[MUSIC] I'm Carli Miller at the University of Illinois, and the topic of discussion today is the Phylum Chordata and the Subphylum Vertebrata of which you are a member. So you are a vertebrae, and we will be discussing the specific characteristics that define this phylum and the subphylum. And the reason why we would like to go into depth with this is because we are kind of marching through geologic time and we're observing that organisms are getting more and more complex, more organized, and generally more sophisticated. So there are three common characteristics that the phylum chordata exhibits during their ontogeny, which is development from the embryological stage to adulthood. And the first of those common characteristics is the presence of a hollow dorsal neural tube. And what that is, is it basically comprises your spinal cord and your brain, so your central nervous system. Secondly, there is the presence of a notochord, which again is some kind of axial support, usually going up the dorsal side of the organism. So it's providing support for that organisms body. Lastly, it will exhibit gill slits which is a way of drawing in oxygen from your environment and even you have exhibited gill slits some point in your embryological stages. So that is the third common characteristic that an organism in the final chordata will exhibit. So, if we're going down in taxonomical hierarchy, we're now in the sub filing vertebrata which is a member of the phylum chordata. And these organisms also exhibit certain characteristics. And kind of the primary one that distinguished a vertebrate, from an invertebrate, for example, is that the notochord which again provides that axyl support is surrounded or replaced by vertebrae. So those vertebrae can be actually composed of a softer cartilage material or hard bone. And so that's actually important to consider because if we think back to how an organism is preserved in the rock record, those soft versus hard parts, could introduce a bias in the fossil record. So, an organism with a cartilaginous vertebra or vertebral column may not be as well or as accurately represented in the rock record as a really robust hard skeleton would be represented. So what we need to consider moving forward when thinking about the organisms as they emerge and radiate through geologic time is that any organism in the subphylum vertebrata will exhibit these features. And so that's just something that we want to keep in mind if we're thinking about fish, to tetrapods, to amphibians, to mammals, dinosaurs, and all the way up through modern day humans. [MUSIC]