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 witnessed a world populated by dinosaurs. While giant plant-eaters munched their way through ferns and conifer forests, large carnivores chased them down for lunch.
 
At the height of the Age of Dinosaurs, they were found on every continent. They thrived in the warm environments of the time.
 
But, dinosaurs were not always so prominent. Fossil evidence shows that they arose about 230 million years ago during the Triassic period. But they remained scarce as other reptiles took center stage. Many mammal forerunners, such as the large plant-eater Placerias, prospered. 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 radically changed life on land and in the sea. And it paved the way for dinosaur diversification and prominence.
 
What happened was so important that it caused more than half of all life on Earth to go extinct. The large crocodile-like reptiles that had dominated the landscape were eliminated. So were 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 on How Fossils Explain the Rise of Dinosaurs. It is airing 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 (133)
  • joeg-orv
    9/23/2015 - 12:48 p.m.

    Scientists rely on fossils over photographs because you are able to measure and fell the fossils. they can also analyze and study better having the the direct object with them.

  • evanterrell-bak
    9/23/2015 - 01:11 p.m.

    Awesome!I love dinos! I wonder how dinos got wiped away or died. I want to learn more about them! I want to teach the class about them! P.S can we learn about them?

  • mattsimonsen-bak
    9/23/2015 - 01:13 p.m.

    can someboty read this Please?

  • Jason0421-YYCA
    9/23/2015 - 02:57 p.m.

    I think that it is interesting that there were harsher and bigger things than just dinosaurs. What I think is more amazing than that is that half of all Earth was extinct. I believe that if these harsher and bigger things were to arise now, that could possibly the end for humankind.

  • emmah-bon
    9/23/2015 - 05:19 p.m.

    I thought it was cool learning about what was the "boss" before dinosaurs!

  • corbiny-bon
    9/23/2015 - 05:40 p.m.

    the smilosuchus is HUGE I think people could learn form that crocodile like animal!

  • virginiam-2-bar
    9/23/2015 - 06:28 p.m.

    Scientists rely on fossils instead of photographs because there was no cameras or human(that we know of) to take the picture. I found it interesting that something happened 200 years ago that was so big it caused all dinosaurs to go extinct.

  • carlosp-6-bar
    9/23/2015 - 09:18 p.m.

    Scientists rely of fossils not photos because cameras were not invented back than and the only thing that are still from that time where the animals that had died and are in rocks.
    I think this is a good article because most people think that dinosaurs where the only thing before humans and this tells us that the were other animals that were before dinosaurs.

  • horvath,tyler-cas
    9/23/2015 - 10:26 p.m.

    1.) Scientists rely on fossils instead of photographs to study dinosaurs because now and days a photograph can be fake or copied. If they use a fossil, it is proof of the dinosaur living thousands of years ago and can describe the dinosaur.
    2.) This article really shocks me. I never would have thought their were other great prehistoric living creatures before the dinosaurs. I actually wish some of these creatures were still alive to this day because I would love to see them with my own eyes. All of these dinosaurs and creatures before them really fascinate me.

  • flores,joseph-cas
    9/24/2015 - 08:21 a.m.

    1. Scientists rely on fossils instead of photographs because photographs didn't exist during the time period that the dinosaurs existed.
    2. I think it's cool that dinosaurs weren't always at the top of the food chain.

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