Skulls - Components, jaws Flashcards
Function of branchial arches III-VII in most fish
Support gills
Who has modified hyostyly?
Actinopterygii
What does the splanchnocranium form?
7 branchial arches & their derivatives (jaws, middle ear bones)
What feeding method do actinopterygiians use?
Suction feeding
Embryonic origin of splanchnocranium
Neural crest cells (-> cartilage, ossifies in most teleostomi)
Describe branchial arches III-VII
Made of 5 pieces (usually)
Precise functions of dermatocranium
- Cover chondrocranium & brain (dorsal, ventral)
- Cover & protect gills (opercular bone)
- Cover parts of jaw splanchnocranium
Describe modified hyostyly
Quadrate: Articulation point of upper jaw, not fused to chondrocranium
Articular: Articulation point lower jaw
Hyomandibula & symplectic bone: suspend jaws from chondrocranium
-> Many joints = highly kinetic (suction feeding)
Describe paleostyly
All branchial arches used to support gills; no jaws
Lower jaw bone in teleostomi
Dentary (encases Meckel’s cartilage except for ossified back portion; part of dermatocranium)
General function of dermatocranium
Form hard, protective structures
Function of branchial arches III-VII in amniotes
Form cartilage around trachea & larynx
Who has a dermatocranium?
Teleostomi (Osteichthyes, Tetrapods, not Agnathans, Chondrichthyes b/c no bone)
Who has paleostyly?
Agnathans
Adaptations of actinopterygiian skull to feed by biting prey
2° loss of cranial kinesis by bone fusion to provide strength
Upper jaw bones of teleostomi
Premaxilla, maxilla (dermatocranium)
Embryonic origin: chondrocranium
Neural crest cells, mesodermal mesenchyme
Describe Autostyly
Palatoquadrate: Upper jaw, fused to chondrocranium
Meckel’s cartilage: lower jaw
Hyoid arch: gill support
Embryonic origin & final tissue type: Dermatocranium
Mesenchyme from dermatome epimere mesoderm -> Dermal bone
Who has hyostyly?
Most sharks
Describe metautostyly
Quadrate (upper) and articular (lower) form jaw joint; quadrate fused or articulates w/ chondrocranium; II -> columella in middle ear (not for jaw suspension)
Who has craniostyly?
mammals
Describe adaptations of actinopterygiian skull for suction feeding
- Maxilla connected loosely to chondrocranium & lower jaw (rotates forward as jaw opens)
- Premaxilla connected loosely to maxilla (can be projected forwards faster)
- Chondrocranium rotates at spinal connection (rises as lower jaw drops)
- Hyoid apparatus: struts in buccal cavity floor, pulled perpendicular to push out lateral walls as mouth opens
=> Creates suction
How does hyostyly affect feeding?
Allows jaws to swing forwards to open wider & for teeth to contact prey at same time (good for grabbing slippery prey)
Regions of brain protected by chondrocranium
All vertebrates: ventral, lateral, posterior
Agnathans & chondrichthyans: dorsal (-> forms entire braincase)
Chondrocranium tissue type
Cartilage: initially, all; remains in agnathans, chondrichthyes
Bone (replacement): teleostomi
Who has metautostyly?
Amphibians, sauropsids
Who has autostyly?
Holocephali (ratfish), dipnoi (lungfish)
Describe hyostyly
Palatoquadrate: Upper jaw, not fused to chondrocranium
Meckel’s cartilage: lower jaw
Hyomandibula: Forms swinging bridge attaching jaw to chondrocranium
-Spiracle: reduced pharyngeal slit between mandibular & hyoid arches
Describe amphistyly
Palatoquadrate: upper jaw, held to chondrocranium by ligament
Meckel’s cartilage: lower jaw
Hyomandibula: stabilizes back of palatoquadrate, also gill support
3 components of the skull
Chondrocranium, splanchnocranium, dermatocranium
Describe craniostyly
Entire upper jaw fused to chondrocranium Dentary (lower) articulates with squamosal (upper) Jaws entirely dermatocranium I & II in middle ear Quadrate -> Incus Articular -> Malleus Hyomandibula -> Stapes
Who has amphistyly?
6-gilled sharks
