Fossil of the month: Megalodon teeth
Among the KGS specimen collections is a group of fossilized teeth from ancient sharks, known as megalodons. These extinct sharks are among the largest sharks of all time. Think of a hefty great white shark on steroids!
Although fossil megalodon teeth are found in many parts of the world, they are not found in Kentucky. The Kentucky Geological Survey has many samples in its paleontological collection, however, thanks to a donation from Mary Ann Russell.
Description. Megalodon teeth are similar in shape but larger and broader than the teeth of the modern great white shark. Teeth are triangular, broad at the base, and thin toward the peak, like a chisel or wedge, although sometimes they curve toward the cusp. Teeth have a root, which has a V-shaped notch at its base, and an enamel-covered crown. The root has a rough, porous, bone-like texture, whereas the enamel is smooth and polished, but sometimes broken by vertical cracks. The outward-facing (lingual) side of the tooth bulges outward. The inward-facing (labial) side of the tooth is generally flat to slightly curved. The border between the crown and root on the lingual side of the tooth is marked by a chevron-shaped feature called the bourlette or dental band. The edges of the teeth are serrated like steak knives.
Megalodon teeth are generally 3 to 5 inches in height (from base of root to apex of crown), with the largest teeth exceeding 7 inches! For comparison, the largest great white shark teeth are 2 to 3 inches tall. For both great whites and megalodon, teeth in the front of the mouth (anterior teeth) are larger and more symmetrical (equal width on either side of the midline) in shape than those farther back along the jaw. Rear (posterior) teeth cusps are commonly asymmetrical, with cusps slanted slightly backward along the jaw (Gottfried and others, 1996; Pimiento and others, 2010; Pimiento and Balk, 2015; Shimado and others, 2020; Perez and others, 2021).
As with modern sharks, megalodon had a skeleton composed of cartilage, which doesn't fossilize well, so only the teeth remain as clues to the existence of this ancient predator. Because the teeth are large and similar in shape to the modern great white shark, scientists hypothesize what megalodons looked like and how they lived based on studies of modern great white sharks.
Scientific Name. "Megalodon" is a species name, which means "large tooth." Historically, the megalodon shark was thought to be an ancestor of the modern great white shark (Carcharodon carcharias), so was given the same genus name and called Carcharodon megalodon. The lineage of megalodon has been debated, however, and it may not be a direct ancestor, or even in the same family, as the modern great white shark (Casier, 1960; Nyberg and others, 2006). Hence, several new names have been suggested, including Carcharocles megalodon, Megaselachus megalodon, Procarcharodon megalodon, and more recently, Otodus megalodon (Cooper and others, 2020). Otodus megalodon is the current official genus name, but don't be confused; these all refer to the same giant-toothed shark.
Range and distribution. Megalodons lived in the world's oceans during the Neogene Period, from the middle Miocene Epoch (15.9 million years ago) to the early Pliocene Epoch (2.6 million years ago) (Pimiento and Balk, 2015). This was a time after the dinosaurs were extinct, but prior to the great ice ages. Megalodons lived in most of the world's oceans, and teeth are found in marine coastal deposits around the world. In the United States, they are mostly found along the southeastern Atlantic coast in Florida, Georgia, North and South Carolina, and Maryland.
Paleoecology: How long was Megalodon? How do you estimate the size of an organism when fossils of its body are not preserved? In the case of megalodon, scientists studying modern sharks found that tooth size increased proportionally with the shark's body size (Gottfried and others, 1996). Researchers have used data from modern great white sharks to suggest that if megalodon had a similar body shape, then its body size should also be proportional to its tooth size. From this simple "if-then" statement, and many measurements of tooth size and body length in great white sharks (and in some cases, other kinds of large sharks), researchers have devised formulas for estimating the size of extinct megalodon from their teeth (Randall, 1973; Gottfried and others, 1996; Shimada, 2002; Pimiento and others, 2010; Cooper and others, 2020; Shimada and others, 2020; Perez and others, 2021).
Modern great white sharks are usually 6 to 13 feet in length (females are larger than males), but may be as much as 20 feet long (Randall, 1973; Klimley, 1994). Megalodon may have been two to four times larger, averaging 34 feet long, and as much as 60 feet long (Gottfried and others, 1996; Pimiento and Balk, 2015) to 67 feet long (Wroe and others, 2008). At 60 to 67 feet, the largest megalodon would be larger than all but the largest whales on the planet today, and longer than Tyrannosaurus rex! The largest modern shark is the whale shark (Rhincodon typus). According to Guinness World Records (2021), the longest whale shark is 41.5 feet long. The largest megalodons may have been 18 to 25 feet longer!
