|Basic info||Taxonomic history||Classification||Relationships|
|Morphology||Ecology and taphonomy||Age range and collections|
Rhynchonellata - Orthida - Plaesiomyidae
Jin et al. (2007) proposed to abolish the genus Pionorthis because its type species, Orthis sola Billings, 1866, belongs to the dalmanelloid genus Mendacella. Billings’ original type specimen has rarely been examined, and the specimen (YPM S-760; see Pl. 13, figs. 14–20) used as O. sola, initially by Schuchert and Cooper (1932) and subsequently in the two editions of the Treatise (Williams and Wright 1965; Williams and Harper 2000), belongs to P. carletona.
It was reranked as Pionorthis by Williams et al. (2000) and Sepkoski (2002); it was replaced with Plaesiomys by Jin et al. (2007).
It was assigned to Dinorthis by Schuchert and Cooper (1932); to Plaesiomyinae by Williams et al. (2000); and to Orthida by Sepkoski (2002).
If no rank is listed, the taxon is considered an unranked clade in modern classifications. Ranks may be repeated or presented in the wrong order because authors working on different parts of the classification may disagree about how to rank taxa.