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Hybodus

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Hybodus
Temporal range: Early Jurassic [1] Possible Cretaceous record[2]
Hybodus hauffianus
Life restoration of Hybodus hauffianus, showing female (top) and male (bottom)
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Elasmobranchii
Order: †Hybodontiformes
Family: †Hybodontidae
Genus: †Hybodus
Agassiz, 1837
Type species
†Hybodus reticulatus
Agassiz, 1837
Species[1]
  • †H. reticulatus
  • †H. hauffianus

Hybodus (from Greek: ύβος hybos, 'crooked' and Greek: ὀδούς odoús 'tooth')[3] is an extinct genus of hybodont that lived from the Middle Triassic to the Late Cretaceous periods.[4] Species closely related to the type species Hybodus reticulatus lived during the Early Jurassic epoch.[1] Numerous species have been assigned to Hybodus spanning a large period of time, and it is currently considered a wastebasket taxon that is 'broadly polyphyletic' and requires reexamination.[5][6][1]

Description

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Skeletal reconstruction of an indeterminate species of Hybodus

Hybodus species typically grew to about 2 metres (6.6 ft) in length, with larger specimens of H. hauffianus reaching about 3 metres (9.8 ft).[7] It possessed a streamlined body shape similar to modern sharks, with two similarly sized dorsal fins.[8] As in other Hybodontiformes, dentinous fin spines were present on the dorsal fins of Hybodus, which in this genus exhibit a rib-like ornamentation located towards the tip of the spine, with rows of hooked denticles present on the posterior side.[9] The males possessed claspers, specialized organs that directly insert sperm into the female, and which are still present in modern sharks.[8]

Species

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Specimen of "Hybodus" fraasi from the Solnhofen Limestone of Germany, which is now tentatively included in Egertonodus

Several Hybodus species, including H. butleri, H. rajkovichi, and H. montanensis, were later reassigned to Meristodonoides.[10] H. basanus and H. fraasi are now included in the genus Egertonodus,[11] though the placement of the latter in the Egertonodus is considered tentative, due to the strong differences in tooth morphology between the two species.[12] H. obtusus represents a junior synonym of Asteracanthus ornatissimus.[13] A new species from Spain, H. bugarensis, is described in 2013.[14] Two new species from China, H. xinzhuangensis and H. chuanjieensis are named in 2018, and H. houtienensis is considered,[15] while other species from China and Thailand are no longer part of the genus and requires reassessment.[16] However, the only two species that should be retained within the genus Hybodus are the type species H. reticulatus and the other species H. hauffianus.[1] The problem is that even those two species require reassessment.[17]

Paleobiology

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A reconstruction of the head of Hybodus
A reconstruction of the full body of Hybodus, displaying anguilliform locomotion
Large numbers of belemnite rostra have been found as gut contents in Hybodus fossils

Hybodus is thought to have been an active predator which was capable of consuming swiftly moving prey,[18] probably predominantly cephalopods and, to a lesser extent, fish.[19] Based on fossilized stomach contents, it has been proposed that Hybodus was a more active hunter than its close relatives like Asteracanthus, which likely fed on benthic prey.[13] A preserved specimen of Hybodus hauffianus has been found with over 100 belemnite (a type of extinct squid-like cephalopod) rostra (hard mineralized internal elements) in its stomach, which may have resulted in its death.[20] Hybodus' varied dentition would have allowed it to opportunistically exploit a variety of food sources; sharper teeth would have been used to catch slippery prey, while flatter teeth probably helped them crush shelled animals. The large spines on the first and second dorsal fins were likely defensive structures intended to protect against attacks from Hybodus' own predators.[8]

