Description:  The most common occurrences of this shark are that of its teeth.  Their teeth are fairly small, usually about 7 mm (about .25 in) in height if the roots are present.  More often than not the tooth is recovered with the small root missing leaving only the enamel.  The main cusp is rather plain looking and unornamental except for some faint plications in the enamel on the basal margin of the tooth.  Their teeth possess little or no cusplets but they do display lateral extensions of the enamel along the root margins.

Dorsal fin spines are less common than its teeth.  The fin spines in life could be as long as 15 cm (about 6 in) but due to their fragile nature and to stream wear, most sections are only a few centimeters long.  They are similar to the fin spines of the ratfish but the leading edge possesses ornamentation of small bumps.  The trailing edge has a single row of alternating curved projections, unlike the double row of the ratfish.

Cephalic claspers of the hybodont shark also occurs at Big Brook, but are uncommon an only present on the males.  The hook part resembles a fishhook without the barb.  The root is divided into three flattened lobes that are equal in size.  The hook and the three root lobes are usually broken off due to stream wear, leaving the more resistant root.  These hooks served as claspers and helped hold the male to the female during mating.  All modern shakes possess sexual claspers on their pelvic fins, but Hybodonts also had them on thier heads.  Except for the ratfish and the hybodont shark, the cephalic claspers of other sharks where only stiffened cartilage and did not fossilize.

They did not possess calcified vertebra so it is beveled that little if any of their vertebra are recovered at this locality.

Commonality:  Hybodus is fairly common in the earlier formations along the Atlantic Coastal Plain.  By the Maastrichtian, they went into a severe decline.  At Big Brook their remains are fairly rare.

Similar fossils:  The teeth are distinctive and are hard to confuse with other locality teeth.  The presence of the ornamentation and the single row of projections on the trailing edge can distinguish the spine of the hybodont shark from the spines of the ratfish.  The cephalic clasper resembles the cephalic clasper from the ratfish but they have some differences.  Unlike the hooks of the ratfish, the pelvic hooks of the hybodont shark have a curved hook and lack the angle.  The root lobes are also equal in size.

Size:  The hybodont shark did not get very large and was about 1 to 2 meters (about 3 to 7 feet) long

Notes:  Among the vast array of modern type sharks that occur at the end of the Cretaceous, Hybodus was a carry over from the older Carboniferous.  The hybodont sharks were one of the first modern types of sharks to appear in the fossil record.  Some paleontologists believe that during the Jurassic, the hybodont line diverged into today's modern shark lineage.  The hybodonts though displayed some primitive and different characteristics than the main body of sharks of that time.  Hybodont sharks do not appear in the fossil record after the Cretaceous in the Atlantic Coastal Plain and went into a worldwide decline during the Paleocene.
Hybodont Shark
Hybodus sp.
Hybodus sp.
Tooth
a. Picture without the root  b. Drawing of idealized tooth
Dorsal Fin Spine
a. Picture of sections  b. Drawing of complete spine
Cephalic Clasper
a. Top    b. Side   c. Worn specimen  d. Drawing of complete specimen
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Drawing of location of dorsal fin spines