Chondrichthyes: Cartilaginous Fishes Review Superclass Gnathostomata - Jawed fishes I. Chondrichthian characteristics & groups • Class Placodermi (plate-skinned) extinct II. Holocephali • Class Acanthodii (spiny sharks) extinct III. Elasmobranchii A. Evolution of elasmobranchs • Class Chondrichthyes living B. Elasmobranch basic characteristics • Class Sarcopterygii living C. Elasmobranch basic adaptive patterns • Class Actinopterygii living D. Taxonomy of elasmobranchs Classes: An alternative view Jawed vertebrates of the phylogeny of Placodermi {extinct} fishes •Chondrichthyes Superclass are not ancestral Chondrichthyes to bony fishes Gnathostomata cartilaginous fishes •based on DNA instead of morphology Acanthodii {extinct} Arnason et al. 2001 Sarcopterygii lobe-finned fishes, tetrapods Actinopterygii ray-finned fishes Subclass Elasmobranchii (sharks & rays, strap gills) 930 Class Chondrichthyes, two major groups: living spp. Infraclass Cladoselachimorpha (1 extinct order) Infraclass Xenacanthimorpha (1 extinct order) Subclass Elasmobranchii (sharks & rays) Infraclass Euselachii (2 extinct orders; 13 living orders in 2 subdivisions) Subclass Holocephali (chimaeras, whole heads) 35 living Subclass Holocephali (chimaeras) spp. Superorder Paraselachimorpha (6 extinct orders) Superorder Holocephalimorpha • 6 extinct orders • Chimaeriformes (1 living order) 1 Characteristics of Chondrichthyes: • cartilaginous skeleton (w/ endoskeletal calcification) • male intromittent organs (claspers) ceratotrichia • placoid scales • teeth not fused to jaws (only to connective tissue) • lipid (squalene) filled livers • fin rays soft and unsegmented (ceratotrichia) • swim bladder and lung absent • high concentrations of urea and trimethylamine oxide (TMAO) in blood (for osmoregualtion) Subclass Holocephali (whole head) Order Chimaeriformes: 3 families, 35 spp. Superorder Holocephalimorpha Order Chimaeriformes - chimaeras (ratfishes) Characteristics that separate them from Elasmobranchs: • upper jaws attached to braincase (autostylic suspension) • single opercular opening, covering 4 gill openings • all are oviparous • separate anal and urogenital opening - no cloaca • mostly scaleless 3 orders of Chimaeras: longnose Other cool things about chimaeras: Rhinochimaeridae • first dorsal has venomous spine • some males have a tenaculum on forehead • tend to live very deep and are rare ploughnose Callorhynchidae shortnose (ratfishes) Chimaeridae 2 Subclass Elasmobranchii (sharks & rays) 1st elasmobranch radiation: Infraclass Cladoselachimorpha (cladoselachid sharks) Evolution of Elasmobranchs • arose in early Devonian (400 mya) Cladodont (branched tooth): all had a three-cusped tooth • modern forms in place by early Cretaceous (144 mya) • three major radiations: (1) Infraclass: Cladoselachimorpha Infraclass : Euselachii (2) Hybodonts (3) modern elasmobranchs Characteristics: Cladoselache 1. terminal mouth 2. fins broad-based and stiff, long radial elements 3. no anal fin Cladoselache 4. homocercal caudal fin • pelagic predators of 5. body supported by placoderms, acanthodians, notochord only and bony fishes 6. spines often in front of dorsal, pectoral, pelvics • fed by engulfing or slashing Stethacanthus Symmorium 2nd elasmobranch radiation: Hybodus Infraclass Euselachii: Hybodonts early Mesozoic (250 mya) Hybodont = humpback tooth 1. terminal mouth (same as cladoselachids) 2. fins flexible and mobile 3. anal fin Front teeth Back teeth 4. caudal fin heterocercal grasping crushing 3 spines on D fin 3rd elasmobranch radiation: notochord with neural arches coming of the modern sharks Hybodus mid-Mesozoic (200 mya) • Jaws: subterminal mouth with protrusible upper jaw • Dentition: tooth replacement system terminal mouth multiple basal elements with cartilage supports • Fins: ceratotrichia supporting the fin calcified vertebral centra • Vertebrae: calcified vertebrae instead of notochord Squalus improved feeding and locomotion (parallel changes were occurring in bony fishes) 3 fused basal elements - radials ventral mouth flexible, horny rays - ceratotrichia protrusible jaw Teeth replaced differently in modern sharks Spiral tooth replacement Modern sharks: rows of replacement teeth Helicoprion (spiral saw) Extinct sharks (e.g. Helicoprion): spiral replacement of teeth Hexanchiformes + Echinorhiniformes Sixgill sharks Bramble sharks Living Elasmobranchs (strap gills) 2 families, 5 spp Selachii 1 families, 2 spp 9 orders 2 subdivisions: Squaliformes 32 families Dogfish sharks 6 families, > 97 spp • Selachii (sharks) > 400 spp Pristiophoriformes Saw sharks 2 superorders 1 family, 9 spp - Galeomorphi (4 orders) ( shark form ) Squatiniformes Angel sharks - Squalomorphi (5 orders) (dogfish form) 1 family, 15 spp Heterodontiformes Bullhead sharks 