References

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  1. ^ a b c d e Maisch, M. W., & Matzke, A. T. (2016). A new hybodontid shark (Chondrichthyes, Hybodontiformes) from the Lower Jurassic Posidonienschiefer Formation of Dotternhausen, SW Germany. Neues Jahrbuch Für Geologie Und Paläontologie - Abhandlungen, 280(3), 241–257. https://doi.org/10.1127/njgpa/2016/0577
  2. ^ Sørensen, Anne Mehlin; Surlyk, Finn; Lindgren, Johan (2013-05-01). "Food resources and habitat selection of a diverse vertebrate fauna from the upper lower Campanian of the Kristianstad Basin, southern Sweden". Cretaceous Research. 42: 85–92. Bibcode:2013CrRes..42...85S. doi:10.1016/j.cretres.2013.02.002. ISSN 0195-6671.
  3. ^ Roberts, George (1839). An etymological and explanatory dictionary of the terms and language of geology. London: Longman, Orme, Brown, Green, & Longmans. p. 79. Retrieved 30 December 2021.
  4. ^ Dica, E. P., & Codrea, V. (2006). On the Hybodus (Euselachii) from the Early Jurassic of Anina (Caraş Severin District, Romania). https://digitalcommons.usf.edu/cgi/viewcontent.cgi?article=1247&context=geologia
  5. ^ Leuzinger, L., Cuny, G., Popov, E., & Billon-Bruyat, J.-P. (2017). A new chondrichthyan fauna from the Late Jurassic of the Swiss Jura (Kimmeridgian) dominated by hybodonts, chimaeroids and guitarfishes. Papers in Palaeontology, 3(4), 471–511. https://doi.org/10.1002/spp2.1085
  6. ^ Korneisel, D., Gallois, R. W., Duffin, C. J., & Benton, M. J. (2015). Latest Triassic marine sharks and bony fishes from a bone bed preserved in a burrow system, from Devon, UK. Proceedings of the Geologists’ Association, 126(1), 130–142. https://doi.org/10.1016/j.pgeola.2014.11.004
  7. ^ Maisey, John G.; Bronson, Allison W.; Williams, Robert R.; McKinzie, Mark (2017-05-04). "A Pennsylvanian 'supershark' from Texas". Journal of Vertebrate Paleontology. 37 (3): e1325369. Bibcode:2017JVPal..37E5369M. doi:10.1080/02724634.2017.1325369. ISSN 0272-4634. S2CID 134127771.
  8. ^ a b c Palmer, D., ed. (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. p. 28. ISBN 978-1-84028-152-1.
  9. ^ Maisey, John (1978). "Growth And Form Of Fin Spines In Hybodont Sharks" (PDF). Palaeontology. 21 (3): 657–699.
  10. ^ Underwood, Charlie J.; Cumbaa, Stephen L. (July 2010). "Chondrichthyans from a Cenomanian (Late Cretaceous) bonebed, Saskatchewan, Canada". Palaeontology. 53 (4): 903–944. Bibcode:2010Palgy..53..903U. doi:10.1111/j.1475-4983.2010.00969.x.
  11. ^ Maisey, J. G. (1987). "Cranial anatomy of the Lower Jurassic shark Hybodus reticulatus (Chondrichthyes: Elasmobranchii), with comments on hybodontid systematics". American Museum Novitates (2878): 1–39. hdl:2246/5208.
  12. ^ Rees, Jan; Underwood, Charlie J. (2008-01-17). "Hybodont Sharks of the English Bathonian and Callovian (Middle Jurassic)". Palaeontology. 51 (1): 117–147. Bibcode:2008Palgy..51..117R. doi:10.1111/j.1475-4983.2007.00737.x. S2CID 48229914.
  13. ^ a b Stumpf, Sebastian; López-Romero, Faviel A.; Kindlimann, René; Lacombat, Frederic; Pohl, Burkhard; Kriwet, Jürgen (2021-01-13). Cavin, Lionel (ed.). "A unique hybodontiform skeleton provides novel insights into Mesozoic chondrichthyan life". Papers in Palaeontology. 7 (3): 1479–1505. Bibcode:2021PPal....7.1479S. doi:10.1002/spp2.1350. ISSN 2056-2799.
  14. ^ Pla, Cristina., Márquez-Aliaga, Ana. & Botella, Héctor. (2013). The chondrichthyan fauna from the Middle Triassic (Ladinian) of the Iberian Range (Spain), Journal of Vertebrate Paleontology, 33:4, 770-785, https://doi.org/10.1080/02724634.2013.748668
  15. ^ SUN Baidong, WANG Wei, LIU Junping, SONG Donghu, LÜ Boye, XU Yunfei, WANG Lu. (2018). New fossil materials of hybodus (Chondrichthyes) in the Middle Jurassic found in Chuanjie Basin of central Yunnan Province[J]. Geological Bulletin of China, 37(11): 1991-1996.
  16. ^ Cuny, G., Mo, J., Amiot, R., Buffetaut, E., SUTEETHORN, S., Suteethorn, V., & Tong, H. (2017). New data on Cretaceous freshwater hybodont sharks from Guangxi Province, South China. Research & Knowledge, 3(1), 11–15. https://doi.org/10.14456/randk.2017.4
  17. ^ Stumpf, S., & Kriwet, J. (2019). A new Pliensbachian elasmobranch (Vertebrata, Chondrichthyes) assemblage from Europe, and its contribution to the understanding of late Early Jurassic elasmobranch diversity and distributional patterns. PalZ, 93(4), 637–658. https://doi.org/10.1007/s12542-019-00451-4
  18. ^ Maisey, J. G. (April 2012). "What is an 'elasmobranch'? The impact of palaeontology in understanding elasmobranch phylogeny and evolution". Journal of Fish Biology. 80 (5): 918–951. Bibcode:2012JFBio..80..918M. doi:10.1111/j.1095-8649.2012.03245.x. ISSN 0022-1112. PMID 22497368. ...including forms considered to be active predators of fast-moving prey (e.g. Hybodus)...
  19. ^ Stumpf, Sebastian; Kriwet, Jürgen (December 2019). "A new Pliensbachian elasmobranch (Vertebrata, Chondrichthyes) assemblage from Europe, and its contribution to the understanding of late Early Jurassic elasmobranch diversity and distributional patterns". PalZ. 93 (4): 637–658. Bibcode:2019PalZ...93..637S. doi:10.1007/s12542-019-00451-4. ISSN 0031-0220.
  20. ^ Klug, Christian; Schweigert, Günter; Hoffmann, René; Weis, Robert; De Baets, Kenneth (December 2021). "Fossilized leftover falls as sources of palaeoecological data: a 'pabulite' comprising a crustacean, a belemnite and a vertebrate from the Early Jurassic Posidonia Shale". Swiss Journal of Palaeontology. 140 (1): 10. Bibcode:2021SwJP..140...10K. doi:10.1186/s13358-021-00225-z. ISSN 1664-2376. PMC 8549986. PMID 34721282.

Sources

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