Dinosaurs 101 | National Geographic

Summary

Dinosaurs, which first appeared 245 million years ago, dominated Earth for millions of years, evolving into over 1,000 species. They split into two main groups, Saurischia and Ornithischia, based on pelvic structure. Dinosaurs ranged from small species like Compsognathus to massive ones like Dreadnoughtus. Some were herbivores with specialized teeth, while carnivores like Deinonychus hunted in packs. Evidence suggests some dinosaurs traveled in herds and laid eggs in communal sites. Despite their vast diversity, most dinosaurs went extinct around 66 million years ago, likely due to an asteroid impact, though other factors played a role. Their legacy lives on through birds and fossil records.

Takeaways

• 😀 Dinosaurs struck fear and awe in humans, with their earliest appearance dating back to 245 million years ago during the Triassic Period.
• 🌍 The supercontinent Pangaea began to break apart during the Triassic Period, leading to the separation and diversification of dinosaur species.
• 🔬 Dinosaurs are descendants of reptiles called Archosaurs, with two major groups: Saurischia and Ornithischia, based on pelvic bone structure.
• 🐲 Saurischian dinosaurs, like Tyrannosaurus Rex and Brachiosaurus, had a pelvis where the pubis bone faces forward and down.
• 🦖 Ornithischian dinosaurs, such as Stegosaurus and Hadrosaurs, had a pelvis with the pubis bone facing backward and down.
• 📏 Dinosaur size varied greatly, from small species like Compsognathus to gigantic ones like Dreadnoughtus, which measured 85 feet long and weighed 65 tons.
• 🥦 Herbivorous dinosaurs, like Hadrosaurs, had specialized teeth for grinding tough plant material.
• 🍖 Carnivorous dinosaurs made up 40% of dinosaur species, with some, like Deinonychus, hunting in packs.
• 👣 Some dinosaurs exhibited social behaviors, traveling together in herds, and making annual visits to specific sites to lay their eggs.
• 🌠 The most widely accepted explanation for the extinction of dinosaurs is an asteroid strike, though multiple contributing factors are likely, with many species already in decline before the event.
• 🦅 Some dinosaurs survived the extinction event and evolved into the birds we see today, preserving the legacy of dinosaurs in modern creatures.

Q & A

When did the earliest dinosaurs appear?

The earliest dinosaurs appeared about 245 million years ago, during the Triassic Period.

What was the state of the Earth's landmasses during the appearance of the first dinosaurs?

At the time the first dinosaurs appeared, most of the Earth's landmasses were still joined together as the supercontinent Pangaea.

How did the separation of Pangaea affect dinosaurs?

The separation of Pangaea caused dinosaurs to become geographically isolated, leading them to adapt to specific habitats and diversify into many different species.

How many dinosaur species are estimated to have roamed the Earth?

It is estimated that more than 1,000 species of dinosaurs roamed the Earth.

From what reptilian group did dinosaurs descend?

Dinosaurs descended from reptiles called Archosaurs.

What are the two major groups of dinosaurs, and how are they classified?

Dinosaurs are classified into two major groups: Saurischia and Ornithischia. They are classified based on the shape and orientation of their pelvis.

What is the main difference in pelvis structure between Saurischian and Ornithischian dinosaurs?

In Saurischian dinosaurs, like Tyrannosaurus Rex and Brachiosaurus, the pubis bone faces forward and down, whereas in Ornithischian dinosaurs, like Stegosaurus and Hadrosaurs, the pubis bone faces backward and down.

What were some of the size extremes seen in dinosaurs?

Dinosaurs varied greatly in size. For example, Compsognathus was small, barely larger than a chicken, while Dreadnoughtus was gigantic, measuring 85 feet long and weighing 65 tons.

What kind of diets did dinosaurs have, and what were some adaptations they had for these diets?

Dinosaurs had varied diets. Herbivores, like Hadrosaurs, had specialized teeth for grinding tough plant material, while carnivores, such as raptors like Deinonychus, were predators that often hunted in packs.

What evidence suggests that some dinosaurs had social behaviors?

Evidence like footprints and trackways shows that some dinosaurs traveled together, and there is also evidence that herds may have made annual visits to certain sites to lay their eggs.

What is the most well-known explanation for the extinction of dinosaurs, and was this the only factor?

The most well-known explanation for the extinction of dinosaurs is an asteroid strike. However, the dinosaur population was already in severe decline before the asteroid impact, suggesting multiple factors contributed to their extinction.

Which dinosaur species survived the mass extinction event, and what did they evolve into?

Some dinosaur species survived the mass extinction event, and many of them evolved into today's birds.

What is the legacy of dinosaurs today?

Though the world has never again seen land creatures as great as the dinosaurs, their legacy lives on through their descendants and the fossils they left behind.