Extrinsic Snout Musculature in Afrotheria and Lipotyphla

Abstract

As currently recognized, the mammalian order Lipotyphla contains six extant families: Chrysochloridae, Erinaceidae, Solenodontidae, Soricidae, Talpidae, and Tenrecidae. Although most mammalogists have accepted this taxon, the morphological support for Lipotyphla is relatively weak, and recent phylogenetic studies using molecular data have concluded that it is not monophyletic. Instead, these molecular studies place chrysochlorids and tenrecids in the proposed clade Afrotheria, together with aardvarks, elephants, elephant shrews, hyraxes, and sirenians. Despite strong molecular support, Afrotheria has received little or no morphological support. It was recently suggested that a mobile snout might be a morphological feature uniting afrotherians. To test this proposal, I dissected the extrinsic snout musculature in an assortment of lipotyphlan and afrotherian mammals. These muscles provide support for Lipotyphla but not for Afrotheria. The snout is moved by different muscles in different afrotherian taxa, suggesting that the mobile snout is not homologous across different afrotherian lineages. In contrast, lipotyphlans have a distinctive set of five snout muscles moving the snout tip that appears to be unique to these six families. In addition, in soricids and talpids, four of the five snout muscles originate posterior to the zygomatic arch, supporting sister-taxon status for these two lineages. Although the extrinsic snout musculature does not support Afrotheria as presently proposed, it is consistent with an Afrotheria that does not include chrysochlorids and tenrecids.