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Cartilaginous fishes
Temporal range: 430–0 Ma[1][2] Late Silurian to Present
Example of cartilaginous fishes : at the top of the image, Elasmobranchii and at the bottom of the image, Holocephali.
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Clade: Eugnathostomata
Class: Chondrichthyes
Huxley, 1880
Subclasses and Orders


Within the infraphylum Gnathostomata, cartilaginous fishes are distinct from all other jawed vertebrates.



The skeleton is cartilaginous. The notochord is gradually replaced by a vertebral column during development, except in Holocephali, where the notochord stays intact. In some deepwater sharks, the column is reduced.[3]

As they do not have bone marrow, red blood cells are produced in the spleen and the epigonal organ (special tissue around the gonads, which is also thought to play a role in the immune system). They are also produced in the Leydig's organ, which is only found in certain cartilaginous fishes. The subclass Holocephali, which is a very specialized group, lacks both the Leydig's and epigonal organs.


Apart from electric rays, which have a thick and flabby body, with soft, loose skin, chondrichthyans have tough skin covered with dermal teeth (again, Holocephali is an exception, as the teeth are lost in adults, only kept on the clasping organ seen on the caudal ventral surface of the male), also called placoid scales (or dermal denticles), making it feel like sandpaper. In most species, all dermal denticles are oriented in one direction, making the skin feel very smooth if rubbed in one direction and very rough if rubbed in the other.

Originally, the pectoral and pelvic girdles, which do not contain any dermal elements, did not connect. In later forms, each pair of fins became ventrally connected in the middle when scapulocoracoid and puboischiadic bars evolved. In rays, the pectoral fins are connected to the head and are very flexible.

One of the primary characteristics present in most sharks is the heterocercal tail, which aids in locomotion.[4]

Body covering[edit]

Chondrichthyans have toothlike scales called dermal denticles or placoid scales. Denticles usually provide protection, and in most cases, streamlining. Mucous glands exist in some species, as well.


The old placoderms did not have teeth at all, but had sharp bony plates in their mouth. Thus, it is unknown whether the dermal or oral teeth evolved first. It has even been suggested[by whom?] that the original bony plates of all vertebrates are now gone and that the present scales are just modified teeth, even if both the teeth and body armor had a common origin a long time ago. However, there is currently no evidence of this.

Respiratory system[edit]



Nervous system[edit]

Regions of a Chondrichthyes brain colored and labeled on dissected skate. The rostral end of the skate is to the right.

In chondrichthyans, the nervous system is composed of a small brain, 8-10 pairs of cranial nerves, and a spinal chord with spinal nerves.[5] They have several sensory organs which provide information to be processed. Ampullae of Lorenzini are a network of small jelly filled pores called electroreceptors which help the fish sense electric fields in water. This aids in finding prey, navigation, and sensing temperature. The Lateral line system has modified epithelial cells located externally which sense motion, vibration, and pressure in the water around them. Most species have large well-developed eyes. Also, they have very powerful nostrils and olfactory organs. Their inner ears consist of 3 large semicircular canals which aid in balance and orientation. Their sound detecting apparatus has limited range and is typically more powerful at lower frequencies. Some species have electric organs which can be used for defense and predation. They have relatively simple brains with the forebrain not greatly enlarged. The structure and formation of myelin in their nervous systems are nearly identical to that of tetrapods, which has led evolutionary biologists to believe that Chondrichthyes were a cornerstone group in the evolutionary timeline of myelin development.[6]

Immune system[edit]

Like all other jawed vertebrates, members of Chondrichthyes have an adaptive immune system.[7]



Capture-induced premature birth and abortion (collectively called capture-induced parturition) occurs frequently in sharks/rays when fished.[8] Capture-induced parturition is often mistaken for natural birth by recreational fishers and is rarely considered in commercial fisheries management despite being shown to occur in at least 12% of live bearing sharks and rays (88 species to date).[8]



