Mosasaurus (Clidastes) conodon Marsh       Halisaurus platyspondylus Marsh
Proghathodon rapax (Hay)                       Mosasaurus maximus Cope
Description: There are several species of one of the most impressive groups of marine lizards, the mosasaurs, represented at Big Brook by their teeth and vertebrae. The majority of the mosasaur material is from Mosasaurus conodon.

There are three main types of teeth that come from
M. conodon, the ectopterygoid (teeth in the back of the roof of the mouth), the upper lateral and the lower lateral teeth. The ectopterygoid teeth are the most common and are conical shaped, but may be prismatic with a slight curve. They also have an oval cross section with a small height as compared to large base. The upper lateral teeth are similar to the ectopterygoid teeth but have a lens shaped cross section and a larger height verses a smaller base. The lower lateral teeth are more slender and have more of a circular cross section. All teeth have carinae (the cutting edges) on their teeth. The ectopterygoid and the lower lateral teeth have the carinae on both the front and the backside. The lower lateral teeth have carinae on the anterior side and one 90 degrees from the first edge. The ectopterygoid teeth are usually between 2 to 3.5 cm (about .75 to 1.5 in) long. The lower lateral and the anterior teeth are usually about the same height but are more massive. The upper lateral teeth may have many fine serrations on the carinae. The tips are usually worn from tooth usage during life. They are striated with very fine lines down the length of the tooth along with small growth cracks. In the base of the tooth, there is a steep conical shaped cavity so it could be attached to the jaws. Sometime teeth usually are found which have relatively shallow cavities.

A more uncommon mosasaur
Proghathodon rapax also occurs at Big Brook. The teeth of P. rapax are somewhat similar to M. conodon but have a steep curve in their teeth and are usually smaller with carinae on both the anterior and the posterior edges. Curiously, some Proghathodon teeth display very different morphologies. Some teeth become more squat and acorn shaped towards the back of the jaw.

The teeth of
M. maximus have been reported from Big Brook but are very rare. These are similar in structure to M. conodon but are larger about 5 to 7.5 cm (about 2 to 3 in).

Other parts of the skeleton are usually preserved as well, mostly vertebrae. Mosasaur vertebrae are somewhat uncommon but can be found. The centrum, or the main cylindrical part of the vertebra, is usually the only part that is recovered. They are usually lacking any of the other structures of the vertebrae other than the centrum because they are easily broken. The centrum is cylindrical and one end is rounded while the other is concave. Mosasaur vertebrae are usually 3 to 5 cm (about 1.25 to 2 in) in length and have a diameter of about 4 cm (about 1.5 in). Much larger vertebrae of
M. maximus may occur but based on the size and commonality most are probably M. conodon.

The rare species,
Halisaurus, has vertebrae that are distinguishable by the conical shape of the vertebrae. The main difference is that they are tapered toward the convexed end of the centrum and lack the divot of "crocodile" vertebrae.

Other mosasaur bones are not easily distinguishable and are usually very scrappy.

Commonality: One of the more common reptile remains that are found at Big Brook are from the mosasaurs, but compared to some of the other area fossil finds, are somewhat less common. Teeth are found most frequently with vertebrae less common and other identifiable bones very uncommon. Jaw sections are found rarely and it is very rare to find jaw sections with teeth still in them. Teeth and vertebrae from M. conodon are found most commonly. Proghathodon material is less common and Halisaurus and M. maximus are rare.

Similar fossils: Mosasaur teeth are distinguished from the teeth of the gavil-like "crocodile" by size and prismatic nature. "Crocodile" teeth are purely conical and usually less then 1 cm (about .75 in) in length while mosasaur teeth are larger. "Crocodile" teeth also usually lack prominent carinae. The teeth of the mosasaurs can also be confused with the teeth of the plesiosaurs, which are more slender and lack carinae all together. Since mosasaur teeth along with "crocodile" and plesiosaur teeth display a wide range of forms and characteristics, so some teeth may not fit any of these descriptions.

Mosasaur vertebrae are distinguishable from crocodile vertebra by the cylindrical shape, instead of the general conical shape of the vertebra of the crocodile. This is not always true because the vertebrae of
Halisaurus also possess this general shape. The convexed end in Halisaurus centra lacks a pronounced divot. The vertebrae of Halisaurus are rare and most of the vertebrae that display this shape are usually "crocodile".  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 the mosasaurs, and almost impossible to tell which species it belongs to.

Size: The Cretaceous seas of New Jersey were one of the few places where the mosasaurs reached a large size. Mosasaurs maximus may have reached a maximum length of 13 meters (about 40 feet), where as M. conodon, Proghathodon, and Halisaurus commonly reached between 3.6 to 6 meters (about 11 to 20 feet).

Notes: The mosasaurs were a large and varied group of marine reptiles that roamed the open surface waters of the sea. They feed on the abundant schools of fish, cephalopods, small turtles, and anything else that it happened upon. They competed for this food supply with the plesiosaurs and "crocodiles". By the late Cretaceous, the plesiosaurs were in a worldwide decline while the mosasaurs were flourishing. This would explain the rarity of plesiosaur material at Big Brook. Mosasaurs, along with the plesiosaurs, flourished worldwide, but became extinct at the end of the Cretaceous with no living relatives.

Interestingly, the mosasaurs could shed damaged or worn teeth and grow new ones, although they could not do this as fast as the sharks did. This accounts for the fact that most teeth are not in the best of conditions, while stream wear also takes its toll.
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M. maximus Skull
(State Muesum Specimen, Trenton)
M. conodon Teeth
M. conodon Tooth
M. maximus Tooth socket & Jaw
M. conodon Tooth
M. conodon Tooth in Jaw
(Ned Gilmore Specimen)
M. conodon Tooth in Jaw
(Tom Witamore Specimen)
H. platyspondylus Vertebra & Teeth
(State Museum Specimen, Trenton)
M. conodon Vertebra
(Ned Gilmore Specimen)
P. rapax Tooth
M. conodon Vertebra, Skull fragment, Jaw, & Tooth
I think that this is a baby mosasaur tooth