Shark Biology and evolution

View mindmap
  • Chondrichthyan Biology and the Origin of Cartilaginous fish
    • Jaw Suspension
      • Autostylic
        • Palatoquadrate articulates with the underside of the skull in what is perhaps the original condition for jawed vert
          • Primitive: placoderms; palatoquadrate firmly attaches to underside of chondrodranium: helps open and close mouth to trap in smaller fish to eat
          • Secondary: mammals, amphibians, holocephalans; platatoquadrate refused to chondrocranium. Hyomandibula used for others functions (e.g. forming stapes of middle ear bones)
      • Amphystylic
        • Upper jaw is suspended by both articulation with braincase and indirectly via hyomandibula
          • Bony fish and chondricthyans: hyomandibula extends as a prop from otic capsule to the caudal end of the palatoquadrate: small amount of chomping and chewing smaller prey
      • Hyostylic
        • jaws suspended by the hyoid arch only
          • Modern chondricthyans and osteichthyes: flexible jaws; projection more downward/forward. Palatoquadrate held by hyomandibula: easier open and close and tug and chew on food
    • Respiration
      • water enters gill chambers through mouth or spiracles and exits via 5-7 pairs of gill slits
        • small hole behind eye that opens to mouth: caught between jaw arch and hyoid arch
        • Spiracles provide oxygenated blood directly to eye and brain (through separate blood vessel)- not in ALL cartilaginous and bony fish
      • Gill rakers (cartilaginous projections on gill support strucutre) protect delicate gill filaments from particles in water that might damage them
    • Digestion
      • U shaped stomach leads to spiral valve in many species; this portion is twisted to increase surface area (increases nutrient absorption)
      • After spiral valve, tract leads to rectum to then cloaca
    • Circulation
      • Heart: two-chambers S-shaped tube
        • small in proportion to body size
        • blood flows from heart to gills to body tissues
      • Veins are near, so heat from warmer veins go to cooler arteries
      • Sharks have a low blood pressure
      • Pericardium walls (membranous sacs enclose heart) are rigid, creating a suction within it to maintain flow of blood.
      • Many sharks must swim continuously
      • Fast swimming sharks: body temp higher than surrounding water (up to 8c higher) bc of red muscle  generating heat
    • Senses
      • Have many Ampullae of Lorenzini
        • Sensitive to changes in temperature, H2O pressure, electrical fields, and salinity
      • Determine direction of scent based on the timing of scent detection in each nostril
      • External nostrils located underside of rostrum anterior to jaws
      • Nasal flap separates incurrent from excurrent opening: H2O passes into and out of olfactory sac, permitting the shark to detect the odors of H2O
    • Evolution
      • Cladoselachida
        • Shark-like chondrichthyan
        • Broad-based paired pectoral and pelvic fins (used as hydrofoils)
        • 2 dorsal fins w/ dorsal spine in front of each
        • Causal fin heterocercal internally but symmetrical externally
        • Dual jaw attachment
        • Large gape
        • Teeth pointed and 3-cusped
        • Skin sparsely covered w/ dermal denticles
      • Symmoriiformes
        • shark-like chondrichthyans
        • Broad-based paired pectoral and pelvic fins (used as hydrofoils)
        • long, pointed fin axis (&extension from pectoral fin)
        • Dorsal fins without dorsal spines
        • Causal fin heterocercal internally, but symmetrical externally
        • Unique 'brush-like spine' that originates dorsally at the base of the head
      • Eugeneodontiformes
        • Median tooth whorl on symphasis of lower jaw (fit in cavity between 2 similar series in upper jaw) function unclear
        • Single dorsal fin w/out spines
        • Pectoral fins supported by long radials (1-2 segments) articulating on girdle
        • No anal or pelvic fins??
        • Long rostrum
        • Somee lost upper jaw or fuse it with cranium
      • Petalodotiformes
        • Bizzare chondrichthyans
        • Rounded / flattened body
        • Extensive round fins
        • Ridged teeth that were probably used for crushing
      • Xenacanthiformes
        • Freshwater sharks
        • Endoskeleton of pectoral and pelvic fins similar to that of modern sharks
        • Tail long and tapering (diphycercal) and not heterocercal
        • 1 dorsal fin
        • Dorsal spine originated directly behind the head
        • Tri-cusped teeth, but central cusp was shortest
      • Ctenacanthiformes
        • 2 dorsal fins supported by anterior spines w/ pectinate ornamentation, and by basal cartilages w/ radials
        • Tail heterocercal
        • Cleaver-shaped palatoquadrate and broad otico-occopital region of braincase
        • Pectoral fin basal cartilage rods fused to form 1-2 larger basals
        • Long metapterygium of pectoral fins and anal fin
        • Compound scales
      • Hybodontiformes
        • paired fins show signs of intrinsic musculature, and greater flexibility, implying that they were used in steering
        • Heterocercal tail, anal fin and dual jaw suspension
        • Heterodont dentition, with cutting teeth in front part of the jaw and crushing teeth in the back part
        • 1-2 pairs of hooked cephalic spines
      • Acanthodians (spiny sharks)
        • Large spines
        • Subterminal mouths
        • System of rays and scales in cheek regions
        • Orbits larges (anterior on the skulls, with circumorbital plates)
        • Fin spines (all except the causal fin)
        • Tooth-bearing jaw bones (attached to jaw cartilages)
        • Onion-like scales
        • Heterocercal tail

Comments

No comments have yet been made

Similar zoology resources:

See all zoology resources »See all Shark biology and evolution resources »