Five things to know about prehistoric sharks

Author: Jack Cooper

Sharks are among the oldest marine vertebrates on Earth – over 450 million years old to be precise. To put that into context; that is older than grass, that is older than trees, and that is even older than Saturn’s rings! As such, there is an awful lot of knowledge out there about sharks that lived over that 450-million-year history, most of which are no longer with us and have only left fossils behind. Here are five key things scientists have learned about prehistoric sharks.

1. Shark teeth are some of the most common fossils on Earth

Shark skeletons rarely preserve in the fossil record. This is because they’re made of soft cartilage, which typically decomposes after a shark dies. Their teeth, however, are much harder and therefore easily preserve as fossils. On top of that, sharks constantly shed their teeth, with individuals losing thousands of teeth throughout their lifetimes. Add that to millions of sharks across millions of years, and this has left shark teeth as some of the most common remains in the entire marine fossil record.

Examples of the diversity of fossil shark teeth. Sourced from Figures 3 and 4 of Perez (2022).

1. Sharks have survived every major mass extinction event

There have been five major mass extinction events in geological history, often referred to as the “Big Five”. They are as follows: (1) the End-Ordovician extinction event ~445 million years ago; (2) the Late Devonian extinction event ~372 million years ago; (3) the End-Permian extinction event ~252 million years ago, the largest of them all that wiped out up to 81% of marine species; (4) the End-Triassic extinction event ~201 million years ago; and (5) the End-Cretaceous extinction event ~66 million years ago that famously wiped out the dinosaurs and even rendered up to 60% of sharks at the time extinct. With the oldest known fossil shark, Tantalepis, dating back as far as 460 million years ago, this indicates that sharks have persisted through all of these major extinction events! 

Microscope photographs of the scales of Tantalepis from the middle Ordovician period. They’re small and don’t look like much, but these may be the oldest remains of a shark in the entire fossil record; more than 450 million years old. Sourced from Figure 2 of Sansom et al. (2012)

Indeed, sharks are known to have survived several other extinction events too not classified as one of the big five. An extinction of marine megafauna (i.e., the largest marine animals) at the end of the Pliocene epoch was one such extinction that sharks survived through. One study has even suggested that pelagic (open ocean) sharks faced an enormous extinction event some 19 million years ago, for reasons that have not yet been determined, surviving even this mysterious event. It could therefore be said that sharks are among nature’s great survivors! 

Timeline of all of the “Big 5” mass extinction events in geological history, shown in a chart of the number of marine families. 

1. Some prehistoric sharks were unlike any shark living today

There are over 500 living shark species today, while thousands more extinct species have existed over prehistoric times. And some of those species were very strange-looking indeed.

Here are just five of these weird sharks.

Stethacanthus, which lived over 360 million years ago, had an odd-shaped dorsal fin resembling an iron board. This had led to Stethacanthus sometimes being referred to as the “ironing board shark”. Precisely what this dorsal fin was used for is still unclear. They have so far only been confirmed in fossils of male individuals, and so one theory is that these strange dorsal fins may have been used for finding a mate.  

Complete fossil and palaeo-artistic reconstruction of Stethacanthus, the “ironing board” shark. Artist unknown. Sourced from the Instagram of Andrew Schwartz of the Las Vegas Natural History Museum.

Edestus, which lived over 300 million years ago, has been called the “scissor tooth shark” due to its strange jaws. These jaws are shaped as curved blades, with rows of serrated teeth placed in the midline of the upper and lower jaws. Unusual teeth likely meant a distinctive form of feeding not seen in today’s sharks. 

Palaeo-artistic reconstruction of Edestus and its weird jaws. Artwork by Julio Lacerda.

Its relative, Helicoprion, is perhaps even weirder. Living ~290 million years ago, this shark is famous for its fossil “tooth whorls”. These are clusters of fused teeth, structured circularly. Exactly what these teeth were used for, and where they even were in the skull, was a mystery for decades. It was only in the 2010s that a previously overlooked skull specimen was scanned, revealing that these whorls were situated in the lower jaw, most likely used to feed on fish and squid. 

 The iconic “tooth whorl” fossils from a Helicoprion, truly unlike any shark teeth today.

