Abstract
Dicynodontia represent the most diverse tetrapod group during the Late Permian. They survived the Permo-Triassic extinction and are central to understanding Permo-Triassic terrestrial ecosystems. Although extensively studied, several aspects of dicynodont paleobiology such as, neuroanatomy, inner ear morphology and internal cranial anatomy remain obscure. Here we describe a new dicynodont (Therapsida, Anomodontia) from northern Mozambique: Niassodon mfumukasi gen. et sp. nov. The holotype ML1620 was collected from the Late Permian K5 formation, Metangula Graben, Niassa Province northern Mozambique, an almost completely unexplored basin and country for vertebrate paleontology. Synchrotron radiation based micro-computed tomography (SRµCT), combined with a phylogenetic analysis, demonstrates a set of characters shared with Emydopoidea. All individual bones were digitally segmented allowing a 3D visualization of each element. In addition, we reconstructed the osseous labyrinth, endocast, cranial nerves and vasculature. The brain is narrow and the cerebellum is broader than the forebrain, resembling the conservative, “reptilian-grade” morphology of other non-mammalian therapsids, but the enlarged paraflocculi occupy the same relative volume as in birds. The orientation of the horizontal semicircular canals indicates a slightly more dorsally tilted head posture than previously assumed in other dicynodonts. In addition, synchrotron data shows a secondary center of ossification in the femur. Thus ML1620 represents, to our knowledge, the oldest fossil evidence of a secondary center of ossification, pushing back the evolutionary origins of this feature. The fact that the specimen represents a new species indicates that the Late Permian tetrapod fauna of east Africa is still incompletely known.
Highlights
Dicynodonts are an exclusively herbivorous clade of synapsids
We describe the anatomy of a new dicynodont genus and species from northern Mozambique, investigate its phylogenetic relationships and biostratigraphic implications, and assess its ontogenetic stage based on gross morphology and bone histology
As part of this work, we present the first fully segmented 3D model of a dicynodont skull and mandible derived from high-resolution micro-computed tomography data (Figure S1)
Summary
Dicynodonts are an exclusively herbivorous clade of synapsids. They comprise more than 100 species that are known from the Middle Permian the Late Triassic periods Dicynodonts were morphologically disparate and presented a wide range of sizes and putative ecological niches, including semi-aquatic, fossorial, arboreal and grazing [1]. Recent advances in nondestructive imaging techniques such as high resolution computed tomography, neutron tomography, and synchrotron radiation based micro-computed tomography, hold the potential to provide significant new insight into fossil skull morphology. Subsequent geologic work correlated the Metangula Graben fossiliferous layer to the South African Tropidostoma Assemblage Zone [29,30,31]. We describe the anatomy of a new dicynodont genus and species from northern Mozambique, investigate its phylogenetic relationships and biostratigraphic implications, and assess its ontogenetic stage based on gross morphology and bone histology. As part of this work, we present the first fully segmented 3D model of a dicynodont skull and mandible derived from high-resolution micro-computed tomography (mCT) data (Figure S1). The model and associated digital endocast provide novel information on the ethmoid, parasphenoid, and prootic, as well as new insights on the osseous labyrinth, cranial nerves, cranial vasculature, and brain anatomy
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