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77-546: Sharks are a great model organism to study because they continually produce highly mineralized tissues. Sharks continually shed their teeth and replace them through a tooth replacement system. Through this system, sharks replace their teeth relatively quickly with replacement teeth that are ready to rotate because their teeth often get damaged while catching prey. They will replace teeth that are broken and young sharks can even replace their teeth weekly. Although sharks constantly shed their teeth, factors such as water temperature affect

154-472: A constant rate. These " molecular clocks ", however, are fallible, and provide only approximate timing: for example, they are not sufficiently precise and reliable for estimating when the groups that feature in the Cambrian explosion first evolved, and estimates produced by different techniques may vary by a factor of two. Organisms are only rarely preserved as fossils in the best of circumstances, and only

231-412: A day. 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

308-426: A depiction of a shark's head bearing such teeth. 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. In Oceania and America , shark teeth were commonly used for tools, especially on weapons such as clubs and daggers, but also as blades to carve wood and as tools for food preparation, such as

385-426: A fraction of such fossils have been discovered. This is illustrated by the fact that the number of species known through the fossil record is less than 5% of the number of known living species, suggesting that the number of species known through fossils must be far less than 1% of all the species that have ever lived. Because of the specialized and rare circumstances required for a biological structure to fossilize, only

462-499: A hierarchical classification system still in use today. Darwin and his contemporaries first linked the hierarchical structure of the tree of life with the then very sparse fossil record. Darwin eloquently described a process of descent with modification, or evolution, whereby organisms either adapt to natural and changing environmental pressures, or they perish. When Darwin wrote On the Origin of Species by Means of Natural Selection, or

539-519: A large "megatoothed" shark . It is known that there is at least one genus in the family Otodontidae , that being Otodus . But the names and number of the genera in Otodontidae is controversial and the family's accepted phylogeny varies among paleontologists in different parts of the world. In the US and Britain the most widespread genus name for otodontids with serrated teeth is Carcharocles , and

616-418: A mid-Ordovician age. Such index fossils must be distinctive, be globally distributed and occupy a short time range to be useful. Misleading results are produced if the index fossils are incorrectly dated. Stratigraphy and biostratigraphy can in general provide only relative dating ( A was before B ), which is often sufficient for studying evolution. However, this is difficult for some time periods, because of

693-536: A mutation first appeared. Phylogenetics and paleontology work together in the clarification of science's still dim view of the appearance of life and its evolution. Niles Eldredge 's study of the Phacops trilobite genus supported the hypothesis that modifications to the arrangement of the trilobite's eye lenses proceeded by fits and starts over millions of years during the Devonian . Eldredge's interpretation of

770-399: A past geological age . Examples include bones , shells , exoskeletons , stone imprints of animals or microbes , objects preserved in amber , hair , petrified wood and DNA remnants. The totality of fossils is known as the fossil record . Though the fossil record is incomplete, numerous studies have demonstrated that there is enough information available to give a good understanding of

847-570: A portion of the deceased organism, usually that portion that was partially mineralized during life, such as the bones and teeth of vertebrates , or the chitinous or calcareous exoskeletons of invertebrates . Fossils may also consist of the marks left behind by the organism while it was alive, such as animal tracks or feces ( coprolites ). These types of fossil are called trace fossils or ichnofossils , as opposed to body fossils . Some fossils are biochemical and are called chemofossils or biosignatures . Gathering fossils dates at least to

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924-594: 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" as pendants or kept them in their pockets as good-luck charms. This interpretation was corrected in 1611 by the Italian naturalist Fabio Colonna , who recognized them as ancient shark teeth, and, in 1667, by the Danish naturalist Nicolaus Steno , who discussed their composition and famously produced

1001-400: A richly diverse assembly of early multicellular eukaryotes . The fossil record and faunal succession form the basis of the science of biostratigraphy or determining the age of rocks based on embedded fossils. For the first 150 years of geology , biostratigraphy and superposition were the only means for determining the relative age of rocks. The geologic time scale was developed based on

1078-448: A small percentage of life-forms can be expected to be represented in discoveries, and each discovery represents only a snapshot of the process of evolution. The transition itself can only be illustrated and corroborated by transitional fossils, which will never demonstrate an exact half-way point. The fossil record is strongly biased toward organisms with hard-parts, leaving most groups of soft-bodied organisms with little to no role. It

