The type species of Priosphenodon, P. avelasi, was described in 2003 from the Late Cretaceous (Cenomanian-Turonian) aged Candeleros Formation of Argentina.

[1] In 2014, a second smaller species, P. minimus was described from the same formation, though from an earlier unit suggested to be Early Cretaceous (Albian) in age.

[3] With some individuals reaching over 1 metre (3.3 ft) in total length, Priosphenodon avelasi is the largest known terrestrial sphenodontian.

[1] P. avelasi exhibited variable but generally slow growth rates, with a probably sexually mature individual confirmed to be at least 13 years old by bone histology was still growing and only around 40% maximum size at the time of death.

[2] During feeding the dentary teeth of Priosphenodon slotted between the maxillary and palatine tooth rows, which in turn with backward and forward (propalinal) motion of the jaw, served to shred plant material.