Ptychodus Explained

Ptychodus (from Greek, Modern (1453-);: πτυχή 'fold' and Greek, Modern (1453-);: ὀδούς 'tooth')[1] is a genus of extinct large durophagous (shell-crushing) lamniform sharks from the Cretaceous period, spanning from the Albian to the Campanian. Fossils of Ptychodus teeth are found in many Late Cretaceous marine sediments worldwide.[2]

At least 16 species are considered valid, with the largest members of the genus suggested to have grown up to 10abbr=offNaNabbr=off long. The youngest remains date to around 85 million years ago. A large number of remains have been found in the former Western Interior Seaway.[3]

Discovery

Due to a global distribution Ptychodus is well represented in the fossil record; many fossils have been uncovered such as isolated teeth, fragments of dentition, calcified vertebral centra, denticles, and associated fragments of calcified cartilage.[4] The very first remains of Ptychodus were found in England and Germany in the first half of the 18th century.[5] [6] Ptychodus teeth have long been identified as palates of diodon, or porcupinefish (Osteichthyes, Diodontidae), well-known for their ability to inflate their bodies in defense. At the beginning of the 19th century, several authors including Swiss paleontologist Louis Agassiz eventually demonstrated the affinities of Ptychodus teeth with those of elasmobranchs (rays and sharks). The first discovery of Ptychodus teeth in Kansas came in 1868 when Leidy reported and described a damaged tooth near Fort Hays, Kansas.[7] [8] After, many more teeth were uncovered in almost perfect conditions and other species within the genus were identified.[8]

Fossils of species within this genus have been found in the marine strata of United States, Brazil, Canada, the Czech Republic, France, Germany, India, Israel, Japan, Jordan, Mexico, Sweden, and the United Kingdom. The fact that so many fossils of Ptychodus have been found in different regions of the world provides evidence of a distribution of species during the Albian-Turonian time.[4]

The generic name Ptychodus comes from the Greek words (fold/layer) and (tooth), so "fold teeth" describing the shape of their crushing and grinding teeth.[9]

Taxonomy

While the affinity of Ptychodus as some kind of cartilaginous fish has long been accepted, the exact position in the group was long uncertain. A 2016 publication found that Ptychodus are likely true sharks belonging to Selachimorpha, rather than hybodonts or batoids as previously thought.[10] A 2024 study of a complete skeleton concluded that they belong to the Lamniformes (mackerel sharks).

Description

Size

Ptychodus was a large shark, previously estimated at 10abbr=offNaNabbr=off long based on extrapolation from tooth.[11] [12] The subadult specimen with the largest vertebra showed that it could reach lengths of, so a length is possible, but more analysis is required for verification.[13]

Dentition

Unlike the colossal nektonic planktivores Rhincodon (whale sharks) and Cetorhinus (basking sharks) which relied upon gill rakers to acquire their food, the Ptychodus had a massive arrangement of crushing plate teeth. A Ptychodus jaw contains many teeth, up to 550 teeth, 220 of which are on the lower jaw and 260 in the upper jaw. These teeth were very large as well—Paleontologists believe that the largest tooth plate measured 55 centimeters in length and 45 centimeters in width. There are two distinct formations of tooth plates between the genus; one being juxtaposed, non-overlapping tooth rows, and another being imbricated tooth rows.[14] It is believed that the shape coincides with the diet of the species and their geographic locations, but the time it lived has a big part as well. Ptychodus marginalis teeth differ from Ptychodus polygyrus. P marginalis was in the Middle Cenomanian to Middle Turonian deposits in the English Chalk, while P. polygyrus was in the Late Santonian-Early Campanian deposits.[15]

Body

The only known complete body remains are from the Agua Nueva Formation in Mexico, which suggest that Ptychodus had a fusiform body, with a large and elongate head, the primarily dorsal fin was large and placed forward on the body while the second posterior dorsal fin was much smaller, with a small anal fin being present. The overall body form closely resembles that of the great white shark and Lamna (which includes the porbeagle and salmon shark).

Paleobiology

Based on analysis of vertebrae from Spain, it is suggested that species of Ptychodus lived relatively long lives and were slow growing and produced large offspring and small litters.

