Bone histology of a gorgonopsian skeleton from the upper Madumabisa Mudstone Formation, Zambia

Gorgonopsians were an iconic group of non-mammalian therapsids that lived during the middle–late Permian, most known for their long, saber-like canine teeth. While not close relatives of mammals, gorgonopsians share a suite of mammalian skeletal traits, but their paleobiology and growth dynamics are poorly understood. Recent histological analyses of South African (Karoo Basin) gorgonopsians show that fast, cyclic growth is typical for the clade, with environmental influences playing a key role. To assess the life history of gorgonopsians outside of the main Karoo Basin, I sampled six skeletal elements from an indeterminate species from the Luangwa Basin of Zambia. My results show that despite excellent surface preservation, the bone tissue of this species has taphonomic overprinting in the form of filamentous and globular structures that may represent bioerosion. Intact bone tissue type varies across elements, leading to differences in growth rates and vascular orientation. Growth is generally composed of parallel-fibered bone with small, longitudinal primary osteons. One growth mark appears in the femur, and growth spurts are indicated by highly vascularized bone in the tibia and radius. The individual had not reached somatic maturity before death. Compared with Karoo Basin gorgonopsians, which exhibit fast, cyclical growth with abundant growth marks, this Zambian specimen grew more slowly with fewer growth marks. This suggests that small- to medium-sized gorgonopsians displayed a range of moderate to fast growth rates during early ontogeny.