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Anonymous
Anonymous asked in Science & MathematicsZoology · 1 month ago

Does it mean anything that animals were so big in size millions of years ago compared to now? What could you tell from this?

Dinosaurs, mammoths, giant snakes, giant birds, giant sharks (megalodon), giant insects. They are all a lot smaller now. What is nature or science trying to tell us?

14 Answers

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  • 1 month ago

    There are various reasons why animals were bigger in the past.  If you go back far enough, it's because there was more oxygen in the atmosphere which made it easier for them to respire in the case of insects.  However, nowadays there are only small animals on the whole because of competition with humans and a tendency for us to kill them.  Animals are also more likely to be nocturnal nowadays for the same reason.

  • Herve
    Lv 6
    1 month ago

    it was warmer in the Jurassic and there was a higher concentration of oxygen in the atmosphere, allowing insects and arachnids to grow larger.

  • ?
    Lv 7
    1 month ago

    A blue whale is the largest animal that has ever existed.

    Why the thumbs down? It’s just a fact. 

  • 1 month ago

    What it means is that you are no paleontologist. There were small dinosaurs too.

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  • Anonymous
    1 month ago

    Scientists who study extinctions often ask the question: bad luck or bad genes. So, do large animals have "bad genes" or do they merely have bad luck, if they are more likely to become extinct? .But first, we have to decide whether large animals are in fact more likely to become extinct than small animals. Scientific data shows that many small animals have become extinct too.  For example when the dinosaurs were wiped out, a huge number of birds (almost all of them were small)  were also wiped out.  They were classified as enantiornithine birds, also called opposite birds, because their leg bones fuse in the opposite direction as modern, living birds. Not a single species of living bird is an enantiornithine bird. All of the ancient enantiornithine birds were wiped out, and yet none of them was as big as an ostrich.  Therefore large animals do not seem to be any more likely to become extinct than small animals. Further, lots of small dinosaurs had become extinct during the age of dinosaurs, long before the giant meteor struck. Compsognathus and SInosauropteryx were small dinosaurs but they were extinct for tens of millions of years before the end of the Cretaceous. The ancestors of T. rex and Triceratops were smaller but they were also extinct before the meteor struck.  So, it would appear that small dinosaurs did not necessarily have better genes than large ones.  May be they simply had bad luck. 

    Animals that survived the end of Cretaceous extinction include sea turtles, the largest species of turtles. Also crocodilians survived, and they are not small either. It is true that a whole bunch of large mammals because extinct 13,000 years ago, at the end of the last ice age, but again, it is not because they were large, but because they were large mammals and because they were living in the wrong place at the wrong time. Lots of large mammals, such as the African and Asian elephants, the rhino, the hippo, and the giraffe survived.  In fact, mammals like horses and camels became extinct in North America but they survived in Asia and Africa. 

    If size was not the reason animals became extinct, then we must look for reasons why they did become extinct. For dinosaurs and enantiornithine birds, they became extinct because they were living in the wrong place at the wrong time. 65 million years ago, a giant meteor struck the earth at high speed and it resulted in oven-like temperatures on land,. The heat instantly wiped out 100% of the dinosaurs, enantinorithine birds and all marsupial mammals that were living above ground, but because heat rises, small animals that spent a lot of time below the ground (e,g,  shrews, toads, snakes, lizards, salamanders) survived. Another group of animals survived because they live in or near the water (e..g. turtles, crocodilians, frogs, shorebirds, platypus), because water takes a lot of energy to warm up just a few degrees.  So, size was not a critical factor but location was more important as to who survived and who did not. 

    13,000 years ago, there was an abrupt rise in global temperatures when the last ice age was ended by a small comet hitting North America. Temperatures in North America and nearby Europe increased so much that it killed a lot of large mammals. Because mammals generate their own body heat, a heat wave can kill them if they cannot get rid of the excess body heat quickly enough to avoid heat stroke). Because the temperature increase was more local, large mammals in Africa and Asia that are about the same size as those in North America were able to survive. Elephants are larger than camels and horses, and yet camels and horses that lived in North America were wiped out but elephants that lived in Africa were not. So, it is simply bad luck (being the wrong kind of animals physiologically at the wrong place and at the wrong time) that many animals (regardless of size) were wiped out. As for giant snakes, they are reptiles and reptiles depend on the environment for body heat. When the climate cools, as it did 35 million years ago when Antarctica froze for the very first time, the giant reptiles simply could not stay warm enough because their small body surface to volume ratio makes it hard to gain heat from the environment. The same thing happened at the end of the Jurassic, a large number of large dinosaurs and pterosaurs became extinct when the climate suddenly cooled drastically. The earth warmed up again in the Cretaceous, and large dinosaurs like T. rex and Triceratops evolved near the end of the Cretaceous. Unfortunately for them, bad luck soon wiped them out when the giant meteor struck the earth at the end of the Cretaceous. The meteor impact was so devastating that lots of insects were wiped out too. Insects are anything but large but their small size could not save them because they lived above ground. Some people think that mostly large animals were wiped out at the end of the Cretaceous. They are of course incorrect. Just because museums mostly show large extinct species (because they fascinate the public more) does not mean that large ones are more likely to become extinct. 

  • Anonymous
    1 month ago

    Natural selection.  Those of certain size for a given environment (water/food/temp/defend) tend to live longer and reproduce more.

  • 1 month ago

    There were periods when the Earth had a nice stable climate for millions of years.  We just recently came out of an ice age, and, surprise, the giant ice age fauna died out.

  • 1 month ago

    That the Earth supported a COMPLETELY different environment 100 million years ago.

  • 1 month ago

    You forget about all the worms, tiny nsects, and plankton that DIDN'T leave any fossil record (at very little).

  • 1 month ago

    Either God killed of the giant animals so they wouldn't be a threat to humans, or else humans killed of the giant animals for the fun and challenge of it (love of hunting and killing) or else because humans perceived these animals as a threat to humans.  Maybe they got tired of being on the menu of these giants.

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