Hybodus

Hybodus (from Greek: ύβος hybos, 'crooked' and Greek: ὀδούς odoús 'tooth')[2] is an extinct genus of hybodont, a group of shark-like elasmobranchs that lived from the Late Devonian to the end of the Cretaceous. 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.[3][4][1] The first fossilized teeth from Hybodus were found in England around 1845; since then teeth (and dorsal spines) have been recovered from Europe. During the Triassic, Jurassic, and Cretaceous periods, the hybodonts were especially successful and could be found in shallow seas around the world. For reasons that are not fully understood, the hybodonts became extinct near the end of the Late Cretaceous period.

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

Description

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).[5] It possessed a streamlined body shape similar to modern sharks, with two similarly sized dorsal fins that would have helped it steer with precision.[6] As in other Hybodontiformes, dentinous fin spines were present on the dorsal fins of Hybodus. The fin spines of Hybodus exhibit a rib-like ornamentation located towards the tip of the spine, with rows of hooked denticles present on the posterior side.[7] The spines may have played a role in defending the animal from predators.

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 the flatter teeth probably helped them crush shelled creatures. The males also possessed claspers, specialized organs that directly insert sperm into the female, and which are still present in modern sharks.[6]

Species
Specimen of "Hybodus" fraasi from the Solnhofen Limestone of Germany, now tenatively included in Egertonodus

Several Hybodus species, including H. butleri, H. rajkovichi, and H. montanensis, were later reassigned to Meristodonoides.[8] H. basanus and H. fraasi are now included in the genus Egertonodus,[9] though the placement of the latter in the Egertonodus is considered tentative, due to the strong differences in tooth morphology between the two species.[10] H. obtusus represents a junior synonym of Asteracanthus ornatissimus.[11] A new species from Spain, H. bugarensis, is described in 2013.[12] Two new species from China, H. xinzhuangensis and H. chuanjieensis are named in 2018, and H. houtienensis is considered,[13] while other species from China and Thailand are no longer part of the genus and requires reassessment.[14] 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.[15]

References
  1. 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. 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.
  3. 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
  4. 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
  5. 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.
  6. Palmer, D., ed. (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. p. 28. ISBN 978-1-84028-152-1.
  7. Maisey, John (1978). "Growth And Form Of Fin Spines In Hybodont Sharks" (PDF). Palaeontology. 21 (3): 657–699.
  8. 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.
  9. 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.
  10. 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.
  11. 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. doi:10.1002/spp2.1350. ISSN 2056-2799.
  12. 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
  13. 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.
  14. 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
  15. 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

Sources
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