A recent Journal of Vertebrate Paleontology Memoire provided much needed and appreciated insight into the speciation of Dicynodon (Kammerer, Angielczyk and Fröbisch 2011), the dicynodont that gave its name to the clade. In their excellent phylogenetic analysis of the dicynodontia, these authors unfortunately placed Biseridens (Liu et al. 2009) at the base.
Testing That Nesting
In a study of basal therapsids, including many not considered by Kammerer, Angielczyk and Fröbisch (2011), Biseridens nested between Syodon and Titanophoneus, not at the base of the Dicynodontia. At the base of the Dicynodontia we find Nikkasaurus, Niaftasuchus, Microurania and Tiarajudens preceding Dicynodon (Fig. 1). That means the tusks of dicynodonts were secondarily developed after loss in earlier and more basal taxa.
As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.
Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data
Kammerer CF, Angielczyk KD and Fröbisch NJ 2011. A comprehensive taxonomic revision of Dicynodon (Therapsida, Anomodontia) and
its implications for dicynodont phylogeny, biogeography, and biostratigraphy. Journal of Vertebrate Paleontology 31, Supplement 1: 1-158
Liu J, Rubidge B and Li J 2009. A new specimen of Biseridens qilianicus indicates its phylogenetic position as the most basal anomodont. Proceedings of the Royal Society B 277 (1679): 285–292.