Chondrichthyes Flashcards
Chondrichthyes division
Holocephali
Elasmobranchii
Shark evolution
Silurian period (440mya)
Shark radiation events
Paleozoic
Early Mesozoic
Late Mesozoic
Holocephali vs Elasmobranchii
Holocephali have one gill opening
Elasmobranchii have multiple gill openings
Both have cartilaginous endoskeleton
Both have sophisticated structures but have also maintained primitive characteristics
Holocephali
Anatomy not well known (found at 80m)
Lay eggs in shallow water
Rostral projections (hanging lower part of mouth)
-linked with predation
Elasmobranchii
Found in different shapes
- can be cylindrical with 5-7 gill openings
- dorsoventrally flattened (skates/rays) feed on ground materials and don’t need to move much
The first event
Paleozoic
All organisms looked like sharks & had a large gait
Had wide mouth to catch prey
Three pronged teeth
Did not need sophisticated dental structure due to open water living
Locomotion
Caudal fin at tail end of animal
Top section allows animal greater thrust and allows balance
Also plays a role in buoyancy
Hemal arches
Protect veins and arteries under skin
Prevent internal bleeding during aggressive interactions
The second event
Early Mesozoic
Internal clasps at pelvis for reproduction
-optimizes reproduction
Third event
Late Mesozoic
Large body size developed to prevent predation
Why are sharks good predators
Large rostellum Feeding apparatus Reinforced vertebrae Predatory response Cranial kinesis - allows for eating large chunks of meat -linked with predation
Sensory system
Lateralis system - mechanoreception (tubes in head region detect movement)
Ampula of Lorenzini - tubules filled with mucus detect electric fields
Chemoreception sensors - works with sharks sense of smell (1:1billion)
Tapetum lucidum - mirrors in eye that aid in sight with rod cells