1155-449: Is a notable example of how knowledge encoded by the fossil record continues to contribute otherwise unattainable information on the emergence and development of life on Earth. For example, the research suggests Markuelia has closest affinity to priapulid worms, and is adjacent to the evolutionary branching of Priapulida , Nematoda and Arthropoda . Despite significant advances in uncovering and identifying paleontological specimens, it

1232-450: Is an extinct species of large sharks in the genus Otodus of the family Otodontidae , closely related to the sharks of the genus Otodus , and also closely related to the later species megalodon . The largest individuals were about 9.5 metres (31 ft) long. Its teeth were large, having coarse serrations on the cutting edge, and also with two large cusplets. The teeth can reach up to 130 millimetres (5.1 in), and belonged to

1309-479: Is generally accepted that the fossil record is vastly incomplete. Approaches for measuring the completeness of the fossil record have been developed for numerous subsets of species, including those grouped taxonomically, temporally, environmentally/geographically, or in sum. This encompasses the subfield of taphonomy and the study of biases in the paleontological record. Paleontology seeks to map out how life evolved across geologic time. A substantial hurdle

1386-710: Is relatively large - from 25 to 114 millimetres (0.98 to 4.49 in). However, it is smaller than that of megalodon and Otodus angustidens ; the tooth length of O. megalodon is 38 to 178 millimetres (1.5 to 7.0 in) and O. angustidens 25 to 117 millimetres (0.98 to 4.61 in). Smaller individuals were about 4 metres (13 ft) long. Most O. auriculatus teeth come from South Carolina and North Carolina . However, many Eocene shark teeth are known from Khouribga Plateau , in Morocco and Seymour Island , in Antarctica . Fossil teeth have also been found in

1463-438: Is replete with the mollusks , the vertebrates , the echinoderms , the brachiopods and some groups of arthropods . Fossil sites with exceptional preservation—sometimes including preserved soft tissues—are known as Lagerstätten —German for "storage places". These formations may have resulted from carcass burial in an anoxic environment with minimal bacteria, thus slowing decomposition. Lagerstätten span geological time from

1540-470: Is the difficulty of working out fossil ages. Beds that preserve fossils typically lack the radioactive elements needed for radiometric dating . This technique is our only means of giving rocks greater than about 50 million years old an absolute age, and can be accurate to within 0.5% or better. Although radiometric dating requires careful laboratory work, its basic principle is simple: the rates at which various radioactive elements decay are known, and so

1617-405: Is the evolution of Isurus hastalis , the extinct giant mako, into the great white shark , Carcharodon carcharias . There exist teeth that 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

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1694-413: Is the science of deciphering the "layer-cake" that is the sedimentary record. Rocks normally form relatively horizontal layers, with each layer younger than the one underneath it. If a fossil is found between two layers whose ages are known, the fossil's age is claimed to lie between the two known ages. Because rock sequences are not continuous, but may be broken up by faults or periods of erosion , it

1771-467: Is very difficult to match up rock beds that are not directly adjacent. However, fossils of species that survived for a relatively short time can be used to match isolated rocks: this technique is called biostratigraphy . For instance, the conodont Eoplacognathus pseudoplanus has a short range in the Middle Ordovician period. If rocks of unknown age have traces of E. pseudoplanus , they have

1848-584: The māripi of the Māori . For example, various weapons edged with shark teeth were used by the Native Hawaiians (see example here), who called them leiomano . Some types were reserved for royalty . The Guaitaca (Weittaka) of coastal Brazil tipped their arrows with shark teeth. The remains of shark tooth-edged weapons, as well as chert replicas of shark teeth, have been found in the Cahokia mounds of

1925-801: The Cambrian period to the present . Worldwide, some of the best examples of near-perfect fossilization are the Cambrian Maotianshan Shales and Burgess Shale , the Devonian Hunsrück Slates , the Jurassic Solnhofen Limestone , and the Carboniferous Mazon Creek localities. A fossil is said to be recrystallized when the original skeletal compounds are still present but in a different crystal form, such as from aragonite to calcite . Replacement occurs when

2002-576: The Late Ordovician period , and are mostly known by their fossilized teeth and dermal denticles . However, the most commonly found fossil shark teeth are from the Cenozoic era (the last 66 million years). Though sharks often are highly specialized, as a category they have ranged widely in their adaptations. Their teeth reflect this, ranging widely in form and function. There are a number of common types of shark teeth, that vary according to

