History UsefulNotes / Animals

* Predators of similar sized prey: These are the most famous predators, probably. T-Rex attacking a Triceratops, crocodiles dragging large animals into the water, sharks attacking seals. On a smaller scale, squid catching fish, spiders catching larger insects, some flatworms preying on earthworms also fit this category, among many others. While successful catches are most commonly shown, in practice most attempts fail, or few attempts are made. A similar sized prey animal is a ''lot''of food, just imagine a person dealing with about 100-150 ib/75 kg of meat. A person needs about 2-4 pounds of meat a day if that's the only food item, so a carnivorous version of a human could catch something like a deer or large fish roughly every couple weeks, and accounting for inedible parts, still have have enough food for themselves plus feeding a family, or group, or just leaving it for other animals if too difficult to carry, and people need more food for our body size than most other animals. With this much food, lots of missed hunting attempts are perfectly survivable, while prey facing death is under much more pressure to escape.\\

* Predators of smaller prey, or other prey that can't fight back: Think anteaters or chimps eating an insect hive, baleen whales catching schools of fish, starfish attacking clams, birds eating worms, or similar. Obviously, such prey can't physically fight back effectively, but it may still have other defenses such as shells or poison that the predator has to work around. A big challenge is finding enough food, smaller prey can often hide, and requires much total individuals eaten. Colonies or clusters are good targets for predators. Nutritionally, smaller prey and larger prey are similar.\\

* Roughage eaters, or grazers, browsers, leaf eaters, and such: Eaters of general plant material, in other words. Horses and cows eating grass, termites eating wood, leafcutter ants eating leaves....there's a lot of these. By mass, plants are the most abundant animals on earth, so these organisms have plenty of food to eat. However, outside some specific parts, plants are poorly nutritious, and are hard to digest. The main component of plants, cellulose, can't be digested by many animals, in human nutrition it is one of the main dietary fiber chemicals that pass through. Plants can't fight or escape, but can have poisons, and some are physically tough or have spines, needles, or other physical defenses.\\

Earthworms and leeches, among others. Includes a number of deep sea worms, attached to the seafloor or nutrient sources such as sunken whale corpses or hydrothermal vents (including the red and white tubeworm pictures), polychaetes are the main group of these. Annelids grow in segments, each segment repeats some organs with a similar structure, with blood vessels, nerves, a digestive system running through, and similar connecting organs running through; they were once united with arthropods for this reason, but molecular analyses don't support this. Most have little hairlike things off the sides to help them move. The larger than normal ring you see on earthworms is a reproductive section, used to store eggs.\\

Coral, Sea Anemones, Jellyfish, and some others. Cnidarians have an unusual reproduction system, cycling between a fixed in place form and a free floating or swimming form; a few species can in theory live forever by changing between these forms. Cnidarians are radially symmetric, the same going around in a circle, and have a digestive system where food goes in and waste goes out through the same opening, many have some sort of tentacles or arms.\\

These days, with lots of ocean creatures dying off for various reasons (pollution, temperature, acidification, overfishing) jellyfish have been filling in the gaps. Not too economically useful, cause cause further problems if jellyfish eat too much larvae of other creatures, its one of many environmental issues going today. Though many sea turtles eat the things, so will be happy.\\

To figure out how life is related, including animals, scientists look for certain types of similarities, preferably ones that are difficult to change through evolution, or are more or less random and don’t affect survival much. Physical structures might use shell or bone structure if the animal has one, or structures of organs where multiple forms can work well. Genetic studies use mutations, often in noncoding DNa or genes with minor effects, to measure the time between splits and similarity between animals; these assume that mutations are more or less random, and when groups split a different collection of mutations will build up over time.\\

* Animals are Eukaryotes. All earth life is made of cells (viruses are borderline), some cells have lots of mini organs including a nucleus that stores genes, these are Eukaryotes, Eukaryotes also include fungi, algae, plants, many kinds of microbes, but not bacteria, or a group called Archea that has some chemical differences to bacteria.
* Animals are muticellular. Like plants, fungi, and some of the algae, animal bodies are made of lots of cells. These cells specialize, changing shape and other properties to fill specialized roles in the body. Most animals have distinct tissues, which combine similar cells into a larger structure,
* Animals need food: The word for needing to eat other living organisms, or artificial imitations, is heterotroph. Plants and some algae are autrophs, they can use nonliving sources of energy such as the to power themselves. All animals need to eat things is the result.

* Animals need Oxygen: Aerobic is the word. Some organism can break down material with no oxygen to get enough energy. Some Animals can do this for short bursts, like your muscles when sprinting, but a=outside those short periods animals need oxygen for energy.
* Animal cells lack cell walls: Plants, fungi, and many bacteria have a rigid structure surrounding their cells. This provides support in plants and fungi, helping them stand up. Animals lack this, having flexible cells instead. In most groups, this flexibility allows movement.

