Occlusal and morphogenetic field evolution in the dentition of European Nyctitheriidae (Euarchonta, Mammalia)

Abstract

The nyctithere genera Saturninia, Cryptotopos and members of the subfamily Amphidozotheriinae are well-represented by dental remains in the European later Eocene. Their molar occlusal relations are described in detail, demonstrating a diversity of adaptations to insectivory, including dilambdodonty, minor trends in zalambdodonty, development of a large talon shelf in upper first and second molars and a step in the trigon-trigonid shearing surface that provides an extra facet in buccal phase. Minor lingual phase wear is recognized for the first time in the family, but only in relatively worn teeth. Nyctithere molars differ from those of most insectivorous mammals today in having well-developed paraconules and metaconules on upper molars, which in most cases lack a marked bucco-lingual tilt, associated with a more transverse jaw action. Amphidozotherium, however, shows tilting and a basally shifted M¹ hypocone associated with M₁ talonid exodaenodonty and a minor trend in zalambdodonty. Nyctitheres primitively have three deeply notched lobate lower incisors and a large but procumbent premolariform lower canine. Amphidozotheriines have modified their I₃ into a premolariform tooth, by shifting the premolarization field mesially. Amphidozotherium has also shifted this field distally, reducing P_2–3 in size and their roots from two to one.

Keywords:

• Buccal phase
• dilambdodonty
• exodaenodonty
• lingual phase
• premolarization
• zalambdodonty

Acknowledgements

I thank the following: John Quayle and Andy Yule for donating specimens to the NHMUK; Allan Lawson for sorting samples; Margaret Collinson, Andy Currant, Steve Grimes, Angela and Andrew Milner, Nick Sille, Ros Singer and David and Alison Ward for help with field collecting; Tony Tutton (National Trust) and John and Marion Smith for site access; John Alexander, Mike Novacek (AMNH) and Paula Jenkins (NHMUK.LS) for access to collections in their care; Pam Gill for helpful discussion; and Bill Clemens and an anonymous reviewer, whose helpful comments have improved the paper.