CVA

• Understanding head structure becomes increasingly complex throughout evolution.
• In many forms heads increase in relative size and complexity.
• Brain and sensory structures increase in size and importance.
• Supporting structures increase in size.
• Such structures arise from: visceral skeleton, cartilaginous brain case, dermal head skeleton.

• supports gills
• oldest supporting elements in head
• arise from neural crest
• maintain place of pharyngeal tissues for breathing and filter feeding
• supports pharyngeal gill slits.
• In vertebrates unifies and distributes forces from gills
• later distributes forces from jaw muscles
• initially fibrous
• cartilage appears later
• ossification occurs later and these elements become bony
• May consist of as many as five articulated elements on a side: pharyngobranchial, epibranchial, ceratobranchial, hypobranchial, basibranchial

• cartilaginous brain case
• Neurocranium- associated sensory structure capsules included
• forms around brain and major sense organs
• Useful to know where spaces between early elements are - allows identification of nerves and blood vessels passing between them.
• In sharks the structure is a chondrocranium because it is cartilage
• Structures that serve this purpose are ossified in other forms
• These structures develop best where dermal structures are absent
• Appear in several sections.
• Structures arise from head mesenchyme condensations - form elongated cartilages next to the notochord.
• Trabecular cartilages - anterior
• Parachordal cartilages - posterior
• Occipital cartilages - further posteriorly
• Sensory structures have supporting cartilaginous capsules: nasal optic otic

• Contributes to neurocranium formationprotects and supports deep head structures, but does not usually completely enclose the brain.
• Dermal bone provides most of the protection.
• Dermal shield - pattern consistent although elements often fuse.
• Pelagic forms often show dermal shield reduction.
• Dermal bones retained in sedentary swimmers and bottom dwellers.
• Light because it is mostly spongy bone but strong.
• May be superficial as in placoderms, forming an exoskeleton.
• Deper in teleosts, holosteans and tetrapods.
• In these animals it becomes associated with the neurocranium.
• Crossopterygian pattern is similar to tetrapod descendants.
• Number of bony plates is reduced in tetrapods from ancestral and related fishes.

complete skull is assembly of splanchnocrainium, neurocranium, dermatocranium

• During skull development these elements fuse.
• Ethmoid plate forms between nasal capsules and anterior trabeculae.
• Parachordals fuse to form basal plate.
• Occipitals grow dorsally around the spinal cord to form the occipital arch.

• jaws arise from branchial arches that support the mouth.
• Allow animal to eat larger foods.
• Appeared first in acanthodians
• Jawless vertebrate pharynx supported by fused complex (=branchial basket)
• Cartilaginous bars (=pharyngeal bars)
• From splanchnocranium
• Arise from anterior gill arches by several theories.

• Splanchonocranium of jawed forms is simplest because of fewer pharyngeal bars.
• Pharyngeal arches between gill slits are supported by internal bars or separate four jointed sections.
• Sections operate as levers pulled by pharyngeal muscles.
• Jaws develop as one or more cartilaginous pharyngeal bars in wall of the mouth.
• Upper jaw element=palatoquadrate cartilage
• Lower jaw element is Meckel's cartilage (as in adult sharks)
• 2nd pharyngeal element supports jaws.
• Autostylic jaw suspension

• Ancestral jawed fishes had palatoquadrate stabilized against the chondrocranium so only lower jaw could move.
• Later jawed fishes use hyoid arch also to support jaw.
• Ancestors of both bony and cartilaginous fishes have epibranchial of hyoid arch become hyomandibula.
• Hyomandibula stabilizes the posterior aspect of jaws.
• Joins the anterior palatoquadrate process.
• Amphistylic jaw suspension.
• Later fish modify jaw suspension to hyostyly, often with a symplectic bone.
• Mammals show craniostyly with less movement capability.

• Chondrocranium is support for brain and assisted by some splanchnocranial elements.
• Epipterygoid comes form splanchnocranium.
• Splanchnocranium gives rise to hyomandibula, articular, quadrate and hyoid apparatus.
• Dermatocranium encases the chondrocranium (and associated splachnocranial elements).

• more common than akinesis.
• Allows greater mobility of different skull elements and more complex movement patterns.
• Mammals skulls are akinetic.

