Phylogenetic nomenclaturenext section
Phylogenetic nomenclature is used throughout this work, in a way that would be compatible with the ICPN (International Code for Phylogenetic Nomenclature: Cantino and de Queiroz, 2007; earlier drafts were called PhyloCode) if the ICPN were already implemented.
We discontinue our previous usage (Marjanović and Laurin, 2007) and instead follow Cannatella and Hillis (1993), Frost et al. (2006), Wilkinson and Nussbaum (2006) and Jenkins et al. (2007: 358) in using the name Gymnophiona for the caecilian crown group. The name Apoda Oppel 1810 has often (e.g., Trueb and Cloutier, 1991; Ruta and Coates, 2007) been used for the crown group (and Gymnophiona for the total group) in paleontological literature, but it is a junior homonym of the moth genus Apoda Haworth 1809 (Dundee, 1989; Wilkinson and Nussbaum, 2006; Naish, 2008) and should therefore not be used for an amphibian clade.
To facilitate discussion of gymnophionans and their relatives, we introduce the new clade names Gymnophioniformes and Gymnophionomorpha. (Because the ICPN will not be retroactive, and because these names are not registered, they are not hereby established and will need to be published anew once the ICPN is in effect.) Fig. 3 serves as the reference phylogeny (required by the ICPN in Article 9.6) for both, but note that both names can be applied to any phylogeny, not only to the reference phylogeny; the reference phylogeny merely serves to clarify our intent (ICPN Note 9.6.1). Gymnophioniformes has a node-based definition with Caecilia tentaculata L. 1758 and Rubricacaecilia monbaroni Evans and Sigogneau-Russell 2001 as internal specifiers. Gymnophionomorpha has a branch-based definition with Caecilia tentaculata L. 1758 as the internal specifier and Rana temporaria L. 1758, Salamandra salamandra (L. 1758), Albanerpeton inexpectatum Estes and Hoffstetter 1976, Brachydectes newberryi Cope 1868, Rhynchonkos stovalli (Olson 1970), Batropetes fritschi (Geinitz and Deichmüller 1882), and Carrolla craddocki Langston and Olson 1986 as external specifiers. The first three external specifiers serve to prevent Gymnophionomorpha from including any of the other three large lissamphibian (or possibly lissamphibian) clades, taking account of the conflicting hypotheses that exist on their interrelationships. The other four prevent it from including all or many ‘lepospondyls’ in the event of extant amphibian polyphyly: Brachydectes was considered a close relative of Gymnophiona as used here by Moodie (1909) and Eaton (1959); Rhynchonkos has been hypothesized to be the sister-group of Gymnophionomorpha by Carroll (Carroll and Currie, 1975, through Carroll, 2007, and Carroll in Jenkins et al., 2007); and Eocaecilia, the only lissamphibian in the data matrix of Anderson (2001), is the sister-group of Batropetes + (Carrolla + Quasicaecilia) in his most parsimonious tree (Anderson, 2001: fig. 6), while it forms a polytomy with Rhynchonkos, (Batropetes + Quasicaecilia), and Carrolla in the Adams consensus of all trees that are one step less parsimonious (Anderson, 2001: fig. 7) as well as in the strict consensus of the most parsimonious trees found by Vallin and Laurin (2004: fig. 7) in their reanalysis of Anderson’s (2001) matrix. Anderson (2007) and Anderson et al. (2008a) are congruent with Anderson (2001) in the position of Eocaecilia (the other lissamphibians being found as temnospondyls, i.e., in remote branches of the tree). We deliberately do not use Quasicaecilia as an external specifier because it is known from a single, highly incomplete and immature specimen and because its name implies that it should not be automatically excluded from Gymnophionomorpha by definition.
Fig. 3. Reference phylogeny for Gymnophioniformes and Gymnophionomorpha (new clade names) which additionally shows our usage of several other taxon names. Of these, those with node-based definitions are in boldface, those with branch-based definitions in regular typeface, and those without definitions in the font Comic Sans MS. The topology is a strict consensus of the opinions and results of Anderson (2001, 2007 except for Batrachia), Anderson et al. (2008a) except for the position of Albanerpetontidae, Evans and Sigogneau-Russell (2001), Vallin and Laurin (2004), Wilkinson and Nussbaum (2006), Jenkins et al. (2007), Ruta and Coates (2007) and Carroll (2007 and references therein) and fully compatible with McGowan’s (2002; see Fig. 2) and our own results (Fig. 6), as well as with those of the molecular analysis by Frost et al. (2006) (except for the position of Siphonops), and even with Moodie’s (1909) and Eaton’s (1959) opinion that Brachydectes is a close relative of Gymnophiona. Dots mark the first member of clades whose names have node-based definitions, arrows point to the first member of clades whose names have branch-based definitions (the first member lying at the tip of the arrow, not beyond). Teresomata, Neocaecilia and Parabatrachia lack phylogenetic definitions; their first members could lie anywhere in the indicated ranges and still be compatible with the usage by Wilkinson and Nussbaum (2006) respectively Frost et al. (2006).
