A morphological-systematic study of the genus Leavachia (procynosuchidae - cynodontia - therapsida) Broom 1948 with special reference to the dentition

Abstract

Five skulls of Leavachia from the B.P.I. including the type specimens of microps and gracilis and three of duvenhagei were investigated. At the National Museum in Bloemfontein a skull was obtained from the Hendrik Verwoerd Dam collection. After preparation it proved to belong to Leavachia. This skull was described in detail. An intensive study was made of the crown structure of the postcanines in all the skulls as this was important for the exact determination of the relationships between the three species. All the postcanines have a main cusp with an anterior accessory cusp and/or a posterior accessory cusp. A cingulum is present which has a number of cingulum cusps the number and size of which varies with the complexity of the tooth. Tooth replacement was also studied. Most of the morphological differences between the species could be attributed to postmortem distortion and the age of the animal. It was found that there was no grounds for the existence of three different species and consequently only duvenhagei is retained. This view was strongly supported by similarity of the crown structure of the postcanines in all the skulls studied. A study of tooth replacement showed alternate replacement waves which always appeared to move from back to front (forward). Evidence for the addition of posterior postcanines was found but no definite evidence for anterior suppression could be illustrated due to the difficulty of working in the diastema with upper and lower jaws occluded.