The Trapezius Complex in Mammalia

Abstract

Within Mammalia, the five portions of the trapezius complex ‐ sternomastoideus, cleidomastoideus, clavotrapezius, acromiotrapezius, and spinotrapezius ‐ have been adapted for specializations relating to arboreal, aquatic, fossorial, cursorial, and flying locomotor patterns. Yet despite the diversity of forms, features persist which may give us clues about evolutionary history. This is especially important for the controversial clade Afrotheria, which is based on genetic data but has no unifying skeletal or dental characters and a scanty fossil record. My research indicates that there are several characters of the trapezius complex which unite some members of the Afrotheria. For example, the sternomastoideus originates from the mandible, the clavotrapezius inserts on the sternum rather than the clavicle and has a slip to the pinna, and the acromiotrapezius fuses with the scapular head of deltoideus. There are also several characters of the trapezius complex which some members of Afrotheria share with other mammals. For example, some members of Eulipotyphla also have a bifid acromiotrapezius and a lumbar origin of the spinotrapezius, and the aclavicular Afrotherians share with Artiodactyla the fusion of clavotrapezius and cleidomastoideus with the clavicular head of deltoideus.Grant Funding Source: none