| Named By: | Cragin in 1888 |
| Time Period: | Late Cretaceous |
| Location: | Canada - Manitoba. USA - Colorado, Kansas, Texas and Utah |
| Size: | 3 meters long |
| Diet: | Piscivore/Carnivore |
| Fossil(s): | Multiple individuals |
| Classification: | | Chordata | Reptilia | Sauropterygia | Plesiosauria | Polycotylidae | |
| Also known as: | | Ceraunosaurus brownorum | Dolichorhynchops kirki | Dolichorhynchops willistoni | Trinacromerum anonymum | Trinacromerum brownorum | Trinacromerum willistoni | |
Trinacromerum is an extinct genus of sauropterygian reptile, a member of the polycotylid plesiosaurs. It contains two species, T. bentonianum and T. kirki. Specimens have been discovered in the Late Cretaceous fossil deposits of what is now modern Kansas and Manitoba.