| Dicynodonts are one of the most well-studied and speciose groups of extinct mammal
relatives. An abundant dicynodont fossil record in the Permo-Triassic affords insight into
paleobiological questions such as sexual dimorphism. However, dicynodont evolutionary
relationships remain contentious, and some dicynodont groups have received comparatively little
systematic or paleobiological study, notably the large, ornamented, and frequently toothless
clade Cryptodontia. Recovery of new fossil material, including from recent expeditions to the
Luangwa Basin in Zambia, has the potential to shed light on these paleobiological and
evolutionary questions. Here I describe a collection of dicynodont skull material from the late
Permian upper Madumabisa Mudstone Formation, exposed in the Luangwa Basin, Zambia. I
assign these specimens to a new species of Aulacephalodon, the largest member of the highly
ornamented cryptodont clade Geikiidae. This Zambian species is the first geikiid known from the
Luangwa Basin and corroborates previously identified trends in ontogeny and sexual
dimorphism in cranial boss development within Geikiidae, as well as substrate-based foraging in
Aulacephalodon. To assess the systematics and evolution of cryptodont dicynodonts, I present an
expanded phylogenetic dataset of dicynodonts and perform phylogenetic analyses with corrected
character ordering and scaling. This analysis supports recent hypotheses for the broader topology
of Cryptodontia and recovers novel relationships for multiple “problematic” cryptodont
specimens. I reconstruct the evolution of bony skull ornamentation and dentition across the
dicynodont phylogenetic tree, revealing complex evolution of ornamentation and edentulousness
as well as possible reversal of tooth loss, highlighting the evolutionary plasticity in this clade.
Keywords: Dicynodontia, evolution, Luangwa Basin, paleontology, Permian, phylogenetics,
Synapsida, systematics, Zambia |