Diet

Ptychodus is thought to have been durophagous, using its low rounded teeth to crush hard-shelled organisms. Many authors have suggested that Ptychodus fed on bottom dwelling (benthic) prey like bivalves (particularly inoceramids) and crustaceans, while also consuming some hard bodied organisms that lived in open water (pelagic). A 2024 study suggested that based on its body morphology, the species likely primarily consumed pelagic hard prey, like ammonites and marine turtles, rather than benthic prey.[16]

References

External links

Notes and References

  1. Book: Roberts . George . An etymological and explanatory dictionary of the terms and language of geology . 1839 . Longman, Orme, Brown, Green, & Longmans . London . 144 . 31 December 2021 . English.
  2. http://www.paleodb.org/cgi-bin/bridge.pl?action=checkTaxonInfo&taxon_no=34513&is_real_user=1 The paleobioloy Database Ptychodus entry
  3. Web site: Everhart . Mike . Ptychodus mortoni . Ocean of Kansas.
  4. Verma. Omkar. etal. Ptychodus decurrens Agassiz (Elasmobranchii: Ptychodontidae) from the Upper Cretaceous of India. Cretaceous Research. February 1, 2012. 33. 1. 183–188. 10.1016/j.cretres.2011.09.014. 2012CrRes..33..183V .
  5. Brignon, A., 2015, Senior synonyms of Ptychodus latissimus Agassiz, 1835 and Ptychodus mammillaris Agassiz, 1835 (Elasmobranchii) based on teeth from the Bohemian Cretaceous Basin (the Czech Republic). Acta Musei Nationalis Pragae, Series B – Historia Naturalis, 71(1–2): 5–14
  6. Brignon, A., 2019, Le diodon devenu requin : l'histoire des premières découvertes du genre Ptychodus (Chondrichthyes) [The porcupinefish that became a shark: History of the early discoveries of the genus ''Ptychodus'' (Chondrichthyes)]. Published by the author, Bourg-la-Reine, France, 100 pp., : 978-2-9565479-2-1 (printed), 978-2-9565479-3-8 (ebook)
  7. Web site: Everhard. Mike. Ptychodontid Sharks: Late Cretaceous Shell Crushers. Ocean of Kansas.
  8. Everhart . Michael . Caggiano . Tom . 2004 . An associated dentition and calcified vertebral centra of the Late Cretaceous elasmobranch, Ptychodus anonymus Williston 1900 . Paludicola . 4 . 4 . 125–136.
  9. David, Michelle A historical and mechanical description of Ptychodus (Chondrichthyes) dententions with notes on the distribution and systematics of the genus
  10. Hoffman . Brian L. . Hageman . Scott A. . Claycomb . Gregory D. . July 2016 . Scanning electron microscope examination of the dental enameloid of the Cretaceous durophagous shark Ptychodus supports neoselachian classification . Journal of Paleontology . 90 . 4 . 741–762 . 2016JPal...90..741H . 10.1017/jpa.2016.64 . 132252846.
  11. Shimada, K., Rigsby, C. K., & Kim, S. H. (2009). Partial skull of Late Cretaceous durophagous shark,Ptychodus occidentalis(Elasmobranchii: Ptychodontidae), from Nebraska, U.S.A.. Journal of Vertebrate Paleontology, 29(2), 336–349. https://doi.org/10.1671/039.029.0226
  12. Shimada, K., Everhart, M. J., Decker, R., & Decker, P. D. (2010). A new skeletal remain of the durophagous shark, Ptychodus mortoni, from the Upper Cretaceous of North America: an indication of gigantic body size. Cretaceous Research, 31(2), 249–254. https://doi.org/10.1016/j.cretres.2009.11.005
  13. Jambura . Patrick L. . Kriwet . Jürgen . 2020-04-22 . Articulated remains of the extinct shark Ptychodus (Elasmobranchii, Ptychodontidae) from the Upper Cretaceous of Spain provide insights into gigantism, growth rate and life history of ptychodontid sharks . PLOS ONE . en . 15 . 4 . e0231544 . 2020PLoSO..1531544J . 10.1371/journal.pone.0231544 . 1932-6203 . 7176087 . 32320430 . free.
  14. Shimada. Kenshu. Dentition of Late Cretaceous shark, Ptychodus mortoni (Elasmobranchii, Ptychodontidae). Journal of Vertebrate Paleontology. October 31, 2012. 32. 6. 1271–1284. 10.1080/02724634.2012.707997. 2012JVPal..32.1271S . 85133916.
  15. Hamm. Shawn. The Late Cretaceous shark Ptychodus marginalis in the Western Interior Seaway, USA. Journal of Paleontology. May 2010. 84. 3. 538–548. 10.1666/09-154.1. 2010JPal...84..538H . 130948112.
  16. Vullo . Romain . Villalobos-Segura . Eduardo . Amadori . Manuel . Kriwet . Jürgen . Frey . Eberhard . González González . Margarito A. . Padilla Gutiérrez . José M. . Ifrim . Christina . Stinnesbeck . Eva S. . Stinnesbeck . Wolfgang . 2024-04-30 . Exceptionally preserved shark fossils from Mexico elucidate the long-standing enigma of the Cretaceous elasmobranch Ptychodus . Proceedings of the Royal Society B: Biological Sciences . en . 291 . 2021 . 10.1098/rspb.2024.0262 . 0962-8452.