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Brooding Dinosaurs/Feather Length
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 Important Bones
 Parts of a Feather
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Important Bones
    Scientists have long grouped together similar animals for many purposes.  Historically, it has been relatively easy to determine if an animal was an amphibian, reptile, mammal, fish or bird.  They have long known that some dinosaur skeletons were remarkably similar to those of birds, but still it was relatively easy to tell them apart, but the discovery of so many feathered dinosaurs is making it increasingly difficult to distinguish them from one another..
   Lizards and crocodiles have legs that stick out from the body then angle down to the ground, but dinosaurs stood on legs that went straight down to the ground.  Many of the dinosaurs were bipedal (walked on two hind legs), as do birds.  The bipedal dinosaurs had forearms, but in birds the forearms evolved into wings.  It is now know that some dinosaur forearms can be classified as wings. 
   Reptiles are cold-blooded  Many experts paleontologists believe that the initial primary function of feathers on dinosaurs was to provide insulation, meaning the feathers helped them to keep warm.  This suggests that those dinosaurs were warm-blooded, as are birds.
   One of the features that distinguish modern day birds from feathered dinosaurs is the mouth. Birds have beak and most dinosaurs had teeth.  However prehistoric birds also had teeth and Erlikosaurus had a toothless beak, just like a bird.  Experts point out that one characteristic of birds is that they fly, but even this is not always the case.  Penguins and ostriches are two well known examples of modern flightless birds.
   Birds did have what were thought to be two bones unique unto them, but recent discoveries have changed that.   forcing paleontologists to reevaluate many long-held beliefs.  They now realize that the relationship between dinosaurs and birds  may have been far closer than previously imagined.

Pygostyle

   Nomingia gobiensis (see Brooding Dinosaurs) is an oviraptorosaur discovered in Mongolia. It is unique in that the last five vertebrae on its tail are fused together creating what is called a "pygostyle."  Pygostyles are found on only one other group of animals - the birds. They are used to anchor the tail feathers.  This indicates that N. gobiensis had tail feathers too.

Furcula

   This is better known as the "wishbone."  The furcula is a bone long thought unique to modern birds.  It stretches across the chest and provides a strong anchor for wing muscles.  It was recently found on Suchomimus (110-100 MYA) and Microraptor.  One was even found on "Sue," the Tyrannosaur rex now on display at the Field Museum in Chicago.   
    As it now stands, the most consistent distinction between modern day birds and some of the prehistoric dinosaurs is the length of the tail.  Modern birds have comparatively short ones, an attribute that makes them good flyers.  But the  distinction between birds and feathered dinosaurs is becoming increasingly blurred.  Some experts want to reclassify at least some of the feather dinosaurs as birds.  If that happens it is going to be very difficult  to establish standards to determine which is which.

 

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