The Levator Veli Palatini Muscle in Artiodactyls—A Comparative Ontogenetic Study

Abstract

It is accepted in the literature that the levator veli palatini muscle of artiodactyls originates at the ectotympanic bone, a statement based on macroscopic dissection of adult specimens. The study of 34 histological serial sections of fetal heads of 23 species of artiodactyls revealed that this generalization must be modified: in the studied Camelidae, Suidae, Hippopotamidae, Giraffidae, and in some Bovidae (namely Tragelaphus and Antidorcas) the primary attachment of this functionally important muscle is at the tendinous intersection with the tensor veli palatini. Primary ontogenetic attachments are considered as relevant for defining homologies. By outgroup comparison (Felis and Diceros), this structural connection (character state 1) is also found in the Scrotifera—and hence may be considered as plesiomorphic for the Artiodactyla and its subunits. Only in the Tragulidae, Cervidae, Moschidae, and some Bovidae is a secondary attachment at the ectotympanic observed, which is interpreted as apomorphic for these taxa; possibly this character state 2 developed homoplastically several times. Bovidae show a mixed distribution of this character: Tragelaphus, Aepyceros, and Antidorcas show only a connection of the levator with the tensor veli; in Neotragus, Raphicerus, and Sylvicapra there exists an additional insertion at the ectotympanic; only Bos, Cephalophus, Damaliscus, and Ovis have a primary origin at the ectotympanic. It can be demonstrated in late fetal Sus that a secondary insertion of the levator veli at the ectotympanic is established during ontogeny; in a late fetal Ovis a secondary contact with the tensor veli is realized. The interpretation of this character distribution depends not only on an intrinsic polarity (‘Lesrichtung’), but also on the assumed character state of the groundplan of the common ancestor of the Bovidae. The anatomical observations are documented by photographs of relevant histological sections. The character states are mapped on a simplified and synoptic cladogram of extant artiodactyls; their pattern of evolutionary transformation as well as their relevance for the phylogenetic systematics of this mammalian order are discussed.