Skull evolution

Question 1

First jawed fish?

Answer 1

Placoderms. First 3 branchial/gill arches coopted to become maxilla and mandible

Early jaws were toothless - just a bony ridge

Question 2

Skull evolution in fish

Answer 2

Question 3

Jaw -> ear evolution

Answer 3

• Most reptiles articulate their mandibles via the quadrate and articular bones
• These bones are then incorporated into the middle ear

Question 4

Answer 4

Synapsids have a single post-orbital foramen. This is closed/ incorporated as the zygomatic arch in mammals.

Question 5

Australopiths

Answer 5

Lived 4.5-2 Million years ago – more vertical face than early hominins, huge molars/premolars with thick enamel, small anterior teeth

Question 6

Foramen magnum position

Answer 6

Anterior foramen magnum is present in all hominins

Question 7

Cranial base angle

Answer 7

Human babies’ cranial base angle is similar to chimps.

CBA affects vocal tract proportions, which affects ability to produce discrete vowels sounds

Question 8

Neoteny

Answer 8

Generally, chimpanzee and human infants have more similar skull shape; humans retain a more juvenile form (neoteny)

Question 9

How does foramen magnum position affect nuchal muscles?

Answer 9

Question 10

Snouty-ness? Functional purpose?

Answer 10

Prognathism. Reduced prognathism increases mechanical advantage during chewing

Question 11

Nuchal crest

Answer 11

Smaller in humans

Question 12

Enamel evolution

Answer 12

Enamel first was on skull, not teeth

Early teeth were just dentine

Question 13

Heterodonty benefits (what each tooth is good at)

Answer 13

Incisors: shearing

Canines: puncturing

Molars: crushing

Question 14

Ape vs human teeth

Answer 14

Maybe incisors could be smaller b/c diet change or stone tools

Maybe canines not needed for aggressive displays

Molars started small in early hominins, grew huge in australopiths, medium now

Enamel thicker: resists wear from grit/roots/tubers

Large teeth and flaring zygomatics dissapate chewing forces

Question 15

Draw bite force diagram

Answer 15

Question 16

“Chewing machine”?

Answer 16

Paranthropus

Question 17

Modern homonid tooth and face size decrease

Answer 17

Meat in diet = less mechanically challenging calories?

Stone tool processing?

Question 18

Chewing time

Answer 18

Chimps spend 40% of day chewing (diet mostly fruit, leaves, roots)

Humans spend 5% (more meat in diet)

Question 19

Brain size differences btwn chimps and humans

Answer 19

Humans more than 3x chimp brain mass

Humans grow brains faster and for longer after birth

Maybe enables complex social relations

Question 20

Defining characteristics of human skull

Answer 20