HISTOLOGICAL EVIDENCE OF TRAUMA IN A TUSK OF LYSTROSAURUS (SYNAPSIDA: ANOMODONTIA)

The therapsid Lystrosaurus is well-known for surviving the Permo-Triassic extinction. As such, the genus has been instrumental in studying the P-T extinction and its subsequent recovery. The microstructure of Lystrosaurus long bones has been extensively sampled to approach these questions, however, little attention has been paid to the growth marks providing additional information about the lives of these animals.

Here we describe a Lystrosaurus tusk collected from the Lower Triassic of the Koro Basin of South Africa with unusual dentine deposition. The dental histology reveals an irregular infolding of dentine that extends from the pulp cavity, forming a lobed cross-sectional shape instead of the normal circular one. Higher frequency of infoldings were discovered on the medial margin of the specimen, and the depth of infoldings decreases from the apical end of the tusk (towards the root of tusk) towards the cervical end of the tusk (towards the tip of tusk).

The abnormal dentine deposition preserved in this Lystrosaurus is similar to the morphology presented in modern elephants’ tusks that have experienced trauma. This would suggest that the tusk of Lystrosaurus had a function that could have led to trauma (e.g. digging, fighting). This study highlights the importance of sampling microstructure as anomalies like this one can provide evidence into function of structures and behaviour that can improve an understanding of extinction and recovery dynamics.