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Craniata Essay

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The reason Craniata instead of Vertebrata is preferred to describe animals such as lampreys and hagfish relates to there anatomy. The main difference Lampreys and Hagfish have compared to other Vertebrates is that while they do have similar characteristics they both lack a vertebral column that is made of bone. However, they do have a cranium that is composed of bone so calling them a Craniata is a more inclusive term then referring to them by the clade Vertebrata (Nicholls 2009).
The reason Urochordates are more related to Craniates then Cephalochordates is because of phylogenetic evidence. Before genetic evidence was available it was believed that Cephalochordates were the closet relative because of their general morphology. However,
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The Sarcopterygii or lobed finned fish have a fin that extend from a lobe structure opposed to being directly on the body. Since this trait is one that is only present in the Sarcopterygii that makes it a synapomorphy.
In the evolutionary history of vertebrates there are few traits that have as much of an impact as the evolution of jaws and the cleidoic egg. The evolution of the jaw was a trait so important and so impactful that when it came into existence a whole new lineage of creatures evolved with it. Before this trait arose animals such as the hagfish and the lamprey where limited to a very specific diet and consumption practices. Many lampreys are parasitic and have to attach to other creatures in order to feed. Hagfish are limited to only scavenging on dead creatures and eating small bodied invertebrates. While these consumption methods to work for them it requires them to function in particular niches that limit the species. The evolution of the jaw that has now been passed down to all Gnathostomes has allowed for a variety of benefits. Jaws allowed for capture and digestion of a wider variety of food as well as allowing them to become predator species. This allowed jawed fish to spread to a variety of new niches and adapt to them much better then the jawless fish. The significance of jaws can also be illustrated by the number of living species today that posses it. There are around 80 species of
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