Plesiosaur
Cimoliasaurus magnus Leidy
Description: The long necked plesiosaur is represented uncommonly at Big Brook by its teeth, vertebrae, and sometimes other skeletal material. It is the only plesiosaur identified from this locality, so any plesiosaur teeth are readily assignable to Cimoliasaurus.

The teeth of this plesiosaur are conical with an oval cross section at the base becoming more flattened toward the tip. They are long and slender but somewhat flattened without carinae. Their teeth are coated with enamel and are usually smooth with some growth cracks. Plesiosaur teeth have a conical indent in the bottom of the root to fit into the socket of the jaw. These teeth are usually about 2 to 5 cm (about .75 to 2 in) long.

Their vertebrae are somewhat uncommon but when found are very distinctive. The centrum, or the main cylindrical to ovate part of the vertebrae, is usually the only part that is recovered. They are more than likely lacking any of the other structures of the vertebrae other than the centrum because they are easily broken. They have a cylindrical shape with flat ends resembling a soda can. The ends may have a small divot in the center. The sides of the vertebrae may be smooth but more than likely the thin coating of bone around the sides is warn off due to stream action, exposing the very spongy bone structure underneath. There are three holes in the side of the vertebrae; one on the dorsal side while the ventral side has two. Most vertebrae are between 5 to 8 cm (about 2 to 3 in) and about 5 cm (about 2 in) in diameter but can get to about 10 cm (about 4 in) long and wide.

Other plesiosaur bones are not easily distinguishable and are usually very scrappy. The scrappy reptilian bone of mosasaurs, sea turtles, "crocodiles", and plesiosaurs are similar and are all found at this locality. Unless the bones are complete, it is difficult to attribute them to plesiosaurs.

Commonality: Teeth and vertebrae are uncommon. Other identifiable material is rare.

Similar fossils: Plesiosaur teeth are distinguishable from area mosasaur teeth in that they lack the carinae that the mosasaur teeth have. They are also longer and more slender than mosasaur teeth. The teeth of the plesiosaur can also be confused with the teeth from the gavil like "crocodile" which are smaller, usually less than 2 cm (about .75 in) long. Their vertebrae can resemble crocodile or the mosasaur vertebrae but are lacking the convex and concaved ends.

Size: This plesiosaur reached a maximum length of 13 meters (about 40 feet) but commonly reached only 6 meters (about 20 feet).

Notes: The plesiosaurs were a group of large marine reptiles that possessed extremely long necks and tails. They roamed the open surface waters of the sea feeding on the abundant schools of fish and small reptiles. They competed for this food supply with the mosasaurs, "crocodiles", and sharks. Interestingly, plesiosaurs become very scarce in the fossil record before the end of the Late Cretaceous while the mosasaurs (temporarily) and crocodiles become more abundant. This may suggest the more ancient plesiosaurs, that where around since the Jurassic, were becoming out classed by the newer types of mosasaurs, modern types of crocodiles, and sharks.
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Tooth
Typical Vertebra
a. End  b. Top  c. Bottom showing two holes
Vertebra