Paleoecology: What was megalodon's diet? Modern great white sharks feed on other fish, seals, small whales (dolphins, porpoises), turtles, sea birds, and a variety of other things they find in the ocean. What did megalodon eat? Whatever it wanted! Not really, although it likely had a similar diet to the great white shark. Like a great white, megalodon was at the top of the ocean food chain (an apex predator) when it lived (Aguilera and others, 2008; Ehret, 2010; Pimiento and Clements, 2014; Cooper, 2020). Fish and marine mammals also lived during the same time as megalodon. Fossil marine mammal bones have been found with megalodon teeth, and with large bite marks attributed to megalodon (Purdy, 1996; Wroe and others, 2008; Ehret, 2010; Collareta and others, 2017).
During the time when megalodon was hunting in the world's oceans, the ancestors of modern whales were mostly small, less than 30 feet long. The evolution of larger whales appears to have followed megalodon's extinction, beginning around 2.6 million years ago. This change might be coincidental, it may have been related to broader climatic and biological changes in Earth's oceans, or perhaps it was related to the extinction of the apex predator, megalodon (Pimiento and Clements, 2014).
Why aren't megalodon fossils found in Kentucky? Megalodon lived in the world's oceans during the Miocene and Pliocene Epochs. Although Kentucky was covered by shallow seas many times in the geologic past, it was dry land during the Miocene and Pliocene, and neither Miocene or Pliocene deposits are preserved in Kentucky.
Are other shark fossils found in Kentucky? Yes, but they are very different from megalodon fossils. The shark fossils found in Kentucky are from much older Paleozoic strata, and include teeth, scales, and fin spines of ancient sharks and shark-like fish. The fossil shark teeth found in Kentucky have different shapes than megalodon. Most people would not even recognize them as teeth fossils! To learn more about fossil sharks from Kentucky, see the Kentucky Geological Survey's fossil fish webpage.
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- Casier, E., 1960, Note sur la collection des poissons Paleocenes et Eocenes de I'enclave de Cabinda (Congo): Annales du Musee Royal du Congo Beige A. Ser. 3, v.1, p. 1-47.
- Collareta, A., Lambert, O., Landini, W., Di Celma, C., Malinverno, E., Varas-Malca, R., Urbina, M., and Bianucci, G., 2017, Did the giant extinct shark Carcharocles megalodon target small prey?: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 469, p. 84-91, doi.org/10.1016/j.palaeo.2017.01.001.
- Cooper, J.A., 2020, What did Megalodon eat?: The Bristol Dinosaur Project, dinoproject.blogs.bristol.ac.uk/2020/08/13/sharkweek4 [accessed 7/6/2021].
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- Ehret, D.J., 2010, Paleobiology and taxonomy of extinct lamnid and otodontid sharks (Chondrichthyes, Elasmobranchii, Lamniformes): Gainesville, University of Florida, doctoral dissertation, 165 p.
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- Guinness World Records, 2021, Largest cartilaginous fish: www.guinnessworldrecords.com/world-records/84009-heaviest-cartilaginous-fish#:~:text=The%20heaviest%20cartilaginous%20fish%2C%20and,21.5%20tonnes%20(47%2C000%20lb) [accessed 7/6/2021].
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- Perez, V.J., Leder, R.M., and Badaut, T., 2021, Body length estimation of Neogene macrophagous lamniform sharks (Carcharodon and Otodus) derived from associated fossil dentitions: Palaeontologia Electronica, v. 24, no. 1, a09, doi.org/10.26879/1140.
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- Shimada, K., 2019, The size of the megatooth shark, Otodus megalodon (Lamniformes: Otodontidae), revisited: Historical Biology, 8 p., doi.org/10.1080/08912963.2019.1666840.
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- Shimada, K., 2002 The relationship between the tooth size and total body length in the white shark, Carcharodon carcharias (Lamniformes: Lamnidae): Journal of Fossil Research, v. 35, p. 28-33.
- Shimada, K., Becker, M.A., and Griffiths, M.L., 2020, Body, jaw, and dentition lengths of macrophagous lamniform sharks, and body size evolution in Lamniformes with special reference to "off-the-scale" gigantism of the megatooth shark, Otodus megalodon: Historical Biology, 17 p., doi.org/10.1080/08912963.2020.1861608.
- Wroe, S., Huber, D.R., Lowry, M., McHenry, C., Moreno, K., Clausen, P., Ferrara, T.L., Cunningham, E., Dean, M.N., and Summers, A.P., 2008, Three-dimensional computer analysis of white shark jaw mechanics: How hard can a great white bite? Journal of Zoology, v. 276, no. 4, p. 336-342, doi: 10.1111/j.1469-7998.2008.00494.
Text and images by Stephen Greb