Skeletal- Cranial 5b

Cards (38)

  • Splanchnocranium ( MOST Primitive)
    • supports pharyngeal arches but no trace of neural crest
    • predates vertebrae
    • neural crest origin and cartilage/ bone only in vertebrates
    • living agnathans with elastic cartilaginous support of gill pouches
    • not directly comparable to gnathostome gill arches
  • Chondrocranium
    • also known as the neurocranium or endocranium
    • Sharks lost all dermal bone
    • the primary "brain case"
    • present in all vertebrates including the hagfish
    • may remain as cartilage in adult or to be ossified
  • Chondrocranium: Embryology
    • develops as a series of cartilages under the brain and associated with sense organs
    • occipitals probably a modified anterior vertebrae
    • fuse during growth to form a plate and occipital arch
  • Cranium: Embryology
    • Neural crest, mesenchyme -> nasal optic and possibly otic capsules as well as trabecula/ ethmoid plate (sensory organs usually)
    • Neural crest mesenchyme-> anterior dermatocranium (pg6)
  • Cranium embryology -
    • Neural crest mesenchyme -> entire splanchnocranium (and its derivatives) Page 7 - figure 7.4
    • portions of the splanchnocranium may be incorporated into the brain case or be indistinct from rest of skull
  • Jaws Origin:
    • serial theory: mandibular and hyoid arches are modified anterior pharyngeal arches
    • composite theory: anteriormost gill arch contributes to the neruocranium as well as portions of the mandibular arch
  • Jaws Origin
    • embryology supports that jaws are anterior pharyngeal arches
    • pharyngeal slit between mandibular and hyoid arches retained in some fishes as the spiracle and in tetrapods as the eustachian tube
  • Splanchnocranium
    1. Mandibular arch: palatoquadrate (Upper element), Meckel's element (lower)
    2. Hyoid arch: hyomandibula(upper), ceratohyal(middle), hypohyal, Basihyal (bottom) -> serial homology
    3. I-V branchial arches: pharyngobranchial. epibranchial, ceratobranchial, hypobranchial, basibranchial
  • Splanchnocranium-
    • substantially reduced and modified in tetrapods (branchial arches reduced, dermal bone replaces this)
    • especially in mammals where the mandibular arch is not involved with the jaw at all
    • alisphenoid - homologous w/ pterygoid in sharks
    • Slide 12 for diagrams
  • Memorize this chart
  • Jaw Suspension
    • paleostyly (support) in agnathans, NO JAWS
    • splanchnocranium not attached to rest of skull
    • Lamprey, slide 14
  • Jaw Suspension
    • euautostyly in all placoderms and acanthodians
    • no suspension of mandibular arch
  • Jaw suspension:
    • amphistyly in primitive sharks and osteichthyes (2 supports)
    • anteriorly by a ligament from the palatoquadrate to the brain case
    • posteriorly by the hyoid to the brain case
    • mandible swings down
    • immobilized (jaws just flaps down)
  • Jaw suspension
    • hyostyly in most sharks (hyoid pops out)
    • mandibular arch supported only by the hyoid
    • jaws open downward
  • Jaw suspension
    • hyostyly (modified) in teleosts
    • hyoid fixed and mobile symplectic added (open forward)
    • jaws open forward
  • Jaw suspension
    • metautostyly in most tetrapods
    • hyoid not involved with jaw stapes for hearing
    • mandibualr arch reduced to quadrate and articular (meckles in adults)
    • forms joint of jaw made of dermal bones
  • Jaw suspension:
    • Craniostylic(jaw joint fused by dermatocranium) in tetrapods (just mammals)
    • hyoid and mandibular arch reduced to ear ossicles
    • new jaw joint from dermatocranium, squamosal and dentary
  • Jaw suspension:
    • articular and quadrate involved with both jaw suspension and hearing in lower synapsids
    • dentary-squamosal jaw joint assumes function
  • Jaw suspension:
    • exceptional hearing is a vertebrate specialty ub mammals (small ear bones came from jaws)
  • Dermatocranium (thought to be homologous)
    • synapomorphies homologous for osteichthyes -(paired lungs+ bony bone has endochondral bones)
    • made of demal bones from the dermis, sinks in
    • makes most of the cranium of osteichthyes
    • evolutionary trend is loss and function
