[1] Its remains come from the Blue Beach Member of the Horton Bluff Formation, near Hantsport, Nova Scotia.

Letognathus is important for rhizodont systematics because it retains a number of primitive features, such as ossified Meckel's cartilage, are not found in the genera Rhizodus and Strepsodus.

The members of the Rhizodontida have nearly all had complex taxonomic histories[2] due to earlier use of the genus Strepsodus as a wastebasket taxon.

The taxon was originally assigned to the genus Rhizodus by John William Dawson and later to Strepsodus by Arthur Smith Woodward.

A new genus was erected for the Horton Bluff material based on a number of differences from either Strepsodus or Rhizodus.