Today’s filter-feeding sharks tend to be gentle giants, characterized by typical shark bodies. But one filter feeder from the Cretaceous period, 93 million years ago, was not only small at just 1 m long, but looked more like a ray than a shark. Aquilolamna, a shark known from a complete fossil in Mexico, had unusually thin and stretched pectoral fins, giving it a more ray-like appearance than a typical shark. 

The holotype fossil specimen of Aquilolamna (a) accompanied by a line drawing (b) and an artistic reconstruction (c) of this bizarre shark. Sourced from Figure 1 of Vullo et al. (2021).

One final strange prehistoric shark is Ptychodus, which lived ~100 million years ago during the Cretaceous. Originally known from large flat teeth, it was thought that this shark fed on small hard-shelled invertebrates living on the sea bottom like today’s smoothhounds. However, a complete skeleton discovered in Mexico revealed that it looked more like today’s porbeagle or salmon sharks. Between this and its flat teeth, this shark therefore may have been a fast swimmer that may have fed on ammonites or even turtles. 

Palaeo-artistic reconstruction of Ptychodus feeding on ammonites and turtles, accompanied by a fossil body outline from Mexico and an isolated, plate-like tooth. Artwork by Frederik Spindler.

1. Ancestors of our living sharks were living alongside dinosaurs

The earliest “neoselachians” – otherwise known as modern sharks we see today – date back to the Jurassic period, around 200 million years ago. And some of the earliest known modern sharks belong to genera that are still swimming our oceans today. The cow sharks – Hexanchus – which includes species such as the living sixgill sharks, date as far back as 190 million years ago. Similarly, bullhead sharks (Heterodontus) and angel sharks (Squatina) have fossil records dating back to the Jurassic and Cretaceous periods. These periods are famous for being the peak time in which dinosaurs were roaming the land!

Even some of today’s living shark species are extremely old and have extensive fossil records. Most eye-catching of all, the living sand tiger shark (Carcharias taurus) has a fossil record dating as far back as 66 million years ago. That’s right, the big, ragged-toothed sharks you see in aquariums have been swimming our oceans for 66 million years!

The sand tiger shark (Carcharias taurus), a living species with a fossil record extending back 66 million years.

1. Some extinct sharks reached gigantic body sizes

Our largest living sharks include the filter-feeding whale shark and basking shark, which reach sizes of up to 18 and 12 m long, respectively. However, sharks have been capable of attaining large sizes for millions of years, dating back to a time more than 300 million years ago. Here are just a few examples of some of the truly enormous extinct sharks that lived in prehistoric times.

One of the largest early sharks was Saivodus, which lived during the Carboniferous and Permian periods ~300 million years ago, reached 4-5 m long. That’s as big as an adult great white shark and tells us that sharks were getting big even early in their evolution. The weirdly toothed sharks mentioned earlier, Edestus and Helicoprion, lived at a similar time and were larger still. Edestus reached 6.7 m long: even bigger than the largest great white and tiger sharks. Helicoprion, meanwhile, may have been as big as 7.6 m; bigger than any shark alive today that isn’t eating plankton.

The Cretaceous, the last period of the reign of the dinosaurs ~143-66 million years ago, was also home to several very big sharks indeed. Cretoxyrhina, also known as the “Ginsu shark”, was a predatory shark that resembled today’s great white shark and grew about as large at up to 6 m long. Some fossils of this shark may indicate that it even ate pterosaurs! Another Cretaceous shark, Cretodus, which was ecologically similar to a modern tiger shark and eating turtles, may have reached up to 11 m long, almost as big as a basking shark. Finally, the previously mentioned Ptychodus reached up to 10 m long: far beyond the size of today’s sharks with similarly flat teeth. 

Speculative artistic reconstruction of a Cretoxyrhina breaching to prey on a pterosaur; though it should be emphasised that the fossil evidence only supports a bite on a pterosaur, which may well have been scavenging rather than predation of this kind. Artwork by Mark Witton.