    • can be organized as "series"
    • partial organ in brain is light sensitive (low ocean dwellers)
  • Dermatocranium: Trend to ger rid of bones as you go on (reduction/fusion)
    • Facial red( snout) - preamilla, maxilla, nasal
    • Orbital blue ( around the eye) - lacrymal, prefrontal, post frontal, post orbital, jugal
    • Temporal green( posterior) - inter & supratemporal tabular(missing in sauropsids but in mammas) , squamosal, quadratojugal
  • Dermatocranium:
    1. Vault - yellow (skull roof)- frontal, parietal, post parietal
    2. Palatal -orange (roof of mouth) - pterygoid, vomer, palatine, ectopterygoid, parasphenoid (only in ray finned fishes now)
    3. Mandibular- purple (lower jaw) - dentary, splenials, angualr, subangular, periarticular, coronoids
  • Dermatocranium:
    1. Gular (green) - between dentary bones
    2. opercular (purple) - lateral gill protection, includes branchiostegal
  • Ostracoderms- jawless
    • heavy headshield in many - tendency to lighten head sheild + to become more active swimmers
    • no clear relation to any gnathostomes dermatocranium
    • reduction in head armour in multiple groups - divided into parts
    • possible sister group to lampreys, loss of gill openings/ filter feeders
    • active swimmers, did not live on the bottom
  • Placoderms (heavy headshield -head is different than jawed)
    • dermatocranium of placoderms shows little in common with osteichthyan cranial series nor ostracoderm head shields
    • primary jaw overlaid with dermal bone, no teeth (made the biting surface get warn down over time)
    • neck joint may have allowed cranial kinesis (autostylic - head could swing up while bottom swung down)
  • Chondrichthyes
    • no dermatocranium
    • extensive chondrocranium (bc no dermatocranium)
    • palatoquadrate immobile primitively trend to mobile jaws
    • trend for biting
  • Acanthodii
    • dermatocranium of anconthodians might have more in common with osteichthyans
    • opercular series, large number of cranial scales/ bony plates
    • primary jaws
  • Actinopterygii - ray finned
    • many bones, trend to reduce and lighten
    • trend to cranial kinesis (lighten to become mobile)
    • trend to suction feeding
    • suspensorium open jaws rapidly (acts as a lever pulls back so it pivots forward= forward opening jaws= great in water= force and fast)
  • Actinopterygii
    • light skull and protrusible premaxilla in teleosts perfects suction feeding
    • many teeth on jaws and elsewhere
    • often specialized (backwards facing to trap prey)
  • Rhipidistians
    • internal naris and external naris (choana)
    • tear duct
  • Non- Amniotes & Lissamphibia
    • recution+ simplification of bones
    • hyoid is now the stapes (columella)
    • no operculars or gulars
    • branchial arches in larvae
    • hyoid apparatus support tongue
  • Lingual feeding
    • hyoid apparatus often modified to support protractile tongue
  • Amniotes
    • trend to temporal fenestrae
  • Temporal fenestrae
    • provide space for jaw musculature to expand (allows for more contraction of the jaw muscles - temporal)
  • Lepidosauria - diapsid (snakes and lizards)
    • tuatara (NZ) with basic diapsid pattern, living fossil - evovled parallel with lizards
    • squamates with kinetic skull: streptostyly, mobile quadrate, lower temporal bar lost - dermal bone
    • snakes with highly kinetic skulls
    • dentary symphysis of loose tissue
  • Archosauria - crocs, dino, bird
    • crocodilians with rigid skulls
    • bird skull with greatly expanded braincase and cranial kinesis
    • upper mandible can raise sides of jaw can bow out
  • Synapsida - evolutionary trend - rigidifying skull
    • well ossified, akinetic skull, reduction in number of bones - no cranial kinesis EXCEPT in jaw joint
    • fewer teeth in sockets (thecodont)
    • heterodont dentition with precise occlusion ( bigger teeth that fit perfectly together)
    • new jaw joint with mobile mandible
  • Synapsids -
    • enlarged auditory bulla that encase ear ossicles
    • large tympanic bulla
    • extra pallet - secondary pallet
    • secondary palate to allow chewing and breathing at the same time