NJfossils.comFossils from Monmouth County, New Jersey
The Sharks (Chondrichthyes)
Shark teeth are the most common vertebrate find in the area because of their durability and numbers of teeth produced. Shark teeth are also abundant in a single jaw. Each working tooth has on average about 3-5 (varying based on the species) replacement files behind it that are in various stages of development. There are many (~30) such rows in an average jaw (it varies greatly with the species). When a tooth is lost or broken during feeding it is eventually replaced with the one behind it in about a week. This keeps sharp teeth available. Some sharks go through at least 10,000 teeth in their lifetime. Other New Jersey shark fossils include vertebrae, placoid scales, cartilage, fin spines, claspers, and coprolites. The body of the shark almost never fossilizes because it is made out of a cartilaginous skeleton.
There are also 3 abnormalities associated with fossil shark teeth. They are digestion, pathology, in vivo wear, and underdeveloped teeth.
The root and the core of shark teeth are made of osteodentine. The enameloid of shark teeth is 97-98% pure Calcium phosphate (information from Dr. Boessenecker on TheFossilForum). It makes the tooth highly resistant to wear during life and to stream action after fossilization. Once in a while a shark may swallow its own tooth (likely during feeding), leading to digested shark teeth. The enamel has much less nonsoluble/organic components than the osteodentine, allowing it to be more easily digested by the shark’s enzymes/stomach acid (information from Dr. Boessenecker on TheFossilForum).
Tooth deformities occur as bent or twisted tooth crowns, miss-ing or misshaped cusps, atypical protuberances, perforations, and abnormal root struc-tures. Deformed tooth files consisting of unusually overlapped or small teeth, or teethmisaligned in the jaw also occur in modern forms, but deformed tooth files generallyare not recognizable in fossils due to post-mortem dissociation of teeth and jaws. Asurvey of 200 modern lamniform and carcharhiniform sharks as well as literaturesources indicate that such deformities are produced by feeding-related injury to thetooth-forming tissue of the jaws, particularly by impaction of chondrichthian and tele-ost fin and tail spines. Tooth counts for several late Cretaceous genera, based on ma-terial recovered from coastal plain sites from New Jersey to Alabama, suggest that thefrequency of occurrence of deformed teeth in a species varies from about 0.015% inSqualicorax kaupito about 0.36% inParanomotodonsp. Tooth counts for modern lam-niform and carcharhiniform sharks yield a comparable range in frequency of tooth de-formities. Variation in frequency of tooth deformity may reflect interspecific differencesin feeding behavior and dietary preferences.
Becker, M.A, J.A. Chamberlain Jr., and P.W. Stoffer. 2000. Pathologic tooth deformities in modern and fossil chondrichthians: a consequence of feeding-related injury. Lethaia 33: 103-118.
in vivo stress fractures
(Squalicorax cf. “kaupi“)