If we look at the animal world now, you may feel that many mammals are not doing well, especially the large mammals, many of which are teetering on the edge of extinction. But the Cenozoic is undoubtedly the age of mammals, and modern mammals dominate every ecological niche on Earth.
The reason why we think they are not doing well is because of the existence of the terrifying erect ape, Homo sapiens. The emergence of Homo sapiens has caught many creatures by surprise, and has the most significant impact on those who originally occupied a dominant position.
However, if we pull back the time to the Mesozoic Era 65 million years ago, mammals were not so strong. Then dinosaurs were the absolute dominant ones on the earth's land.
Dinosaurs began to show "dominance" in size at the end of the Triassic (the first era of the Mesozoic Era), and large carnivorous dinosaurs and large herbivorous dinosaurs began to appear.
However, for whatever reason, this group never really evolved to live fully in the water, not even penguins among the modern birds (or modern dinosaurs) that are now controversial in dinosaur-bird classification.
Perhaps it was because there were already more ferocious reptiles in the ocean at that time that they had no chance, or perhaps there were structural limitations in their bodies that prevented them from maintaining a good balance in the water.
In short, dinosaurs only dominated the earth's land and did not have oceans. Many people may have misunderstandings about this.
However, everything changed 65 million years ago, at the end of the Mesozoic Era. At that time, periodic changes in the earth's climate and the impact of asteroids brought this animal group that had roamed the land for 150 million years to an end. All non-avian dinosaurs became extinct, but we can still know from the fossil record how prosperous this group was in the past.
There is a very interesting topic on the Internet: If modern mammals traveled back to the Mesozoic era, could they compete with the dinosaurs of that time?
It will indeed be very interesting for a group of new generation "overlords" to compete with a group of Mesozoic era "overlords", but here we must first ban sapiens and deadly pathogens.
Because both dinosaurs and modern mammals can only adapt to pathogens that are closely related to themselves, both may be directly destroyed by the other party's pathogens;
The same goes for Homo sapiens. Homo sapiens is a dimensionality-reducing blow to the animals on earth. If Homo sapiens also traveled back in time, it would probably only domesticate some more dinosaur species.
Well, now we have dinosaurs and mammals competing in the Mesozoic without Homo sapiens and each other's deadly pathogens.
My answer is that mammals will win and will gradually become dominant over time. Dinosaurs may not necessarily become completely extinct, but their size will certainly be greatly reduced.
(Of course this is an open topic and my answer may not be exhaustive.)
My thinking on this topic is mainly based on two points:
One point is that mammals have already shown diversity in the age of dinosaurs. The dinosaurs at that time were already somewhat unable to suppress the rise of low-matching mammals. At least 18 of the 28 orders of modern mammals had already appeared in the Mesozoic Era and were already preying on dinosaurs. This was caused by the evolutionary advantages of mammals themselves;
Picture: Reptiles prey on dinosaurs larger than themselves
Another point is that modern mammals have acquired brain capacity (skull changes), teeth, claws, reproductive mechanisms, vision, hearing, smell, etc. through evolution. These are all very complete. These allow them to have an ultra-wide range of survival methods, so the threat from dinosaurs is not too great. However, mammals pose a greater threat to dinosaurs of the same size. This can be seen from the fact that modern predatory mammals can often prey on animals much larger than themselves.
However, there is one group of mammals that will definitely not survive the Mesozoic Era, and that is herbivores, especially medium and large herbivores. If they return to the Mesozoic Era, they will quickly become extinct.
This is because herbivores rely on special intestinal symbiotic microorganisms, and this digestion method allows them to eat only certain grasses.
In addition to being the age of mammals, the Cenozoic Era is also the age of angiosperms. In some respects, it was the angiosperms—more precisely, the grasses—that made mammals so prosperous in the Cenozoic Era.
Angiosperms only appeared in the middle and late Cretaceous Period (the last period of the Mesozoic Era). In the Mesozoic Era (Early Cretaceous Period, Jurassic Period and Triassic Period) 120 million years ago, the forest trees were composed of ferns and cycads, and those low plant groups were ferns, algae or fungal symbionts (as shown below).
When I was a child, I lived in a rural area. There were many fern "grasses" like the one pictured above on the mountains. People at home liked to scrape them over to make fires, but no mammals liked to eat this plant.
If modern herbivorous mammals went back to the Jurassic of the Mesozoic Era or before, then they would have no chance, and it would be difficult to even find food.
On the other hand, modern medium and large herbivorous mammals usually use body size to reduce the risk of predation, but this will have no effect in the face of large dinosaurs.
Comparison of Spinosaurus and humans, AI translation
The largest known predatory dinosaur is Spinosaurus, which may be related to their hunting in the water. It is believed that this carnivorous dinosaur can grow to 18 meters and 22 tons. It is estimated that wild boars can eat one prey, and elephants may only eat two or three.
