Is there a continent where dinosaur fossils have never been found?

No. It was once thought that Antarctica was the only continent that did not have any dinosaur fossils. But in December 2003, researchers working in separate sites thousands of miles apart in Antarctica found what they believe are the fossilized remains of two species of dinosaurs previously unknown to science one a primitive sauropod. In 2007, yet another dinosaur discovery was made in Antarctica: a new genus and species of dinosaur from the early Jurassic a massive, plant-eating, primitive sauropodomorph called Glacialisaurus hammeri that lived about 190 million years ago.

What kinds of dinosaurs were in the saurischian group?

The saurischians were a diverse group of dinosaurs, with both carnivores and herbivores. They exhibited two-legged and four-legged means of propulsion. The carnivores included the large two-legged Allosaurus, Ceratosaurus, Tarbosaurus, and Tyrannosaurus. There were smaller, two-legged carnivores, too, such as Ornithomimus and the Dromaeosaurus, which had specialized feet and their unique, slashing, raptorial claws. The herbivorous saurischians that are best known are the large, four-legged sauropods, the largest dinosaurs to have walked Earth. These dinosaurs had long necks and tails, with relatively tiny heads. Included in this group are Brachiosaurus, Camarasaurus, Diplodocus, Mamenchisaurus, and Seismosaurus.

What kinds of dinosaurs were in the ornithischian group?

The ornithischians were all herbivores and had two- and four-legged types. There were the four-legged armored dinosaurs such as Ankylosaurus and Stegosaurus.

There were large, horned dinosaurs such as Eucentrosaurus and Triceratops.

Two-legged types included Iguanodon, and many of the duck-billed dinosaurs (hadrosaurs), such as Corythosaurus, Lambeosaurus, and Maiasaura.

What events led to the dominance of dinosaurs in the Mesozoic era?

Approximately 250 million years ago, at the end of the Permian period, or the beginning of the Triassic period (and thus, the end of the Paleozoic era and the beginning of the Mesozoic era), there was a mass extinction. This extinction eliminated close to 90 percent of all the species present on our planet (extraordinarily close to total extinction on Earth). The extinction was not selective; it eliminated organisms in the oceans and on land, including many invertebrates, armored fish, and reptiles.

The true reasons for the extinction are unknown, although there are several theories. One is that a collision with an asteroid or comet caused dust and debris to fly into the upper atmosphere, cutting off sunlight and radically changing the global climate. Another idea is that the moving continents changed the climate, sea levels, and thus, habitats, causing some species to change and adapt, while others died out. Still another theory focuses on Siberian flood basalts, in which tons of volcanic material erupted over a huge area in Asia toward the end of the Permian period, changing the climate and certain habitats.

Whatever the scenario, species that survived did so by adapting to the ecological niches that became vacant, allowing them to further evolve. After the Permian extinction, and throughout the Mesozoic era, it was reptiles in general, and the dinosaurs specifically, that diversified the most and became the dominate species on the planet.

How long were dinosaurs dominant on Earth?

The dinosaurs were the dominate species on Earth for approximately 160 million years. The Mesozoic era, often referred to as the age of the reptiles, lasted from approximately 250 to 65 million years ago. It includes the Triassic, Jurassic, and Cretaceous periods.

Were there dinosaurs at the beginning of the Mesozoic?

It is interesting to note that at the beginning of the Mesozoic, there were no true dinosaurs; other reptiles dominated the landscape. But by the end of the Triassic period, the dinosaurs became dominant, and they stayed that way for around 160 million years. Dinosaurs were not the only form of life that existed during this time. For example, there were smaller, lizard-like reptiles, small early mammals, insects, amphibians, invertebrates, and a wide variety of plants. In fact, these organisms helped the dinosaurs to stay in charge because many of the dinosaurs used this abundance of life for their sustenance and growth.

Swedish naturalist Carolus Linnaeus devised the classification system for plants and animals that is still used today, both for living species and for species of the past such as dinosaurs (iStock).

When did the age of dinosaurs end?

The age of the dinosaurs came to an end approximately 65 million years ago. From this point in time, there are currently no known dinosaur fossils. The time of the great dinosaur (and other species) extinction is used by scientists to delineate the end of the Cretaceous period as well as the end of the Mesozoic era. After this point, the Cenozoic era begins, starting with the Tertiary period.

 
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