The biggest shark of all, however, was none other than Otodus megalodon, known more widely as the “Megalodon”. Fossil teeth of this shark are the size of human hands, up to 7 inches long, and these teeth suggest a shark reaching over 20 m long. Indeed, recent work has suggested that megalodon may have reached as much as 24 m long and almost 100 tonnes in weight, making it the largest shark that has ever existed. It was an apex super-predator that lived across every ocean and was a whale killer, feasting on prey that may have been as big as 7-8 m long. Its extinction over 3 million years ago remains mysterious and may well have been caused by a combination of environmental changes reducing their prey availability, and possibly even competition with today’s living great white shark.

Palaeo-artistic reconstruction of megalodon preying on a baleen whale. Artwork by Juan Jose Giraldo.

SOURCES:

Long JA, 2024. The secret history of sharks: the rise of the ocean's most fearsome predators. Ballantine Books.

Kempf S, Altobelli N, Schmidt J, Cuzzi JN, Estrada PR & Srama R, 2023. Micrometeoroid infall onto Saturn’s rings constrains their age to no more than a few hundred million years. Science Advances, 9, eadf8537.

Hubbell G, 1996. Using tooth structure to determine the evolutionary history of the white shark. Pages 9-18 in AP Klimley & Ainley DG (Ed.), Great white sharks: the biology of Carcharodon carcharias. Academic Press, San Diego.

Perez VJ, 2022. The chondrichthyan fossil record of the Florida Platform (Eocene–Pleistocene). Paleobiology, 48, 622-654.

Raup DM & Sepkoski Jr JJ, 1982. Mass extinctions in the marine fossil record. Science, 215, 1501-1503.

Stanley SM, 2016. Estimates of the magnitudes of major marine mass extinctions in earth history. Proceedings of the National Academy of Sciences, 113, E6325-E6334.

Guinot G & Condamine FL, 2023. Global impact and selectivity of the Cretaceous-Paleogene mass extinction among sharks, skates, and rays. Science, 379, 802-806.

Sansom IJ, Davies NS, Coates MI, Nicoll RS & Ritchie A, 2012. Chondrichthyan‐like scales from the Middle Ordovician of Australia. Palaeontology, 55, 243-247.

Pimiento C, Griffin JN, Clements CF, Silvestro D, Varela S, Uhen MD & Jaramillo C, 2017. The Pliocene marine megafauna extinction and its impact on functional diversity. Nature Ecology & Evolution, 1, 1100-1106.

Sibert EC & Rubin LD, 2021. An early Miocene extinction in pelagic sharks. Science, 372, 1105-1107.

Maisey JG, 2009. The spine-brush complex in symmoriiform sharks (Chondrichthyes; Symmoriiformes), with comments on dorsal fin modularity. Journal of Vertebrate Paleontology, 29, 14-24.

Itano WM, 2015. An abraded tooth of Edestus (Chondrichthyes, Eugeneodontiformes): evidence for a unique mode of predation. Transactions of the Kansas Academy of Science, 118, 1-9.

Tapanila L, Pruitt J, Pradel A, Wilga CD, Ramsay JB, Schlader R & Didier DA, 2013. Jaws for a spiral-tooth whorl: CT images reveal novel adaptation and phylogeny in fossil Helicoprion. Biology Letters, 9, 20130057.

Vullo R, Frey E, Ifrim C, Gonzalez Gonzalez MA, Stinnesbeck ES & Stinnesbeck W, 2021. Manta-like planktivorous sharks in Late Cretaceous oceans. Science, 371, 1253-1256.

Vullo R, Villalobos-Segura E, Amadori M, Kriwet J, Frey E, González González MA, Padilla Gutiérrez JM, Ifrim C, Stinnesbeck ES & Stinnesbeck W, 2024. Exceptionally preserved shark fossils from Mexico elucidate the long-standing enigma of the Cretaceous elasmobranch Ptychodus. Proceedings of the Royal Society B, 291, 20240262.

Paillard A, Shimada K & Pimiento C, 2020. The fossil record of extant elasmobranchs. Journal of Fish Biology, 98, 445-455.

McClain CR, Balk MA, Benfield MC, Branch TA, Chen C, Cosgrove J, Dove AD, Gaskins L, Helm RR, Hochberg FG, Lee FB, Marshall A, McMurray SE, Schanche C, Stone SN & Thaler AD, 2015. Sizing ocean giants: patterns of intraspecific size variation in marine megafauna. PeerJ, 3, e715.

Hodnett JPM, Tweet JS & Santucci VL, 2022. The occurrence of fossil cartilaginous fishes (Chondrichthyes) within the parks and monuments of the National Parks Service. New Mexico Museum of Natural History and Science Bulletin, 90, 183-208.

Tapanila L, Pruitt J, Wilga CD & Pradel A, 2020. Saws, scissors, and sharks: late Paleozoic experimentation with symphyseal dentition. The Anatomical Record, 303, 363-376.

Shimada K, 1997. Skeletal anatomy of the Late Cretaceous lamniform shark, Cretoxyrhina mantelli from the Niobrara Chalk in Kansas. Journal of Vertebrate Paleontology, 17, 642-652.

Hone DW, Witton MP & Habib MB, 2018. Evidence for the Cretaceous shark Cretoxyrhina mantelli feeding on the pterosaur Pteranodon from the Niobrara Formation. PeerJ, 6, e6031.

Amalfitano J, Dalla Vecchia FM, Carnevale G, Fornaciari E, Roghi G & Giusberti L, 2022. Morphology and paleobiology of the Late Cretaceous large-sized shark Cretodus crassidens (Dixon, 1850) (Neoselachii; Lamniformes). Journal of Paleontology, 96, 1166-1188.

Shimada K, 2019. The size of the megatooth shark, Otodus megalodon (Lamniformes: Otodontidae), revisited. Historical Biology, 33, 904-911.

Perez VJ, Leder RM & Badaut T, 2021. Body length estimation of Neogene macrophagous lamniform sharks (Carcharodon and Otodus) derived from associated fossil dentitions. Palaeontologia Electronica, 24, a09.

Shimada K, Motani R, Wood JJ, Sternes PC, Tomita T, Bazzi M, Collareta A, Gayford JH, Türtscher J, Jambura PL, Kriwet J, Vullo R, Long DJ, Summers AP, Maisey JG, Underwood C, Ward DJ, Maisch HM, Perez VJ, Feichtinger I, Naylor GJP, Moyer JK, Higham TE, da Silva JPCB, Bornatowski H, González-Barba G, Griffiths ML, Becker MA & Siversson M, 2025. Reassessment of the possible size, form, weight, cruising speed, and growth parameters of the extinct megatooth shark, Otodus megalodon (Lamniformes: Otodontidae), and new evolutionary insights into its gigantism, life history strategies, ecology, and extinction. Palaeontologia Electronica, 28, a12.

Cooper JA, Hutchinson JR, Bernvi DC, Cliff G, Wilson RP, Dicken ML, Menzel J, Wroe S, Pirlo J & Pimiento C, 2022. The extinct shark Otodus megalodon was a transoceanic superpredator: Inferences from 3D modeling. Science Advances, 8, eabm9424.

Kast ER, Griffiths ML, Kim SL, Rao ZC, Shimada K, Becker MA, Maisch HM, Eagle RA, Clarke CA, Neumann AN, Karnes ME, Lüdecke T, Leichliter JN, Martínez-García A, Akhtar AA, Wang XT, Haug GH & Sigman DM, 2022. Cenozoic megatooth sharks occupied extremely high trophic positions. Science Advances, 8, eabl6529.

Pimiento C, MacFadden BJ, Clements CF, Varela S, Jaramillo C, Velez‐Juarbe J & Silliman BR, 2016. Geographical distribution patterns of Carcharocles megalodon over time reveal clues about extinction mechanisms. Journal of Biogeography, 43, 1645-1655.

Godfrey SJ & Beatty BL, 2022. A Miocene cetacean vertebra showing a partially healed longitudinal shear-compression fracture, possibly the result of domoic acid toxicity or failed predation. Palaeontologia Electronica, 25, a28.

Boessenecker RW, Ehret DJ, Long DJ, Churchill M, Martin E & Boessenecker SJ, 2019. The Early Pliocene extinction of the mega-toothed shark Otodus megalodon: a view from the eastern North Pacific. PeerJ, 7, e6088.