Kingdom Animalia
Phylum Chordata
Class Thelodonti
Order Thelodontiformes
Family Coelolepidae
Genus Thelodus
1st Species Thelodus parvidens
2nd Species Thelodus hoskinsi
3rd Species Thelodus calvus
4th Species Thelodus inauditus
Other attributes
Time Range 443.7-416 mya
Location United Kingdom, Canada, Estonia, Norway, Russia, Sweden, Ukraine
Name Meaning Feeble tooth
Physical Dimensions 15 centimeters-1 meter long
Dietary Classification Planktivore

Thelodus is a coelolepid thelodontiform jawless fish from the Llandovery-Early Devonian of the United Kingdom, Canada, Estonia, Norway, Russia, Sweden, and Ukraine. It was named in 1839 by Louis Agassiz. It was one of the many jawless fishes to swim in the Silurian seas, as well as one of the more advanced ones.


Even though Thelodus had many generic jawless fish traits, such as a mobile tail, a large, oval-shaped body, and eyes positioned near the sides of its head, it was slightly more advanced as well. It had a larger tail fin, a dorsal (back) and anal (near the base of the tail) fin, tiny pectoral (arm) fins, and a forward-facing mouth (rather than one that faced downwards). Its body would have been covered in scaly skin.


Thelodus was a planktivore, sucking up colonies of plankton drifting through the water. Its small, toothless mouth would have been used to filter plankton from the water.


So far, all we know about Thelodus is that it would have had a build that rendered it extremely adapted to life in open water (in this case, a larger tail fin for faster swimming, a dorsal and anal fin, and small pectoral fins for steering), and that it had a forward-facing mouth that made it easier for it to filter plankton from the water; as well as this, due to the fact that it had a more slender body than other jawless fishes, it would have relied on swift swimming speed rather than thick armor to escape predators such as Pterygotus.

Community content is available under CC-BY-SA unless otherwise noted.