Dinosaurs seemed to have generally been so much larger than animals today. Huge dragonflies that dwarf their modern counterparts, turtles 10ft long. What is the mechanism that allowed them to be so large, or conversely makes modern ones smaller? Is it about Oxygen levels, or efficiency, or something else?
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Dinosaurs specifically had spines that “scaled well,” I forget the specific mechanism but it let them get much larger than the theoretically largest mammal.
My unprofessional take is that the big dinosaurs died because they couldn’t adapt as well to the rapidly changing conditions compared to the smaller flying ones during the last mass extinction. Most of the big mammals are gone because we ate all of them or changed their ecosystems. Some of them are still around though, like whales.
Also fossil record goes back a very long time, so it might also be a kind of a selection bias. There might be many giants in the making at the moment but they just haven’t got there yet.
My unprofessional take is that the big dinosaurs died because they couldn’t adapt as well to the rapidly changing conditions compared to the smaller flying ones during the last mass extinction. Most of the big mammals are gone because we ate all of them or changed their ecosystems. Some of them are still around though, like whales.
Also fossil record goes back a very long time, so it might also be a kind of a selection bias. There might be many giants in the making at the moment but they just haven’t got there yet.
Well, to ELI5 this, as you can see from the discussion, we aren’t really sure why. Humongous insects apparently required higher oxygen levels to exist, but not all gigantic land life happened at the same time as giant insects, so that cannot be the only reason.
Some have argued that the one global continent played a role by allowing ready contact for all and thus favoring size as a defensive response (leading to increase in size of predators in a runaway arms race). Some argue that lush conditions (location of land in equatorial regions, difference CO2 levels, and so forth) led to vegetation running wild and allowing large herbivores (and thus large predators) to exist. Climate would be a key factor here. However, even polar regions at the time had some pretty large animals so not clear this idea works as a cause either.
It might even be something as relatively simple as random chance. Once things started to grow big (for no real reason at all), the process snowballed and loads of things became big. Then the asteroid/comet thing hit and we went down a different path that did not result in huge being favored.
What do we actually, truly know? Big animals need more food than small ones. Thus, to have big numbers of large animals requires lots of vegetation for a given range. This suggests that plant availability and size is a major factor. Why plants would be huge, fast growing, and in massive amounts so large animals could survive in large numbers? Climate seems a good candidate to me.
Well, to ELI5 this, as you can see from the discussion, we aren’t really sure why. Humongous insects apparently required higher oxygen levels to exist, but not all gigantic land life happened at the same time as giant insects, so that cannot be the only reason.
Some have argued that the one global continent played a role by allowing ready contact for all and thus favoring size as a defensive response (leading to increase in size of predators in a runaway arms race). Some argue that lush conditions (location of land in equatorial regions, difference CO2 levels, and so forth) led to vegetation running wild and allowing large herbivores (and thus large predators) to exist. Climate would be a key factor here. However, even polar regions at the time had some pretty large animals so not clear this idea works as a cause either.
It might even be something as relatively simple as random chance. Once things started to grow big (for no real reason at all), the process snowballed and loads of things became big. Then the asteroid/comet thing hit and we went down a different path that did not result in huge being favored.
What do we actually, truly know? Big animals need more food than small ones. Thus, to have big numbers of large animals requires lots of vegetation for a given range. This suggests that plant availability and size is a major factor. Why plants would be huge, fast growing, and in massive amounts so large animals could survive in large numbers? Climate seems a good candidate to me.
Larger animals generally require exponentially more calories. A large group of huge animals will decimate all food sources in an area. This results in a few evolutionary behavioral changes.
Larger animals will generally have fewer offspring and will typically be more solitary(or at least maintain smaller groups). The downside of these changes is that they will be more vulnerable to predation, and have fewer breeding options. Losing a single female in a small group will have a greater negative impact than a larger group.
Smaller animals have a competitive advantage in this regard as they can maintain larger populations by having more offspring, and be less concerned with decimating an areas food sources. Safety in numbers, and increased breeding opportunities.
So, here’s the thing. Even just a few tens of thousands years ago, there were still a lot of megafauna in a bunch of places (mammoths, massive ground sloths, big armadillo-like glyptodons, etc.). They largely went away because they were fantastic and (relatively) easy sources of food and resources for us humans, who hunted them to extinction.
If you graph the areas that still contain big animals, the areas that lost the highest percentages of their big animals are all the furthest away from Africa by land. That’s because creatures in Africa and nearby areas evolved with humans, so they had some defense, whereas humans entering the Americas were entering a place that had never seen an apex predator like us before.
If whales hadn’t been intelligent enough to evolve new defense strategies when commercial whaling became a thing, they’d be extinct as well.
Well, to ELI5 this, as you can see from the discussion, we aren’t really sure why. Humongous insects apparently required higher oxygen levels to exist, but not all gigantic land life happened at the same time as giant insects, so that cannot be the only reason.
Some have argued that the one global continent played a role by allowing ready contact for all and thus favoring size as a defensive response (leading to increase in size of predators in a runaway arms race). Some argue that lush conditions (location of land in equatorial regions, difference CO2 levels, and so forth) led to vegetation running wild and allowing large herbivores (and thus large predators) to exist. Climate would be a key factor here. However, even polar regions at the time had some pretty large animals so not clear this idea works as a cause either.
It might even be something as relatively simple as random chance. Once things started to grow big (for no real reason at all), the process snowballed and loads of things became big. Then the asteroid/comet thing hit and we went down a different path that did not result in huge being favored.
What do we actually, truly know? Big animals need more food than small ones. Thus, to have big numbers of large animals requires lots of vegetation for a given range. This suggests that plant availability and size is a major factor. Why plants would be huge, fast growing, and in massive amounts so large animals could survive in large numbers? Climate seems a good candidate to me.
Larger animals generally require exponentially more calories. A large group of huge animals will decimate all food sources in an area. This results in a few evolutionary behavioral changes.
Larger animals will generally have fewer offspring and will typically be more solitary(or at least maintain smaller groups). The downside of these changes is that they will be more vulnerable to predation, and have fewer breeding options. Losing a single female in a small group will have a greater negative impact than a larger group.
Smaller animals have a competitive advantage in this regard as they can maintain larger populations by having more offspring, and be less concerned with decimating an areas food sources. Safety in numbers, and increased breeding opportunities.
Larger animals generally require exponentially more calories. A large group of huge animals will decimate all food sources in an area. This results in a few evolutionary behavioral changes.
Larger animals will generally have fewer offspring and will typically be more solitary(or at least maintain smaller groups). The downside of these changes is that they will be more vulnerable to predation, and have fewer breeding options. Losing a single female in a small group will have a greater negative impact than a larger group.
Smaller animals have a competitive advantage in this regard as they can maintain larger populations by having more offspring, and be less concerned with decimating an areas food sources. Safety in numbers, and increased breeding opportunities.
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