H. ergaster and H. erectus Flashcards
What is important about H. erectus s.l.?
- Conforms to criteria expected in Homo
- Obligate, modern biped
- Big brain, relatively large cranial capacity
- Small teeth - First hominin that is more closely related to modern humans, both cladistically and in terms of adaptions
- First hominin to leave Africa?
Oldest H. erectus specimens
KNM-ER 2598 - Kenya, 1.9mya
KNM-ER 3733 - Kenya, 1.6-1.8mya
Dmanisi sample - Georgia, 1.8mya
Sangiran fossils - Java, 1.8mya
Youngest H. erectus specimens
Ngandong and Sambungmacan - Java, 30-40,000 years ago
Suprisingly young - H. sapiens already living in Asia
H. erectus vs H. habilis
Longer and lower braincase Marked sagittal keel Bigger brain Less prognathic Strong supraorbital torus Strong occipital torus Smaller dental size Thicker cranial bones Pentagonal in rear view
H. erectus morphology and trends
Classic H. erectus: Sagittal keel Double-arched supraorbital torus Large, pneumatised face Long braincase Angled occipital bone Occipital torus
H. erectus s.l.:
Reduction in size of posterior teeth
Increased body size and modern human-like limb proportions
Absolute brain size increase
Association with Oldowan and Acheulean stone tools
Wide geographic distribution outside Africa
Anatomical traits indiicative of modern bipedalism
Body size adapted for distance travel and competition with other carnivores
Brain and body size enter the range of variation observed in modern humans - 40-75kg, 150-185cm, 700-1100cc
Endurance running
Morphology of H. erectus shows selection for bipedal running, not walking
Adaption to running at expense of adaptions to arboreality at 2mya.
Bipedalism very efficient for running long distance
Not good sprinters but can outrun most species over long distances -> chase animals until they die from exhaustion. Hunting without sophisticated tools
Mechanisms of dissipating heat - sweating, hairlessness
Important for hominin dispersal?
H. ergaster vs. H. erectus
H. ergaster - Africa, 1.9-1.0mya
H. erectus - Asia, 1.8mya-30kya
H. erectus (Sangiran 17) has sagittal keel, parasagittal depression, thick browridge, long/flat/low braincase, receding forehead, stronger occipital ridge = absent in H. ergaster (KNM-ER 3733).
H. ergaster less derived than H. erectus
H. erectus generally more massively built - thicker bone cortices, more pronounced supraorbital and occipital torus, more pronounced postcanine dental reduction
H. ergaster - temporal range, holotype, sites
1.9mya to 800kya
Holotype - KNM-ER 992 mandible, Koobi Fora
Sites: Koobi Fora, Kenya West Turkana, Kenya Olduvai, Tanzania Bouri, Ethiopia
KNM-ER 922
Type specimen for Homo Ergaster, found in 1972.
1.5mya
Primitive traits:
Complex premolar crowns
Two-rooted LP3
KNM-WT 15000
Nariokotome Boy
West Turkana, Kenya, 1.5mya
Juvenile male (8-12 years old) with tall, thin, long legs - obligate biped
Modern post-cranial skeleton and more primitive skull
880cc at death - adult estimate 909cc
157cm, 50-53kg at death - adult estimate 176-180cm, 80-83kg OR 151-169cm, 46-69kg
Slower and shorter growth spurt than the adolescent growth spurt in modern humans
OH 9
Olduvai Gorge, Tanzania
1.1-1.2mya - younger than H. ergaster material
Morphology similar to H. erectus s.s.
Cranial capacity 1067cm3
Pronounced supraorbital torus
Local evolution in Africa or relation to Asian H. erectus?
Variation in H. ergaster
OH 9 and KNM-ER 42700 show a high degree of size variation
- high dimorphism?
- large temporal separation - 350,000 years
- two species?
OH 9 - 1067cm3, 1.2mya
KNM-ER 42700 - 691cm3, 1.55mya
UA 31 and BOU-VP 2/66
UA 31 - Buia cranium
BOU-VP 2/66 - Daka calvaria
Dated to 1mya, Ethiopia
Relation to the last common ancestor of Neanderthals and H. sapiens?
Like OH 9, more classic H. erectus features
Gona pelvis
1.4-0.9mya
Female pelvis
Evolving in response to increasing fetal brain size
The obstetric dilemma
Incompatibility between narrow birth canal and large neonatal brain size, resulting from Homo locomotion adaptions and big brains
Consequences
- Humans strongly underdeveloped at birth - altricial
- Only 25% of total brain size at birth
Explanations for human altriciality
- Obstetrical constraints e.g. Rosenberg 1992
- Metabolic constraints e.g. Dunsworth et al. 2012
- Selective advantages related to neural development e.g. Portmann 1969
Altriciality and human brain development
Most brain growth and maturation occurs under massive environmental and social influences in our species
Neural circuits responsible for behaviour are shaped by those influences
Mojokerto child
Java, 1.8mya (disputed)
Only H. erectus infant
1 year old, but perhaps up to 8?
80% of adult brain size (1 year old H. sapiens have 50-60% of adult brain size)
Sangiran, Java
80 hominin fossils including 10 crania and 14 mandibles/maxillae
Classic H. erectus morphology
1mya or more, but many specimens out of context
Pithecanthropus erectus
Trinil, Java
Discovered by Eugene Dubois, 1890
H. erectus holotype
Javanese vs Chinese H. erectus
Javanese ‘Pithecanthropus’:
Sagittal keel
Flat frontal bone
Angled occipital
Chinese ‘Sinanthropus’:
Thick cranial vault
Large supraorbital torus
Surpaorbital sulcus
OOA I
First hominin migration out of Africa - until this moment, human evolution has been an exclusively African phenomenon
Earliest evidence:
Dmanisi, Georgia - 1.8mya -fossil remains
Shangchen, China - 2.1mya - tools
Pleistocene climate oscillations
1.8mya-10kya
Colder and more variable climate starting at 1.8mya
Interval marked by repeated glacial cycles, known as the Ice Age
Huge volumes of water in continental ice sheets
Exposed land bridges connecting continents
Dmanisi fossils
1.8-1.6mya, Dmanisi, Georgia
Closest affinities with H. ergaster
Small bodies and brains
Show more derived features such as an angular occipital bone and sagittal keeling
Arboreal traits in upper arm morphology
Relatively long hindlimbs - modern body proportions
Valgus knee
Foot with arches
550-775cc
145-166cm
40-50kg
