Quck answer
Dinosaurs evolved from small, bipedal reptiles in the late Triassic period, around 230 million years ago. They quickly diversified into a variety of forms, including carnivorous theropods, herbivorous sauropods, and armored ankylosaurs. During the Jurassic and Cretaceous periods, dinosaurs dominated the terrestrial ecosystem, with some species growing to immense sizes. However, around 66 million years ago, a catastrophic event – possibly a meteor impact – caused a mass extinction that wiped out all non-avian dinosaurs. The surviving birds are now considered to be the only living descendants of the once-dominant group of dinosaurs.
Extinct Creatures
Pachycephalosaurus, the dinosaur with a dome-shaped head
Canadian Museum of Nature
The Mesozoic Era, divided into three periods, was dominated by dinosaurs. The Late Triassic saw the emergence of the first true dinosaurs. The Jurassic Period witnessed a rise in the number of dinosaurs. By the Cretaceous Period, a variety of dinosaurs had evolved. Dinosaur ancestors were evolving during the Triassic Period.
Paleontologists examine various types of dinosaurs to determine their relationships with other dinosaurs and their ancestors. This helps scientists understand evolution and the world inhabited by dinosaurs. Isolated dinosaurs evolved differently from those that could migrate. The Linnaean system of classification categorized dinosaurs and other organisms hierarchically. Cladistics, a modern approach, uses the presence of shared morphological features to create the branching tree of dinosaur evolution.
Since information about dinosaurs is incomplete, classifications may change when new information emerges. Each new dinosaur fossil discovered could unlock information about dinosaur evolution and ancestry.
The Linnaean System of Classification
Dinosaur Classification Chart
Collection of Publications International, Ltd.
Carl von LinnГ© (Linnaeus), a Swedish botanist, developed a system to classify all living things during the 1750s. Each living thing has a scientific name consisting of a genus and a species name. The scientist who first describes a new organism gives it a name. Over a million species have been named since Linnaeus introduced this system.
A scientific name is used because living organisms are called different things in different languages. For instance, the house cat is called die Katze in German and le chat in French, but biologists refer to it as Felis catus in English, French, and German.
A scientist may name an organism based on an interesting feature or in honor of a person or place where it was discovered. For example, Tyrannosaurus rex, the enormous meat-eating dinosaur, means “tyrant lizard king” as it ruled over other dinosaurs.
In the Linnaean System, similar species are grouped into a genus, similar genera into a family, similar families into an order, similar orders into a class, similar classes into a phylum, and similar phyla into a kingdom. Canis, the dog genus, includes dogs, coyotes, and wolves. The dog family, Canidae, includes both Vulpes, the fox genus, and Canis. Canidae and Ursidae, the bear family, belong to the order Carnivora (meat-eating animals). Mammals and carnivores belong to the class Mammalia (all mammals). Chordates, animals with backbones, and fishes comprise the phylum Chordata. The kingdom Animalia comprises animals such as chordates and corals. These categories are called taxa, and the study of these classifications is referred to as taxonomy.
Analyzing Evolutionary Relationships through Cladistics
In recent years, researchers have been using a new method called cladistics, also known as phylogenetic systematics, to reconsider the relationships between dinosaurs. Unlike the Linnean system that places organisms into hierarchical categories, cladistics aims to determine the speciation events that led to the branching separation of all organisms. Essentially, cladistics is a way of studying the evolutionary relationships between groups to create a family tree.
Cladistics groups organisms based on shared derived characters, referred to as synapomorphies, and uses a principle called parsimony. This principle suggests that the simplest branching pattern with the fewest steps is likely closest to the true one. While cladistics does not categorize organisms into nested categories like the Linnean system, the Linnean categories are still commonly used to group organisms into categories.
Classification and Evolution
Charles Darwin
FPG/Taxi/Getty Images
After Charles Darwin published his theory of evolution, biologists began to understand why organisms fall into natural groupings. For instance, species in the dog genus Canis look alike because they share a common ancestor. Foxes and dogs do not look as similar because their common ancestor lived further back in time. The farther back a common ancestor lived, the longer its descendants have had to evolve and change.
It is challenging to prove that two species share a common ancestor. However, scientists can show how likely it is that two species are related by making an extensive list of characteristics. The more traits two species share, the more likely they are closely related and got those traits from a shared ancestor.
Convergent evolution occurs when two species evolve similar traits independently, without a common ancestor. For example, sparrows and bats have wings that are arms and hands, but their wings are significantly different. In contrast, the wings of all bird species, such as sparrows, eagles, and ostriches, are similar, indicating that they share a common ancestor.
