L7: The Emergence of Gnathostomes, the Vertebrates with Moveable Jaws
- Created by: ValentineDevil
- Created on: 13-02-19 21:20
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- The Emergence of Gnathostomes, the Vertebrates with Moveable Jaws
- Earliest Jawed Vertebrates: Placodermi
- Massively developed bony fish
- Plates hinged or connected by tissue
- hinge between head shield and thoracic shield
- Bottom dwellers or active swimmers
- Fed close to surface of sea floor or chased prey
- Small female placoderm died during birth with umbilical cord intact
- Skeletal bones in the upper and lower jaws
- Premaxilla
- Maxilla
- Dentary
- Covered in a set of dermal bones
- Teeth attached to dermal bones (bony fish and mammals)
- Modern phylogenetic analysis
- Cartilaginous fish have secondarily lost the dermatocranium
- Diagnostic features
- Opposing moveable jaws, mostly with teeth
- Splanchnocranium (jaws belong to this)
- Dermatocranium (dermal bones make up the outside of the jaws in most Gnathostomes
- Upper palatoquadrate cartilage
- Lower Mackel's cartilage
- Teeth attached to them (cartilaginous fish)
- (primitive) vertical biting of two endoskeletal elements
- Jaw origins
- From anterior pharyngeal arch supporting gills
- Increased respiration efficiency
- Pump H2O across gills
- Feeding as a secondary function before becoming the primary one in many vertebrates
- Paired nasal sacs
- Independent of the nasohypophyseal tube and opening separately to exterior through external nostrils
- Complex gill arches for gill support
- Lie internally to the gill filaments and branchial blood vessels
- Counter current system
- Mainstream tangentially across branchial arches and concentrates particles in the posterior oral cavity; the filtrate exists between gill rakers and passes the gill filaments where gas exchange occurs
- 3 semi-circular canals
- Through addition of a lateral horizontal canal to the pre-existing anterior and posterior vertical canals
- Paired anterior and posterior fins or limbs
- Vertebral elements occuring underneath the notochord
- Opposing moveable jaws, mostly with teeth
- Earliest Jawed Vertebrates: Placodermi
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