Dinosaurs

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By Suraj R
Today I'm talking about dinos. The dinosaurs went extinct about 65 million years ago, at the end of the Cretaceous period, which was a time of high volcanic and tectonic activity. There are a lot of theories why the extinction occurred. The most widely accepted theory is that an asteroid impact caused major climactic changes to which the dinosaurs couldn't adapt. Dinosaurs probably live on today as the birds. All that's left of the dinosaurs are fossils perhaps,the birds. Dinosaur fossils have been found all over the world, maybe even near where you live ! Although dinosaurs' fossils have been known since at least 1818, the term dinosaur (deinos means terrifying; sauros means lizard) was coined by the English anatomist Sir Richard Owen in 1842. The only three dinosaurs known at the time were Megalosaurus, Iguanodon, and Hylaeosaurus, very large dinosaurs.The last found of the dinosaurs was in late Cretaceous period.

Dinosaurs were land-dwelling reptiles that walked with an erect stance. Their unique hip structure caused their legs to stick out under their bodies, and not sprawl out from the side (as with other reptiles). When dinosaurs first evolved from more primitive archosaurs, they were bipedal (they walked on two legs). Much later, some dinosaur groups returned to a four-legged stance, most having rear legs much larger than their front legs. There were many different types of dinosaurs, differing in size and weight, locomotion (two- or four- legged walk, fast or slow speed), diet (meat or plants), and just about every other physiological and anatomical measure.

== Dinosaurs come in different ways. First the meat eaters or therapods and sauropods, the long necks are lizard hipped. They were called Saursichian hip dinosaurs. The other kind which is thyrophra, which are stegosaurs and ankylosaurides, ceratospians, which are dinosaurs with horns, and ornithipods which are duck-billed dinosaurs are bird hip or also known as Ornithischian hip dinosaurs. == = Many dinosaurs were armed with built-in weapons that were used for killing and eating prey, for dealing with interspecies rivalry, or as protection from fellow carnivores (meat eaters). These included: =
 * [[image:http://www.enchantedlearning.com/hgifs/Hipsauris2.GIF width="315" height="214"]] || [[image:http://www.enchantedlearning.com/hgifs/Hipor2.GIF width="242" height="151"]] ||
 * ==Big, sharp, pointed teeth - Largest, sharp teeth of most carnivores are for tearing flesh from prey. ==
 * ==[[image:http://www.enchantedlearning.com/sgifs/Sickleclaw.GIF]]Clawed feet - Many dinosaurs claws on feet and/or hands. Dromaeosaurids and Megaraptor had a huge retractible sickle-like claws on each foot. ==
 * ==Grasping hands with clawed fingers - good for catching and slashing prey. ==
 * ==Large size - Some dinosaurs, like Giganotosaurus and T. rex were so large that they were at the top of the food chain, and could eat any animal that they could catch. ==
 * ==Speed and agility- [[image:http://www.enchantedlearning.com/ugifs/Unen.GIF align="left"]] In order to eat, a predator must catch its prey. The only surviving dinosaurs, the birds, evolved from the speedy, bird-like theropods. ==
 * ==Modern-day birds have excellent good color vision; it is likely that the bird-like dinosaurs (advanced theropods like the coelurosaurs) also had color vision. This would have helped them find and catch their prey (just as hawks use their acute vision to spot preylegged, slow moving herbivore (eats plants): ==

= Dinosaurs were armed with built-in defensive weapons and behaviors that were used for dealing with interspecies rivalry or as protection from carnivores (meat eaters). These included: =

Horns, Claws, and Spikes
==- Many dinosaurs had deadly, knife-like protuberances that were excellent protection from being eaten (for example, Triceratops and Kentrosaurus). Some sauropods had large thumb claws; these were especially prominent in the young and in juveniles. == > ==- Some adult diplodocids (like Apatosaurus, Diplodocus, Supersaurus, etc.) and other dinosaurs were so large that only the hugest carnivores or packs of carnivores were a danger. ==
 * == Large size ==
 * == Armored plating (bony plates fused into leathery skin)  - [[image:http://www.enchantedlearning.com/egifs/Euoplocephalus.GIF]]Ankylosaurids (like Euoplocephalus, Ankylosaurus, and Sauropelta) were plated all over the tops and sides of their bodies. Even their eyelids had armor plating. Only their underbellies were unprotected. To kill an Ankylosaurid, a predator would have had to flip over a terribly heavy animal over - not an easy job ==
 * == Thick, leathery skin ==