Subclasses of cartilaginous fishes
Elasmobranchii Caribbean reef shark.jpg
Myliobatis aquila sasrája.jpg
and rays, skates, and sawfish
Holocephali Callorhinchus callorhynchus.JPG


Extant orders of cartilaginous fishes
Group Order Image Common name Authority Families Genera Species Note
Total CR IUCN 3 1.svg EN IUCN 3 1.svg VU IUCN 3 1.svg
Carcharhiniformes Sphyrna mokarran at georgia.jpg ground
Compagno, 1977 8 51 >270 7 10 21
Heterodontiformes Hornhai (Heterodontus francisci).JPG bullhead
L. S. Berg, 1940 1 1 9
Lamniformes White shark.jpg mackerel
L. S. Berg, 1958 7
+2 extinct
10 16 10
Orectolobiformes Whale shark Georgia aquarium.jpg carpet
Applegate, 1972 7 13 43 7
Hexanchiformes Hexanchus griseus Gervais.jpg frilled
cow sharks
de Buen, 1926 2
+3 extinct
+11 extinct
+33 extinct
Pristiophoriformes Pristiophorus japonicus cropped.jpg sawsharks L. S. Berg, 1958 1 2 6
Squaliformes Spiny dogfish.jpg dogfish
Goodrich, 1909 7 23 126 1 6
Squatiniformes Squatina angelus - Gervais.jpg angel
Buen, 1926 1 1 24 3 4 5
Rays Myliobatiformes Myliobatis aquila sasrája.jpg stingrays
Compagno, 1973 10 29 223 1 16 33
Rhinopristiformes Sawfish genova.jpg sawfishes 1 2 5-7 5-7
Rajiformes Amblyraja hyperborea1.jpg skates
Torpediniformes Torpedo torpedo corsica2.jpg electric
de Buen, 1926 2 12 69 2 9
Holocephali Chimaeriformes Chimaera mon.JPG chimaera Obruchev, 1953 3
+2 extinct
+3 extinct
+17 extinct


Radiation of cartilaginous fishes, based on Michael Benton, 2005.[12]

Cartilaginous fish are considered to have evolved from acanthodians.[by whom?] Originally assumed[by whom?] to be closely related to bony fish or a polyphyletic assemblage leading to both groups, the discovery of Entelognathus and several examinations of acanthodian characteristics indicate that bony fish evolved directly from placoderm like ancestors, while acanthodians represent a paraphyletic assemblage leading to Chondrichthyes. Some characteristics previously thought to be exclusive to acanthodians are also present in basal cartilaginous fish.[13] In particular, new phylogenetic studies find cartilaginous fish to be well nested among acanthodians, with Doliodus and Tamiobatis being the closest relatives to Chondrichthyes.[14] Recent studies vindicate this, as Doliodus had a mosaic of chondrichthyian and acanthodiian traits.[15]

Dating back to the Middle and Late Ordovician Period, many isolated scales, made of dentine and bone, have a structure and growth form that is chondrichthyan-like. They may be the remains of stem-chondrichthyans, but their classification remains uncertain.[16][17][18]

The earliest unequivocal fossils of cartilaginous fishes first appeared in the fossil record by about 430 million years ago, during the middle Wenlock Epoch of the Silurian period.[19] The radiation of elasmobranches in the chart on the right is divided into the taxa: Cladoselache, Eugeneodontiformes, Symmoriida, Xenacanthiformes, Ctenacanthiformes, Hybodontiformes, Galeomorphi, Squaliformes and Batoidea.

By the start of the Early Devonian, 419 million years ago, jawed fishes had divided into three distinct groups: the now extinct placoderms (a paraphyletic assemblage of ancient armoured fishes), the bony fishes, and the clade that includes spiny sharks and early cartilaginous fish. The modern bony fishes, class Osteichthyes, appeared in the late Silurian or early Devonian, about 416 million years ago. The first abundant genus of shark, Cladoselache, appeared in the oceans during the Devonian Period. The first Cartilaginous fishes evolved from Doliodus-like spiny shark ancestors.

