DEVELOPING A PROTOCOL FOR THE CONVERSION OF RANK-BASED TAXON NAMES TO PHYLOGENETICALLY DEFINED CLADE NAMES, AS EXEMPLIFIED BY TURTLES

Journal of Paleontology, Sep 2004 by Joyce, Walter G, Parham, James F, Gauthier, Jacques Armand

First, the largest body of literature that utilizes ICZN-taxon names is neontological, not paleontological. If currently used names are converted and tied to the crown clades, then all statements made in the neontological literature remain accurate (or at least justifiable). Furthermore, neontologists will be able to continue to use the names that they are most familiar with; only paleontologists, a minority to which all three authors of this paper belong, will need to rethink parts of the nomenclature with which they are familiar (de Queiroz and Gauthier, 1992). In other words, we believe that most zoologists would prefer using the familiar names 'Testudines,' 'Cryptodira,' and 'Pleurodira,' rather than the more obscure names 'Casichelydia,' 'Polycryptodira,' and 'Eupleurodira.' All major crown clades deserve a name, and we prefer to christen them with the currently most widely used names for the sake of cognitive efficiency. second, if commonly used names are tied to crown clades, unjustified phylogenetic inferences will be minimized (de Queiroz and Gauthier, 1992). As an example, according to many textbooks on turtles, all members of the Cryptodira retract their necks along a vertical plane (albeit to a variable degree, e.g., Pritchard, 1979; Ernst and Barbour, 1989; Zug et al., 2001), an observation based on living cryptodiran turtles only. Given this information, it seems plausible to infer that Kayentachelys aprix from the Lower jurassic of Arizona, the "oldest known Cryptodire" (Gaffney et al., 1987, p. 289), also retracted its neck vertically. That assertion is not justified, however, because Kayentachelys aprix is currently hypothesized to be situated far outside of crown Cryptodira and to have existed long before vertical neck retraction originated. One might reasonably infer the capacity for that style of neck retraction from structural correlates, but that requires a less secure inferential chain than one derived from direct observations of living species (Gauthier and de Queiroz, 2001).

To accommodate fossil species that are situated outside of crowns, we decided to create new, stem-based clade names. Every crown possesses a plethora of nameable stem clades (Gauthier and de Queiroz, 2001), however, making it once again necessary to choose one among many. We will here name only the most inclusive stems that do not overlap with the stems of any other living taxon. We term this type of stem-the 'total group' of Jefferies (1979)-a 'panstem clade' (pan = whole, entire) or simply 'panstem.' Following Gauthier and de Queiroz (2001), panstems will be formed by addition of the prefix 'pan-' to crown-name roots; hence Tesludinidae' for crown tortoises and 'Pantestudinidae' for panstem tortoises. Cognitive efficiency is thereby increased in two ways. First, merely by adding the prefix 'pan-' to any crown name, any zoologists seeing such a construction would know instantly that the name refers to a panstem, and not to any other stem or node. second, adding only 'pan-' to crown names will effectively reduce by half the number of different names with which anyone will have to contend. In some cases, this practice requires rejecting perfectly good ICZN-taxon names defined by previous authors. Cryptodiromorpha Lee, 1995 is one such example because 'Pancryptodim' would replace it under this convention, even though these names are plainly synonymous, with the former name having publication priority over the latter. Although some may disagree with this approach, we feel confident in overriding priority because the benefits to future generations of zoologists far outweigh the disadvantages created from disrupting the connection with the current literature (it is admittedly difficult to credit priority in the absence of a formal starting date for the PhyloCode). Fortunately, within turtles, this conflict exists only with three panstems, and the names proposed for them have not been used since they were proposed (see Panpleurodira, Pancryptodira, and Pancheloniidae below), thus making it possible to replace them without any true disruption of connection to the current literature.