Earthworms and leeches, among others. Includes a number of deep sea worms, attached to the seafloor or nutrient sources such as sunken whale corpses or hydrothermal vents (including the red and white tubeworm pictures), polychaetes are the main group of these. Annelids grow in segments, each segment repeats some organs with a similar structure, with blood vessels, nerves, a digestive system running through, and similar connecting organs running through. Most have little hairlike things off the sides to help them move. The larger than normal ring you see on earthworms is a reproductive section, used to store eggs.\\

'''Amniotes in general'''\\

Land vertebrates that don’t need to lay eggs in water, or at least had an ancestor with this quality. Some have returned to water, but these are either live birthing in some way, possibly keeping eggs inside the body, or return to land for reproduction. Includes mammals, birds, and rep…actually…\\

No group has been more messed with by phylogenetic classification than “reptiles”. When the original linnean system was created, land vertebrates were divided into furry animals war blooded animals with milk (mammals), feathered warm blooded animals with wings (birds), thin skinned cold blooded animals laying eggs in water (amphibians), and cold blooded animals with drying resistant eggs often with scales, shells, or osteoderms (reptiles). This system still makes sense for vets and zookeepers and people working with modern animals. However, it is not phylogenetic, birds and crocodiles have a common ancestry that lizards don’t, turtles may be associated with this group also. \\

As for higher and lower animals, The evolution link describes opinion well. All animals have had to face a similar set of challenges in living in an environment, finding food, etc., so anything that survives that is well evolved and adapted to its role: Sponges and jellyfish have adapted just as much as cuttlefish, bees, or whales. Complexity involves tradeoffs, more energy, more difficult growth and development are the big ones, so a simpler and less active animal may well work better in certain roles. Vertebrates scientifically are seen as just one group of animals, so invertebrate makes as much sense as nonarthropod or isntmollusc or other-than-cnidarian, though on sites like this one invertebrate gets some use as vertebrates are more more represented in pop culture and other areas. If an animal form has lasted a long time, it means it was very well adapted for an environment, and that said environment has also lasted a long time, so “primitive” animals are those which ended up with a long lasting, useful shape and way of living.\\

A default way of thinking is often that larger animals, more complex animals, and predators “dominate”/”rule over” smaller ones. Mammals are described as scared of dinosaurs, Lions are seen as king, predators are rulers of their environment. At the bottom, we have the [[InvertebrateTropes invertebrates]].\\

As you can guess, especially if you’ve seen UsefulNotes/{{Evolution}}, this is not how scientists think. Individually, a predator or large animal is threatening to smaller ones or prey, but collectively the second groups do just fine, or there would be no prey left. In modern environments with Lions, tigers, and bears, there are plenty of moose, rhinos, gazelles, etc. for the predators to feed on, and smaller animals like raccoons, squirrels, wildcats, lizards, frogs, etc. live out their lives just fine, never mind even smaller things like ants spiders that may well far outnumber the larger ones, possibly outweigh them in total as well. So likely, as those big dinosaurs were walking around in the Jurassic and Cretaceous, mammals were living just fine as well, interacting with smaller creatures, and fossils suggest they started diversifying after an initial bottleneck even before the extinction. And in modern times, those very primitive, simple jellyfish are doing quite well for themselvesl, while bigger, more complex sharks are having problems thanks to various types of ocean pollution.\\

Animals aren’t really trying to achieve anything, just living their lives, but the closest measures to ‘success’ are probably survival, maybe population size. Animals that haven’t changed much over time are called basal/primitive, and suggests they’ve evolved into a design that fits a role very, very well, or their build is very flexible and needs to change little. “Back evolution” is pretty common, flatworm ancestors gained, than lost lots of internal organs, slugs and the octopus/squid group come from ancestors that evolved a shell, ants and ostriches among others had flying ancestors and lost (mostly, for ants) the ability, crocodile ancestors likely had relatively fast metabolisms but these were lost as they became the river creatures we know today, and this writer is thinking of many other examples but the ist is getting long.. If something survives and reproduces, it lasts, whatever properties it may have.\\
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As for Invertebrates, it’s not any more useful a scientific term than, say, nonarthropod or other-than-cnidarian or isn’tmollusc. Vertebrates do have unique characteristics, maybe more than other animal groups depending on how you measure, but most groups are unique in some way and grouping everything else together in a big way doesn’t make much sense. Though since most people interact with vertebrates more obviously than anything else, it remains a useful Trope category\\

Avoiding SmallTaxonomyPools is going to be tricky, there are about a million known animal species, and some estimates go to 5 million or tens of millions, mostly insects. But possibly these groups give you some ideas.