Skull evolution Flashcards
First jawed fish?
Placoderms. First 3 branchial/gill arches coopted to become maxilla and mandible
Early jaws were toothless - just a bony ridge
Skull evolution in fish

Jaw -> ear evolution
- Most reptiles articulate their mandibles via the quadrate and articular bones
- These bones are then incorporated into the middle ear

Synapsids have a single post-orbital foramen. This is closed/ incorporated as the zygomatic arch in mammals.
Australopiths
Lived 4.5-2 Million years ago – more vertical face than early hominins, huge molars/premolars with thick enamel, small anterior teeth
Foramen magnum position
Anterior foramen magnum is present in all hominins

Cranial base angle
Human babies’ cranial base angle is similar to chimps.

CBA affects vocal tract proportions, which affects ability to produce discrete vowels sounds
Neoteny
Generally, chimpanzee and human infants have more similar skull shape; humans retain a more juvenile form (neoteny)
How does foramen magnum position affect nuchal muscles?

Snouty-ness? Functional purpose?
Prognathism. Reduced prognathism increases mechanical advantage during chewing

Nuchal crest
Smaller in humans

Enamel evolution
Enamel first was on skull, not teeth
Early teeth were just dentine
Heterodonty benefits (what each tooth is good at)
Incisors: shearing
Canines: puncturing
Molars: crushing
Ape vs human teeth
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

Draw bite force diagram

“Chewing machine”?
Paranthropus

Modern homonid tooth and face size decrease
Meat in diet = less mechanically challenging calories?
Stone tool processing?
Chewing time
Chimps spend 40% of day chewing (diet mostly fruit, leaves, roots)
Humans spend 5% (more meat in diet)
Brain size differences btwn chimps and humans
Humans more than 3x chimp brain mass
Humans grow brains faster and for longer after birth
Maybe enables complex social relations
Defining characteristics of human skull
