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The Age of Dinosaurs
The Mesozoic Era | What Were Dinosaurs?
The Great Extinction | The Fossil Remains of Dinosaurs

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The Mesozoic Era
The “Age of Dinosaurs” is the Mesozoic Era, which is divided into three periods: the Triassic (245-208 million years ago), Jurassic (208-145 million years ago), and Cretaceous (145-66 million years ago). The earliest dinosaur fossils, recently discovered in Argentina's Ischigualasto basin, have been radiometrically-dated as 228 million years old. (This discovery has led some scientists to characterize the southern region of South America as “The Cradle of Dinosauria.”) After existing for 163 million years, the dinosaurs disappeared at the end of the Cretaceous Period, 66 million years ago.

The Earth's appearance during the Mesozoic Era was quite different from its appearance today. The reason for the difference is that although the surface of our Earth seems rock solid, it is not. The surface of the Earth is changing constantly, although most of the change is extremely slow. For example, the east coast of the United States is moving away from Europe and Africa at a rate of one to three inches per year. This movement is known as “continental drift.”

The rate of continental drift, one to three inches per year, is insignificant to humans, who might see their continent move six feet (1.82 m) or so during their 70- or 80-year lifetimes. But when we speak of the Earth's past, we are talking about hundreds of millions of years. A lot can happen in a million years.

When the Triassic Period began, 245 million years ago, there was only one continent on Earth, a super-continent called Pangea. Pangea separated into two lesser continents, Laurasia and Gondwanaland, during the Jurassic Period; and during the Cretaceous Period, the modern continents began to appear (although they were not in their present-day locations).
You could think of today's world maps as “snap-shots” of the way the continents look today. In the future, they will look quite different.

In general, the climate of the Mesozoic Era was warmer than that of today, and there appears to have been little difference between summer and winter. It is incomplete, however, to picture dinosaurs as moving through either a tropical or desert landscape. These settings did exist, but there were forests, as well, and a range of mild climates. In whatever mental picture of dinosaurs and their environment that one develops, there should be one very common plant missing -- throughout the Mesozoic Era, there were no grasses! Small ferns provided the only ground cover there was.

Evidence suggests that at the beginning of the Triassic Period (245-208 million years ago), before the appearance of dinosaurs, the global temperature averaged around 50º to 60º F (10º to 15º C). Toward the end of period, however, the global climate began to become drier and hotter; deserts began to appear on much of Pangaea's surface area. In the northern hemisphere, gingko and tree fern forests flourished, while near the equator were forests of conifers and cycads. Horsetails grew near bodies of water.

Rainfall increased and the oceans rose during the Jurassic Period (208-145 million years ago). Lush vegetation, resembling the profuse growth in today's rain forests, covered much of Earth's surface, displacing former desert areas. Evidence of the abundant plant life can be found in the extensive coal fields that date from this period. Benettitalean cycads, ferns, and tree ferns (leaves perched high atop thin trunks), conifers, and giant club moss dominated the forests and marshlands.

As the Cretaceous Period (145-66 million years ago) progressed, the giant forests of the Jurassic began to disappear. Toward the middle of the period, a gradual global cooling began, and different vegetation began to develop. Flowering plants (angiosperms) appeared, including beech, fig, and magnolia, and seed ferns became extinct. In the Late Cretaceous, dinosaurs inhabited forests that would have closely resembled those of today.

Footnote: In December, 1994, scientists at the Royal Botanic Gardens in Sydney Australia, announced the discovery of 39 prehistoric pine trees, thought to have been extinct since the Jurassic Period. One of the most significant botanical finds of the century, the trees have been peacefully thriving in a secluded rain forest for 150 million years -- a real-life Jurassic Park.

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