Dinosaurs include extinct animals that we know from fossils and birds that we see today.
What are dinosaurs?
Dinosaurs are classified as reptiles, although some of their characteristics are found in modern mammals and birds, not reptiles. It appears that some dinosaurs were warm-blooded and walked with an upright gait.
The word "dinosaur" means "terrible lizard" in Greek. It was coined in 1842 by Sir Richard Irving, Professor of Comparative Anatomy and Physiology in England.
We generally believe that the extinct animals of the dinosaurs lived in the Mesozoic Era.
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Just as a family tree shows your ancestors and current relatives, an evolutionary tree shows dinosaurs and other animal groups and their relationships with each other. Dinosaurs (and extinct and extant birds) are part of the amniotic evolutionary tree.
The first amniotes were primitive tetrapod reptiles from which all other reptiles and mammals evolved. One branch of early reptiles evolved into archosaurs—a group that includes dinosaurs, crocodiles, and pterosaurs. Dinosaurs themselves are divided into two main groups based on their hip structure, and then into smaller branches based on other common characteristics.
early dinosaur relatives
The oldest known close relative of dinosaurs is a dog-sized quadruped named Asilisaurus kongwe, which lived approximately 240 million years ago. At least 14 individual fossils have been discovered in Tanzania.
Asiliosaurus belongs to the order Sileosaurs and is closely related to dinosaurs. Sileosaurus continued to live alongside dinosaurs until the end of the Triassic period (approximately 200 million years ago). These fossils indicate that the dinosaur lineage diverged from its dinosaur-like relatives at least 240 million years ago.
Rise of the Dinosaurs
When dinosaurs first appeared in the Middle Triassic period, about 230 million years ago, they were just another small group of reptiles in a world teeming with them. By the end of the Triassic, they had dominated the land and remained so for 140 million years until the end of the Mesozoic era.
Was their rise accidental, a product of superiority, or something else? The answer likely includes all of these. A timely extinction event in the Late Triassic wiped out most of their competitors, paving the way for the dinosaurs. We're not sure why they later flourished. Perhaps they were better adapted to arid environments than other animals, or perhaps their more efficient, more upright running style gave them an advantage.
What are the main physical characteristics shared by all dinosaurs?
The main physical characteristics shared by all dinosaurs are:
1. There is a hole in the skull between the eye socket and the nostril.
2. There are two holes in the skull behind the eye sockets.
3. Ankles that bend like hinges on a single plane
4. The hip joint socket has a hole in the center.
5. The limbs are directly fixed under the body.
6. Three or more sacral vertebrae (located near the pelvis)
