Taxon "Deinonychosauria" and phylocode
kinman2 at YAHOO.COM
Thu Jan 5 22:52:53 CST 2006
Anybody want to guess what the taxon "Deinonychosauria" includes? It obviously should include genus Deinonynchus. So in my recent classification of Class Aves, it should be Archaeopterygiformes clade 2 (Dromaeosauridae + Velociraptoridae). Unfortunately, Phylocodists like Sereno define Deinonychosauria very, very differently. In Sereno's 1998 cladistic definition, Deinonychosauria was the common ancestor of Deinonychus and Troodon, and all of its descendants. But in his 2005 definition (see link below), he explicitly excludes modern birds (specified by genus Passer). Therefore according to his 1998 definition, Deinonychosauria equals my Class AVES perfectly. But his 2005 definition is a totally empty set (includes nothing at all), because Troodon and Deinonychus do not clade together to the exclusion of Passer. And this in spite of the fact that I have Troodon and Deinonychus in adjacent clades (it's even WORSE for those who advocate a Bullatosauria clade where Troodon splits off way back with ornithomimosaurs).
The only good thing that I can say is that Sereno's definition of Deinonychosauria will self-destruct when applied to my phylogeny and those of many other workers (i.e., it becomes an empty set). Padian's definitions of Deinonychosauria aren't much better (sometimes they are synonymous with Avialae). Some cladist's phylogenies have a Deinonychosauria that includes all or most of my Order Archaeopterygiformes (which is clearly paraphyletic in my opinion and in the opinion of many other cladists). Whatever definition the Phylocodists formally adopt, it is safe to say that I will simply have to ignore the taxon Deinonychosauria altogether. In my classification, Deinonychus is either a member of Dromaeosauridae or Velociraptoridae (depending on whose analysis you trust more). If Troodontidae clades with them as well, then maybe some Phylocodists will return to Gauthier's (1986) grouping. In any case, the taxon name Deinonychosauria has been rendered virtually useless by the Phylocodists, so when you see the terms Deinonychosauria or deinonychosaur used, there is no telling what they are talking about. Unfortunately, the very same thing could happen to taxon Aves (restricted to Neornithes by Gauthier and a few of his followers). Between that restriction of Aves, and some who would expand it to include ALL maniraptors (or even beyond that), I still prefer a middle course that only expands Aves slightly beyond Archaeopteryx.
More information about the Taxacom