The premaxilla is enlarged and downturned, the nasal bones are absent, the braincase is small and the zygomatic arch is thick and deep. The bones of the skeleton are pachyostotic, which is to say extremely thickened and dense. Adults range in length from 2.4 to 4 m. Reproduction Breeding occurs throughout the year and peak months for birth vary geographically. The exact length of gestation is unknown, but it is presumed to be about 1 year.
Single calves are the norm and twins are rare.
Parturition takes place in shallow water, and newborn calves are able to swim immediately to the surface for their first breath of air. Newborns cling to the mother's back and ride from the surface to grass beds along with the feeding mother. Young suckle underwater beneath the mother in an inverted position. Lactation lasts approximately 18 months, but young are known to eat grass at 3 months. Young may remain with the mother for a year.