skull r

what are the three components of the skull?

splanchnocranium, chondrocranium, dermatocranium

what is the origin, role, and contribution, of splanchnocranium

O= pharyngeal (gill) arches, jaw, and hyoid apparatus and Most ancient part of the skull

C= Forms from pharyngeal arches

R= supports the face, jaws, and gills

what is the origin, role, and contribution, of chondrocranium

O= Develops from head mesenchyme and neural crest cells

C=Forms the base of the skull

Supports the brain, nose, and inner ear

R= Braincase in cartilaginous fish (Chondrichthyes)

In other vertebrates, acts as a scaffold for the brain and sensory structures

what is the origin, role, and contribution, of dermatocranium

O=Evolved from dermal bone that sank inward

C=series of bones:

Facial (snout, upper jaw)

Orbital (around the eyes)

Temporal (side of skull)

Vault (skull roof)

Palatal (roof of mouth)

Mandibular (lower jaw bones)

R=Forms the outer casing of the skull

what are the pharengeyl arches?

mandibular and hyoid

Mandibular arch contains?

Palatoquadrate → upper jaw

Meckel's cartilage → lower jaw

Hyoid arch contains?

Hyomandibula → supports jaw / ear in tetrapods

Ceratohyal → supports tongue and throat

what is the origin, position, and contribution, of brain / braincase

O= Brain develops from the neural tube

Braincase forms from cranial elements that surround the brain

C= Provides protection for the brain

Houses sensory organs (eyes, ears, nose)

Serves as a base for cranial muscle attachment and passage for cranial nerves

P= Brain lies above the notochord, in the cranial cavity

Braincase is located at the front of the vertebral column, enclosing and protecting the brain

Paleostylic

No jaw attachment (e.g., jawless fishes)

Euautostylic

Jaw (mandibular arch) attaches directly to skull, not via hyomandibular

Found in placoderms and acanthodians

Amphistylic

wo connections:

Palatoquadrate to skull

Hyomandibula to skull

Seen in early sharks, some bony fishes

Hyostylic

Jaw attaches mainly through hyomandibula

Found in most modern bony fishes

Metautostylic

Jaw joint: quadrate (upper) to articular (lower)

Seen in amphibians, reptiles, birds

Craniostylic

Jaw joint: dentary (lower jaw) to squamosal (temporal bone)

Found in mammals

Early vertebrates

Early vertebrates: no formed elements of skull evident (e.g.,Haikouella).

Agnathans

Ostracoderms

Cyclostomes

Ostracoderms: bony head shields(dermal)

Cyclostomes: lack bone entirely;branchial arches present; single median nostril

Ancient gnathostomes (jaws)

placoderms

acanthodii

Placoderms: heavy dermal bony shield on head; upper jaw fixed to skull

Acanthodii: similar to modern Chondrichthyes;possessed mandibular bone to reinforce jaw

Modern chondricthyes

No dermatocranium

Chondrocranium = whole braincase

Jaws on ceratohyal & Meckel's cartilage

Front gill slit → spiracle or lost

Jaw protrudes for streamlined swimming

Actinopterygii

High diversity from adaptive radiation

Many extra facial bones

Operculum covers gills

Pectoral girdle bones attach to skull (extrascapular, cleithrum, postcleithrum, posttemporal)

Mobile jaws enable suction feeding (cranial kinesis)

Sarcopterygii

Upper jaw often fused to braincase

Includes Rhipidistians (tetrapod ancestors)

Labyrinthodont teeth (deeply folded)

Hinged joint between ethmoid and oticooccipital bones

Notochord extends into skull

Tetrapods

Facial bones reduced/fused

Hyomandibula → stapes (ear)

Quadrate-articular jaw joint

Operculum lost

Pectoral girdle separated

Simplified dermatocranium & reduced splanchnocranium

Temporal Fenestrae origin, hypothesized role(s), phylogenetic importance

O= penings in the temporal region of the skull (dermatocranium)

R= Muscle attachment sites

Thermoregulation

I=Used to classify major vertebrate groups by skull type

Jaw Articulation Evolution

Early vertebrates: Quadrate-articular jaw joint

Mammals: shift to dentary-squamosal jaw joint

Fate of Jaw Bones in Mammals

Hyomandibula → Stapes (middle ear bone)

Quadrate → Incus (middle ear bone)

Articular → Malleus (middle ear bone)

Nasal Cavity Function

Holds olfactory epithelium for smell

Nasal Cavity in Fish vs. Tetrapods

Actinopterygii: nasal sac does not open to mouth

Tetrapods: nasal sacs

open to mouth via internal nares (choanae)

Nasolacrimal Duct

Drains tears from the lacrimal gland to the nasal sac

Secondary Palate

Separates mouth and nasal cavity

Allows breathing while chewing or suckling

Present in mammals and some reptiles

Rhynchocephalians

Complete upper and lower temporal bars define fenestrae

1 lower and 2 upper tooth rows

Squamates

Lower temporal bar lost in lizards; both bars lost in snakes

Quadrate-articular jaw join to Snake skulls not as fully fused, more movable links

Testudines

Anapsid skulls

Emarginations: inward"scoops" from edge of dermato cranial bones

Lack teeth, keratinized toothplates instead

Crocodilians

fully diapsid, antorbital fenestra lost

Birds

modified diapsid

Braincase inflated

Lack teeth; jaw bones form beako

Upper temporal bar lost; lower bar forms jugal bar

Dinosaurs

fully diapsid

Usually possess both antorbital and mandibular fenestra

synapsids

One hole (temporal fenestra) behind eye

Hole gets bigger and joins eye socket in mammals

Arch of bones (zygomatic) around the hole

Examples: Dimetrodon, therapsids, cynodonts

mammals

Many bones fused together (like sphenoid, temporal)

Two occipital condyles (helps head move better)

Nasal capsule fully turned to bone

Turbinate bones: curled bones for smelling