A shark tooth is one of the numerous teeth of a shark. Sharks continually shed their teeth, and some Carcharhiniformes shed approximately 35,000 teeth in a lifetime. In some geological formations, shark's teeth are a common fossil. These fossils can be analyzed for information on shark evolution and biology, especially because the teeth are often the only part of the shark to be fossilized, in fact fossil teeth comprise much of the fossil record of the Selachimorpha, extending back hundreds of millions of years.
The most ancient types of sharks date back to 450 million years ago, during the Late Ordovician period, and they are mostly known from their fossilised teeth. The most commonly found fossil shark's teeth are however from the Cenozoic (65 million years ago).
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The shape of sharks' teeth vary according to their diet; those species that feed on mollusks and crustaceans have dense flattened teeth for crushing, those that feed on fish have needle-like teeth for gripping, and those that feed on larger prey such as mammals have pointed lower teeth for gripping and triangular upper teeth with serrated edges for cutting. The teeth of plankton-feeders such as the basking shark are greatly reduced and non-functional.[1]
Shark teeth are arranged in lines. The lines can be described as "rows" that are parallel to the line of the jaw, or as "series" which are perpendicular to the line of the jaw. 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.[2] For example, the jaws of a bull shark can have 50 rows of teeth in 7 series, with the outermost series functional. 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.
The oldest known records of fossilized shark teeth having been found, are by Pliny the Elder; he believed that these triangular objects fell from the sky during lunar eclipses.
According to Renaissance accounts, large, triangular fossil teeth often found embedded in rocky formations were believed to be petrified tongues of dragons and snakes and so were referred to as "tongue stones" or "glossopetrae", Glossopetrae were commonly thought to be a remedy or cure for various poisons and toxins. They were used in the treatment of snake bites. Due to this ingrained belief, many noblemen and royalty wore these "tongue stones" pendants or kept them in their pockets as good-luck charms.
This interpretation was corrected in 1667 by a Danish naturalist Nicolaus Steno, who recognized them as ancient shark teeth and famously produced a depiction of a shark's head bearing such teeth.[3] He mentioned his findings in a book, The Head of a Shark Dissected, which also contained an illustration of a C. megalodon tooth, previously considered to be a tongue stone.[4]
As one species evolves into another, its teeth may become difficult to classify, exhibiting characteristics of both species. For example, teeth from Carcharocles auriculatus as it evolved into C. angustidens, are difficult to definitively identify as coming from either species.
A commonly referred to transition is the evolution of Isurus hastalis, the Extinct Giant Mako, into the Great White shark, Carcharodon carcharias. There exist teeth which are believed to represent the transition between the two species. These teeth, from Carcharodon sp. are characterised by the wider, flatter crowns of the Extinct Giant Mako. However, they also exhibit partial, fading serrations which are more pronounced near the root, and disappear towards the tip of the tooth - serrations being found in Great Whites but not Extinct Giant Makos.
C. megalodon teeth are the largest of any shark, extinct or living, and are among the most sought after types of shark teeth in the world. This shark lived during the late Oligocene epoch and Neogene period, roughly about 25 to 1.5 million years ago. The smallest teeth are only 1.2 cm (0.5 in) in maximum height, while the largest teeth are in excess of 17.7 cm (7.0 in) in maximum height. These teeth are in extremely high demand by collectors and private investors, and they can fetch steep prices.
Shark teeth cannot be collected from any type of rock. Any fossils, including fossil shark teeth, are preserved in sedimentary rocks. Shark teeth are most commonly found between Upper Cretaceous and Tertiary periods.[5] 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.[5] 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.[5] Phosphate pits, containing mostly fossil bones and teeth, or kaoline 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. Near New Caledonia, up until the practice was banned, fishermen and commercial vessels used to dredge the sea floor for megalodon teeth.
In Oceania and America, shark teeth were commonly used for tools, especially weapons such as clubs and daggers, but also to carve wood and as tools for food preparation. For example, various weapons edged with shark teeth were used by the Native Hawaiians (see example here[6]), who called them leiomano.[7] Some types were reserved for royalty.[8] The Guaitaca (Weittaka) of coastal Brazil tipped their arrows with shark teeth.[9] The remains of shark tooth-edged weapons, as well as chert replicas of shark teeth, have been found in the Cahokia mounds of the upper Mississippi River valley, more than 1,000 km (620 mi) from the ocean.[10] It is reported that the rongorongo tablets of Easter Island were first shaped and then inscribed using a hafted shark tooth.[11]
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