Shark Biology and evolution
- Created by: ValentineDevil
- Created on: 19-02-19 22:05
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- 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)
- Palatoquadrate articulates with the underside of the skull in what is perhaps the original condition for jawed vert
- 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
- Upper jaw is suspended by both articulation with braincase and indirectly via hyomandibula
- 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
- jaws suspended by the hyoid arch only
- Autostylic
- 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
- water enters gill chambers through mouth or spiracles and exits via 5-7 pairs of gill slits
- 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
- Heart: two-chambers S-shaped tube
- 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
- Have many Ampullae of Lorenzini
- 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
- Cladoselachida
- Jaw Suspension
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