CRANIAL EVOLUTION Flashcards
What is cephalic index
ratio of the maximum width of the head x 100 and divided by its maximum length.
What are the 3 classifications of the cephalic index
Dolicocephaly: head width is less than 75% of length
Mesocephaly: head width is between 75 and 85% of length
Brachycephaly: Head width is more than 80% of length
What are the cranial characteristics of Australopithecus
4.2-2.0 mya
300-500 cm3 capacity
Low forehead
Projecting face
What are the cranial characteristics of Australopithecus
2.7 - 1.1 mya
410 cm3 capacity
Broad cheekbones
Prominent brow ridges
Sagittal crest
Large zygomatic arch
More powerful mastication muscles like temporals and masseter (gives different cranial shape)
What are the cranial characteristics of homo erectus/ergaster
1.9-0.27 mya
Large brow ridges
Projecting nuchal torus (on occipital bone)
Wider at base
Braincase long and low
Supraorbital torus: lack of brow ridge function changes in facial expression
What are the cranial characteristics of Neanderthals
Long, flat and low braincase
Low receding forehead (more vertical)
Larch arching brow ridges
Projecting mid face
Lack of chin
Retromolar space
Occipital bun
What are some of the noted adaptation of Neanderthals similar to modern humans
Projecting face Could help heat flow through nasal passage
Not better adapted to sustain high loads on anterior dentition
Nasal passage improves warming of air but not better than humans
Higher capacity of moving air due to energetically demanding lifestyle and higher calorific intakes
What are the cranial characteristics of early humans
Short, round and high brain case
High forehead
Smaller nose
Presence of chin
No retromolar space
Rounded occipital
Chins
Different nasal morphology (smaller than neanderthals)
What are the implications of early humans having chins
Mechanical significance in chewing
Needed for resistance to loads during incision and mastication
What is palaeoneurology
Study of brain evolution by analysis of brain endocasts to determine endocranial traits and volumes.
What is an endocast
Internal cast of the cranial vault
shows external brain features impressed on cranial bones
can observe trends in cranial capacity changes
What are the average cranial capacities for the 3 phases of development
Phase 1: early hominins = 450-530
Phase 2: early homo = 600-1200 (H habilis to H erectus)
Phase 3: late homo = 1200-1500 (now 1400 modern human)
What are the possible reasons behind the differences in neanderthal and modern human cranial capacity
Neanderthal large brain could be adaptation to cold envrionments
Differences due to changes in brain growth after birth
Obstetric dilemma: Head size smaller than pelvic inlet so brain growth occurs after birth
