What did our ancestors gain, what did they lose, and what did they part with during their long evolution?
In the history of the earth, which is said to be about 4.6 billion years,Life is said to have originated at least 3.95 billion years ago. The first humans appeared about 7 million years ago. From the perspective of Earth’s long history, this is “very recent”.
However, Homo sapiens did not emerge suddenly. It was born at the end of continuous evolution from early life to the present. If we focused on one species, Homo sapiens, and traced its history, what kind of journey would we see?This is a magnificent story about such a journey, focusing on the 70 signposts.『Prehistory of Sapiens: 500 million years of history from vertebrates to humans』is.
this”sapiens prehistory”, we will introduce the “highlights” that you should especially pay attention to from among the 70 signposts. This time, we will explain what kind of animals “mammalia” were, sometimes referred to as mammals in a broad sense, and how they differed from the therapsids of the Paleozoic era.
*This article is based on “Prehistory of Sapiens: 500 million years of history from vertebrates to humans” (Bluebacks) has been reconstructed and re-edited.
Earth after the mass extinction event at the end of the Paleozoic and Permian periods
Approximately 252 million years ago, when an unprecedented mass extinction event occurred, all of the world’s continents gathered and merged, forming the supercontinent Pangea.
Until just before the mass extinction event, some of the therapsids living on this supercontinent had acquired fairly large bodies, several meters in length, lifted their bodies with their limbs, and had large jaws with heterodentate teeth. They had well-developed teeth, perhaps a diaphragm for efficient lung breathing, and took full advantage of their endothermic nature to hunt aggressively.
In short, it was (or should have been) an entity that reigned supreme over the terrestrial ecosystem. At that time, a kingdom of beast archers had been established in the world.
However, the kingdom collapsed due to a mass extinction event. Approximately 252 million years ago, the world that our ancestors had built was destroyed, and a new world centered on reptiles was rapidly established.
What emerges in this new world is the “dinosaurs,” the male sauropods that separated from their ancestors a long time ago.
After the mass extinction event, the age of dinosaurs begins. This era, which lasted for about 186 million years until about 66 million years ago, is called the “Mesozoic Era,” and is named from the oldest to the “Triassic,” “Jurassic,” and “Cretaceous.” The boundary between the Triassic and Jurassic periods was approximately 201 million years ago, and the boundary between the Jurassic and Cretaceous periods was approximately 145 million years ago.
Geological time and five mass extinctions
The stage, the supercontinent Pangea, gradually splits up. It split into north and south, then east and west, and then over 100 million years, it split into various continents. It split into the Laurasia supercontinent in the north and the Gondwana supercontinent in the south, and then during the Jurassic period, the Laurasia supercontinent split into North America and Eurasia. During the Cretaceous period, the supercontinent Gondwana began to break apart, separating the continents of South America and Africa.
This division led to a “discontinuation” of living things.
The breakup of supercontinents cuts off communication between species, causing “isolation,” which leads to the evolution of organisms unique to each continent.
Now, in a world that has undergone drastic changes, cynodonts are among the therapsids that survived the mass extinction event at the end of the Permian period.
