Vertebrates: Origin, Characteristics & Diversity

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  • 0:02 Evolution of Vertebrates
  • 1:36 Non-Vertebrate Chordates
  • 2:36 Jawed Vertebrates
  • 3:21 Tetrapods & Amniotes
  • 5:11 Lesson Summary
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Lesson Transcript
Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

Vertebrates are diverse and widespread across Earth, but this was not always the case. In this lesson you'll learn about the origins and evolution of these animals, as well as explore their vast diversity.

Evolution of Vertebrates

Believe it or not, because of certain characteristics, you are related not only to other mammals like dogs, zebras and rabbits, but you are also related to things like fish, snakes and salamanders!

In fact, all animals that have a backbone are vertebrates. This means that all of the animals just mentioned fall into the same category as humans because they all have a backbone made of vertebrae, which is where the term 'vertebrate' comes from.

As you can see, the vertebrates make up a diverse group of animals representing many different shapes, sizes, colors, habitats and ecosystems. But clearly we are all different from each other; otherwise you wouldn't be able to tell your sister or brother apart from a zebra or a fish. However, there are some similarities that allow us to see how we are all related, even if it doesn't look like it on the outside.

All vertebrates are chordates, which is a group of animals that have a dorsal, hollow nerve cord, a notochord, pharyngeal slits and a post-anal tail. For some chordates, like humans, these features are present only at certain life stages. You can double check, but I bet your post-anal tail disappeared before you were even born. But you did have one during embryonic development, as well as the other features that make chordates unique from other animals.

All vertebrates are also craniates. These animals have the four chordate features, but they also have a head, so they're known as chordates with heads. The word 'cranium' means skull, so this name is quite fitting for us headed chordates!

Non-Vertebrate Chordates

Before we go any further, it's important to note that while all vertebrates are chordates and craniates, the reverse is not always true. There are two animals on Earth that are chordates but lack both a head and a backbone.

One is the tunicate, which is an animal that lives in the ocean and looks like a spouting pouch. The other is a lancelet, which looks like a knife blade floating through the water. While the lancelet does have a small 'brain' at the end of its nerve cord, neither of these animals has a head but are still chordates because they possess those four unique features of the group.

There are also animals that are craniates (and therefore chordates) but not vertebrates. The hagfishes fall into this category. These interesting animals look like an eel but are quite different. They have a head but no backbone and no jaw. Lampreys, which look similar to the hagfishes, also lack a jaw but do have a rudimentary backbone, so they are considered vertebrates.

Jawed Vertebrates

Developing a jaw was a big step for vertebrates because it allowed them to utilize a new variety of feeding opportunities. Can you imagine trying to eat your regular diet without a jaw? I bet it would be pretty difficult! Having a jaw makes a world of difference when it comes to food. Of course, having a jaw is dependent upon having a head, so all of the jawed vertebrates are also craniates.

After jaws developed, so did lungs and rayed and lobed appendages. Our modern fish friends are ray-finned, whereas things like lungfish are lobe-finned. The lobes of these animals are very special because the muscular and skeletal support in these appendages allowed for life to move out of the water and onto land.

Tetrapods and Amniotes

The first vertebrates to make this journey onto land were the tetrapods. These are jawed vertebrates with two pairs of limbs ('tetra' means 'four,' describing the four legs).

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