Class Chondrichthyes: cartilaginous fishes

1. Class Chondrichthyes: cartilaginous fishes • The class Chondrichthyes has two subclasses: • Elasmobranchii, which includes the sharks and rays. • Holocephali: the chimaeras: ratfish and ghostfish.

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4. Class Chondrichthyes • Modern Chondricthyes include the sharks, rays and Chimeras. • The Chondrichthyes’ well-developed jaws, highly developed sense organs, powerful swimming ability and streamlined shape have enabled them to thrive as marine predators for more than 350 million years, as other groups have come and gone. • There are just under 1000 living species, all of which have cartilaginous skeletons, even though they are descended from ancestors that had bone.

5. Class Chondrichthyes • The Chondrichthyes are an ancient group that although not as diverse as the bony fishes have persisted largely unchanged for hundreds of millions of years. • The oldest unambiguous Chondrichthyans are found in the Early Devonian (Devonian -- 416-360 mya). although there are older fossils of scales.

6. Fossil history of Chondrichtyes • One of the best known extinct genera is Cladoselache a pelagic marine predator from the Devonian. • It was shark-like in appearance. About 2 meters long with a large gape and three-pronged teeth. As in modern sharks the teeth were arranged on a ligamentous band in a whorl-shaped arrangement.

7. Fossil history of Chondrichtyes • Cladoselache had two dorsal fins, each preceded by a large spine. • It also possessed paired pelvic and pectoral fins as in modern sharks, but the fins were much more broad based than in later sharks. • The tail was symmetrical externally, but internally asymmetrical with the notochord extending into the upper lobe of the tail.

8. Cladoselache picture Cladoselache http://www.dinosoria.com/poissons/cladoselache_03.jpg Cladoselache lacked the rostrum (snout) of modern sharks

9. Extant radiation of Chondrichthyes • By the Jurassic (200-146 mya) sharks of modern appearance had evolved. Several genera from that era are still extant. • The most distinctive feature of modern sharks is the rostrum or snout that overhangs the mouth. • Less prominent, but also of major importance was the evolution of solid calcified vertebrae. • Finally, the teeth are covered with thicker more complex enamel than in earlier sharks.

10. Megalodon • Megalodon (Carcharodonmegalodon) is another extinct shark species that is the largest predatory shark known. • Megalodon occurred from 28-1.5 mya and at approximately 16m long (and with a mass estimated at 47 metrics tonnes) it resembled a massive great white shark and was the top ocean predator of its era.

11. “Megalodon (gray and red) with the whale shark (violet), great white shark (green), and a human (blue) for scale. Note: The maximum size attained by C. megalodon is indicated by the 20 m scale.” From Wikipedia. http://upload.wikimedia.org/wikipedia/commons/thumb/0/07/Megalodon_scale1.png/220px-Megalodon_scale1.png

12. http://upload.wikimedia.org/wikipedia/commons/thumb/7/7a/Megalodon_shark_jaws_museum_of_natural_history_068.jpg/300px-Megalodon_shark_jaws_museum_of_natural_history_068.jpghttp://upload.wikimedia.org/wikipedia/commons/thumb/7/7a/Megalodon_shark_jaws_museum_of_natural_history_068.jpg/300px-Megalodon_shark_jaws_museum_of_natural_history_068.jpg http://upload.wikimedia.org/wikipedia/commons/thumb/7/71/Megalodon_tooth_ruler.jpg/220px-Megalodon_tooth_ruler.jpg

13. http://upload.wikimedia.org/wikipedia/commons/thumb/1/1f/Carcharodon_megalodon.jpg/220px-Carcharodon_megalodon.jpghttp://upload.wikimedia.org/wikipedia/commons/thumb/1/1f/Carcharodon_megalodon.jpg/220px-Carcharodon_megalodon.jpg

14. Megalodon • Megalodon preyed on anything it wanted including pinnipeds, sea turtles, and frequently whales. • Fossil whale skeletons contemporaneous with Megalodon show bite damage clearly inflicted by Megalodon.

15. Megalodon • Megalodon when attacking large prey is believed to have focused its attack on the rib cage area crushing the delicate organs within. • It also is believed to have bitten off appendages immobilizing the prey.

16. Megalodon • Megalodon’s bite force has been estimated at up to 10 times that of a great white shark and up to five times that of a Tyrannosaurusrex. • The large serrated teeth were deep rooted and Megalodon likely behaved like a great white, which shakes its head after biting, thus sawing through its prey.

17. Extinction of Megalodon • The formation of the Isthmus of Panama three mya resulted in large changes in ocean currents and reduced worldwide ocean temperatures. • Megalodon preferred warmer sea temperatures and the loss of warm water habitat coupled with a substantial decline in the diversity of whales (also as a result of changing ocean temperatures) is most likely the cause of the species extinction.

18. Class Chondrichthyes Thresher Shark http://dsc.discovery.com/sharks/shark-types/thresher-shark.jpg

19. Class Chondrichthyes • About 1000 living species divided into two distinct groups • Neoselachii [also known as elasmobranchs] (sharks, skates and rays) about 950 species. • Holocephalii (ratfishes). About 33 species.

20. Neoselachii • Neoselachii • Galeomorpha: about 279 species of sharks with an anal fin. 1m to perhaps 18m in length. Sand tigers, mackerel sharks, threshers, basking sharks, hornsharks, whale sharks, nurse sharks, mako, great white. “Squalomorpha”: Not a monphyletic group. About 124 species of deep sea sharks, dogfish, angel sharks. 15cm to 7m. Batoidea: skates and rays. At least 534 species. Electric rays, Manta rays, stingrays, skates. 1-6m long and up to 6 m wide.

