At the time of the Permian mass extinction, which occurred 250 million years ago, the Earth faced a catastrophe that marked the end of a brilliant Paleozoic era. Then, as if nothing had happened, new forms of life began to stir on Earth. The era of reptiles was dawning. 

In the Mesozoic, during the first stage known as the Triassic period, several cartilaginous fish continued their lives in the sea, while somewhere along the coast, early marine reptiles, like the small 40 cm long Cartorhynchus, began to fill the empty ecological niches. Some of these creatures, which alternated between land and sea, eventually fully adapted to a terrestrial lifestyle, leading to the emergence of forms like Brachyceratops and Hypsilophodon in the early Mesozoic seas. Meanwhile, on land, primitive amphibians and reptiles that survived the Permian mass extinction thrived.

Among the shared items, there were reptiles resembling crocodiles that exceeded 5 meters in length, such as the Sauruses. These creatures established themselves as significant figures in the ecosystem. However, in a corner of that ecosystem, there was a creature that could not escape its humble existence: the dinosaurs. Early dinosaurs, such as the Eoraptor and Herrerasaurus, appeared around 240 million years ago, but they were merely insignificant reptiles, comprising only about 5% of the animal species at the time. However, an event occurred around 232 million years ago that would turn the tide. A massive volcanic eruption near present-day Alaska released vast amounts of greenhouse gases, leading to rapid climate change on Earth. This event, known as the Late Triassic mass extinction, caused heavy rains and widespread flooding across the planet, while at times also bringing about severe droughts.

You know that a disaster struck the Earth. Many animals went extinct during this time, but unlike other reptiles, the Huanglong, with its elongated limbs and specialized functions, gained an advantage in a dry ecosystem with low oxygen levels due to its efficient breathing and faster mobility. As a result, it was able to survive with fewer resources. In fact, a study published in 2018 by Massimo Bernardi of the research team at Laser Communications revealed that the mass extinction event in the late Triassic period played a significant role in the prosperity of dinosaurs. This makes sense, as dinosaurs initially only made up 6% of the animal population at the beginning of the Triassic period, but by the end of the Triassic, that percentage skyrocketed to 90%. Taking advantage of this fortunate opportunity, most dinosaurs at that time were characterized by their unique pelvic bone structure.

Carnivorous dinosaurs dominated, but among them, some were herbivores. Some of these branched out into unique evolutionary paths, gradually becoming more diverse. However, this rapid adaptation was not limited to land; some reptiles expanded their skin membranes, evolving into pterosaurs like Dimorphodon, Pteranodon, and Quetzalcoatlus. This marked the moment when vertebrates first took to the skies. Of course, in the early days, creatures like Pterosauria had membranes on their legs rather than their arms. One important point to clarify is that pterosaurs are not dinosaurs. The easiest way to distinguish them is by looking at the hip bones of dinosaurs, which have a hole where the thigh bone fits in, while pterosaurs do not.

The pelvic cavity is not a hole; rather, the thigh bone is located in the indented area here, which is why it is not a dinosaur. The dinosaur's pelvic structure resembles a belly shape, and this is a crucial point that will come up again at the end of the video, so I hope you remember it. Now, getting back to the main topic, the initial input shows that the species you commonly see, the Mya, was very small. When its wings were spread, it measured 1 meter in length, and its body length was only 10 centimeters. In comparison, in the depths of the ocean, a wave of evolution was occurring among fish. About 230 million years ago, some marine reptiles began to evolve into forms like Plesiosaurus, branching out in their evolutionary paths. Of course, later on, short ones also appeared. In this way, during the Triassic period, various reptiles in the sky, on land, and in the sea began to gradually establish themselves. Then, about 200 million years ago, as the Pangaea supercontinent began to break apart, large-scale changes occurred.

Volcanic activity occurred, and large amounts of greenhouse gases were released all over the Earth. This led to the Triassic mass extinction, resulting in the complete disappearance of large amphibians and some reptiles, remnants of the Paleozoic era. Thanks to this, the dinosaurs and other reptiles that survived at this time were able to fill ecological niches more rapidly. In particular, among the dinosaurs, the ornithischians diversified even further. Earlier, we discussed that ornithischians had a pelvic bone structure that looked like this. Do you remember? However, in the case of the ornithischian dinosaurs, the pubis bone is oriented towards the back. This results in a relatively larger space for the digestive organs. Consequently, herbivorous ornithischian dinosaurs developed larger digestive tracts, gaining an advantage in food competition, and subsequently thrived during the Late Triassic and into the Cretaceous period.

During the late Jurassic period, the concentration of oxygen increased, allowing herbivorous dinosaurs to thrive. Their intestines grew larger to digest the abundant plant life, and as a result, their bodies became gigantic. By the late Jurassic, famous sauropods like Brachiosaurus and Giraffatitan, along with large carnivores like Allosaurus, roamed the continents. Naturally, some of their predators, the theropod dinosaurs, also underwent a selection for larger body sizes. However, the most significant change among theropods at that time was the emergence of feathered species, such as Ornitholestes and Caenagnathus, around 150 million years ago. These would eventually evolve into forms unimaginable to us today, including birds. Now, what were our human ancestors doing during the Jurassic?

