History SoYouWantTo / CreateBelievableAliens

20th Nov '14 2:51:31 PM tracer
Is there an issue? Send a Message
Oops — therapsids are a subgroup of reptiles. Mammals are a subgroup of therapsids.
But pretty soon, one sub-group of the mammals, called the therapsids, hit upon another strategy for thermal regulation. They produced extra heat ''inside their own bodies'' via chemical reactions. The glucose respiration their cells relied upon for energy also gave off some heat, so by "burning" extra glucose they could keep themselves warm even when the environment got cold. We call it ''endothermy'' (not to be confused with an endothermic chemical reaction, which is a reaction that absorbs heat rather than giving it off; animal endothermy requires exothermic chemical reactions). Endothermy allowed them to keep active on cold nights, when other animals could barely move, and to survive in colder climates.
to:
But pretty soon, one sub-group of the mammals, reptiles, called the therapsids, hit upon another strategy for thermal regulation. They produced extra heat ''inside their own bodies'' via chemical reactions. The glucose respiration their cells relied upon for energy also gave off some heat, so by "burning" extra glucose they could keep themselves warm even when the environment got cold. We call it ''endothermy'' (not to be confused with an endothermic chemical reaction, which is a reaction that absorbs heat rather than giving it off; animal endothermy requires exothermic chemical reactions). Endothermy allowed them to keep active on cold nights, when other animals could barely move, and to survive in colder climates.
19th Nov '14 7:13:31 PM tracer
Is there an issue? Send a Message
Added DiffLines:
By the end of the Paleozoic era, therapsids had diversified until they filled nearly the same ecological niches as the mammals of today. There were great grazing herds that roamed the grasslands, there were predators who fed on the grazing herds, there were tree-dwelling arboreals, there were coastal swimmers; nearly every niche filled by a mammal today had an analog among the therapsids. An alien visitor would find little difference between Earth at the end of the paleozoic and Earth in the modern era. And then, disaster struck.
19th Nov '14 7:01:48 PM tracer
Is there an issue? Send a Message
Eventually, reptiles emerged, who produced hard-shelled eggs that could be safely stowed away on land. They out-competed the amphibians in much the same way that the amphibians had out-competed the insects. But like the insects, the fish, and the amphibians -- in fact, like every other organism living on Earth at this point in history -- reptiles were cold-blooded. Their body temperature depended entirely on the temperature of their surroundings.
to:
Eventually, reptiles emerged, who produced hard-shelled eggs that could be safely stowed away on land. They out-competed the amphibians in much the same way that the amphibians had out-competed the insects. But like the insects, the fish, and the amphibians -- in fact, like every other organism living on Earth at this point in history -- reptiles were cold-blooded. Their body temperature depended entirely on the temperature of their surroundings. surroundings. Since a lot of biological processes depend on chemical reactions that only happen within a certain narrow range of temperatures, they had to evolve all sorts of tricks to keep warm. Some got large enough that they wouldn't lose heat very quickly in cold weather. Some evolved enormous sails on their backs which they could turn toward the sun for gathering heat, and then fold up at night to prevent heat loss. But pretty soon, one sub-group of the mammals, called the therapsids, hit upon another strategy for thermal regulation. They produced extra heat ''inside their own bodies'' via chemical reactions. The glucose respiration their cells relied upon for energy also gave off some heat, so by "burning" extra glucose they could keep themselves warm even when the environment got cold. We call it ''endothermy'' (not to be confused with an endothermic chemical reaction, which is a reaction that absorbs heat rather than giving it off; animal endothermy requires exothermic chemical reactions). Endothermy allowed them to keep active on cold nights, when other animals could barely move, and to survive in colder climates. Warm bloodedness came at a price, however. To produce all that chemical heat, you needed much more glucose than you'd use otherwise. Over 75% of the glucose consumed by a human's metabolism goes solely into producing heat, for example. That means needing a ''lot'' more food. A warm blooded creature has to eat, and eat, and eat, nearly all the time. The 3 meals a day we humans take for granted as normal is in stark contrast to the one meal every week, or every month, that a reptile needs. As a consequence, a much smaller percentage of warm blooded creates could afford to be carnivores. While 1 in 5 cold-blooded fish or reptiles is carnivorous, only about 1 in 100 warm-blooded creatures are carnivorous, because a warm-blooded carnivore has to kill and eat a lot more prey than a cold-blooded one does. (Kinda backwards from the notion of the "cold-blooded killer," isn't it?) On an alien world, there's no guarantee that endothermy would have evolved as the dominant strategy for thermal regulation. Sails, fins, or gigantothermy could have taken over. So could the strategy of the Galapagos diving iguanas, who sunbathe on rocks and then immerse themselves in the cold oceans for a short time to make use of their stored heat. Other strategies that never appeared on Earth are also possible.
