Reisz 2018 reports,
“Varanopidae is a clade of small to medium sized carnivorous synapsids whose fossil
record spans the Late Pennsylvanian to late Permian, one of the longest known temporal
ranges of any Paleozoic eupelycosaur clade. It has also been recently suggested that this clade may not be part of Synapsida, but may instead nest within Diapsida.”
In the large reptile tree (LRT, 1306 taxa, subset Fig. 1) Vaughnictis is the last common ancestor of Diapsida and Synapsida. Varanodon nests within the Synapsida. A series of former varanopids nest as pre-diapsids.
Reisz 2018 concludes,
“A revised and expanded data matrix and phylogenetic analysis that integrates Permo-Carboniferous synapsids and reptiles does recover a monophyletic Varanopidae within Synapsida, with Varanodon and its varanodontine sister taxa, Watongia, Varanops, Tambacarnifex, as apex, gracile predators of the early Permian, contemporaries of the larger, more massively built sphenacodontid synapsids.”
Unfortunately taxon exclusion
prevents Dr. Reisz from seeing the big picture (subset Fig. 1), published online in 2015 here and expanded since then.
Reisz RR 2018. Varanodon and the evolution of varanopid synapsids. SVP abstracts.