2079-586: The Phacops fossil record was that the aftermaths of the lens changes, but not the rapidly occurring evolutionary process, were fossilized. This and other data led Stephen Jay Gould and Niles Eldredge to publish their seminal paper on punctuated equilibrium in 1971. Synchrotron X-ray tomographic analysis of early Cambrian bilaterian embryonic microfossils yielded new insights of metazoan evolution at its earliest stages. The tomography technique provides previously unattainable three-dimensional resolution at

2156-569: The Renaissance . Leonardo da Vinci concurred with Aristotle's view that fossils were the remains of ancient life. For example, Leonardo noticed discrepancies with the biblical flood narrative as an explanation for fossil origins: If the Deluge had carried the shells for distances of three and four hundred miles from the sea it would have carried them mixed with various other natural objects all heaped up together; but even at such distances from

2233-602: The Song dynasty during the 11th century, who kept a specific seashell fossil with his own poem engraved on it. In his Dream Pool Essays published in 1088, Song dynasty Chinese scholar-official Shen Kuo hypothesized that marine fossils found in a geological stratum of mountains located hundreds of miles from the Pacific Ocean was evidence that a prehistoric seashore had once existed there and shifted over centuries of time . His observation of petrified bamboos in

2310-402: The law of superposition ) preserved different assemblages of fossils, and that these assemblages succeeded one another in a regular and determinable order. He observed that rocks from distant locations could be correlated based on the fossils they contained. He termed this the principle of faunal succession . This principle became one of Darwin's chief pieces of evidence that biological evolution

2387-403: The thunderbird . There is no such direct mythological connection known from prehistoric Africa, but there is considerable evidence of tribes there excavating and moving fossils to ceremonial sites, apparently treating them with some reverence. In Japan, fossil shark teeth were associated with the mythical tengu , thought to be the razor-sharp claws of the creature, documented some time after

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2464-417: The upper Mississippi River valley, more than 1,000 km (620 mi) from the ocean. It is reported that the rongorongo tablets of Easter Island were first shaped and then inscribed using a hafted shark tooth. Fossil A fossil (from Classical Latin fossilis , lit.   ' obtained by digging ' ) is any preserved remains, impression, or trace of any once-living thing from

2541-453: The 16th century. Roman naturalist Pliny the Elder wrote of " tongue stones ", which he called glossopetra . These were fossil shark teeth, thought by some classical cultures to look like the tongues of people or snakes. He also wrote about the horns of Ammon , which are fossil ammonites , whence the group of shelled octopus-cousins ultimately draws its modern name. Pliny also makes one of

2618-739: The 19th century that certain fossils were associated with certain rock strata led to the recognition of a geological timescale and the relative ages of different fossils. The development of radiometric dating techniques in the early 20th century allowed scientists to quantitatively measure the absolute ages of rocks and the fossils they host. There are many processes that lead to fossilization , including permineralization , casts and molds, authigenic mineralization , replacement and recrystallization, adpression, carbonization , and bioimmuration. Fossils vary in size from one- micrometre (1 μm) bacteria to dinosaurs and trees, many meters long and weighing many tons. A fossil normally preserves only

2695-413: The 8th century AD. In medieval China, the fossil bones of ancient mammals including Homo erectus were often mistaken for " dragon bones" and used as medicine and aphrodisiacs . In addition, some of these fossil bones are collected as "art" by scholars, who left scripts on various artifacts, indicating the time they were added to a collection. One good example is the famous scholar Huang Tingjian of

2772-615: The Preservation of Favoured Races in the Struggle for Life , the oldest animal fossils were those from the Cambrian Period, now known to be about 540 million years old. He worried about the absence of older fossils because of the implications on the validity of his theories, but he expressed hope that such fossils would be found, noting that: "only a small portion of the world is known with accuracy." Darwin also pondered

2849-566: The Proterozoic and deeper still in the Archean is only "recounted by microscopic fossils and subtle chemical signals." Molecular biologists, using phylogenetics , can compare protein amino acid or nucleotide sequence homology (i.e., similarity) to evaluate taxonomy and evolutionary distances among organisms, with limited statistical confidence. The study of fossils, on the other hand, can more specifically pinpoint when and in what organism

