Triodus is an extinct genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of xenacanthida
Xenacanthida is an order of prehistoric sharks that appeared during the Lower Carboniferous period. The family includes the families Xenacanthidae, Diplodoselachidae, and Orthacanthidae. The most notable members of the group are the genera Xenacanthus and Orthacanthus. Some Xenacanthus may have...

n shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....

 that lived in the Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...

. It was a freshwater shark, and fossils have been found in Germany.


  • The Rise of Fishes: 500 Million Years of Evolution by John A. Long
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