Tarsals of the extinct insectivoran family Nyctitheriidae (Mammalia): evidence for archontan relationships

Astragali and calcanea from the English late Eocene, attributed to the exti nct 'insectivoran' family Nyctitheriidae, are described for the first time. They contrast with those of the strict sense insectivorans, the Lipotyphla , in which order nyctitheres have usually been placed, and compare more clo sely with those of Scandentia (tree shrews) and the extinct Plesiadapiforme s. Functional analysis demonstrates that inversion of the foot was possible between the astragalus and calcaneum of nyctitheres, allowing them to be i nterpreted as having had a tree-dwelling, probably scansorial, mode of life . These tarsal bones are compared with those of other placental mammals. Cl adistic analysis of tarsal characters places nyctitheres as sister group to the Plesiadapiformes within the superorder Archonta, excluding Chiroptera (bats). An independent analysis of dental characters places them as sister group to the rest of the Archonta, but still excluding bats. Combining the dental and tarsal characters places nyctitheres as sister group to Plesiada piformes and all modern groups of archontans except bats. A new osteologica l synapomorphy is proposed for the Archonta, which is thus considered to co mprise Chiroptera, Deccanolestes, Nyctitheriidae, Plesiadapiformes, Dermopt era (including Mixodectidae), Scandentia and Primates. Insectivorans s.l. h ave long been at the centre of arguments on placental origins, although lip otyphlans are usually regarded as a monophyletic group, rather than paraphy letic stem placentals. Reidentification of an extinct lipotyphlan family as having archontan relationships raises the possibility of advances in other areas of insectivoran phylogeny when more postcranial elements become know n. The early Oligocene extinction of nyctitheres may be causally related to the rise of insectivorous microchiropteran bats, which, because of their f lying ability, would have been able to forage more widely. (C) 2001 The Lin nean Society of London.