21. Diversity of sharks

22. Hammerhead Shark

23. Great White Shark Hammerhead sharks Whale shark Two skates

24. Skate (left) and ray (right)

25. Spotted Ratfish http://www.elasmodiver.com/BCMarinelife/images/Spotted-ratfish.jpg

26. Sharks • Sharks represent a little less than half of the elasmobranchs and most are specialized predators. • The largest species is the whale shark, which is a plankton feeder, as is the basking shark and the megamouth shark, but most of the others are predators of fish, marine mammals, crustaceans and whatever else they can catch.

27. Basking Shark http://oursurprisingworld.com/wp-content/uploads/ 2008/02/disgusting_fishes_7-basking-shark.jpg Whale shark http://animals.nationalgeographic.com/ staticfiles/NGS/ Shared/StaticFiles/animals/images/ primary/whale-shark-with-fish.jpg

28. Sharks • The extant sharks include at least two lineages and molecular studies suggest there may be several others included within these two. • The squaloid sharks are smaller brained, mostly live in cold, deep water and include the various species of dogfish, the megamouth, and cookie-cutter sharks.

29. Lesser spotted dogfish http://www.malcolmnobbs.com/favourite/medium/lesser_spotted_dogfish2.jpg

30. Megamouth shark http://upload.wikimedia.org/wikipedia/commons/d/dd/Megamouth_shark_japan.jpg Cookie cutter sharks http://vivaldi.zool.gu.se/Fiskfysiologi_2001/Course_material/ Introduction_fish_evolution/Images/Cookie_cutters.GIF

31. Spiny dogfish http://elasmodiver.com/Sharkive%20images/Spiny%20dogfish%20059.jpg

32. Sharks • The galeoid sharks are the dominant carnivores of shallow, warm, species-rich parts of the ocean. • They include hammerheads, tiger sharks, threshers, mackeral sharks, and the whale shark.

33. Sharks • Sharks are very well streamlined, but are heavier than water (because they lack a swim bladder) and sink if not swimming forward. • Sharks increase their buoyancy by having a large oil-filled liver that reduces their density, but not enough to prevent them from sinking.

34. Fossil history of Chondrichtyes • The elasmobranchheterocercal tail contains numerous radial skeletal elements which make it flexible and the vertebral column extends into the dorsal lobe. • Its shape can be controlled by intrinsic muscles. • When undulated from side to side the tail because of its shape generates both forward and upward thrust, which counteracts a shark’s tendency to sink, while the large flat pectoral fins also provide lift to keep the head up.

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36. Sharks • A typical shark is about 2m long, but they range in size from a few miniature forms that are 25 cm long up to perhaps 18m in length. • Despite their range of sizes all modern sharks share a suite of characteristics.

37. Characteristics of sharks • The cartilaginous vertebral centra of sharks are distinctive. • Adjacent vertebrae have depressions in their faces into which fit spherical remnants of the notochord. • This arrangement of a rigid vertebral column of calcified cartilage swivelling on bearings of notochord allows the axial skeleton to swing from side to side.

38. Characteristics of sharks • In addition to the neural and hemal arches in the vertebral column, which protect the spinal cord and blood vessels, all sharks possess additional intercalary plates that provide extra protection to the nerve cord and blood vessels.

39. Dorsal intercalary plate

40. Shark skin • Unlike earlier sharks, living species have their skin entirely covered in dermal placoid scales, which are small tooth-like structures (with enamel, dentine and pulp just like real teeth). • These scales give sharkskin a tough, leathery and abrasive feel. The skin is also very streamlined.

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42. Shark skin repels barnacles • Barnacles are a major source of drag on boats and on many marine mammals e.g. whales. However, shark skin doesn’t allow barnacles to grip and grow. • http://www.youtube.com/watch?v=1hihcIPG7xo&feature=relmfu

43. Mako shark skin • The shortfin mako shark is capable of swimming in brief bursts at speeds approaching 50mph (kph). • Recent research has shown that its skin is able to reduce drag by bristling, which creates tiny depressions across the surface of the skin (like those on a golf ball).

44. Shortfin mako Shark http://elasmodiver.com/images/Shortfin-Mako-022.jpg

45. Mako shark skin • The 200 micrometer long scales when held at 90 degrees to the shark’s body cause tiny vortices to form in between the scales. • These vortices prevent a turbulent wake from forming, which would exert a backwards pull. • (Lang et al. 2008. Bioinspiration and Biomimetrics; New Scientist 15 Nov 2008, p.16)

46. Shark teeth • The placoid scales are modified in the mouth to produce the rows of replaceable teeth characteristic of sharks. • Each tooth in a shark can be rapidly replaced as it becomes worn or damaged. Teeth are not embedded in the jaw but arranged on a spiral or whorl shaped cartilaginous band in which replacement teeth are always developing behind the functional tooth. • Teeth in young sharks may be replaced as often as once every 8 days.

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48. http://www.sharkattackphotos.com/Shark_Miscellaneous.htm

49. Sand tiger shark (note multiple rows of teeth)

50. Variation in tooth structure • The type of teeth a shark possesses is dictated by the prey it eats. • Sharks that feed on crustaceans, mollusks and similar hard shelled prey have dense arrays of flattened teeth designed for crushing. • Fish feeders have long pointed needle-like teeth for gripping.