EVOLUTION OF THE DINOSAURS
What is a dinosaur?
Dinosaur is a term used to describe certain types of animals that lived during the Mesozoic era in geologic history. It is difficult to generalize about dinosaurs, but two things are definitely agreed upon. They were, in general, the largest creatures to ever walk on Earth, even though there were many smaller species of dinosaurs. In addition, these animals were some of the most successful organisms that ever lived, existing as species for at least 160 million years.
What does the term dinosaur mean?
Dinosaur comes from the term dinosauria, which is a combination of the Greek words deinos and sauros. It means terrible reptiles or terrible lizards. The term was invented by the well-known British anatomist Sir Richard Owen (1804-1892). He coined the term in 1842 to describe the 175-million-year-old fossil remains of two groups of giant reptiles that corresponded to no known living creatures. In 1854, Owen prepared one of the first dinosaur exhibits for display at the Crystal Palace in London, England.
DINOSAUR ANCESTORS
How did life evolve after the early one-celled organisms?
Over hundreds of millions of years after the evolution of single-celled organisms, the oceans abounded with a huge variety of life. The first soft-bodied animals, such as worms and jellyfish, evolved toward the close of the Pre-Cambrian (also seen as Precambrian) era roughly 600 million years ago; the first animals with hard parts, such as shelled mollusks, evolved during the first period after the Pre-Cambrian known as the Cambrian period of the Paleozoic era.
Still around today, jellyfish were some of Earths first soft-bodied life forms (iStock).
What are vertebrates?
The first vertebrates, or animals with backbones, evolved during the late Cambrian to early Ordovician periods as jawless freshwater fish that looked much like todays hag- fish and lampreys. By the Devonian period (the age of fishes), jawed and armored fishes dominated the oceans. Around 380 million years ago, a line of fish with bony skeletons developed air-breathing lungs and limbs strong enough to support them. These were the precursors to the amphibians, creatures that made their first move toward land probably in response to the spread of plants to land around the early Silurian period.
What were the early amphibians and when did they live?
Amphibians were the first air- breathing land vertebrates, evolving from lobe-finned fish and primitive tetrapods. Tetrapods were animals with fishlike heads and tails, and with limbs that were little more than jointed, lobed fins. They evolved around 340 million years ago during the late Devonian period. So far, the oldest of these pre-amphibian fossils have been dated at approximately 360 million years old. These animals could do something that no fish could do: breathe air. The changeover from gills to lungs came during the early larval stage of the amphibian. These early amphibians were direct descendants from the early fish, and represent an important transitional stage from water-dwelling to land-dwelling animals. They were also the first vertebrates to eventually evolve true legs, tongues, ears, and voice boxes.
The word amphibian comes from the Greek amphi, meaning both, and bios, meaning life (sometimes translated as living a double life). The name signifies that these animals could live both in and out of the water.
The Carboniferous period of the Paleozoic era, from approximately 360 to 280 million years ago, brought about a proliferation of amphibians, as did the Permian, from about 280 to 248 million years ago. Much of the worlds climate during both time periods was warm and humid, with many swamps, marshes, and lakes dominating the landscape a perfect environment for the water needs of the amphibians. In some texts, the Carboniferous or the Permian periods are called the age of amphibians (although many scientists agree that reptiles began to take over the amphibians domain during the Permian).
