Question

1- Explain the phylogenetic relationship between hagfish and lampreys. Use the terms agnatha, cyclostomes, craniates, vertebrates

2-- Fish represent a ‘not natural’ group. What word describes this type of group?

3- Give the name of the extinct group that many consider to be the most ancient jawed vertebrates.

Answer 1

1.Lampreys and hagfish, which together are known as the cyclostomes or ‘agnathans’, are the only surviving lineages of jawless fish. They diverged early in vertebrate evolution, before the origin of the hinged jaws that are characteristic of gnathostome (jawed) vertebrates and before the evolution of paired appendages. However, they do share numerous characteristics with jawed vertebrates. Studies of cyclostome development can thus help us to understand when, and how, key aspects of the vertebrate body evolved.

2.Osteichthyes or bony fish

3. Acanthodii or spiny sharks are the most ancient jawed vertebrates that are extinct