Anatomy and phylogenetic value of the mandibular and coronoid canals and their associated foramina in proboscideans (Mammalia)

Abstract

Characters associated with the mandibular canal are differently distributed amongst proboscidean lineages and provide useful information on the systematics and relationships of proboscideans. The aim of this paper is to describe the pattern of the mandibular canal and its associated foramina in proboscideans in order to fully appreciate the extent of interspecific variation of these structures within the group and to discuss its systematic and phylogenetic value. Outgroup comparison indicates that the condition presented by the basal proboscidean Phosphatherium is morphotypic for proboscideans. Primitive proboscidean characters are: the low position of the mandibular foramen, and its crescent-shaped outline, the occurrence of a coronoid foramen (canal), the occurrence of two lateral mental foramina, the posterior one at the level of (or slightly behind) the posterior margin of the symphysis, the anterior one in a more distal position, the absence of a medial mental foramen (MMF), the mandibular canal set just below the tooth row. The occurrence of a single lateral mental foramen may represent a shared derived character of Daouitherium, Numidotherium, and Barytherium. A unique derived feature of the Elephantinae mandible is the occurrence of a medial mental foramen on the medial side of the incisive part of the mandible. MMFs have never been observed in other proboscideans excluding elephantines. The very high frequency of MMFs observed in Mammuthus meridionalis-Mammuthus trogontherii-Mammuthus primigenius (>93 per cent of the studied specimens) could be considered a synapomorphy of this group. © 2010 The Linnean Society of London.