In the large reptile tree these two clades (procolophonids and diadectomorphs) nest together. No one has ever seen that before or since.
A new discovery
(Liu and Bever 2015) links these two clades closer together. Unfortunately, Liu and Bever used outdated cladograms. Taxon exclusion was the source of their errors. From their abstract: “Diadectomorpha is a clade of Late Palaeozoic vertebrates widely recognized as the sister group of crown-group Amniota* and the first tetrapod lineage to evolve high-fibre herbivory**. Despite their evolutionary importance, diadectomorphs are restricted stratigraphically and geographically, with all records being from the Upper Carboniferous and Lower Permian of North America and Germany. We describe a new diadectomorph, Alveusdectes fenestralis, based on a partial skull from the Upper Permian of China. The new species exhibits the derived mechanism for herbivory and is recovered phylogenetically as a deeply nested diadectid. Approximately 16 Myr younger than any other diadectomorph, Alveusdectes is the product of at least a 46 Myr ghost lineage. How much of this time was probably spent in Russia and/or central Asia will remain unclear until a specimen is described that subdivides this cryptic history, but the lineage assuredly crossed this region before entering the relatively isolated continent of North China. The discovery of Alveusdectes raises important questions regarding diadectomorph extinction dynamics including what, if any, ecological factors limited the diversity of this group in eastern Pangea. It also suggests that increased sampling in Asia will likely significantly affect our views of clade and faunal insularity leading up to the Permo-Triassic extinction.”
* This is an error.
Diadectomorpha are derived from Milleretta and kin in the large reptile tree.
** Another error.
Basalmost lepidosauromorphs were all herbivores.
In dorsal view
the skull of Alvuedectes has a strongly triangular appearance, similar to that of procolophonids. Most of the skull must be restored because it is missing. And it can be restored in at least two ways (Fig. 2).
Liu and Bever did not compare
their find to any procolophonids, only diadectomorphs. This is why the large reptile tree was created, to provide an umbrella study to provide taxa for more focused studies. It is unfortunate that Liu and Bever did not reference this study, which has been online for over four years. Procolophonids continued to the Late Triassic, which makes procolophonids the “last diadectomorphs.”
Liu J and Bever GS 2015. The last diadectomorph sheds light on Late Palaeozoic tetrapod biogeography. Biol. Lett.11: 20150100.