In a description of a new dicynodont, Thliptosaurus,
Kammerer 2019 presented a comprehensive cladogram of the dicynodonts, the dromasaurs and several outgroup taxa (Fig. 1), including the dinocephalians, Biseridens (Fig. 2), Archaeosyodon and Titanophoneus.
Kammerer 2019 excluded several outgroup and ingroup taxa pertinent to the origin of dicynondonts and anomodonts. In the Therapsid Skull Tree (TST, 67 taxa, Fig. 4), the Anomodontia (dicynodonts, dromasaurus and kin) arise from basalmost therapsids, like Cutleria, Stenocybus (Fig. 3) and Hipposaurus. These appear prior to Biarmosuchus. Elsewhere on the cladogram, Biseridens and Titanophoneus arise from more derived tapinocephalids unrelated to basal Anomodontia, more distant descendants of Biarmosuchus.
Kammerer 2019 was attempting to produce a cladogram
of the clade Anomodontia. I cannot comment on the tree topology of dicynodonts, because the TST includes so few of them. However, Kammerer followed tradition by including Biseridens and Titanophoneus as outgroup taxa, omitting those recovered by the LRT and TST.
So… taxon exclusion
put a small damper on an otherwise comprehensive report. This happens way too often in paleontology.
Biseridens (Fig. 2) was too distinct
to be the ancestor to the tiny dromasaurs, Suminia and Galepus (Fig. 3) and the rest of the Anomodontia. The taxa shown above (Fig. 3) demonstrate a more gradual accumulation of traits, better modeling deep time events.
Yesterday we looked at the uncontroversial key role
two small dromasaurs, Patranomodon and Galeops (Fig. 3), played in the origin of the Dicynodontia. Kammerer’s tree and the TST are in agreement on that point. Likewise the two trees agree that Eodicynodon is the basalmost dicynodont and that Suminia is closely related to Otsheria + Ulemica, close relatives of Venjukovia.
Kammerer CF 2019. A new dicynodont (Anomodontia: Emydopoidea) from the terminal Permian of KwaZulu-Natal, South Africa. Palaeontologia africana 53: 179–191. ISSN 2410-4418.