In the midst of these dinosaurs, they quietly lived in hiding. The first ancestors of mammals that appeared in the Cretaceous period were no larger than a finger and were merely prey for the dinosaurs. Thus, the Jurassic was truly the golden age of dinosaurs. As time passed and the era shifted into the Cretaceous, the continents continued to divide, leading to a geographical differentiation of dinosaur species.

However, despite the prominence of dinosaurs, one of the most significant events of the Cretaceous was the emergence of flowers. Flowering plants adopted a strategy of cooperation with various insects such as beetles, bees, and butterflies for pollination, which led to successful reproduction. This not only ensured their survival but also established them as the foundational plants of ecosystems even to this day. Furthermore, the insects that pollinated flowers, like butterflies and bees, also thrived during this time.

It was a classification group, but alongside flowers, it has transformed into a gigantic classification that belongs to the top class today. Meanwhile, the species of dinosaurs that broke their eggs declined, and their descendants passed on to armored dinosaurs like Triceratops. Relatives of these dinosaurs also thrived, with Pachycephalosaurus being a representative example. Of course, many gigantic creatures did go extinct during this time, but in the south, the largest sauropod in Earth's history, such as Argentinosaurus, appeared, igniting the last flames of their existence. This phenomenon among reptiles also occurred in the skies. Thanks to the continuously increasing oxygen levels, the size of the flying creatures kept growing. A notable example that emerged in the late Cretaceous is Quetzalcoatlus, whose wingspan reached an astonishing ten meters, standing as tall as a giraffe, with a weight of 200 kilograms.

이 시기에 백악기의 모든 비행기들이 다시 땅으로 내려왔습니다. 공룡 중에서는 수각류가 크게 번성했으며, 특히 슈퍼스타인 티라노사우루스가 등장했습니다. 이때 스피노사우루스와 기타 다양한 수각류들도 백악기 대륙에서 활발히 존재했습니다. 물론, 아주 작은 수각류도 있었는데, 흥미로운 점은 약 6800만 년 전 마다가스카르 섬에 이들을 잡아먹는 초거대 양서류가 살았다는 사실입니다. 또한, 백악기 대륙은 나눠져 있었기 때문에 대부분의 공룡들이 격리되어 있었지만, 모두가 그런 것은 아니었습니다. 육지의 연결 덕분에 이 구아노는 유럽에서 아시아와 북아메리카 양쪽으로 진출할 수 있었습니다. 티라노사우루스는 패딩 6구를 통해 아시아로 이동했습니다.

The dinosaurs evolved as they moved to the American continent. A representative piece of evidence for their migration to such different continents is the fossilized remains found in China and far-off places like Canada and the western United States. During that time, dinosaurs became even more diverse than in the Jurassic period. In the skies, pterosaurs thrived, and in the seas, marine reptiles like Mosasaurus enjoyed a prosperity that had not been seen before, at least until 65 million years ago. 

Then, as if by fate, an asteroid suddenly struck the Earth, wiping out countless reptiles across the sky, land, and sea. Dinosaurs were no exception, and most of them disappeared into the annals of history. However, the term most is important here. Not all dinosaurs went extinct; some, like certain theropods, survived.

It is because they survived. Do you remember the pelvic bones I mentioned earlier? There are holes in the pelvic girdle, and when the thigh bone fits into the upper hole, they can all be separated. I said that crocodiles, birds, and dinosaurs are not the same because their pelvic bones are different. Surprisingly, the pelvic bones of birds seem to resemble those of dinosaurs. In other words, birds are dinosaurs, and modern chickens, as well as us and pigeons, are all dinosaurs. This is the current consensus in paleontology. So, if we classify them, dinosaurs are included within reptiles, and birds fall under dinosaurs. However, this leads to the absurd situation where birds are categorized as reptiles. Therefore, recently, birds and reptiles are not classified separately but are grouped together with dinosaurs and referred to as avian reptiles. To reinterpret, birds are theropod dinosaurs that thrived during the Late Cretaceous period.

신생대에도 나름 잘 번성했다는 거죠. 땅에서는 봉포제 같은 거대한 새가 등장해 최상위 포식자의 지위를 누렸으며, 1명이 사라지면 하늘 역시 맹금류들이 독차지하게 됩니다. 이 과정에서 박어캐 착화 플러스에 버금가는 아겐타비스라는 거대한 새가 등장하기도 했죠. 이처럼 오늘날 세라는 공룡은 남북은 물론 지구 전역에서 여전히 번성하고 있습니다. 현재 푸르가 5천 5백여 중 조류가 1만여 중이라는 사실을 떠올리면, 신생대를 과연 포유류의 시대라고 말할 수 있는가는 다시 생각해 볼 문제입니다. 중생대 시절, 공룡들 틈바구니에서 쭈글이처럼 지내며 이들의 목에 깜에 불과했던 포유류. 그러나 먼 훗날 아주 우연한 계기로 지능을 갖춘 이들의 후회가 굉장해 공룡을 먹고 있다는 사실이 정말 아이러니하게 다가오지 않나요? 과학은 세상을 보는 창입니다. 지금까지 과학 드리며 씁니다.

Thank you very much for watching the long video.

중생대 연대기: 大파충류의 시대! (ft.공룡 편향 주의)

과학으로 재미와 지식을 더해 드리는 채널입니다.
한 때는 과학을 좋아했던, 지금도 과학을 좋아하는, 
그리고 앞으로 과학을 좋아할 사람들이 제 채널과 함께였으면 합니다.
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