Hadrodus priscus (Leidy)

Age  Cretaceous - Occurrence  Uncommon*
 

In New Jersey the fossil remains of the boney fish Hadrodus priscus is represented by two types of teeth. The front (oral) teeth, a crushing type arranged in irregular rows and uneven in size and the back pharyngeal teeth which formed a comb like structure thought to retain food and possibly help reduce it by crushing or grinding. All the front teeth I’ve found to date have been identified by Earl Manning as being juvenile teeth. These are small (3-4 mm ≈ 1/8^th inch in diameter), having a round or oval translucent button type shape which often shows a heavy wear pattern. The incisors have an eerie similarity to a human baby tooth. The back pharyngeal teeth are small and flat with a hook-like appearance. It's thought that the young lived in protected near shore waters, while the adults lived in deeper, open water environment.      

(Earl Manning, pers. comm. 2012)
Based on the transparency and very small size (they also often have tiny "dimples" on the worn occlusal surface), I'd say all of these are juvenile (adult teeth are far larger) Hadrodus priscus teeth, they just aren't all from the same part of the jaws. The circular and oval ones are oral (cavity) teeth, equivalent to the vomerine (up.) and prearticular (lw.) toothplate teeth of pycnodonts. The two on the rt. are only different in being less worn, so that the dentine doesn't show up in the middle of the occ. surface. The incisor-like tooth in the bottom center is an incisor   

Scale 5 mm = 0.197 in

One of the more common oval forms of the front teeth.
Scale 5 mm = 0.197 in

Hadrodus priscus
Left - Front tooth with root - Right - Heavily worn teeth show as circle, easy to miss. 
H. priscus did not shed it's front teeth and many specimens will show heavy wear patterns.
 

Hadrodus priscus back pharyngeal teeth.
These teeth would have been found near the back of the throat arranged in a comb-like structure
and is thought to help further process food.
Scale 5 mm = 0.197 in

At just a little under 1/2 inch this is this large pharyngeal tooth and retains most of the root.
Note the transparent nature of the hook on the right.
 

*Commonality - I've lumped both the front oral teeth and back pharyngeal teeth
together although the pharyngeal teeth are found much more frequently.

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