Biseridens qilianicus (Li and Cheng 1997; Liu, Rubidge and Li 2009). Middle Permian ~260 mya was derived from a sister to Phthinosuchus + Titanophoneus and was basal to Tapinocephalians like Moschops and Jonkeria.
Liu, Rubidge and Li 2009 argued, "The following synapomorphies distinguish Biseridens as an anomodont and not an eotitanosuchian as previously described: short snout; dorsally elevated zygomatic arch and septomaxilla lacking elongated posterodorsal process between nasal and maxilla. The presence of a differentiated tooth row; denticles on vomer, palatine and pterygoid; contact between tabular and opisthotic; lateral process of transverse flange of pterygoid free of posterior ramus and absence of mandibular foramen exclude it from other anomodonts." They did not test more than 15 taxa.
Biseridens has two rows of short, flat post-canine teeth, unlike any other therapsid. The orbit and reflected lamina are larger than in related taxa, so perhaps Biseridens was nocturnal.