Madumabisa is a genus of dicynodont, an extinct type of therapsid (a group which modern mammals also belong to), that lived in eastern Africa during the Late Permian period. Fossils of Madumabisa have been discovered in what is now Zambia from rocks of the Madumabisa Mudstone Formation, which it is named after. The type and only known species is M. opainion, named in 2025. Madumabisa is an early member of the family Lystrosauridae and a close relative of the well-known and highly specialised Lystrosaurus. The specialised morphology of Lystrosaurus is only incipiently developed in Madumabisa, and it appears transitional between Lystrosaurus and more typical dicynodontoids like Dicynodon. Madumabisa is one of the most abundant species found in the upper Madumabisa Mudstone Formation, demonstrating that lystrosaurids were (at least in some places) major components of late Permian ecosystems that were already thriving prior to the end-Permian mass extinction, rather than only flourishing in its aftermath with the extinction of other dicynodonts.
History of discovery
The first fossils of Madumabisa were collected by Thomas S. Kemp in 1974 on a joint expedition from the University of Oxford and the Geological Survey of Zambia to the Luangwa Basin of northeast Zambia. The fossils were assigned to the genus Dicynodon, which at the time acted as a wastebasket taxon for many Permian dicynodonts. The specimens were tentatively assigned to Dicynodon cf. huenei, a species which has since been reassigned to Daptocephalus. These specimens consist of a partial skull missing the back end, and a collection of eight skulls (six complete) and abundant postcranial remains of young juveniles. These specimens, formerly in T. S. Kemp's own collections in Oxford, are now housed in the Natural History Museum, London (NHMUK). Madumabisa would not be recognised as its own genus until new fossils were collected during a series of expeditions returning to the Luangwa Basin from 2009 to 2019 by a multi-institutional research group studying the Permo-Triassic fossils of eastern Africa. As of 2025, these specimens are held in the National Heritage Conservation Commission (NHCC) in Lusaka, Zambia, but will be permanently housed in Zambia's Livingstone Museum. Madumabisa was described and named in 2025 by Christian Kammerer, Kenneth Angielczyk and Jörg Fröbisch. The holotype specimen is a nearly complete skull with a femur and partial rib fragments, catalogued as NHCC LB37. Three other nearly complete skulls were collected, NHCC LB206, LB822 (both with lower jaws) and the smaller LB794, as well as the front half of a fourth skull, NHCC LB857. Combined with the specimens collected by Kemp, Madumabisa is known from a nearly complete growth series and is one of the most abundant dicynodonts in the upper Madumabisa Mudstone Formation. The genus is named after the Madumabisa Mudstone Formation itself due its abundance, which itself is named for "Ndumebiza", a prominent hill in the Hwange District of Zimbabwe where rocks of this formation are also exposed. The specific name opainion is derived from the Ancient Greek words ὀπαῖος (opaios), meaning "with a hole", and ἰνίον (inion), referring to the occipital bone or the back of the skull in general. The combination refers to the unique additional pair of holes in the back of the skull below the post-temporal fenestra in Madumabisa. All fossils of Madumabisa come from the protected Munyamadzi Game Management Area of the Luangwa Valley of Zambia's Muchinga Province. The fossils were found in the upper layers of the Madumabisa Mudstone Formation, which is exposed in the Luangwa Basin of northeastern Zambia and further south in the Mid-Zambezi Basin along the Zambia-Zimbabwe border. The stratigraphy of the Madumabisa Mudstone Formation has not been formally subdivided, however its fossil fauna is recognised as falling into at least a distinct lower and upper faunal assemblage. These assemblages have been correlated with those of the well-studied framework in the Karoo Basin of South Africa, which correlates the upper Madumabisa Mudstone Formation with the Daptocephalus Assemblage Zone (AZ) of the Karoo. The Daptocephalus AZ has been dated to between 255.2 and roughly 252 million years ago. Within the upper assemblage, fossils of Madumabisa come from the stratigraphically highest (and so the youngest) rocks in the Madumabisa Mudstone Formation. Below them, the fauna is comparable to the Dicynodon-Theriognathus Subzone (Sz) of the Daptocephalus AZ. The abundance of Madumabisa stratigraphically higher may suggest the uppermost portion of the Madumabisa Mudstone Formation correlates to the Lystrosaurus maccaigi-Moschorhinus Sz of the Daptocephalus AZ, paralleling the increase of lystrosaurids in the Karoo. The L. maccaigi-Moschorhinus Sz has been approximately dated to between 253 and 252 million years ago.
Description
Madumabisa is mostly known by its complete skull, including the lower jaws. The largest skulls have lengths approaching 20 centimetres (7.9 in), mid-sized amongst dicynodonts. Some postcranial remains are also known, but they mostly belong to young juveniles (except for a partial femur and rib fragments) and have not been thoroughly prepared or described, and so little can be said of its postcranial anatomy. Like other dicynodonts, Madumabisa has a short snout with a turtle-like beak and only a pair of tusk-like teeth in its jaws. Madumabisa is characterised by two unique traits (autapomorphies) amongst dicynodonts. Below the post-temporal fenestra on the back side of the skull (the occiput) Madumabisa has an additional pair of deep and well-defined depressions (fossae) excavated into the paroccipital processes, the "paroccipital fossae". Each paroccipital fossa is directly beneath the post-temporal fenestra, and they are separated only by a sharp ridge. No other dicynodonts have paroccipital fossae. Likewise, the shape of the preparietal bone is unique. The preparietal is a singular midline bone unique to dicynodonts and some other therapsids that sits in front of the parietal foramen. In Madumabisa it has a tab-like shape that broadens towards the front, before constricting into a pointed spur at the tip. This shape is unique to Madumabisa, and the front of the preparietal is usually more bluntly rounded in other dicynodonts.
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