2926-413: The beach, indicating the fossils were once living animals. He had previously explained them in terms of vaporous exhalations , which Persian polymath Avicenna modified into the theory of petrifying fluids ( succus lapidificatus ). Recognition of fossil seashells as originating in the sea was built upon in the 14th century by Albert of Saxony , and accepted in some form by most naturalists by

3003-714: The beginning of recorded history. The fossils themselves are referred to as the fossil record. The fossil record was one of the early sources of data underlying the study of evolution and continues to be relevant to the history of life on Earth . Paleontologists examine the fossil record to understand the process of evolution and the way particular species have evolved. Fossils have been visible and common throughout most of natural history, and so documented human interaction with them goes back as far as recorded history, or earlier. There are many examples of paleolithic stone knives in Europe, with fossil echinoderms set precisely at

3080-815: The bottom of the ocean floor. This was the first common style of shark tooth, present in the Devonian , four hundred million years ago. Sharks with needle-like teeth commonly feed on small to medium-sized fish, sometimes including small sharks. These teeth are especially effective for such prey because they can easily grip their slippery and narrow bodies. Modern examples include the blue shark and bull sharks . These sharks specifically use their teeth to feed on small prey like squid , flounder , stingrays , and even hammerhead sharks . This combination of pointed lower teeth, with triangular upper teeth are especially useful for cutting prey that consist of large mammals and fish. The combination of teeth entails serrated edges to cut

3157-510: 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

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3234-670: The deity Sopdu , the Morning Star, equivalent of Venus in Roman mythology. Fossils appear to have directly contributed to the mythology of many civilizations, including the ancient Greeks. Classical Greek historian Herodotos wrote of an area near Hyperborea where gryphons protected golden treasure. There was indeed gold mining in that approximate region , where beaked Protoceratops skulls were common as fossils. A later Greek scholar, Aristotle , eventually realized that fossil seashells from rocks were similar to those found on

3311-425: The diet of the shark. Examples include dense flattened teeth for crushing; long needle-like teeth for gripping; pointed lower teeth for gripping combined with serrated, triangular upper teeth for cutting, and teeth that are tiny, greatly reduced, and non-functional. Dense flattened teeth are used to crush prey like bivalves and crustaceans. These sharks include nurse sharks and angel sharks. They are typically found at

3388-466: The dry northern climate zone of what is now Yan'an , Shaanxi province, China, led him to advance early ideas of gradual climate change due to bamboo naturally growing in wetter climate areas. In medieval Christendom , fossilized sea creatures on mountainsides were seen as proof of the biblical deluge of Noah's Ark . After observing the existence of seashells in mountains, the ancient Greek philosopher Xenophanes (c. 570 – 478 BC) speculated that

3465-415: The earlier known references to toadstones , thought until the 18th century to be a magical cure for poison originating in the heads of toads, but which are fossil teeth from Lepidotes , a Cretaceous ray-finned fish. The Plains tribes of North America are thought to have similarly associated fossils, such as the many intact pterosaur fossils naturally exposed in the region, with their own mythology of

3542-550: The earliest known stromatolites are over 3.4 billion years old. The fossil record is life's evolutionary epic that unfolded over four billion years as environmental conditions and genetic potential interacted in accordance with natural selection. The Virtual Fossil Museum Paleontology has joined with evolutionary biology to share the interdisciplinary task of outlining the tree of life, which inevitably leads backwards in time to Precambrian microscopic life when cell structure and functions evolved. Earth's deep time in

3619-464: The earth during earthquake and subsidences, and petrifies whatever comes into contact with it. As a matter of fact, the petrifaction of the bodies of plants and animals is not more extraordinary than the transformation of waters. From the 13th century to the present day, scholars pointed out that the fossil skulls of Deinotherium giganteum , found in Crete and Greece, might have been interpreted as being

3696-478: The existence of a world previous to ours, destroyed by some kind of catastrophe. Interest in fossils, and geology more generally, expanded during the early nineteenth century. In Britain, Mary Anning 's discoveries of fossils, including the first complete ichthyosaur and a complete plesiosaurus skeleton, sparked both public and scholarly interest. Early naturalists well understood the similarities and differences of living species leading Linnaeus to develop