A Bayesian analysis of molecular data suggests that the Holocephali and Elasmoblanchii diverged in the Silurian (421 million years ago) and that the sharks and rays/skates split in the Carboniferous (306 million years ago).

Devonian (419–359 mya)
Early Shark.jpg Cladoselache Cladoselache was the first abundant genus of primitive shark, appearing about 370 Ma.[20] It grew to 6 feet (1.8 m) long, with anatomical features similar to modern mackerel sharks. It had a streamlined body almost entirely devoid of scales, with five to seven gill slits and a short, rounded snout that had a terminal mouth opening at the front of the skull.[20] It had a very weak jaw joint compared with modern-day sharks, but it compensated for that with very strong jaw-closing muscles. Its teeth were multi-cusped and smooth-edged, making them suitable for grasping, but not tearing or chewing. Cladoselache therefore probably seized prey by the tail and swallowed it whole.[20] It had powerful keels that extended onto the side of the tail stalk and a semi-lunate tail fin, with the superior lobe about the same size as the inferior. This combination helped with its speed and agility which was useful when trying to outswim its probable predator, the heavily armoured 10 metres (33 ft) long placoderm fish Dunkleosteus.[20]
Carboniferous (359–299 Ma): Sharks underwent a major evolutionary radiation during the Carboniferous.[21] It is believed that this evolutionary radiation occurred because the decline of the placoderms at the end of the Devonian period caused many environmental niches to become unoccupied and allowed new organisms to evolve and fill these niches.[21]



Stethacanthus1DB.jpg Stethacanthidae
Steth pair1.jpg

As a result of the evolutionary radiation, carboniferous sharks assumed a wide variety of bizarre shapes; e.g., sharks belonging to the family Stethacanthidae possessed a flat brush-like dorsal fin with a patch of denticles on its top.[21] Stethacanthus' unusual fin may have been used in mating rituals.[21] Apart from the fins, Stethacanthidae resembled Falcatus (below).

Falcatus.jpg Falcatus Falcatus is a genus of small cladodont-toothed sharks which lived 335–318 Ma. They were about 25–30 cm (9.8–11.8 in) long.[23] They are characterised by the prominent fin spines that curved anteriorly over their heads.
Permian Permian (298–252 Ma): The Permian ended with the most extensive extinction event recorded in paleontology: the Permian-Triassic extinction event. 90% to 95% of marine species became extinct, as well as 70% of all land organisms. Recovery from the Permian-Triassic extinction event was protracted; land ecosystems took 30M years to recover,[24] and marine ecosystems took even longer.[25]
Jurassic Jurassic (201–145 Ma):
Cretaceous Cretaceous (145–66 Ma): The end of the Cretaceous was marked by the Cretaceous–Paleogene extinction event (K-Pg extinction). There are substantial fossil records of jawed fishes across the K–T boundary, which provides good evidence of extinction patterns of these classes of marine vertebrates. Within cartilaginous fish, approximately 80% of the sharks, rays, and skates families survived the extinction event,[27] and more than 90% of teleost fish (bony fish) families survived.[28]
Squalicorax falcatusDB.jpg Squalicorax falcatus Squalicorax falcatus is a lamnoid shark from the Cretaceous
Ptychodus mortoni.jpg Ptychodus Ptychodus is a genus of extinct hybodontiform shark which lived from the late Cretaceous to the Paleogene.[29][30] Ptychodus mortoni (pictured) was about 32 feet (9.8 meters) long and was unearthed in Kansas, United States.[31]
VMNH megalodon.jpg Megalodon
External video
Megalodon battle History Channel
The Nightmarish Megalodon Discovery

