (and which, as far as can be made out, never had breathing difficulties). Some have suggested that a nearby supernova caused cosmic rays to penetrate the atmosphere and destroy the dinosaurs, but a supernova that close to the Earth would have done considerably more than wipe out a few little reptiles on its surface, and in any case the claim is not justified by evidence.
Here is the most likely hypothesis currently available. The extinction began with an increase in volcanic activity during the last few million years of the Cretaceous period, which would have introduced toxic gases and ash clouds into the atmosphere. This interfered with the relatively stable weather conditions the dinosaurs had enjoyed all over the globe (most of the Mesozoic era was comparatively stable, at least when compared with the turbulent climate changes of most of the Cenozoic era). Certainly, the fossil evidence suggests they were already in a state of decline (at least in North America) when the fateful meteor, about 65.5 million years ago, [[Rocks Fall, Everyone Dies|collided with the Gulf of Mexico]], producing the Chicxulub crater.
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* Not all the surviving lineages are still alive today. Multituberculate mammals and champsosaurs survived the extinction but died later in the Cenozoic.
[[Vindicated by History|Dinosaurs]] are now a pretty big hit in popular culture. Just go see the [[Tropesaurus Index]], and you'll find links to the legacy that the dinosaurs left behind. Yes, that includes the bird index, too.
If you are interested in specific kinds of dinosaurs, just [[Stock Dinosaurs True Dinosaurs|check]] [[Prehistoric Life/Dinosaurs|here]] some info.
{{reflist}}
[[Category:Tropesaurus Index]]
[[Category:Dinosaurs]]
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