3773-712: The food when passing water through their gills. Basking sharks feed by swimming towards their prey with their mouth open and straining their food. Through this process the shark is able to successfully eat hundreds of pounds of zooplankton each day. Whale sharks feed by using rakers on their gill bars and strain them from their gill slits after sweeping krill and other prey into their mouths. As one species evolves into another, its teeth may become difficult to classify, exhibiting characteristics of both species. (Example: teeth from Otodus auriculatus as it evolved into O. angustidens ) are difficult to definitively identify as coming from either species. A commonly referred to transition

3850-519: The hand grip, dating back to Homo heidelbergensis and Neanderthals . These ancient peoples also drilled holes through the center of those round fossil shells, apparently using them as beads for necklaces. The ancient Egyptians gathered fossils of species that resembled the bones of modern species they worshipped. The god Set was associated with the hippopotamus , therefore fossilized bones of hippo-like species were kept in that deity's temples. Five-rayed fossil sea urchin shells were associated with

3927-539: The larger prey into smaller portions in order to easily swallow the pieces. The most famously known shark with these teeth is the great white shark , which feeds on animals such as sea lions , dolphins , other sharks, and even small whales. The teeth of plankton-feeders, such as the basking shark and whale shark , are greatly reduced and non-functional. These sharks filter feed on prey by opening their mouths to let tiny organisms get sucked into their mouths to feed without using their teeth at all, instead filtering

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4004-609: The largest teeth are in excess of 17.7 cm (7.0 in). The smaller teeth ranging from 3 + 1 ⁄ 2 " and 4 + 1 ⁄ 2 " are more common finds, while teeth over 5", 6", and 7" are more rare. These teeth are in extremely high demand by collectors and private investors, and they can fetch steep prices according to their size and deterioration. The larger teeth can cost as much as 3,000 dollars. 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

4081-535: The limits of fossilization. Fossils of two enigmatic bilaterians, the worm-like Markuelia and a putative, primitive protostome , Pseudooides , provide a peek at germ layer embryonic development. These 543-million-year-old embryos support the emergence of some aspects of arthropod development earlier than previously thought in the late Proterozoic. The preserved embryos from China and Siberia underwent rapid diagenetic phosphatization resulting in exquisite preservation, including cell structures. This research

4158-464: 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

4235-422: The official state fossil in 1976. 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

4312-425: 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

4389-475: The owners of unserrated ones Otodus . In countries of the former USSR, like Ukraine or Russia , all of these genera were attributed to Otodus , because scientists like Zhelezko and Kozlov thought that the absence or presence of tooth serrations is not enough to place these sharks in different taxa . O. auriculatus was a large lamniform shark, with the largest individuals reaching a body length of 9.5 metres (31 ft). The tooth length of O. auriculatus

4466-474: The pattern of diversification of life on Earth. In addition, the record can predict and fill gaps such as the discovery of Tiktaalik in the arctic of Canada . Paleontology includes the study of fossils: their age, method of formation, and evolutionary significance. Specimens are usually considered to be fossils if they are over 10,000 years old. The oldest fossils are around 3.48 billion years to 4.1 billion years old. The observation in

4543-545: The problems involved in matching rocks of the same age across continents . Family-tree relationships also help to narrow down the date when lineages first appeared. For instance, if fossils of B or C date to X million years ago and the calculated "family tree" says A was an ancestor of B and C, then A must have evolved earlier. It is also possible to estimate how long ago two living clades diverged, in other words approximately how long ago their last common ancestor must have lived, by assuming that DNA mutations accumulate at

4620-443: The ratio of the radioactive element to its decay products shows how long ago the radioactive element was incorporated into the rock. Radioactive elements are common only in rocks with a volcanic origin, and so the only fossil-bearing rocks that can be dated radiometrically are volcanic ash layers, which may provide termini for the intervening sediments. Consequently, palaeontologists rely on stratigraphy to date fossils. Stratigraphy

4697-462: The relative ages of rock strata as determined by the early paleontologists and stratigraphers . Since the early years of the twentieth century, absolute dating methods, such as radiometric dating (including potassium/argon , argon/argon , uranium series , and, for very recent fossils, radiocarbon dating ) have been used to verify the relative ages obtained by fossils and to provide absolute ages for many fossils. Radiometric dating has shown that

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4774-498: The root, and disappear towards the tip of the tooth - serrations being found in great whites but not extinct giant makos. Otodus 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, about 28 to 1.5 million years ago, and ranged to a maximum length of 60 ft. The smallest teeth are only 1.2 cm (0.5 in) in height, while

