Note: "Pan-clades"

In systematics one must distinguish between crown clades and total clades. While the total clade includes all extant and extinct members of a given clade, the crown clade comprises just part of it, i.e. the last common ancestor of the extant representatives of that clade and all its descendants. In other words, the crown clade does not encompass the stem group fossils. 

The distinction between crown clades and total clades poses the question how to separate them taxonomically. Following the Principle of Priority, as both ICZN and ICPN suggest (Louchard et al, 2013; de Queiroz, 2007; Cantino & de Queiroz, 2020; de Queiroz et al., 2020), would often lead to uncertainties regarding the original reference as well as having entirely different names for intimately related clades.

Therefore, I strongly favour to follow the proposal of Lauterbach (1989) to simply add the hyphenated prefix "Pan-" to the crown-clade name to create an informal taxonomic name, e.g. Pan-Aves. In my view this rule should be applied throughout, without any exception. [Unfortunately the Lauterbach paper was written in German and is not easily accessible]. 

Example: In their paper on Strisores, Chen & Field (2020) use the terms Pan-Trochilidae and Pan-Apodiformes for the respective total clades, but at the same time suggest the name Caprimulgimorphae for the total clade of Strisores (instead of Pan-Strisores). Personally, I regret this hybrid solution and hope that both ICZN and ICPN will finally agree on implementing a consistent "Pan-"clade solution. [The unfortunate outcome of not doing so is well-illustrated in the afore-mentioned paper: while the term Apodiformes refers to a crown clade, the term Aegotheliformes and others refer to total clades.] 

  

References

Cantino PD, and de Queiroz K (2020), International code of phylogenetic nomenclature (PhyloCode), version 6. www.phylonames. org. (link)

 

de Queiroz K (2007), Toward an integrated system of clade names. Syst. Biol. 56 (6), 956-974. (pdf)

 

de Queiroz K, Cantino PD, and Gauthier JA (2020), Phylonyms - A companion to the PhyloCode. CRC Press, Boca Raton, FL, USA(link)

 

Haug C, and Haug JT (2015), The ambiguous use of the prefix 'Pan' in arthropod systematics, RRJZS 3 (1), 19-24. (pdf)

 

Joyce WG, Anquetin J, Cadena EA, Claude J, Danilov IG, Evers SW, Ferreira GS, Gentry AD, Georgalis GL, Lyson TR, Perez-Garcia A, Rabi M, Sterli J, Vitek NS, and Parham JF (2021), A nomenclature for fossil and living turtles using phylogenetically defined clade namesSwiss J. Palaeontol., 140:5. (pdf)

 

Lauterbach KE (1989), Das Pan-Monophylum: Ein Hilfsmittel für die Praxis der phylogenetischen Systematik. Zool. Anz. 223, 139-156. 

 

Louchart A, Viriot L, and Dubois A (2013), The use of the prefix Pan- and other problems in zoological family-level nomenclature, Zootaxa 3750 (2), 197-200. (pdf)

 

Meier R, and Richter S (1992), Suggestions for a more precise usage of proper names. Ambiguities related to the stem lineage concept, J. Zool. Syst. Evol. Res. 30 (2), 81-88.