Dinosaur

Neognathae

LA-Triceratops mount-2

Dromaeosaurus skull en

Sprawling and erect hip joints - horizontal

William Buckland c1845

Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago, although the exact origin and timing of the evolution of dinosaurs is the subject of active research. They became the dominant terrestrial vertebrates after the Triassic–Jurassic extinction event 201 million years ago; their dominance continued throughout the Jurassic and Cretaceous periods. The fossil record shows that birds are modern feathered dinosaurs, having evolved from earlier theropods during the Late Jurassic period. As such, birds were the only dinosaur lineage to survive the Cretaceous–Paleogene extinction event approximately 66 million years ago.

Dinosaurs are a varied group of animals from taxonomic, morphological, and ecological standpoints. Birds, at over 10,000 living species, are the most diverse group of vertebrates besides perciform fish. Traditional dinosaurs are informally divided into two major groups: the Saurischia, which includes the theropods (predominantly carnivorous dinosaurs) and sauropodomorphs (long-necked dinosaurs), and the Ornithischia, which includes the various dinosaurs that were primarily herbivores. Dinosaurs are characterized by their upright stance, with the legs positioned directly beneath the body in most species. Many extinct dinosaurs are known from a rich fossil record that includes bones, teeth, skin impressions, and even evidence of feathers.

Evolution and Extinction

The exact origin of dinosaurs is still subject to research, but they are believed to have evolved from earlier reptiles known as archosaurs. Their rise to dominance was gradual, following the end of the Triassic period and the extinction event that cleared the way by eliminating most of the competition. Dinosaurs evolved into a wide variety of forms and sizes, from the small bird-like Microraptor to the enormous Sauropods like Brachiosaurus and Diplodocus. The reasons behind the success of dinosaurs are still studied, with factors such as their social behavior, growth patterns, and reproductive strategies being considered.

The Cretaceous–Paleogene extinction event is the most famous extinction event that led to the demise of all dinosaur groups except for the lineage that led to today's birds. This event is often attributed to a massive asteroid impact combined with volcanic eruptions and climate changes.

Classification

Dinosaurs are divided into two main orders: the Saurischia, which includes the theropods and sauropodomorphs, and the Ornithischia, which includes various herbivorous dinosaurs. This classification is based on the structure of the hip bones. In the Saurischia, the pubis bone points forward, while in the Ornithischia, it points backward.

Theropods

Theropods were primarily carnivorous dinosaurs, although some groups evolved to become herbivores, omnivores, and insectivores. This group includes the ancestors of birds, the only dinosaur lineage to survive the Cretaceous–Paleogene extinction event.

Sauropodomorphs

Sauropodomorphs were long-necked dinosaurs that included the largest animals to ever walk the Earth. They were primarily herbivorous and known for their enormous size and long necks and tails.

Ornithischians

Ornithischians were diverse herbivorous dinosaurs that included a variety of forms such as the armored Ankylosaurus, the horned Triceratops, and the duck-billed Hadrosauridae.

Paleobiology

The study of dinosaur paleobiology involves examining the behaviors, reproduction, and diets of these ancient creatures. Evidence from fossils, including nests, eggs, and footprints, provides insight into the complex lives of dinosaurs. Their diets varied widely, from the strictly carnivorous habits of theropods to the herbivorous diets of sauropodomorphs and ornithischians.

In Popular Culture

Dinosaurs have captured the public's imagination since the first fossils were described in the early 19th century. They have been featured in various forms of media, including books, films, and television shows. The Jurassic Park series, in particular, has had a significant impact on the public's perception of dinosaurs.