Dinosaurs as Archosaurs
Allosaurus watches Camarasaurus in the water
Vernall Field House
Bones are used to classify dinosaurs, but only a few of them are known from complete or nearly complete skeletons. Almost half of the known species are based on teeth or bone fragments. It is challenging for paleontologists to describe an incomplete fossil skeleton and determine what the animal looked and acted like based on a few fossilized remains. The discovery of new fossils of a poorly known dinosaur or a new dinosaur species may alter the family tree. The family tree of dinosaurs will always be incomplete since we cannot know all the different dinosaur groups that lived.
The classification of dinosaurs as reptiles does not mean that all reptiles belong to a single clade. There are two reptilian clades – the Sauropsida, which includes living reptiles, dinosaurs, ichthyosaurs, plesiosaurs, and birds, and the Theropsida, which includes mammals and extinct mammallike reptiles. Crocodilians and birds belong to a smaller sauropsid clade called the Archosauria, which also includes large predatory dinosaurs like Allosaurus and Tyrannosaurus. Lizards and snakes belong to a separate clade called Lepidosauria. The earliest archosaurs were found in rocks from the Permian era, before the Mesozoic era began. During the Mesozoic era, the archosaurs quickly expanded and spread, with some groups like the Pterosauria, Saurischia, and Ornithischia surviving until the end of the era. Birds have not been found in the Triassic era, but some birdlike animals have been discovered in Asia, Europe, and Texas.
Among the archosaurs, two important evolutionary changes occurred. They changed from sprawling, lizardlike animals to animals with their legs directly under their bodies, like dinosaurs. They also changed from a cold-blooded, lizardlike metabolism to a warm-blooded, birdlike metabolism, which only occurred in birds and some advanced predatory dinosaurs. The development of a stronger ankle occurred in the ancestors of dinosaurs, pterosaurs, and birds. Small bipedal archosaurs like Lagosuchus, Lagerpeton, and Pseudolagosuchus had advanced ankles and were closely related to dinosaurs.
FAQ
1. What was the first dinosaur?
The first dinosaur, Eoraptor, lived about 230 million years ago during the Late Triassic Period. It was a small, bipedal, meat-eating dinosaur that stood about 3 feet tall and weighed around 20-30 pounds. Eoraptor is considered one of the earliest known dinosaurs and is believed to have given rise to all other dinosaur groups.
2. How did dinosaurs evolve?
Dinosaurs evolved from a group of reptiles called archosaurs, which also includes birds and crocodiles. The earliest dinosaurs were small and bipedal, but over time, they diversified and evolved into a wide variety of shapes and sizes, including some of the largest land animals to ever exist. Factors that likely influenced dinosaur evolution include changes in climate, geography, and competition with other animals.
3. What caused the extinction of the dinosaurs?
The extinction of the dinosaurs is one of the most debated topics in science. The most widely accepted theory is that a massive asteroid impact, which occurred about 66 million years ago, caused a chain reaction of events that led to their extinction. The impact caused widespread fires, earthquakes, and a “nuclear winter” effect, which ultimately led to the demise of the dinosaurs and many other species.
4. Did all dinosaurs go extinct?
No, not all dinosaurs went extinct. Birds are considered to be a type of dinosaur, as they evolved from small, feathered theropods during the Jurassic Period. Birds are the only surviving members of the dinosaur group, and there are over 10,000 species of birds in the world today.
5. How do we know what dinosaurs looked like?
We know what dinosaurs looked like based on a variety of evidence, including fossilized bones, teeth, and footprints. By studying these remains, scientists can reconstruct the anatomy and behavior of dinosaurs. Additionally, some dinosaurs, such as those with feathers, left behind impressions that provide clues to their appearance. Paleontologists also use computer modeling and biomechanical analysis to better understand how dinosaurs moved and interacted with their environment.
6. How long did dinosaurs live?
Dinosaurs lived for a long time, spanning a period of over 160 million years. The earliest dinosaurs appeared in the Late Triassic Period, about 230 million years ago, and they went extinct at the end of the Cretaceous Period, about 66 million years ago. Some dinosaur groups, such as the sauropods, lived for tens of millions of years, while others, such as the tyrannosaurs, had a relatively short existence.
7. What is the largest dinosaur ever discovered?
The largest dinosaur ever discovered is Argentinosaurus, a massive plant-eating sauropod that lived about 100 million years ago during the Late Cretaceous Period. Argentinosaurus weighed an estimated 70-100 tons and measured up to 100 feet long. Its bones were so large that they were initially mistaken for those of a giant crocodile.
8. Are there any living relatives of the dinosaurs?
Yes, birds are the closest living relatives of the dinosaurs. In fact, birds are considered to be a type of dinosaur, as they evolved from small, feathered theropods during the Jurassic Period. Birds share many anatomical and behavioral traits with their extinct relatives, including a lightweight, hollow bone structure and the ability to lay eggs.
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