Dinosaurs and their relatives

Dinosaurs include the extinct animals we know from fossils and the birds we see today.

What is a dinosaur?

Dinosaurs are classified as reptiles, although some of their characteristics are found in mammals and birds living today rather than in 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 Owen, a British professor of comparative anatomy and physiology.

The extinct animals we usually think of as dinosaurs lived during the Mesozoic Era.

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Just like a family tree shows your ancestors and current relatives, an evolutionary tree shows how dinosaurs were related to other groups of animals and to each other. Dinosaurs (extinct and living birds) are part of the amniote evolutionary tree.

The first amniotes were the primitive four-legged reptiles from which all other reptiles and mammals evolved. A branch of early reptiles evolved into archosaurs—a group that includes dinosaurs, crocodiles, and pterosaurs. The dinosaurs themselves are divided into two main groups based on the structure of their hips, and then into smaller branches based on other common characteristics.

Relatives of early dinosaurs

The oldest known relative of dinosaurs is a dog-sized quadruped named Asilisaurus kongwe, which lived about 240 million years ago. Fossilized skeletons of at least 14 individuals have been found in Tanzania.

Asilisaurus is a member of the cilisaurids and is closely related to dinosaurs. Silisaurus continued to live alongside the dinosaurs until the end of the Triassic period (approximately 200 million years ago). The fossils suggest that the dinosaur lineage split from 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 group of small reptiles in a world filled with reptiles. By the end of the Triassic, they became dominant on land and continued for 140 million years until the end of the Mesozoic.

Was their rise by chance, superiority, or something else? The answer may include all of these. A "well-timed" extinction event in the late Triassic era wiped out most of their competitors, clearing the way for the dinosaurs. We're not sure why they flourished afterwards. Perhaps they were better adapted to arid conditions than other animals, or perhaps their more efficient, 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. A hole in the skull between the eye socket and nostril

2. There are two holes in the skull behind the eye sockets

3. An ankle that bends in a single plane like a hinge

4. There is a hole in the center of the hip joint socket

5. The limbs are fixed directly under the body

6. Three or more sacral (located near the pelvis) vertebrae

animal tags： Dinosaur