The tooth-like microfossils of an extinct group of jawless vertebrates are called conodonts. The name refers both to the animals and, commonly, to their tiny mineralized feeding elements.
Conodonts lived in marine environments from the Cambrian, more than 500 million years ago, until the beginning of the Jurassic, around 200 million years ago. For much of the nineteenth and twentieth centuries, paleontologists knew them only from isolated cone-, bar-, and platform-shaped fossils, typically measuring about 0.2 to 5 millimeters.
Those elements were not teeth set in jaws. They formed a sophisticated feeding apparatus inside an eel-shaped, soft-bodied animal. Fossils discovered in the early 1980s and later in South Africa preserved muscles, fins, eyes, and a notochord, confirming that conodont animals were primitive vertebrates or very close vertebrate relatives.
A common mix-up is confusing conodonts with foraminifera or radiolarians. Those are microscopic organisms used in paleontology, but conodont elements are phosphatic structures from vertebrate animals. Their rapid evolution and distinctive shapes also make them valuable index fossils for dating rock layers.