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Dinosaurs: Some were small enough to hold in your hand; others taller than houses

The image shows how a human size relates to that of a sauropod dinosaur. Sauropod dinosaurs lived in North America during the Late Jurassic, about 154–150 million years ago. The dinosaurs were the largest land animals that ever lived. They had a long neck and tail, stood on four legs, and were herbivorous. (Wikimedia Commons)

The imagination we have of a dinosaur is a reptilian creature with threatening teeth, claws, spikes. They roamed Earth about 175 million years ago. How did dinosaurs evolve? What did they eat? How did they move? What killed the dinosaurs?

Scientists’ amazement with dinosaurs arose during the 1820s. When scientists discovered bones of a gigantic terrestrial reptile buried in the English countryside, they gave it the nickname Megalosaurus (“great lizard”). The term “dinosaur” was originally used in 1842 by Sir Richard Owen, a pioneering palaeontologist in Britain.

The Megalosaurus, Iguanadon (“iguana teeth”), and Hylaeosaurus (“woodland lizard”) bones have all been studied by Owen. Each of them walked with their legs squarely beneath their bodies rather than out to the sides. They also lived on land, were larger than any existing reptile.

Using this knowledge, Owen concluded that the three comprised a unique classification of reptiles he dubbed Dinosauria. The name is derived from the Greek words deinos, which means “awful,” or “terrible,” and sauros, which means “lizard” or “reptile.”

Palaeontologists have since discovered dinosaur fossils across the globe and have analysed them to learn more about the numerous varieties of these beasts that once existed. The two orders of dinosaurs—the “bird-hipped” Ornithischia and the “lizard-hipped” Saurischia—have historically been separated by scientists. From there, dinosaurs were divided into multiple genera (principal categories), such as Triceratops or Tyrannosaurus.

When did dinosaurs live?

Most dinosaurs lived in what’s called the Mesozoic Era, a time roughly 245 to 66 million years ago. Scientists generally divide this period into three separate ages.

  • Triassic Period (252 to 201 million years ago). The era when reptiles first evolved into creatures we know as dinosaurs. However, the Earth they lived on was different from the one we live on today. Then, almost all animals lived on one extremely hot and dry landmass, known as Pangaea.
  • Jurassic Period (201 to 145 million years ago). During this period, temperatures on Earth fell, leading to more water, plants, and dinosaurs.
  • Cretaceous Period (145 to 66 million years ago). With more continents forming around the globe, more dinosaurs started evolving independently. This led to more types of dinosaurs.  

How did dinosaurs move?

Some dinosaurs walked on two legs and were called bipedal. Some walked on four legs and were quadrupedal, walking on four legs, and some could alternate between these two gaits.

Some dinosaurs had a kind of body armour, and some of them had feathers like their modern relatives, birds. While some of them moved fast, others proceeded slowly and lumberingly.

What did dinosaurs eat?

Some dinosaurs ate lizards, turtles, eggs, or early mammals. Some hunted other dinosaurs or scavenged dead animals. Most, however, ate plants (but not grass, which hadn’t evolved yet), says U.S. Geological Survey, the sole science agency for the Department of the Interior.

Rocks that contain dinosaur bones also contain fossil pollen and spores that indicate hundreds to thousands of types of plants existed during the Mesozoic Era. Many of these plants had edible leaves.

There were flowering (fruiting) plants in the latter part of the dinosaur age. Although the exact time of origin for flowering plants is still uncertain, the last of the dinosaurs certainly had fruit available to eat, says U.S. Geological Survey.

Some dinosaurs were herbivores (plant eaters), others were carnivores (meat eaters), and the rest were scavengers (ate dead animals). This adaptation improved their survival rate.

How did dinosaurs learn how to fly?

Not all dinosaurs were big. One group, known as paravian theropods, were small. But like most dinosaurs, the first paravians had hair-like feathers, probably for keeping them warm.

Over time, the paravians became smaller, their feathers became larger and more packed together. Then more feathers grew on their arms to form wings. At first, the wings were too small to help them fly.

Later, the wings were large enough to give them lift and keep these paravians airborne. From these flapping ancestors arose today’s birds, reports BBC’s Science Focus.

What killed the dinosaurs?

All the present-day continents of the Earth were one during the time the dinosaurs evolved. The single landmass called Pangaea was encircled by a vast ocean called Panthalassa. Around 200 million years ago, during the Early Jurassic Period, Pangaea started to separate into distinct continents, and dinosaurs would have witnessed significant changes in the environment during their existence.

At the conclusion of the Cretaceous Period, some 66 million years ago, dinosaurs inexplicably vanished.

There are various competing ideas as to what caused this mass extinction. It also resulted in the extinction of numerous plant and animal species at roughly the same time.

Although some scientists theorised a flurry of volcanic activity wiped out the reptiles, research now points to a major asteroid strike off the coast of modern-day Mexico about 66 million years ago.

The impact left behind a crater off the coast of Mexico’s Yucatan Peninsula measures 150 kilometres across and 20 kilometres deep. It is thought to have triggered tsunamis, earthquakes, and volcanic eruptions. These led to the demise of the dinosaurs and almost three-quarters of all plant and animal life on Earth.

After blasting into the Earth, scientists say the asteroid would have released particles and gases, which blocked out the Sun and caused a lengthy winter.

Without water and sunlight, plants and algae perished, eradicating the planet’s herbivores. After a time of feeding on the remains of these herbivores, predators would have perished as well.

While this caused the extinction of many dinosaurs, many species that later evolved into birds survived.

Birds, the only living descendants of dinosaurs

Even though they no longer roam the planet as they did during the Mesozoic Era, birds, the successors of dinosaurs, nevertheless bear unmistakable signs of these massive reptiles. Palaeontologists continue to study dinosaurs, and dinosaurs still exist, and are the subject of ongoing research.

Dinosaurs continue to strongly hold public’s imagination as shown in films and television. This is one area, in which, dinosaurs appear to be in no danger of going extinct.

About Kelvin Mugambi

Kelvin Karani is a computer science student at Strathmore University in Nairobi. In his spare time, he studies and writes about the Earth, atmosphere, and outer space. His hobbies include cooking, exercise, motoring, and sports.

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