Vertebrates 6 - Cranial Skeleton

Question 2

Three parts of cranium

Answer 2

Dermatocranium (hard), chondrocranium (around brain), splanchnocranium (gills and mouth).

Question 3

Roles of the cranium

Answer 3

Protect brain and sensory structures, air/water entry, feeding

Question 4

Dermatocranium (specifically in fish)

Answer 4

Outer bones of skull. Dermal roof bones, lower jaw bones, dermal opercular bones (over gills)

Question 5

Chondrocranium

Answer 5

Made from cartilage; protects the brain and allows entry of nerves in fish; in birds and mammals it protects brain as embryo, mostly replaced by skull, forms base of skull, some of the turbinate bones and contains inner ear

Question 6

Splanchnocranium

Answer 6

mandibular arch, hyoid arch, other visceral arches b/w and around pharyngeal pouches

Question 7

Chondrichthyes and agnathans

Answer 7

No dermatocranium. Just the other two

Question 8

Evolution of jaws

Answer 8

First jawed fish: silurian - 420mya. Bony arches became the jaws

Question 9

Placoderms

Answer 9

First fish to develop jaws. Needed to break through shells of invertebrates. They don’t have some of the bones that modern fish have (not an ancestor).

Question 10

Changes in splanchnocranium

Answer 10

Agnathans have more gill slits and arches than jawed fish. Gill arches have hinges. Aganthan mouth has no jaw. Arches may have changed in size and orientation, form canal. Muscles evolve to attach.

Question 11

What did the gill arches become?

Answer 11

Palatoquadrate cartilage (top) and mandibular cartilage (bottom), supported by hyoid arch, remaining gill arches still present.

Question 12

What else contributed to formation of jaws?

Answer 12

Molecular evidence. A few key genes in jaws. KO do not form jaws.

Question 13

Evolution in changes in skulls of vertebrates

Answer 13

Dermal roof, lower jaw, and opercular bones.

Question 14

Herring vs bowfin and extinct fish

Answer 14

Herring has larger and more spaces in dermal roof, lighter, saves energy (schooling for protection - doesn’t need it all). Bowfin is example of “ancient” cranium, more complete dermal roof.

Question 15

Tetrapod skull

Answer 15

No opercular bones anymore because it has no gills/gill arches

Question 16

Anapsid

Answer 16

No fenestra (hole) in the back of the skull. Early condition. Modern amphibians and turtles.

Question 17

Temporal fenestra

Answer 17

Opening in skull. Early anapsids didn’t have room for much mandibular muscle, so the fenestra make more room for muscles and increase bite force

Question 18

Diapsid

Answer 18

Two temporal fenestrae. Early diapsids include lizards, snake, crocodiles. Late diapsids include dinos and birds.

Question 19

Synapsid

Answer 19

Have one temporal fenestrae (usually a bit lower and very large). Mammals.

Question 20

Evolution towards mammals

Answer 20

Seymouria (anapsid), dimetrodon (early synapsid - not a dino!), therapsids (early reptile-mammal intermediate, late synapsid), mammals

Question 21

Mammalian skull

Answer 21

Large temporal fenestra, differentiated (heterodont) teeth, double occipital condyle, complete secondary palate

Question 22

Smilodon

Answer 22

Saber-tooth cat. Teeth so big, not much room with open mouth. Kill with a bite through the neck, puncturing the carotids and jugular. Modern big cats have a sleeper hold on the neck, but don’t pierce it.

Question 23

Evolution of secondary palate (to first mammals)

Answer 23

When eating, the choana would be blocked, so it could still breath. Also made larger nasal cavity - better smell, helps filter air and warm it up (important for endotherm),

Question 24

Modern mammals palate

Answer 24

Complete secondary palate, separate air and food passages, suckling (hard to breath while suckling)

Question 25

Changes in lower jaw of vertebrates - fish to derived synapsids

Answer 25

Fish and reptiles have homodont teeth, articular bone. Early synapsid, still pretty similar. Derived synapsid: mostly dentary bone, still have articular bone.

Question 26

Changes in lower jaw of vertebrates - mammals

Answer 26

Modern mammals: only dentary, heterodont teeth, coronoid proess; articular and quadrate are not the hinge, they are now the malleus and incus (respectively)

Question 27

Coronoid process

Answer 27

Where temporalis muscle attaches to dentary bone.