Ischyodus

Ischyodus (from Greek: ισχύς ischýs, 'power' and Greek: ὀδούς odoús 'tooth') is an extinct genus of cartilaginous fish belonging to the subclass Holocephali, which includes the modern-day chimaeras. Fossils are known from Europe (including Russia), North America, and New Zealand.

Ischyodus
Temporal range: Middle Jurassic to Miocene
Ischyodus avitus
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Order: Chimaeriformes
Family: Callorhynchidae
Genus: †Ischyodus
Egerton, 1843
Species
  • Ischyodus bifurcatus
  • Ischyodus brevirostris
  • Ischyodus dolloi
  • Ischyodus gubkini
  • Ischyodus incisus
  • Ischyodus latus
  • Ischyodus lonzeensis
  • Ischyodus minor
  • Ischyodus mortoni
  • Ischyodus planus
  • Ischyodus rayhaasi
  • Ischyodus thurmanni
  • Ischyodus townsendi
  • Ischyodus williamsae
  • Ischyodus yanshini
  • Ischyodus zinsmeisteri

Ischyodus was rather similar to the present-day chimaera Chimaera monstrosa, which is found in the Atlantic Ocean and Mediterranean Sea. Just like C. monstrosa, Ischyodus had large eyes, a long whip-like tail, small lips, large pectoral fins and dorsal fin, and a dorsal spike attached to the front of the dorsal fin. The spike probably served as a method of protection against predators, and may have been venomous, as it is in modern chimaeras.[1]

Dental plates of at least two species, Ischyodus rayhaasi and Ischyodus dolloi, have been found at several sites in North Dakota.[2]

Based on complete specimen, total length is 21 times larger than mesiodistal length of mandibular tooth plate. For example, I. bifurcatus with mandibular plate length of 3.2 in (8.2 cm) possibly belongs 5 ft 8 in (1.72 m) long specimen.[3]

References
  1. Palmer, D., ed. (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. p. 29. ISBN 1-84028-152-9.
  2. Hoganson, J. W. and J. M. Erickson. 2005. A new species of Ischyodus (Chondrichthyes: Holocephali: Callorhynchidae) from Upper Maastrichtian shallow marine facies of the Fox Hills and Hell Creek formations, Williston Basin, North Dakota, USA. Palaeontology 48: 709-721. doi:10.1111/j.1475-4983.2005.00475.x
  3. Johnson-Ransom, Evan D.; Popov, Evgeny V.; Deméré, Thomas A.; Shimada, Kenshu (2018-10-01). "The Late Cretaceous Chimaeroid Fish, Ischyodus bifurcatus Case (Chondrichthyes: Holocephali), from California, USA, and Its Paleobiogeographical Significance". Paleontological Research. 22 (4): 364–372. doi:10.2517/2018PR004. ISSN 1342-8144.
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