Trichechus hesperamazonicus is known by two fragmentary mandibles and part of the palate. Compared with other manatees, it has a wide space between the posterior lower tooth row and ascending ramus of
dentary, where the
buccinator muscle is located, and a wide ascending ramus of the
mandible, which covers the posterior end of the tooth row. It also shares some characteristics with living species, as relatively few large teeth and few mental foramina as
T. manatus and
T. senegalensis (in contrast with the many smaller teeth and many mental foramina of
T. inunguis) and a straight and shallow mandibular symphysis as
T. inunguis and
T. senegalensis (in contrast with the downturned snout and deep mandibular symphysis of
T. manatus). The affinities of this species are still not fully resolved, being recovered in a polytomy with
T. inunguis and a clade formed by
T. manatus and
T. senegalensis: == Distribution ==