Megalodon is an extinct species of shark that lived about 28 to 1.5 Ma. It looked much like a stocky version of the great white shark, but was much larger with fossil lengths reaching 20.3 metres (67 ft).[32] Found in all oceans[33] it was one of the largest and most powerful predators in vertebrate history,[32] and probably had a profound impact on marine life.[34]

Extinct orders of cartilaginous fishes
Group Order Image Common name Authority Families Genera Species Note
Holocephali †Orodontiformes
†Petalodontiformes Belantsea montana.JPG
†Iniopterygiformes Iniopteryxrushlaui.JPG
†Symmoriida StethacanthusesDB 2.jpg [35]
Helicoprion bessonovi1DB.jpg [36]
Position uncertain
Other †Squatinactiformes Stethacanthus BW.jpg
Early Shark.jpg
†Xenacanthiformes Triodus1db.jpg
†Hybodontiformes Ptychodus mortoni.jpg


Subphylum Vertebrata
└─Infraphylum Gnathostomata
      ├─Placodermiextinct (armored gnathostomes)
      └Eugnathostomata (true jawed vertebrates)
         ├─Acanthodii (stem cartilaginous fish)
         └─Chondrichthyes (true cartilaginous fish)
             ├─Holocephali (chimaeras + several extinct clades)
             └Elasmobranchii (shark and rays)
                ├─Selachii (true sharks)
                └─Batoidea (rays and relatives)


  • Note: Lines show evolutionary relationships.

See also[edit]


