Molar morphology and occlusion of the Early Jurassic mammaliaform Erythrotherium parringtoni

Abstract

The South African Early Jurassic morganucodontan Erythrotherium is considered by some authors to be potentially synonymous with Morganucodon, due to similar tooth morphology. However, despite their similar dental morphology, the occlusal pattern of Erythrotherium parringtoni has been described as embrasure occlusion, close to the mode of Megazostrodon rudnerae, rather than that of Morganucodon. In this study the molars of Erythrotherium were re-examined and the two alternative occlusal hypotheses were tested using the Occlusal Fingerprint Analyser (OFA). Morphological comparison of the molars of Erythrotherium parringtoni to those of Morganucodon watsoni showed similarities in cusp height and shape in lingual/buccal views, but the molars and individual cusps of Erythrotherium parringtoni are considerably narrower linguo-buccally, and more gracile. With cusps a and c close together in Erythrotherium parringtoni, cusp positioning differs from that of Morganucodon watsoni and shows similarities to the pattern in Megazostrodon rudnerae. Also, the upper molars of Erythrotherium parringtoni are aligned in a straight row and lack the angle, relative to the longitudinal axis, between the first and second upper molars that is present in Morganucodon watsoni. This results in embrasure occlusion being the only viable occlusal mode for Erythrotherium parringtoni, which was confirmed by the OFA analysis. A Morganucodon-like occlusion would allow only the main cusps a/A to contact their antagonists and thus major gaps would be present, causing considerable reduction of functionality of the dentition. Based on the morphological evidence and the differing occlusal mode, the perpetuation of Erythrotherium parringtoni as a separate genus is confirmed.

Keywords

• mammalia
• morganucodonta
• dental morphology
• occlusion
• dental function
• mesozoic
• lesotho
• south africa