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            I like animals. I’ve always liked animals. If you asked five year old me to name an animal, I would not stop talking for hours. How my parents put up with it - I’ll never know. The point is I love animals so much that I decided to write an essay about animals. Specifically Vertebrates and all the different kinds of vertebrates. Why Vertebrates? Cause certain kinds of invertebrates are really hard to explain.

    First we must ask: What is a vertebrate? Simply put a vertebrate is any animal with a backbone or internal skeletal structure. So animals like arthropods and molluscs do not count. I would explain what those are, but I’m writing about vertebrates.

    Vertebrates are members of a sub-phylum within the phylum Chordata. Vertebrate classes are grouped according to classical taxonomic lines rather than by clade, which is a true representation of each group's real relationship with the other groups of chordates. In other words the ones that built the same are grouped together.

    Next we ask ourselves: How many kinds of vertebrates are there. If you said five, like most people, then you are probably wrong. I say probably because depending on who you ask the number of vertebrate types ranges from 5 to 7. You probably didn’t know this because grade-school science classes like to keep thing simple and basic. Conventional classification has vertebrates grouped into seven classes: Agnatha, Chondrichthyes, Osteichthyes, Amphibia, Reptilia, Aves, and Mammalia.

    The unexpected problem with the numbering starts with the Agnatha, the Chondrichthyes, and the Osteichthyes. Three different fancy ways to say Fish. Fish, as in, the animals distinguishable by being ectothermic and entirely aquatic. (PS ectothermic means cold blooded, as in they can’t regulate their body temperature.) All their bodies are built the same: they’re shaped for swimming, they’re propelled by fins, and they filter oxygen through their gills. Reproduction is the same too, in which the female lays the soft embryonic eggs somewhere, and fertilization goes to the first male who finds it. The difference of these classifications stem from the animal’s bone structure. Which under the subcategories of vertebrates make sense in a way.

     Agnatha are jawless fish with no scales, whose backbone barely covers its entire body. Essentially the closest one to an invertebrate. There aren’t many fish under this classification. In fact there are only two that aren’t extinct. The Lamprey which is a blood sucking parasite that sticks to the bottoms of larger aquatic creatures, and the hagfish, a fish well known for being gross. By that I mean it naturally secretes two gallons of rancid slime to stop predators either by choking them or gluing their mouth shuts. It literally survives by being gross.

    Then there’s the Chondrichthyes which are your sharks and rays. The thing about their skeletons is that they don’t have bones. Technically that’s not true, they have bones just not hard ones. They have a hard rubber like cartilages in the place of the usual bone materials. The only place that isn’t made of cartilage is the animal’s teeth, which is why the teeth are the only thing that remains when the shark decomposes. It is also notable that the Chondrichthyes have scales but very hard and tiny ones, this explains why a shark’s skin is so rough.

    Reaming fish are classified under Osteichthyes, or bony fish. These would be your Salmon, Tuna, clown fish, Marlin, flying fish, archer fish, red herring, snakehead, lung fish, parrot fish, lion fish, catfish, Eel, sturgeon, pufferfish, flounder, grouper, angler fish, elephant fish, and all else that are similar. Simply put it they have a lot of bones - many tiny and sharp bones. So many that it does not matter how the sign says “boneless” you have to double check. Also their scales are big, flat and grow on the derma.

    From Fish we move on to the Amphibia. Amphibians are animals that spend their lives in both land and water. They are born in water with gills and fins, and eventually grow into walking air-breathers. Like fish they are ectothermic, and lay soft embryonic eggs. Unlike fish they don’t have scales but rather very moist skin. Their skin must remain moist to aid in breathing, if they dry up, then they die. Which is why global warming is causing a decrease in the amphibian population. Classic examples of amphibians are frogs, toads, salamanders, newts, axolotl, and everybody’s favourite the caecilian.

    Then there are the Reptilia, which in a way are the opposite of the amphibians. Reptiles only breathe air, and their skins are extremely dry. Note: extremely dry, not slimy. Similar to fish and amphibians, most reptiles are cold-blooded. However unlike amphibians and fish, reptile eggs are covered with a white shell, or amniote eggs. However Reptile egg shells differ from bird and monotreme egg-shells by being leathery and soft, while the latter are hard and brittle. The most distinct thing about reptiles are their scales which are different from fish scales. Reptile scales grow on the epidermis making like hair or fingernails, while fish scales grow on the dermis. The result allows reptiles to shed their hard skin, while fish cannot. A Reptile’s appearance are very interesting to most, as they tend to be closes looking animals to those of dinosaurs. Examples of reptiles include: lizards, crocodiles, tortoises, alligators, turtles, snakes, terrapins, and the famous tuatara.

    Another problem with the number of vertebrates arises when we talk about the Aves, or more commonly known as birds. Birds are very distinguishable animals. They have beaks, they are bipedal, most are endothermic (meaning the can regulate their body temperature), and most can achieve flight. However the bird’s most prominent feature are its feathers. Because no other animal has feathers. Now we are all familiar with the different kinds of birds out there – parrots, hummingbirds, penguins, owls, cranes, birds-of-paradise, cuckoos, toucans, emu, ostriches, parakeets, penguins, cassowaries, sparrows, eagles, woodpeckers, ducks, storks, herons, albatrosses, hornbills, kiwis, potoos, sandpipers, cormorants, fregatidaes, falcons, shoebills, geese, flamingos, roosters, grosues, peacocks, spoonbills, and pelicans – just to name a few, but we may not be as familiar with them as we think. For the reason that according to some birds are actually a sub-category of reptiles. Which sounds crazy but makes sense when you think about it. You see reptiles are mostly defined by their scales, and birds have scales on their feet which have the same properties of reptile skin. So the theory is that feathers are modified scales used to achieve flight, further supporting the idea that dinosaurs might have feathers. Along with that some reptiles are known to have beaks, and both species have three chamber hearts. Of course the theory isn’t perfect, because unlike reptiles birds are warm-blooded and bipedal. Right now there’s just too big a gap between species for taxonomists to draw any permanent conclusions.

    Last but certainly not least of the vertebrate classifications are the mammals, or subphylum Mammalia. Mammals are notable by three characteristics: fur, warm-blood, and mammary glands, as mammals are the only animals that breast feed. There are two kinds’ mammals, the ones that give live birth, and the weird ones that lay eggs AKA monotremes. If you’re surprised by this - don’t be. Like the Agnatha, there are only two of these things: the echidna, and the platypus. One is a spiny anteater, the others an otter with a bill. The point is monotremes are weird. Also, among vertebrates, Mammals are the biggest in terms of numbers. There are so many different kinds of mammals. I mean, who could forget such iconic species such as the Okapi, the caracal, the markhor, the dugong, the mandrill, the slow loris, the pangolin, the Gerenuk, the babirusa, the baiji, the fossa, and everybody’s favorite, the saiga antelope? Do I even need to explain what theses real, and not made-up animal, even are? Of course not.

    So that concludes the topic on vertebrates. Now some of the facts I featured here may not be 100% accurate (like my grammar) but that is because science tends to evolve the more information scientist discover. Certain theories may change for better or for worth. But it is important for us to acknowledge these truth for us to properly progress. Like animals survival relies on adapting to your environment. All information I feature is to the best of my knowledge and research. If I’m factually incorrect in any of these statements then you can write a corrected version in your own essay. If you’re not going to write an essay on vertebrates, then you’re just going to have to trust my word.