  1. ^ Botella, H.A.; Donoghue, P.C.J.; Martínez-Pérez, C. (2009). "Enameloid microstructure in the oldest known chondrichthyan teeth". Acta Zoologica. 90 (Supplement): 103–108. doi:10.1111/j.1463-6395.2008.00337.x.
  2. ^ "Chondrichthyes". PalaeoDB. Retrieved 26 November 2013.
  3. ^ Sharks of the World: An Annotated and Illustrated Catalogue of Shark Species Known to Date
  4. ^ Wilga, C. D.; Lauder, G. V. (2002). "Function of the heterocercal tail in sharks: quantitative wake dynamics during steady horizontal swimming and vertical maneuvering". Journal of Experimental Biology. 205 (16): 2365–2374. PMID 12124362.
  5. ^ Collin, Shaun P. (2012). "The Neuroecology of Cartilaginous Fishes: Sensory Strategies for Survival". Brain, Behavior and Evolution. 80 (2): 80–96. doi:10.1159/000339870. ISSN 1421-9743. PMID 22986825.
  6. ^ de Bellard, Maria Elena (15 June 2016). "Myelin in cartilaginous fish". Brain Research. 1641 (Pt A): 34–42. doi:10.1016/j.brainres.2016.01.013. ISSN 0006-8993. PMC 4909530. PMID 26776480.
  8. ^ a b Adams, Kye R.; Fetterplace, Lachlan C.; Davis, Andrew R.; Taylor, Matthew D.; Knott, Nathan A. (January 2018). "Sharks, rays and abortion: The prevalence of capture-induced parturition in elasmobranchs". Biological Conservation. 217: 11–27. doi:10.1016/j.biocon.2017.10.010.
  10. ^ Leonard Compagno (2005) Sharks of the World. ISBN 9780691120720.
  11. ^ Haaramo, Mikko. Chondrichthyes – Sharks, Rays and Chimaeras. Retrieved 22 October 2013.
  12. ^ Benton, M. J. (2005). Vertebrate Palaeontology (3rd ed.). Blackwell. Fig 7.13 on page 185. ISBN 978-0-632-05637-8.
  14. ^ Burrow, CJ; Den Blaauwen, J.; Newman, MJ; Davidson, RG (2016). "The diplacanthid fishes (Acanthodii, Diplacanthiformes, Diplacanthidae) from the Middle Devonian of Scotland". Palaeontologia Electronica. doi:10.26879/601.
  15. ^ Maisey, John G.; Miller, Randall; Pradel, Alan; Denton, John S.S.; Bronson, Allison; Janvier, Philippe (2017). "Pectoral Morphology in Doliodus: Bridging the 'Acanthodian'-Chondrichthyan Divide" (PDF). American Museum Novitates. 3875 (3875): 1–15. doi:10.1206/3875.1.
  16. ^ Andreev, Plamen S.; Coates, Michael I.; Shelton, Richard M.; Cooper, Paul R.; Smith, M. Paul; Sansom, Ivan J. (2015). "Ordovician chondrichthyan-like scales from North America". Palaeontology. 58 (4): 691–704. doi:10.1111/pala.12167.
  17. ^ Sansom, Ivan J.; Davies, Neil S.; Coates, Michael I.; Nicoll, Robert S.; Ritchie, Alex (2012). "Chondrichthyan-like scales from the Middle Ordovician of Australia". Palaeontology. 55 (2): 243–247. doi:10.1111/j.1475-4983.2012.01127.x.
  18. ^ Andreev, Plamen; Coates, Michael I.; Karatajūtė-Talimaa, Valentina; Shelton, Richard M.; Cooper, Paul R.; Wang, Nian-Zhong; Sansom, Ivan J. (2016). "The systematics of the Mongolepidida (Chondrichthyes) and the Ordovician origins of the clade". PeerJ. 4: e1850. doi:10.7717/peerj.1850. PMC 4918221. PMID 27350896.
  21. ^ a b c d R. Aidan Martin. "A Golden Age of Sharks". Biology of Sharks and Rays. Retrieved 26 November 2013.
  22. ^ Ward, P.; Labandeira, C.; Laurin, M.; Berner, R. A. (2006). "Confirmation of Romer's Gap is a low oxygen interval constraining the timing of initial arthropod and vertebrate terrestrialization". Proceedings of the National Academy of Sciences. 103 (45): 16818–16822. Bibcode:2006PNAS..10316818W. doi:10.1073/pnas.0607824103. PMC 1636538. PMID 17065318.
  23. ^ "Archived copy". Archived from the original on 21 August 2008. Retrieved 4 September 2008.CS1 maint: archived copy as title (link) Fossil Fish of Bear Gulch 2005 by Richard Lund and Eileen Grogan Accessed 2009-01-14
  26. ^ "extinction". Retrieved 26 November 2013.
  29. ^ Fossils (Smithsonian Handbooks) by David Ward (Page 200)
  30. ^ The paleobioloy Database Ptychodus entry accessed on 8/23/09
  31. ^ "Giant predatory shark fossil unearthed in Kansas". BBC - Earth News. 24 February 2010.
  33. ^ Pimiento, Catalina; Dana J. Ehret; Bruce J. MacFadden; Gordon Hubbell (10 May 2010). Stepanova, Anna (ed.). "Ancient Nursery Area for the Extinct Giant Shark Megalodon from the Miocene of Panama". PLOS One. 5 (5): e10552. Bibcode:2010PLoSO...510552P. doi:10.1371/journal.pone.0010552. PMC 2866656. PMID 20479893.
  35. ^ Coates, M.; Gess, R.; Finarelli, J.; Criswell, K.; Tietjen, K. (2016). "A symmoriiform chondrichthyan braincase and the origin of chimaeroid fishes". Nature. 541 (7636): 208–211. Bibcode:2017Natur.541..208C. doi:10.1038/nature20806. PMID 28052054.
  36. ^ Tapanila, L; Pruitt, J; Pradel, A; Wilga, C; Ramsay, J; Schlader, R; Didier, D (2013). "Jaws for a spiral-tooth whorl: CT images reveal novel adaptation and phylogeny in fossil Helicoprion" (PDF). Biology Letters. 9 (2): 20130057. doi:10.1098/rsbl.2013.0057. PMC 3639784. PMID 23445952.[permanent dead link]

Further reading[edit]