Trinacromerum is a genus of medium-sized plesiosaur in the family Polycotylidae. It originally lived from 99.7 to 70.6 million years ago, during the Cenomanian to Maastrichtian ages of the late Cretaceous period, and its fossils have been discovered in the Americas. Two species, Trinacromerum bentonianum and Trinacromerum kirki, are known.