Head butting
- ==<span style="color: #ff00ff; display: block; font-family: Arial,Helvetica,sans-serif;">Pachycephalosaurs (like Pachycephalosaurus, Stegoceras, Wannanosaurus, etc.) and other thick-skulled dinosaurs may used head butting to repel predators. ==

==<span style="color: #ff00ff; display: block; font-family: Arial,Helvetica,sans-serif;">It had long been thought that Pachycephalosaur's thick domes may have been used for ramming rivals during mating and dominance combat, for attracting mates, and as a last-ditch self-defense against predators. Paleontologist Mark Goodwin of the University of California at Berkeley has analyzed many pachycephalosaur skulls (including those of Pachycephalosaurus), finding no evidence of healed scars. Also, under close analysis, the thick skull bone is not rigid and solid, but porous and fragile when put under extreme pressure. ``It's time to kill the myth ... It certainly wouldn't be in their own best interests to ram heads in a fight, said Goodwin ``They would have killed each other, and a couple of bowling balls would hardly make good targets. ==
 * == Speed [[image:http://www.enchantedlearning.com/sgifs/Stegoceras.GIF width="67" height="28"]] Leaving a fight can be easier and safer than fighting. ==
 * == Bludgeon-like tail clubs [[image:http://www.enchantedlearning.com/agifs/Ankylosaurus.GIF width="96" height="42"]] Ankylosaurids (like Euoplocephalus and Ankylosaurus) had bony tail-clubs that could easily have been used for defense, which would have been useful for these lumbering, plated grazers. Also, some theropods, like Shunosaurus, Omeisaurus and maybe Mamenchisaurus had tail clubs for protection. ==
 * == Whip-like tail - Some people believe that sauropods[[image:http://www.enchantedlearning.com/dgifs/Diplodocus.GIF]] may have used their massive tails as a whip to lash at their attackers. This theory seems unlikely given the amount of physiological damage to tail tissue that would be caused by the sudden acceleration near the end of the tail (and the deceleration upon impact). Also, the large sauropods probably grazed on tree leaves, giving them no room to whip their tail around without hitting tree trunks and getting severe tail damage. ==

How old did the dinosaurs get to be? That question is very hard to answer.
== Recently scientists have found that most dinosaur bones have growth rings (called lines of arrested growth, abbreviated LAG) that may answer this question. These lines are only visible using a microscope. The bones have to be sliced into thin section and viewed with a polarized lens in the microscope. It's a bit like looking at the growth ring of trees to determine the age of a tree. Each year of growth leaves a trace in the bone (or tree trunk). == == Another way to estimate life span is based on body size, the known life spans of modern-day animals, and the fact that large animals generally live longer lives than smaller ones. It has been estimated that the huge sauropods, like Apatosaurus, Brachiosaurus, Diplodocus, and Supersaurus lived to be roughly 100 years old. Smaller dinosaurs probably lived shorter life spans. ==

Scientists have determined the following estimates:

 * == Troodon- (Weight: 50 kg) 3-5 years to reach adult size (Varricchio, 1993). ==
 * == the ceratosaur Syntarsus rhodesiensis - (Weight: 25+ kg) 7-8 years to reach adult size (Anusiya Chinsamy, 1994). ==
 * == the prosauropod plateosaurus[[image:http://www.enchantedlearning.com/mgifs/Masso.GIF link="http://www.enchantedlearning.com/subjects/dinosaurs/dinos/Massospondylus.shtml"]]- (Weight: 250+ kg) 15 years to reach adult size (Chinsamy, 1994). ==
 * == the sauropod Bothriospondylus madagascariensis - (Weight 17500 kg) 43 years to adult size (Ricqlés, 1983) ==
 * == the ceratopsian Psittacosaurus mongoliensis - (Weight 80 kg) was 10 to 11 years old (Erickson and Tumanova, unpublished data) ==
 * == Growth Rates: Growth rates based on maximum growth rates of modern-day reptiles, even though there are probably major metabolic differences. Protoceratops: Adult 177 kg, hatchling 0.43 kg (hatchling weight calculated to be about 90% of the weight of 0.5 liter egg). Age to adulthood calculated to be roughly 26-38 years. Hypselosaurus : Adult 5300 kg, hatchling 2.4 kg. Age to adulthood calculated to be about 82-188 years. If this is true, this would seem to indicate that dinosaurs either lived for an incredibly long time or else, using the growth rate of living reptiles is not appropriate, and Hypselosaurus grew at a much faster rate that modern-day reptiles (indicating that it had a much faster metabolism than living reptiles), or maturity came long before they reached their adult size. ==