Skeletal- Cranial 5b

• 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