A small, lens-shaped radial sesamoid embedded into the APL tendon is a primitive state found in all known Carnivora genera except in the red and giant pandas and the extinct Simocyon where it is hypertrophied (enlarged) into a sixth digit or a so called "false thumb", a derived trait that first appeared in ursids.
Biomechanical approaches have been adopted to investigate the progression of cardiac hypertrophy for these two different types.