What is the nature and purpose of a type specimen?
September 13, 2016
It’s been interesting seeing the response to my comment on the ICZN petition to establish Diplodocus carnegii as the replacement type species of the genus Diplodocus. In particular, Mickey Mortimer’s opposition to the petition seems to be based primarily on this argument:
The dinosaur community has recently lost sight of the fact that the type concept was never meant to indicate the most well preserved or described specimen/species.
I find this unconvincing, on the basis that the ICZN was never designed with dinosaurs in mind in the first place. For the great majority of the species that have been named under its rules, the selection of the obvious holotype has been perfectly adequate, because extant animals — by far the majority — are nearly all represented by complete and well-preserved specimens.
Dinosaurs — which in many cases are represented by eroded and distorted fossils of a tiny part of the animal — are already an aberration from the perspective of the ICZN, and that is why they sometimes need special treatment.
What are type specimens for, after all? The Code itself says “The fixation of the name-bearing type of a nominal taxon provides the objective standard of reference for the application of the name it bears” (Article 61.1); and comments that type specimens “are the international standards of reference that provide objectivity in zoological nomenclature” (Article 72.10). That is a role that YPM 1920 is simply not capable of fulfilling — and, more to the point, a role that it is not filling. The Diplodocus carnegii holotype CM 84 is the international standard of reference that provides objectivity in Diplodocus nomenclature. Slavishly following the usual provisions of the Code to retain the fiction that YPM 1920 fulfils this role simply does not reflect reality.
Some people occasionally object to the nomination of neotype specimens or replacement type species on the grounds that the Code does not require this. Of course it doesn’t: if it did, there would be no need for petitions. The fact that the Code allows for petitions constitutes explicit recognition that its usual provisions do not always suffice to produce the “sense and stability for animal names” that the Commission’s web-site used to have as its banner before the last redesign. Petitions exist precisely to allow the setting aside of the usual rules when sense and stability is served by doing do.