Who was boss before the dinosaurs? Large hippo-like mammal forerunner ("Placerias") that lived, and died off, during the Triassic. (National Park Service Image)
Who was boss before the dinosaurs?
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The Jurassic saw a world filled by dinosaurs. Giant plant-eaters munched their way through ferns and conifer forests. Large carnivores chased them down for lunch.
 
They were found on every continent. This was at the height of the Age of Dinosaurs. They thrived in the warm environments of the time.
 
But dinosaurs were not always so noticeable. Fossil evidence shows that they arose about 230 million years ago. This was during the Triassic period. But they remained scarce. Other reptiles took center stage. 

Many mammal forerunners did very well. One example is the large plant-eater Placerias. Huge crocodile-like animals like Smilosuchus were the top predators of the Triassic.
 
Paleontologists who study the fossil record have discovered that something big happened 200 million years ago. It totally changed life on land and in the sea. And it paved the way for dinosaur diversification and prominence.
 
What happened was so big that it caused more than half of all life on Earth to go extinct. The large crocodile-like reptiles that had led the landscape died off. So did many of the mammal forerunners.
 
Find out more about the events that opened the door for the Age of Dinosaurs. Join us on Thursday, October 8, 2015, for a "Smithsonian Science How" live webcast. It is called How Fossils Explain the Rise of Dinosaurs. It airs at 11 a.m. and 2 p.m. EDT on the Q?rius website. Paleontologist Dr. Hans Sues from the National Museum of Natural History will appear live to discuss and answer questions. Get teaching resources to support your webcast experience.

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CRITICAL THINKING QUESTION
To study dinosaurs, why do scientists rely on fossils instead of photographs?
Write your answers in the comments section below


COMMENTS (20)
  • taylornelson-bak
    9/23/2015 - 12:58 p.m.

    this text is awsome!!!!I love the facts!!!

  • peytonnelson-bak
    9/23/2015 - 05:37 p.m.

    It's so cool that there was a reptile bigger then a dinosaur

  • derekzangerle-bak
    9/25/2015 - 07:19 a.m.

    It is cool that dinosaurs were alive. I would like to dig up fossils.

  • tracew-mel
    9/30/2015 - 10:03 a.m.

    Good job ????????!!!!????????????????????????????

  • makanip-
    9/30/2015 - 03:21 p.m.

    they are really dinosaurs

  • samt-mel
    10/01/2015 - 09:53 a.m.

    History is very interesting, and so are the people who study it!

  • lukass-mel
    10/01/2015 - 09:56 a.m.

    That sounds ptetty good????

    • jacksonb-mel
      10/06/2015 - 09:57 a.m.

      Fossils can tell you more information. This story is really good,!!!!!!!!

  • jacksonb-mel
    10/05/2015 - 10:05 a.m.

    Fossils can tell you what Dinosaur it is and it can give you more information

  • keairnesj-rei
    10/06/2015 - 03:54 p.m.

    They rely on fossils instead photographs because photographs might have been photo shopped or maybe has been ran through a scanner and got deleted and fossils will always be buried in rock until you dig it up and find out the mysterys of the dead

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