| Thalassotitan | |
|---|---|
| |
| Syntype skull and jaws (MNHM.KH.231) of T. atrox from Ouled Abdoun Basin, Morocco | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Order: | Squamata |
| Clade: | †Mosasauria |
| Family: | †Mosasauridae |
| Tribe: | †Prognathodontini |
| Genus: | †Thalassotitan Longrich et al., 2022 |
| Type species | |
| †Thalassotitan atrox Longrich et al., 2022
| |
Thalassotitan ("titan of the seas") is an extinct genus of large mosasaurs (a group of extinct marine lizards) that lived during the late Maastrichtian of the Cretaceous period in what is now Morocco, around 67 to 66 million years ago. The only known species is T. atrox, described in 2022 from fossils discovered in the Ouled Abdoun Basin, initially identified as coming from other genera such as Mosasaurus or Prognathodon. Hypothetical Thalassotitan specimens may have been found in other corners of the world, although researchers also note the possibility that they come from distinct, related taxa. It is considered to be close to the genera Prognathodon and Gnathomortis, together forming the tribe Prognathodontini. The prognathodontines are separated from other mosasaurs based on their massive jaws and robust teeth.
Thalassotitan is one of the largest known mosasaurs, having an estimated size of around 9 to 10 m (30 to 33 ft) long. This genus shows definitely that mosasaurs evolved to take over the apex predator niche in the oceans of the Late Cretaceous which is now filled by sharks and orcas. Heavy wear on its teeth and fossils found in the vicinity of the holotype etched by acid wear from partial digestion suggest that this mosasaur had a diet consisting of smaller mosasaur species, plesiosaurs, large predatory fish, and sea turtles.