Vertebrates Jawless fishes. The ealiest vertebrates were the jawless fishes, now represented by hagfishes and lampreys. They have hardened cartilaginous vertebrae that are used for muscle attachment allowing more vigourous swimming. The first fishes with jaws that developed from gill arch supports are represented today by sharks and rays. They have cartilaginous skeletons and teeth that developed from scales.
Teeth can grab, hold, tear, crush, and macerate food.
They have about the same salt concentration as we do - not like the ocean. Four fins for steering - the precursor to arms and legs. There are more species and strange types than all other vertebrates put together. A gas bladder containing oxygen evolved for control of density that evolved into lungs for amphibians. Number of gill arches reduced and operculum helps pump water through the gills.