19th Nov '14 6:31:54 PM tracer
Is there an issue? Send a Message
Added DiffLines:
Eventually, reptiles emerged, who produced hard-shelled eggs that could be safely stowed away on land. They out-competed the amphibians in much the same way that the amphibians had out-competed the insects. But like the insects, the fish, and the amphibians -- in fact, like every other organism living on Earth at this point in history -- reptiles were cold-blooded. Their body temperature depended entirely on the temperature of their surroundings.
19th Nov '14 6:12:08 PM tracer
Is there an issue? Send a Message
Much is made about the "first animals to leave the oceans", with most folks usually pointing to either lizard-like amphibians that used their arms for brachiation under water, or lungfish that could pull themselves across land for short distances. The people that think these were the first animals to leave the oceans are ''hopelessly'' vertebrate-centric in their thinking. The first land animals weren't fish. They weren't amphibians. They were '''insects.''' Insects evolved the ability to breathe air and survive on land 40 million years before vertebrates did. With no vertebrate predators to threaten them, some of these insects grew to nearly 3 feet long. They couldn't get any bigger than this, though; without an endoskeleton, all the squishy guts inside their bodies have to be anchored to the inside of their chitinous exoskeletons. The bigger the insect, the more those guts will inevitably "sag" toward the bottom of their body cavity, and the thicker (relative to the overall length of the insect) the exoskeleton needs to be. It's the insect version of the SquareCubeLaw, and it piles up a lot quicker than the square-cube law does for us bones-on-the-inside vertebrates.
to:
Much is made about the "first animals to leave the oceans", with most folks usually pointing to either lizard-like amphibians that used their arms for brachiation under water, or lungfish that could pull themselves across land for short distances. The people that think these were the first animals to leave the oceans are ''hopelessly'' vertebrate-centric in their thinking. The first land animals weren't fish. They weren't amphibians. They were '''insects.''' Insects evolved the ability to breathe air and survive on land 40 million years before vertebrates did. With no vertebrate predators to threaten them, some of these insects grew to nearly 3 feet long. They couldn't get any bigger than this, though; without an endoskeleton, all the squishy guts inside their bodies have to be anchored to the inside of their chitinous exoskeletons. The bigger the insect, the more those guts will inevitably "sag" toward the bottom of their body cavity, and the thicker (relative to the overall length of the insect) the exoskeleton needs to be. It's Compoounding this problem was the need to extract oxygen from the air. Insects have neither lungs nor oxygen-carrying blood; they have to draw air in from ''spiracle'' valves on their skin, and carry it directly to the tissues through networks of tiny tubes. This means no point inside an insect's body can be more than a couple of centimeters from its exterior.[[note]]The earth's atmosphere also had a higher partial pressure of oxygen in the Paleozoic than it does today. A three-foot-long insect would probably asphyxiate in today's air.[[/note]] These twin problems form the insect version of the SquareCubeLaw, and it piles up a lot quicker than the square-cube law does for us bones-on-the-inside vertebrates.
19th Nov '14 6:00:01 PM tracer
Is there an issue? Send a Message
Eventually, some of these chordates found a new niche to inhabit, that no animals had inhabited before: The brackish, less-salty-than-the-ocean waters at the mouths of river deltas. They of course had to evolve a kidney to expel all the excess water they took on in these low-salinity environments, but they also faced another problem. Sodium salts aren't the only salts dissovled in ocean water. There are a lot of minerals in sea water, including calcium, and calcium had long ago become a mineral that much of their biology depended on. So, now, they needed a way to ''store'' calcium inside their bodies, for those times when the brackish waters didn't have enough calcium dissolved in them for their daily needs. Big lumps of calcium have the approximate consistancy of rocks, so they needed a place in their bodies to store these "calcium rocks" which wouldn't interfere with their breathing, eating, mobility, etc.. What better place to store them than ''hanging in little bundles off of their notochords!'' This is how the notochord gradually became a true ''backbone''. Eventually these lumps of calcium started getting formed into deliberate, interlocking shapes which could flex between the segments without wasting space or pinching the notochord (now called the spinal cord) they were wrapped around.
