Thursday, March 4, 2010

Asilisaurus and how not to name new clades

The good news is that we have a new taxon of basal dinosauriform.  The bad news is the clade the authors placed their new genus is.  Based on their phylogenetic analysis, Nesbitt et al. found it to be in the same group as Silesaurus and Lewisuchus, exclusive of Dinosauria.  The idea of this clade has been floating around for a while, and was actually named by Langer et al. (2010) earlier this year.  Which authorship and definition have priority is not the subject of this post however, and in any case Nesbitt et al. are innocent as far as that goes since their paper was in review when Langer et al.'s came out.  What I care about here is that Nesbitt et al. named their clade Silesauridae, yet Paul named Lewisuchinae (and thus also Lewisuchidae, as the ICZN states all family-level taxa are named once one is) back in 1988.  I could just urge everyone to please Google any family-level version of your new clade's genera before you give it a new name.  Basically all proposed archosaur nomenclature is online, so this will stop you from creating another junior synonym.

Yet the solution isn't that easy, because Silesauridae sensu Nesbitt et al. is an example of an increasingly common trend to name taxa as "clades, not Linnaean ranks."  Thus the authors claim the ICZN's rules of priority don't apply, since Silesauridae isn't really a family.  Now I'm a huge fan of phylogenetic nomenclature, but to that I'm afraid I must reply "Bullshit."  I think most dinosaur paleontologists agree nowdays that Linnaean ranks have no objective meaning.  One family is not necessarily more similar to another family than to another order, they're just all labels for taxa.  The only way to tell that a particular group is a family is that it ends in -idae.  I'd also say most dinosaur paleontologists only recognize monophyletic taxa (clades) in their taxonomy.  So basically whenever we talk about dinosaur families, we are talking about clades whose names end in -idae.  So why would anyone name a clade with an -idae suffix and not intend it as a family?!  Just to avoid priority?  I always thought it was a respectful (and interesting) task to go through historically proposed taxonomy and credit the first author who proposed a name for a group.  To do otherwise is too similar to Sereno's habit of finding new more complete remains probably belonging to poorly known but named taxa, giving his specimen a new name, and calling the already existing taxon a nomen dubium.   Just rewriting taxonomy with our own labels as we go along.  Or do the authors do this as a rebellious example of the fact no one has to follow the ICZN?  That it has no real power over us and is an archaic system whose subjective rules shouldn't be obeyed lest we fall into the unscientific idea of tradition?  I hate to have to play the part of a conservative, but the truth is we have no other code at the moment.  I'll jump on board Phylocode once it's enacted, and think it's great to start following Phylocode rules beforehand but that doesn't mean we have to disobey the ICZN.  Since Phylocode won't be retroactive anyway, nothing we publish now will count towards it, and following only its rules means you're not really following any rules at all.  You're just following a game of pretend that leaves us who actually try to follow the rules asking how we're supposed to treat your actions.  We could ignore what you say and treat Silesauridae as a family, and thus a junior synonym of Lewisuchidae (which will probably be my strategy).  We could treat Lewisuchidae as a family and Silesauridae as an unranked taxon, the first only including Lewisuchus itself (which results in making Lewisuchidae redundant and gives the impression of nested families).  We could redefine Silesauridae to be the sister taxon of Lewisuchidae (which would create a third definition for Silesauridae, and all before any of them are official).  We could petition the ICZN to sink Lewisuchidae (not likely to happen).  It just makes things so complicated, yet some of it could have been solved if you just used a non-family group suffix and named it Silesauria instead, if you were insistant on basing the clade on Silesaurus.  Senter et al. (2004) provided a great example when naming Microraptoria instead of Microraptoridae/inae.

In conclusion, I ask everyone to please-
- Google any family-level version of your new clade's genera before you give it a new name.
- Follow the ICZN's rules at least until Phylocode is enacted.
- Don't use a Linnaean rank suffix if your intent is to name a rankless taxon that doesn't compete for priority in the ICZN.

Langer, Ezcurra, Bittencourt and Novas. 2010. The origin and early evolution of dinosaurs. Biological Reviews of the Cambridge Philosophical Society. 85, 55–110.

Nesbitt, Sidor, Irmis, Angielczyk, Smith and Tsuji, 2010. Ecologically distinct dinosaurian sister group shows early diversification of Ornithodira. Nature. doi:10.1038/nature08718

Senter, Barsbold, Britt and Burnham, 2004. Systematics and evolution of Dromaeosauridae. Bulletin of Gunma Museum of Natural History. 8, 1-20.


  1. I agree that naming it "Silesauria" would be preferable. However, this sort of issue is going to crop up. It's unavoidable. There are certain ranked names out there that are just too ubiquitous not to convert. And thus there will be cases where the ICZN gives priority to "XIDAE" while the PhyloCode gives priority to "Yidae" for a taxon with the same content (given the right phylogeny and the right ranked taxonomy, of course--this is all dependent on context).

    However, it should be pointed out that the existing codes have the exact same issue. Their domains overlap (within "Protista"), and sometimes the zoological and botanical codes have different names for the same taxon.

    The thing to remember here is that synonymy is only defined within a code, not between codes. A name must be seen in the context of its governing code.

    I do agree that this sort of thing should be minimized, however, and new clade names should not be given rank-associated suffixes.

  2. "Silesauria" still wouldn't be a great name, in my opinion. Why call the whole group "Silesian saurians" when their distribution is now known to be essentially Pangaean?

  3. Yeah, but how many names are there where the etymology is off? You could name it something cooler like "Parapredentata"--but then you're screwed if they turn out to be basal predentatans.

  4. You're especially screwed given they don't have proper predentaries anyway. :)