Remarks on the functional morphology of the earliest mammals

Abstract

The earliest mammals are characterized by a series of derived characters when compared to their synapsid predecessors. In comparison to non-mammalian synapsids, these features include highly efficient teeth, a small body size, a parasagittal limb posture, as well as a reduced number of ribs and girdle elements and light-weighted tails. We argue that the mammalian body construction and its functionality are constituted by a set of partially interrelated morphological traits, including akinetic skulls, tooth anatomy, and food processing; body size, locomotor speed, and tail reduction; the posture of the body and the construction of the girdle elements; as well as body torsion and rib reduction. By discussing these features from a biomechanical view, we demonstrate that high speed was the most important evolutionary advantage of the small earliest mammals over their larger synapsid ancestors, as well as over dinosaurs at the end of the Mesozoic.