1 family, 9 spp • Batoidea (skates & rays) (4 orders) Orectolobiformes Carpet sharks 7 families, 32 spp > 75% of species Lamniformes in 2 orders Mackerel sharks 7 families, 15 spp Carcharhiniformes Ground sharks 8 families, >224 spp 4 Rajiformes Skates & Guitarfishesdae Characteristics of living Elasmobranchs: Batoidea 285 spp 4 orders 725 1. cartilaginous skeleton 17 families 2. gill slits (usually 5-7) not covered by an operculum > 530 spp. 3. paired ventral nostrils 4. subterminal mouth (usually) Pristiformes Sawfishes, 7 spp 5. protrusible upper jaw (usually) (hyostylic suspension) 6. fin rays are unsegmented, soft, epidermal = ceratotrichia 7. placoid scales Torpediniformes Electric rays, 59 spp 8. enlarged liver for buoyancy 9. spiral valve intestine Myliobatiformes 10. electrical field receptors: Ampullae of Lorenzini Stingrays, 183 sppdae 11. cloaca (shared urogenital and anal opening) Rhinobatidae Guitarfishes, 42 spp 12. internal fertilization (males have claspers) now placed in Rajiformes (Nelson 2006) Hyostylic suspension – allows protrusion of the upper jaw Resting position Snout lifted, lower jaw depressed Snout dropped down, Palatoquadrate rotated forward and down, palatoquadrate retracted lower jaw forward and upward normal position Placoid scales Sand tiger shark with palatoquadrate rotated forward and downward 5 large, lipid-filled liver intromittent organs: claspers ampullae of Lorenzini spiral valve intestine female male Biological Attributes: Biological Attributes: 4. Reproduction: 1. distribution: mostly marine a) in general: 2. generally adapted for movement at low energy costs: - mature late (6 - 35 yrs) - heterocercal tails - produce few relatively large young - placoid scales - internal fertilization (male claspers) - cartilaginous skeletons - static buoyancy mechanism - enlarged liver with squalene b) Modes: 1. Oviparous: lay eggs externally 3. feeding: most are predators, carnivorous, and tend to be 2. Viviparous: live-bearing large 6 Biological Attributes: 5. Sensory physiology: non-visual senses are extremely acute 6. Vital statistics: - low fecundity - slow growing - long-lived … thus very susceptible to overfishing Threats to sharks: finning Biological Attributes: 7. Tend to be highly mobile • Nicole, 12.5 ft female great white shark • tagged off S. Africa • showed up 99 days later off W. Australia, 11,000 km away. • 6 months later, she was back in S. Africa! Living Orders of Elasmobranchs: Class Chondrichthyes Subdivsion Selachii Subclass Elasmobranchii Galeomorphi Subdivision Euselachii 1. Heterodontiformes (8 species) Order Heterodontiformes 2. Orectolobiformes (32 species) 3. Lamniformes (15 species) - 1 family, 8 species 4. Carcharhiniformes (224 species) Squalomorphi - examples: bullhead shark, horn shark 5. Hexanchiforrmes (5 species) 6. Echinorhiniformes (2 species) 7. Squaliformes (97 species) 8. Squatiniformes (15 species) 9. Pristiophoriformes (5 species) Subdivision Batoidea 1. Torpediniformes (59 species) 2. Pristiformes (7 species) 3. Rajiformes (285 species) 4. Myliobatiformes (183 species) 7 Order Heterodontiformes Sleeping Horn shark • 2 dorsal fins, each with a spine • anal fin • 5 gill slits • large pectorals • two types of teeth grasping crushing • benthic, smallish (max. size 165 cm) Horn shark egg Order Orectolobiformes carpet sharks Order Orectolobiformes - 7 families, 32 spp. - examples: whale shark, nurse shark, wobbegong • 2 dorsal fins, no spines • anal fin • 5 gill slits • small teeth, terminal mouths • mouth usually with barbels • tropical shelf fishes Epaulette shark Wobbegong 8 Whale shark: the largest living fish nurse shark Order Lamniformes (mackerel sharks) Order Lamniformes - 7 families, 15 spp. • 2 dorsal fins w/o spines - examples: • anal fin • sand tiger • 5 gill slits • thresher • no nictitating membrane • megamouth • mouth extends well beyond eyes • basking • epipelagic, often coastal • great white • generally large, active sharks • mako • salmon Carcharodon megalodon, extinct lamniform, estimated to 16 m in length White shark 9 Basking shark Megamouth shark mako sharks sand tiger Order Carcharhiniformes (ground sharks or requiem sharks) Order Carcharhiniformes • 7 families, 224 spp. • 2 dorsal fins w/o spines • anal fin examples: tiger, bull, hammerhead, blue, leopard, • 5 gill slits smoothhound • nictitating membrane • dominant in tropics (90% of all sharks there) • pelagic and coastal 10 Hammerhead Leopard shark Blue shark Order Hexanchiformes 2 families, 5 spp. examples: frilled, sixgill, & sevengill sharks Order Hexanchiformes Order Echinorhiniformes (bramble sharks) • single dorsal fin, far back, without spine 1 family, 2 spp. • anal fin examples: bramble shark, prickly shark • six or seven gill slits • cone-like teeth (eat sharks,