<P> Shark teeth cannot be collected from just any type of rock . Any fossils, including fossil shark teeth, are preserved in sedimentary rocks after falling from their mouth . The sediment that the teeth were found in is used to help determine the age of the shark tooth due to the fossilization process . Shark teeth are most commonly found between the Upper Cretaceous and Tertiary periods . Only after about 10,000 years will a shark tooth fossilize . The teeth commonly found are not white because they are covered with sediment from fossilization . The sediment prevents oxygen and bacteria from attacking and decaying the tooth . </P> <P> Fossilized shark teeth can often be found in or near river bed banks, sand pits, and beaches . These teeth are typically worn, because they were frequently moved and redeposited in different areas repeatedly before settling down . Other locations, however, yield perfect teeth that were hardly moved during the ages . These teeth are typically fragile, and great care should be taken while excavating them . Phosphate pits, containing mostly fossil bones and teeth, or kaolin pits, are ideal places to look for fossil shark teeth . One of the most notable phosphate mines is in Central Florida, Polk County, and is known as Bone Valley . Most of the teeth found here range from 3 to 10 million years old . Near New Caledonia, up until the practice was banned, fishermen and commercial vessels used to dredge the sea floor for megalodon teeth . In the state of Georgia, shark teeth are found so often that they decided to make shark teeth the official state fossil in 1976 . </P> <P> In taxonomy, shark teeth are counted as follows: rows of teeth are counted along the line of the jaw, while series of teeth are counted from the front of the jaw inward . A single tooth row includes one or more functional teeth at the front of the jaw, and multiple replacement teeth behind this . For example, the jaws of a bull shark can have 50 rows of teeth in 7 series, with the outermost series functional, but most sharks have five series with the average shark having about 15 rows of teeth in each jaw . The small teeth at the symphysis, where the two halves of the jaw meet, are usually counted separately from the main teeth on either side . Sharks are also known to lose at least one tooth per week . Due to their specific arrangement of rows and series however, lost teeth can be replaced within a day . </P> <P> Identification of most sharks are found through a combination of tooth counts and tooth shapes . Teeth can even lead to the identification of shark species like the requiem shark . The fossilized records of teeth helps illustrate evolutionary history, and isolated teeth are used to study and analyze specific linear measurements of the species . In order to identify teeth and specific information about the teeth, research can be done on a shark tooth . This research may uncover many different aspects about the tooth itself, and the shark species . This proves complicated, however, due to the fact that most fossilized teeth are found mixed and scattered . To collect information on basic - life history and get dispersal estimates of a shark tooth, molecular - based technology is very efficient . To further shark population studies, collection of mtDNA can be extracted from shark jaws and teeth . To study the caries - reducing effect in sharks, studies are done on the fluorine atoms that are bound covalently to calcium atoms in the teeth . Each tooth has a complex fluorapatite structure enameloid . In order to reduce effects of deterioration in the teeth, it is useful to sample only the surface of the enameloid of the tooth for this specific research . Studying and researching shark teeth betters our understandings of shark feeding behaviors, evolutionary changes, and mechanisms . This helps us to identify the teeth, and even the species . </P>

How many rows of teeth to sharks have