to:
Eventually, some of these chordates found a new niche to inhabit, that no animals had inhabited before: The brackish, less-salty-than-the-ocean waters at the mouths of river deltas. They of course had to evolve a kidney to expel all the excess water they took on in these low-salinity environments, but they also faced another problem. Sodium salts aren't the only salts dissovled in ocean water. There are a lot of minerals in sea water, including calcium, and calcium had long ago become a mineral that much of their biology depended on. So, now, they needed a way to ''store'' calcium inside their bodies, for those times when the brackish waters didn't have enough calcium dissolved in them for their daily needs. Big lumps of calcium have the approximate consistancy consistency of rocks, so they needed a place in their bodies to store these "calcium rocks" which wouldn't interfere with their breathing, eating, mobility, etc.. What better place to store them than ''hanging in little bundles off of their notochords!'' This is how the notochord gradually became a true ''backbone''. Eventually these lumps of calcium started getting formed into deliberate, interlocking shapes which could flex between the segments without wasting space or pinching the notochord (now called the spinal cord) they were wrapped around.
19th Nov '14 5:23:14 PM tracer
Is there an issue? Send a Message
Fixed a typo
As mentioned above, purple bacteria eventually moved in to the interiors of eukaryotes and entered into a symbiotic relationship with them, eventually evolving into mitochondria. All modern eukaryotes contain mitochondria. However, purple bacteria weren't the only organisms to do this. The same cyanobacteria that caused the Oxygen Holocaust ''also'' found a home in some -- but not all -- eukaryotes, after the point at which multicellularity had emerged, and eventually evolved into enosymbiontic organelles called ''chloroplasts''. The eukaryotes lucky enough to harbor these chloroplasts could now use both photosynthesis (which generates oxygen) and respiration (which consumes oxygen), thereby never having to get up off the couch. These eukaryotes eventually evolved rigid cell walls -- very different in chemical composition from bacterial cell walls -- and became the Algae and the Plants.
to:
As mentioned above, purple bacteria eventually moved in to the interiors of eukaryotes and entered into a symbiotic relationship with them, eventually evolving into mitochondria. All modern eukaryotes contain mitochondria. However, purple bacteria weren't the only organisms to do this. The same cyanobacteria that caused the Oxygen Holocaust ''also'' found a home in some -- but not all -- eukaryotes, after the point at which multicellularity had emerged, and eventually evolved into enosymbiontic endosymbiontic organelles called ''chloroplasts''. The eukaryotes lucky enough to harbor these chloroplasts could now use both photosynthesis (which generates oxygen) and respiration (which consumes oxygen), thereby never having to get up off the couch. These eukaryotes eventually evolved rigid cell walls -- very different in chemical composition from bacterial cell walls -- and became the Algae and the Plants.
19th Aug '13 2:04:40 AM Nohbody
Is there an issue? Send a Message
Perhaps a species of herbivores, such as LarryNiven's Puppeteers, would be motivated to see what's over the horizon by a simple desire to ensure the safety of the herd -- if they discovered a leopard, they could prepare for it and thus decrease their odds of getting eaten. Or perhaps the grass that the Puppeteers graze on (or whatever ground-covering organism passes for grass on their planet) only grows in random patches that last a few weeks, so they have to find the next grass patch or starve to death.
to:
Perhaps a species of herbivores, such as LarryNiven's Creator/LarryNiven's Puppeteers, would be motivated to see what's over the horizon by a simple desire to ensure the safety of the herd -- if they discovered a leopard, they could prepare for it and thus decrease their odds of getting eaten. Or perhaps the grass that the Puppeteers graze on (or whatever ground-covering organism passes for grass on their planet) only grows in random patches that last a few weeks, so they have to find the next grass patch or starve to death.
17th Apr '13 9:24:22 AM tracer
Is there an issue? Send a Message
Added DiffLines:
Nevertheless, when amphibians ''did'' move onto the land, they completely wiped out all the giant insects. A giant, thick exoskeleton full of sagging guts just could not compete with an endoskeleton. Today, the largest surviving insects are creatures like the rhinoceros beetle, less than half a foot long. These early land vertebrates still had to lay their eggs in the water; the evolution of the hard-shelled egg that could survive out in the open air came later. Many "WhatIf" scenarios come to mind when imagining the timing of the moves onto land. What if the plants and insects had ''not'' colonized the land before the vertebrates did? Then the vertebrates would still have needed to forage for food in the water. The ability to walk on land would have been a way to avoid predators rather than a way to find new food sources, and would thus have evolved in the smaller prey animals first. While the oceans and waterways would have been be filled with the full gamut of vertebrate sizes, the land would have been home to only the smaller critters.
17th Apr '13 9:15:09 AM tracer
Is there an issue? Send a Message
Added DiffLines:
Incidentally, while insects were the first land animals, they weren't the first land eukaryotes. Plants beat the insects onto land by 75 million years.
This list shows the last 10 events of 37. Show all.