Ruta and Coates (2007) have found Gymnophionomorpha (represented by Eocaecilia) and Albanerpetontidae as sister-groups; the undefined name Parabatrachia Frost et al. 2006 (“the taxon composed of living caecilians + Eocaecilia”; Frost et al., 2006: 356) might be used for such a clade.
Within Gymnophiona, Wilkinson and Nussbaum (2006: 44) have suggested “the anatomically neutral Neocaecilia” as a replacement for the anatomically misleading name Stegokrotaphia Cannatella and Hillis 1993 (not all stegokrotaphians have a stegokrotaphic [= unfenestrated and unembayed] skull, nor is the stegokrotaphic condition necessarily an apomorphy of any clade within Gymnophionomorpha or even Lissamphibia). We nonetheless retain Stegokrotaphia for “the most recent common ancestor of Caeciliaidae [sic], Ichthyophiidae, Scolecomorphidae, and Uraeotyphlidae, and all of its descendants” (Cannatella and Hillis, 1993: 2) because this name is older and because, unlike Neocaecilia, it has a phylogenetic definition (although none of the specifiers of that definition are ‘species, specimens or apomorphies’, which is required by the ICPN in Article 11.1). Perhaps Neocaecilia could be used for a slightly more inclusive clade in the future, if extinct taxa closer to Stegokrotaphia than to Rhinatrematidae will be identified, in analogy to the successful resolution of former synonyms such as Salientia and Anura, Caudata and Urodela, Eutheria and Placentalia, Metatheria and Marsupialia, Rhynchocephalia and Sphenodonti(d)a, Ophidia and Serpentes, or Testudinata and Testudines. (Wilkinson and Nussbaum [2006: 45] specify that Neocaecilia is a clade and mention an autapomorphy, but they do not provide information which indicates whether that clade has a node-based, branch-based, or apomorphy-based definition.)
We would like to provide a few comments about the status and correct spelling of a few relevant taxon names (discussed in other sections of this paper) in the context of rank-based (‘Linnaean’) nomenclature. Contrary to common usage, Boulengerul a is feminine (by virtue of not being ‘Boulengerulus’), so that B. taitan us Loveridge 1935 is an incorrect original spelling and automatically corrected to B. taitan a by ICZN Articles 31.2 and 34.2 (International Commission on Zoological Nomenclature, 1999). According to the same articles, no formal emendation is necessary, and the correct spelling must be attributed to Loveridge 1935. All this also holds if the likewise feminine Afrocaecilia (of which B. taitana is the type species) is recognized.
Likewise, Albanerpeton is neuter, which makes the original spelling of the type species, A. inexpectat um, correct and those of A. nexuos us, A. gracil is and A. pannonic us incorrect; the correct spellings (which again must be attributed to the original authors) are A. nexuos um, A. gracil e and A. pannonic um. Anoualerpeton, Chunerpeton, Pangerpeton and Sinerpeton, too, are neuter, so that A. unic us, A. prisc us, C. tianyiens is, P. sinens is and S. fengshanens is are correctly spelled A. unic um, A. prisc um, C. tianyiens e, P. sinens e and S. fengshanens e.
Finally, Heyler (1994) appears to be wrong in claiming that only the International Commission on Zoological Nomenclature has the authority to designate neotypes and that therefore the designation of a neotype for Apateon pedestris by Boy (1986) is invalid: whenever “no name-bearing type specimen (i.e. holotype, lectotype, syntype or prior neotype) is believed extant and an author considers that a name-bearing type is necessary to define the nominal taxon objectively”, that author has the right to designate a neotype (ICZN Article 75.1). Boy’s (1986) designation of a neotype for A. pedestris fulfills all requirements of Article 75 and is therefore, to the best of our knowledge, valid.