Clidastes is an extinct genus of mosasaur lizard from marine environments of the Late Cretaceous. Clidastes was an agile and fast swimmer that hunted in the surface or shallow waters. It was the smallest of the mosasaurs, averaging 2-4 meters (7-12 feet) in length, with the largest specimens reaching 6.2 meters (20 feet) long. It possessed a delicate and slim form with an expansion of the neural spines and chevrons near the tip of the tail and this enabled it to chase down the fastest of prey.

Globidens was 6 meters (20 ft) in length and in appearance very much like other mosasaurs. However its teeth were vastly different from other mosasaurs, as they were globular suggesting it may have specialised in armored prey like small turtles, ammonites, nautili, and bivalves. Like its larger relative, Mosasaurus, Globidens had a robustly built skull with tightly-articulating jaws. Such features no doubt played a large role in its ability to penetrate the armor of its shelled prey.

Kronosaurus ("Lizard of Kronos") is an extinct genus of short-necked pliosaur. It was among the largest pliosaurs, and is appropriately named after the leader of the Greek Titans, Kronos.

Liopleurodon is a genus of large, carnivorous marine reptile belonging to the Pliosauroidea, a clade of short-necked plesiosaurs. Four strong paddle-like limbs suggest that Liopleurodon was a powerful swimmer. Its four-flipper mode of propulsion is characteristic of all plesiosaurs. A study involving a swimming robot has demonstrated that although this form of propulsion is not especially efficient, it provides very good acceleration - a desirable trait in an ambush predator. Studies of the skull have shown that it could probably scan the water with its nostrils to ascertain the source of certain smells.

Mosasaurus was a genus of mosasaur, a carnivorous, aquatic lizard, somewhat resembling a flippered crocodile, with elongated heavy jaws. The genus lived in the Maastrichtian age of the Cretaceous period (Mesozoic era), around 70-65 millions years ago in the area of modern Western Europe. Mosasaurus was among the last mosasaur genera, and among the largest. The skull was more robustly built than other mosasaurs, as the mandibles articulated very tightly with the skull. It had a deep, barrel-shaped body, and with its fairly large eyes, poor binocular vision, and poorly developed olfactory bulbs, experts believe that Mosasaurus lived near the ocean surface, where it preyed on fish, turtles, ammonites, and possibly smaller mosasaurs. The animal remained near the surface and although it was able to dive, it evidentially did not venture into deeper waters.

Platecarpus is an extinct genus of aquatic lizard belonging to the mosasaur family, living around 75 million years ago during the end of the Cretaceous period. Fossils have been found in Belgium and the United States. Like other mosasaurs, Platecarpus had a long, laterally flattened tail, steering flippers, and deadly, tooth-lined jaws. It was around 4.3 metres (14 ft) long, with half of that length being taken up by its sinuous tail. It probably swam in a snake-like fashion. Platecarpus probably fed on fish, squid, and ammonites. They were medium sized animals, reaching about 7 metres (23 ft) in length.

Trinacromerum is an extinct genus of sauropterygian reptile belonging to the plesiosaur suborder. It lived during the Late Cretaceous period in what is now Kansas. It was 3 meters (10 feet) long. Its teeth show it fed on small fish. The long flippers of Trinacromerum enabled it to achieve high swimming speeds. Its physical appearance was described by Richard Ellis as akin to a "four-flippered penguin."

Tylosaurus was a mosasaur, a large, predatory marine lizard closely related to modern monitor lizards and to snakes. Along with plesiosaurs, sharks, fish, and other genera of mosasurs, it was a dominant predator of the Western Interior Seaway during the Late Cretaceous. A distinguishing characteristic of Tylosaurus is its elongated, cylindrical premaxilla (snout) from which it takes its name and which may have been used to ram and stun prey and also in intraspecific combat. Stomach contents associated with specimens of Tylosaurus proriger indicate that this ferocious mosasaur had a varied diet, including fish, sharks, smaller mosasaurs, plesiosaurs, and flightless diving birds such as Hesperornis. In some paleoenvironments, Tylosaurus seems to have preferred shallow, nearshore waters, while favoring deeper water farther out from shore in other environments.