| Most jawless species went extinct long ago and are known only from the fossil record. |
| When the fossilized lamprey lived, there were probably many types of jawless vertebrates. |
| Some 450 million years ago, both jawed and jawless vertebrates began relying on cells called lymphocytes to support the burgeoning adaptive immune system. |
| These were jawless, armored fish informally called ostracoderms, but more correctly placed in the taxon Pteraspidomorphi. |
| In short, this analysis finds that conodonts are more derived than any of the living jawless vertebrates. |
| At a quick glance, jawless fish such as the lamprey above don't appear to have much in common with jawed fish or any other back-boned creature. |