Comparison of Tyrannosaurus rex and humans, AI translation
More famous than Spinosaurus is naturally Tyrannosaurus Rex. They can grow up to 12 meters long and weigh up to 10 tons, which is a little larger than the African statue, the largest land animal on earth today.
Moreover, Tyrannosaurus rex is considered to be the animal with the strongest bite force in the history of earth's land. They are different from many carnivores. It can be known from their teeth that they can crush bones. The rough fur of modern mammals is not worth mentioning.
Generally speaking, modern medium and large herbivorous mammals will basically become extinct quickly if they return to any period in the Mesozoic Era.
Of course, the predatory mammals that crossed over were adapted to herbivorous mammals, and the disappearance of these herbivorous mammals would be a big blow to the predatory mammals, but they should be able to adjust quickly, adapting to new prey just like powerful invasive species.
You may ask, why do they become a powerful invasive species in a completely different new environment?
This is about talking about the advantages and disadvantages of dinosaurs and the advantages and disadvantages of mammals.
Many people think of the advantages of dinosaurs: they had a more efficient respiratory system than mammals - an original air sac structure, which is one of the reasons why they were so huge.
A better breathing method would naturally make it easier for dinosaurs to win in the chase.
However, the atmospheric oxygen content of the Mesozoic Era was higher than that of the Cenozoic Era. In other words, if modern mammals returned to the Mesozoic Era, they would have undergone "plateau training", so the breathing advantage of dinosaurs did not exist.
In this contest, the biggest advantages of dinosaurs are their "home game" and their huge size.
However, I have to mention here again that not the entire Mesozoic Era is the age of dinosaurs. To be precise, the Mesozoic Era is the age of reptiles.
Dinosaurs appeared 235 million years ago, in the middle of the Triassic period. The earliest dinosaurs were just a group of "cute little animals" - not much bigger than your corgis and without any sense of dominance.
Comparison between Metasuchus and humans Dr.JeffMartz/NPS
In the early and middle Triassic, the land was dominated by ancient relatives of modern crocodiles.
Crocodiles at that time were very diverse, including carnivorous crocodiles with two legs that chased large prey, "armadillo-like" crocodiles covered in bone shields and spikes, and fern-devouring crocodiles with beaks that were almost like ostriches.
The first batch of large herbivorous dinosaurs evolved at the end of the Triassic Period (about 214 million years ago). The main reason why dinosaurs changed in size was because of climate change, which helped them clear out those large crocodiles.
At the end of the Triassic, strong volcanic eruptions in the central part of Pangea changed the global climate, causing the earth to swing between heat and cold. Cold-blooded crocodiles were unable to adapt to such an environment and became extinct one after another.
Mark Garlick—SciencePhotoLibrary/GettyImages
Dinosaurs may have survived this climate change with their warm-blooded metabolism and insulating feathers and quickly replaced crocodiles.
If warm blood and feathers were the advantages of dinosaurs in the Triassic, then modern mammals also have these two advantages. Therefore, if modern predatory mammals competed with dinosaurs in the Triassic, mammals would have a size advantage.
In fact, the biggest advantage of predatory mammals is not their size, but they are heavier, smarter, and have teeth.
The bone density of mammals is higher than that of dinosaurs. This advantage is that they are not easily knocked down, but are easier to knock down prey. Longer canine teeth can kill prey quickly, and being smarter allows them to cooperate in hunting and ambush prey better. This is why mammals can hunt prey that is much larger than themselves.
Dinosaurs are lighter, and they are more adapted to hunting prey smaller than themselves. We mentioned earlier that dinosaurs could not adapt to aquatic life because they were too light. This makes sense. If you throw an irregular, lighter toy into the water, you will find that it is difficult to maintain a proper balance.
In general, predatory mammals also have an advantage in hunting, so the Triassic dinosaurs didn't have any chance of winning.
By the Jurassic and Cretaceous periods, dinosaurs had become dominant on land. If predatory mammals competed with dinosaurs at this time, they would indeed have a huge disadvantage in size.
However, as long as they win among the same size, they may also collapse the original dinosaur ecosystem from bottom to top. Of course, modern mammals will definitely win over dinosaurs of the same size.
Therefore, my answer is that no matter when modern mammals travel to the Mesozoic Era, dinosaurs have no chance of winning.
at last
There is actually a lot more that can be said about this topic.
For example, small carnivorous mammals and omnivorous mammals, this group can definitely mix well in the dinosaur era, and will cause serious persecution to dinosaurs, because all dinosaurs lay eggs, think about the persecution of a weasel to chickens.
However, this group of mammals already existed during the age of dinosaurs, and they are estimated to be more easily replaced by modern mammals than dinosaurs.
There is also a group of marine mammals. If this group goes back to the Mesozoic Era, marine reptiles will not be able to compete with it. The length of this article is limited. I will continue to expand this topic if I have the opportunity in the future.