4851-429: The sea and that they were still living when the strait of Gibraltar was cut through. In the mountains of Parma and Piacenza multitudes of shells and corals with holes may be seen still sticking to the rocks.... In 1666, Nicholas Steno examined a shark, and made the association of its teeth with the "tongue stones" of ancient Greco-Roman mythology, concluding that those were not in fact the tongues of venomous snakes, but

4928-423: The sea we see the oysters all together and also the shellfish and the cuttlefish and all the other shells which congregate together, found all together dead; and the solitary shells are found apart from one another as we see them every day on the sea-shores. And we find oysters together in very large families, among which some may be seen with their shells still joined together, indicating that they were left there by

5005-658: The shape of teeth in which "juvenile teeth start out more narrow and robust, while adult teeth are broader and thinner". In some formations, shark's teeth are a common fossil . These fossils can be analyzed for information on shark evolution and biology ; they are often the only part of the shark to be fossilized. Fossil teeth comprise much of the fossil record of the Elasmobranchii , extending back to hundreds of millions of years. A shark tooth contains resistant calcium phosphate materials. The most ancient types of shark-like fish date back to 450 million years ago, during

5082-489: The shell, bone, or other tissue is replaced with another mineral. In some cases mineral replacement of the original shell occurs so gradually and at such fine scales that microstructural features are preserved despite the total loss of original material. Scientists can use such fossils when researching the anatomical structure of ancient species. Several species of saurids have been identified from mineralized dinosaur fossils. Otodus auriculatus Otodus auriculatus

5159-586: The skulls of the Cyclopes of Greek mythology , and are possibly the origin of that Greek myth. Their skulls appear to have a single eye-hole in the front, just like their modern elephant cousins, though in fact it's actually the opening for their trunk. In Norse mythology , echinoderm shells (the round five-part button left over from a sea urchin) were associated with the god Thor , not only being incorporated in thunderstones , representations of Thor's hammer and subsequent hammer-shaped crosses as Christianity

5236-467: The sudden appearance of many groups (i.e. phyla ) in the oldest known Cambrian fossiliferous strata. Since Darwin's time, the fossil record has been extended to between 2.3 and 3.5 billion years. Most of these Precambrian fossils are microscopic bacteria or microfossils . However, macroscopic fossils are now known from the late Proterozoic. The Ediacara biota (also called Vendian biota) dating from 575 million years ago collectively constitutes

5313-451: The teeth of some long-extinct species of shark. Robert Hooke (1635–1703) included micrographs of fossils in his Micrographia and was among the first to observe fossil forams . His observations on fossils, which he stated to be the petrified remains of creatures some of which no longer existed, were published posthumously in 1705. William Smith (1769–1839) , an English canal engineer, observed that rocks of different ages (based on

5390-497: 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

5467-479: The teeth, and even the species. The oldest known records of fossilized shark teeth are by Pliny the Elder , who 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

5544-502: 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

5621-550: The tooth. 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

5698-539: The turnover rate. While warmer water temperatures produced faster rates, cold water temperatures slowed tooth replacement rates in nurse sharks. They are only shed once new teeth are formed underneath and push them out of the connective tissue that was holding them in place. The sex of the shark also plays a role in the development of teeth and the differences in teeth in species due to gender is called sexual heterodonty. Usually, females have larger teeth because on average they are usually larger than males. Also, age can change

5775-524: The world was once inundated in a great flood that buried living creatures in drying mud. In 1027, the Persian Avicenna explained fossils' stoniness in The Book of Healing : If what is said concerning the petrifaction of animals and plants is true, the cause of this (phenomenon) is a powerful mineralizing and petrifying virtue which arises in certain stony spots, or emanates suddenly from

5852-458: Was adopted, but also kept in houses to garner Thor's protection. These grew into the shepherd's crowns of English folklore, used for decoration and as good luck charms, placed by the doorway of homes and churches. In Suffolk , a different species was used as a good-luck charm by bakers, who referred to them as fairy loaves , associating them with the similarly shaped loaves of bread they baked. More scientific views of fossils emerged during

5929-408: Was real. Georges Cuvier came to believe that most if not all the animal fossils he examined were remains of extinct species. This led Cuvier to become an active proponent of the geological school of thought called catastrophism . Near the end of his 1796 paper on living and fossil elephants he said: All of these facts, consistent among themselves, and not opposed by any report, seem to me to prove

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