I was thinking that while I have said a few things that I am not in previous posts, I have really only scratched the surface. There are an awful lot of things I’m not and I can’t go through them species by species or even genus by genus or I will never cover them all. Therefore I have decided to make this post to explain in broad strokes all of the things I am not.
Living vs. non-living
Let’s start simple. If all things can be divided into living or non-living (which is harder than you might think), I definitely fall on the living side. I am not a rock or a car or a planet or a liquid or a volcano or a galaxy. All of those things are not alive, even though some of them move. And I’m not sure anyone knows whether viruses and things like prions should fall in the living or non-living category.
Capybaras are Living!
Major types of living things (or Kingdoms)
Back in the day, all life used to be divided into two kingdoms, animals and plants. Things aren’t so simple anymore. Now the number of kingdoms is disputed, there could be five or six or even more.
Here are the six kingdoms as proposed by Cavalier-Smith in 2004.
I could go into why I am not in one of the top five groups but instead let’s just say why I am in the sixth group, the animals.
Animal cells do not have cell walls like plants or fungi do. Our cells are surrounded by membranes that hold their contents in.
Some animals are only one cell and some animals are lots of cells. Being lots of cells, or multicellular, isn’t enough to make a living thing an animals. Lots of plants and fungi are also multicellular. My favorite plants, grasses, have lots of cells.
Animals are heterotrophs, that’s just a fancy word that means that animals have to eat other living things; animals cannot make their food out of non-living stuff like sunlight, air, water, soil, sulfur or whatnot. I eat grass, which is in the Plants group, and that is part of what makes me an animal.
Capybaras are Animals!
Types of Animals (or Animal Phyla)
A phylum (or phyla when it is plural), is a big group of living things that all share some characteristics that are pretty fundamental to their way of life. For example, the sponges are in the phylum Porifera and they all share the characteristic of not have much internal structure or cohesion. You can put a sponge though a sieve so that each cell is separated from ever other and it can come back together and be one sponge. Capybaras certainly can’t do that.
Another phylum that’s really interesting is Radiata. All of the animals in radiata are built on circular plans. A good example of that is starfish. You can draw more than one line through a starfish and as long as it goes through the center, the two halves are identical. You can’t do that to a capybara.
Another way animals can be organized is bilaterally. That means that there is only one line that you can draw down the middle of them and have the two sides be about the same. Most animals are bilaterally symmetrical including humans and capybaras.
Here’s a chart that I stole from wikipedia showing the different groups of animals.
You can see that there are lots of types but, and this is an amazing fact, almost all animals are arthopods! Like capybaras, arthopods are bilaterally symmetrical but they are different from us in lots of other ways. For example, they have their skeleton on the outside of their bodies! There are three types of arthopods in the image at the top of this post, a caterpillar, a lady bug and some aphids. Those are all insects! In fact, most arthopods are insects and that means that most animals are insects. It’s kind of weird to think about.
Even though insects are so plentiful, I am glad I am not an insect. They don’t get very big, partly because they don’t have any lungs and just breath through holes in their skin. That sounds kind-of creepy.
Mollusks, animals in the phylum Mullusca, are some of my favorites. Like capybaras, they are bilaterally symmetrical but they don’t even have skeletons! Lots of them, like clams and snails, have shells but some mollusks don’t even have that.
Cuttlefish, like the one that my owner saw at the Houston Museum of Natural History, have a thing called a cuttlebone that helps keep their body rigid but octopus and squid don’t have anything and they can fit even very large bodies into tiny holes. I might like to be able to do that. And see how this one has a purple rim? That is because it can turn itself into a lamp! Can you imagine how fun it would be if capybaras could do that?
Well, it turns out that capybaras belong in the group Chordata because we have spinal cords. That is a bundle of nerves that from our brains all the way down our backs. Humans are also chordates. So are dogs, horses, cats, goldfish, eels, birds and lots of other commonly known animals.
Capybaras are Chordates!
I think I am going to have to stop now and finish this in another post. I guess there are two many types of things that I am not to explain it all at one time, even when I try to make just very broad distinctions. I hope you are finding this interesting. Leave me a comment to let me know if you want to hear more.
To sum up what we’ve covered so far, capybaras are: