There’s an old saying, “life imitates art.”
The last few days have seen renewed discussion of the proposal to split Anolis into multiple genera. In their most recent paper, Nicholson et al. (2014) explain why they want to split up Anolis: “Starting with Savage (1973), we have made clear our conclusion that the beta section of Williams (1976) deserves generic status (Norops).” The reason, as they explain in the preceding paragraph: “Anyone who has caused a squamate’s tail to separate from its body, and has read Etheridge’s paper, understands immediately why we conclude that the beta condition within anoles is as important to understanding the diversity of that group as the toe lamellae of anoles is to understanding the evolution of Dactyloidae.” In other words, the caudal vertebral structure of Norops, “a derived condition of the caudal vertebrae unique among squamates,” is so notable and distinctive that Norops needs to be recognized as a genus to call attention to and emphasize this evolutionary transition.
This approach follows the rationale of Ernst Mayr’s Evolutionary Systematics Classification system, whose goal was to highlight major evolutionary transitions. This approach has generally fallen out of favor, however, because it often led to the recognition of paraphyletic groups, such as “reptiles,” when birds are elevated due to their evolutionary significance.
Nicholson et al. (2014) solve this problem, however, by recognizing the clade they consider important, Norops, but then recognizing as many other clades as necessary to render all clades monophyletic: “Therefore, the seven additional genera that we propose as replacements for the alpha section represent the minimum number of genera needed to eliminate the problem of the previous taxonomy” once Norops is elevated to generic status. Evolutionary classification meets phylogenetic systematics!
Nicholson et al., however, are not the first to take this approach in revising anole classification. Just last year, another paper considering anole classification came to exactly the same conclusion. Dimedawter et al. (2013), writing in Nature Herpetology, propose: “This approach is implemented readily enough and entails nothing more than identifying evolutionarily important clades, recognizing them at the appropriate taxonomic level, and then revising the remaining taxonomy to ensure that all taxa are monophyletic.” Taking the approach to its logical extreme, they then illustrate it using Anolis. However, rather than Norops, Dimedawter et al. start with Chamaeleolis and Chamaelinorops, two clades so distinctive that the authors contend they should be recognized at the generic level, as they once were.
But what constitutes evolutionary significance is in the eye of the beholder. Dimedawter et al. survey anoles and note a number of other clades that seem distinctive enough to warrant generic recognition. Among these are the padless anole of Venezuela (Tropidactylus); twig giants and dwarves of South America (Phenacosaurus); the aquatic anole of Hispaniola (A. eugenegrahami); Xiphocercus, the medium twig anole of Jamaica; Deiroptyx as originally constituted (vermiculatus and bartschi); among others. All of these anoles are cool and distinctive in their own way, and so it seems reasonable to recognize them as distinct genera. In sum, they identify 11 clades worthy of generic level designation. To maintain monophyly of all anole clades, that requires recognizing 34 more clades, for a total of 45 anole genera.
Dimedawter et al. then go one step further. Agreeing with Nicholson et al. (2012), they argue that phylogenies should be informative of phylogenetic relationships. However, they fault Nicholson et al. for not going far enough—after all, their proposal does not provide insight on the relationships among the 150 Norops, or even among the six Chamaeleolis in their own system. So, they propose a new approach, Maximally Informative Phylogenetic Clustering (MIPC), which allows one to always know the sister taxon of a species from the classification. Applying this approach to anoles, they propose the recognition of 133 anole genera.
Exciting times for anole classification!