• Is composite structure made of three elements.
• Osteostracans had a single dermal head shield.
• Dorsal, close set eyes separated by a single pineal opening.
• Single anterior nostril.
• Lateral line sensory fields laterally on head shield.
• Low profile, bottom (benthic) dwellers.
• Branchial arches head by head shield, supported by paired gill lamellae or interbranchial septae.
• Cartilage plates and muscles actions drew water into mouth to pass over gills.
• Suspended particles extracted before water was expelled.

• had more active lifestyles.
• Different body forms.
• Deeper bodies, small scales on heads not head shields.
• May have had marginal pointed scales around mouth.
• Suction feeding arose with water column intake.
• May have had predacious tendancies, but lacked strong jaws.

• water entered mouth.
• Flowed over gills suspended in branchial pouches.
• Into common chamber and exiting barnchial pore.
• Bony plates form head shield.
• Small plates toward tail allowed for movement.

• lack bony skeleton
• rasping tongues
• parasitic lifestyles

• dermal head shields
• ossified braincases with attached jaws
• joint between head and first vertebra
• no spiracles
• predators 1-6 meters long.

• earliest jawed fishes
• small, stremlined, active swimmers.
• Small, non-overlapping scales but plates on head.
• Gills protected by an operculum
• lateral cranial fissure gap that partially divided posterior braincase.
• Gap provided exit for cranial nerve X
• Large eyes
• Mandubular arch similar to that in sharks and bony fishes
• Hyoid arch with five successive banchial arches present.

• little, if any bone
• Dermal ossicles only
• Cartilaginous skeletons
• Chondrocranium forms braincase
• Splanchnocranium and six gill arches present primitively.
• Palatoquadrate supported by hyomandibula
• Modern sharks have spiracle and detached upper jaw.
• Modern sharks can protrude upper jaw for feeding.

• Bony skeletons
• Opercular and extrascapular bones
• Long jaws for feeding
• Diversity of body and head forms in modern Teleosts.
• Jaw opening in primitive actinopterygian:
• Suspensorium allows jaw rotation around it.
• Suspensorium articulates with opercular bones.
• Pectoral girdle relatively fixed but neurocranium can rotate on it to lift the head.

All work similarly but different proportions allow animals to do different things.

• Early lung fishes
• Upper jaws fused to braincases
• Fed on hard foods
• Coelacanths have cranial kinesis

• Strong jaws
• Sharp, pointed labyrinthodont teeth.
• Draincases jointed, not as in modern lungfishes.
• Persistent notochord that extended into the head for more support.
• Nasal sac opens into the mouth as choanae.
• Choanae are as in tetrapods.
• Modern amphibians have reduced splanchnocrania

• skull elements reduced and fused.
• Light skulls for hopping forms.

• Shift in jaw muscle attachment to the skull.
• Anapsids with no temporal openings - all muscles attach deep to dermatocranial elements. Muscles - neurocranium to lower jaw.
• Therapsids with temporal openings - jaw muscles shift position to edges of openings.
• Forms initial zygomatic arch.
• Jaw muscles move onto dermatocranial surface in therapsids and modern mammals.

• 3 kinds, depending on where the joint is and what parts move.
• 1. Metakinesis, joint at back of skull
• 2. Mesokinesis, joint behind eye
• 3. Prokinesis, joint in front of eye.

• solve the muscle position and space problem another way.
• Posterior skull bones=emarginated for muscle origin.
• Trend increases through time.

• diapsids with lower border of lower opening missing, increasing cranial kinesis.
• Joints allow the snout to lift or bend downward.
• Changes angle at which teeth engage prey to prevent its squirting out of mouth from teeth at wrong angle to grasp it.

• use the tongue to capture prey.
• Supported by large hyoid apparatus (which branchial arch derivative?)

• ex: water moccasin
• mechanical model of machine that allows kinesis in the animal.

• lacks kinesis
• Kineic-inertial feeding mechanism instead

have kinesis also because they are light and bones bend, even though adult skulls are fused.

• Nasofrontal hinge, allows bill to flex upward.
• Range of movement and gape has increased by cranial kinesis.
• Additional flexibility is allowed by the tips of the beak themselves.

They continue the synapsid line and have great body form diversity.

• These bones=composites, arising from more than one center of ossification.
• Occipital, sphenoid, temporal
• Before this was understood, they were given different names.

it allows you to chew and breath at the same time.

• interception of food particles in water.
• Can regulate particle size because larger ones cannot enter the small sieve space.

Terrestrial salamander catches a tasty worm by extending and shaping tongue to surround and scoop up the prey.  This is called lingual feeding.