(Late Cretaceous – Early Paleocene)

The Champsosaurus was a large aquatic reptile that lived in slow-moving freshwater rivers, swamps, and ponds during the Cretaceous period and into the Paleogene epoch. Champsosaurus was an odd-looking animal, with a crocodile-like body and an elongated snout which was useful in ambush hunting for fish. Despite their similarities to crocodilians, they are not closely related in the slightest.

Coniophis precedens (Late Cretaceous)

Coniophis precedens was roughly 7cm long and one of – if not the – first ever snake species. Coniophis precedens acts as a ‘missing-link’ species, demonstrating that snakes diverged from terrestrial lizards as opposed to marine reptiles. Like modern snakes, it had no limbs, but it had not yet developed the jaw structure found in modern snakes which allows them to eat larger prey. This means that Coniophis precedens would have had to eat smaller prey items like salamanders and lizards. 

 Toxochelys (Late Cretaceous)

Toxochelys was a genus of sea turtle that live in the Western Interior Seaway, and its fossils are found in the United States and Canada. Toxochelys lived a similar life as modern sea turtles, feeding mostly on jellyfish, squids, mollusks, crustaceans, and marine vegetation. However, Toxochelys was larger, growing up to 6 feet in length.

This specimen was found by museum staff in the Coon Creek Formation in Tennessee.

Plesiosaurs (Late Triassic – Late Cretaceous)

Plesiosaurs were marine reptiles that lived during the age of the dinosaurs. Though not a dinosaur itself, Plesiosaurs are well-known for their distinctive body shape which inspired the famous cryptid, the Loch Ness Monster. While many believers argue that a Plesiosaur could still be in Loch Ness in Scotland, they unfortunately all went extinct at the same time at the non-avian dinosaurs following the K-Pg Impact. Their diet was comprised of fish and cephalopods. Plesiosaurs came in different shapes and sizes; some where large and long-necked like the Zarafasaurus oceanis who were generally pacifistic and solitary animals, while some like the Pliosaurus had short necks and large heads and were much more aggressive hunters.

The first complete Plesiosaur fossil was found by famous female paleontologist Mary Anning in 1823.

Mosasaurs were large marine reptiles that dominated the oceans of the Cretaceous period. Though they lived at the same time as many dinosaurs and have a name reminiscent of a dinosaur’s, Mosasaurs are not dinosaurs at all. In fact, they closest living relatives are monitor lizards and snakes. Mosasaurs gained popular fame with the release of Jurassic World (2015), which depicts them as gargantuan, bulky-bodied giants. However, Mosasaurs in reality were sleeker and generally far smaller than the film’s depiction. The longest type of Mosasaur was the Tylosaurus, which reached up to 45-50 feet in length.

As ocean dwellers, Mosasaur fossils are found throughout the world. One freshwater variation was even found in Hungary. They were formidable predators whose diet included all types of smaller marine creatures like ammonites, fish, smaller mosasaurs, and even sea birds. While Mosasaurs stalked the ocean similar to modern sharks, as reptiles they still had to breach the surface for air like whales or sea turtles. Also similar to whales, it is likely that Mosasaurs had live births.

Alligator mississippiensis (Pliocene – Present)

Crocodilians have been around for around 80 million years and have successfully survived several mass extinction events relatively unchanged. The modern American Alligator first developed during the Pliocene period (23-5 million years ago) and has changed very little since then. Their tough scales, efficient hunting techniques, and relatively low demand for food makes them incredibly good at surviving whatever comes their way. Today, American Alligators are found in the American Southeast, predominately in Florida and Louisiana.