Mastodons, like elephants, always have a pair of upper tusks, while the earlier ones likewise have a short pair in the lower jaw, which is prolonged into a snout-like symphysis for their support.
Only in the ostrich the distal ends of the pubes meet, forming a daggershaped symphysis, which is curved forwards.
In some of those birds which have a peculiarly harsh or trumpeting voice, the trachea is lengthened, forming loops which lie subcutaneously (capercally, curassow), or it enters and dilates the symphysis of the furcula (crested guineafowl); or, e.g.
Ventral fins below or in front of the pectorals, the pelvic bones posterior to the clavicular symphysis and only loosely attached to it by ligament.
The pelvic girdle and the hind-limbs show the least reduction found in any recent snakes, ilia, pubes and ischia being still distinguishable, the last even retaining their symphysis, and there are small vestiges of the femurs.