Pleistocene Hominins Flashcards
Describe australopithecine dentition generally
Australopithecines have
• reduced anterior dentition in comparison to African apes
• relatively large molars
How much time do chimps spend feeding
Chimps spend ~ 50% of each day feeding
What is Tm
How is it calculated
Torque (Tm): the force a muscle produces around a joint
Tm = Fm * lever arm
Fm= contractile force of muscle (proportional to its cross‐sectional area)
Lever arm= perpendicular distance between the muscle’s line of action and the centre of rotation
Fr = the vector sum of all the separate muscle forces
What is Tb
How is it calculated
Torque (Tb): the force a bite produces
Tb = Fb * load arm
Fb= bite force (= Fr * Fr lever arm/load arm)
Load arm= perpendicular distance between bite force vector and centre of rotation
What is mechanical advantage
MA: muscle’s mechanical advantage measures the efficiency of torque generation (bite force per
contraction; trade‐off with angular velocity)
MA = lever arm/load arm length
What species are in the Paranthropus genus
†P. aethiopicus
†P. robustus
†P. boisei
What species is the Black Skull from
What was it originally thought to be from
When is the skull dated to
Paranthropus aethiopicus
originally named Australopithecus
boisei
• Dated to 2.5 Ma
Why was the species P aethiopicus revived
Similarities between the Omo 18 mandible, and the
two fossils from West Turkana (KNM‐WT 17000 and
KNM‐WT 16005) led to the reviving of the species
aethiopicus
What are the sites and dates of the fossils of P. aethiopicus
• Omo, Shungura, Members C to F, Ethiopia (2.7‐
2.3 Ma)
• oldest fossil: L55s‐33 mandible fragment from level C6, Omo, 2.7 Ma
• Lomekwi, West Turkana, Kenya (2.5‐2.35 Ma)
• Laetoli, Tanzania (2.7‐2.5 Ma)
Describe the Black Skull (7)
What species is this
FM?
- cranial capacity 410 cc
- Long, flat cranial base
- > sagittal orientation of the petrous bone
- Very large nuchal muscles, oriented vertically
- Very large sagittal crest
- Large, very prognathic face
- anterior position of root of zygomatic arches
Paranthropus aethiopicus
more medial FM
How do the bones of the black skull demonstrate the efficacy of Paranthropus aethiopicus’ mastication
Flaring zygomatics inverted inferiorly – massive attachment for masseter, high sagittal crest, small vault, prognathic face – huge temporal fossa – for huge temporalis from here and sagittal/ nuchal crest, bar like supraorbital torus, disproportionately maxilla with huge sockets for molar and premolars
Increased mechanical advantage based on the improved lever positions of the muscles, anterior position of z arches puts masseter more forward (lengthening lever arm in sagittal plane)
All post canine teeth v large
Prognathicism would limit masticatory efficiency
Have any juvenile aethiopicus fossils been found
L 338y‐6 juvenile cranium • ~ 10 yrs old? • 420‐440 cc • Omo Shungura, Member E, Unit E‐3 • 2.4 – 2.3 Ma
- How do the fossil records of aethiopicus and boisei compare?
- Most fossils: boisei
* Fewest fossils: aethiopicus
What was the first fossil (type specimen) of boisei
OH 5, Olduvai Gorge ~ 1.8 Ma discovered in 1959 by Mary Leakey Paranthropus boisei Previous names: Zinjanthropus boisei Australopithecus boisei
Give the key features of P boisei fossil KNM-ER 406 from the front
KNM-ER 406
510cc
Flared zygomatics
Sagittal crest
Flat face
High nuchal crest tilted up, different to OH5
Distinct morphology between these fossils
What is the cc of boisei
510cc
Describe the inferior features of the boisei skull
Nuchal crest projects down instead of out – massive nuchal musculature
Massive palate
Big temporal fossa
Molarised premolars
Reduced anterior dentition
Much bigger mandibles that australopithecius
Why does the boisei fossil from Konso differ from other specimens
1.4 Ma
Dry grassland environment
Different combination of the typical “robust” features:
• Configuration of sagittal crest like P. aethiopicus
• Broad and short palate, unlike other boisei
• Less concave face‐zygomatic complex than other boisei
Why might boisei be considered (one of) the most successful hominins?
Long lasting 2.3-1.1/1.2 ma
Does boisei fossils display sexual dimorphism
KNM-ER 732 is smaller than 406 but similar cc
No sagittal crest in 732
consistent dimorphism between males and females with african apes but less than in gorillas or mandrills
How does boisei cc compare to aethiopicus
increasing brain size in boisei
What features of KNM-ER 406 are repeated in other fossils from Koobi Fora?
What does this suggest -
KNM-ER13750 23000 show similar medial depression in arched supraorbital torus
extremely flared zygomatics
population level variation
What is important about Konso boisei fossils
Konso is most northern location where boisei is found, also very recent 1.4mya
different to other boisei -
• Broad and short palate, unlike other boisei
• Less concave face‐zygomatic complex than other boisei
suggests variation in time or space
Why is it difficult to be sure of Paranthropus boisei’s stature
only a few elated fossils have been found eg OH80 femur
because Paranthropus is contemporaneous with Homo it is difficult to know who it belongs to
What is the estimated size of boisei stature
Give the study that worked out these estimates
Extrapolation from the size of linea aspera of the
OH 80 femur (using regression formulae for H.
sapiens femur‐stature patterns):
• Femoral length ~ 400 mm
• Estimated ≥ stature: 156 ± 3.91 cm
• Estimated weight: between 50 – 61.7 kg
Dominguez‐Rodrigo M et al. 2013
What is interesting about the OH80 radius
most robust hominin forearm known
foveae seem similar to great apes - climbing adaptations?
What are the key robust adaptations of boisei (5)
flaring of zygomatics pronounced post‐orbital constriction sagittal and nuchal crests massive mandible Orthognathic, concave face
most extreme morphology of robust hominins
Give the megadont features of boisei (3)
Hyper‐megadont
very thick enamel
molarised premolars
small anterior dentition
Why can robustus, like boisei, be considered a “successful” hominin?
Robustus is the only Paranthropus in south Africa - 2ma to 1ma – lived for at least a million years – uncertainty about when it went extinct
Where is the richest fossil record of Paranthropus
Swartkrans is richest fossil record of Paranthropus – has oldest and most recent fossils – complex stratigraphy
What does “premolar molarization” mean?
Premolars developing molar characteristics
How does the temporal fossae of robustus compare to boisei
Larger than austrolapithecus but smaller than boisei
What was Paranthropus robustus’ cranial capacity?
475-530cc
Describe the face of SK48
P robustus
small flat face with laterally flaring zygomatics
Enormous palate and posterior dentition
Why is DNH 155 interesting?
(P robustus)
larger than DNH7 with unique features
eg alveolar prognathism and No “zygomaticomaxillary step”
How is sexual dimorphism expressed in Paranthropus robustus?
Very few fossils so hard
absent sagittal crest
Size difference:
McHenry 1991
F:110 cm
M:132 cm
Grabowski et al. 2015
(based on 9 femoral fragments)
F:~ 24 kg
M:~ 32 kg
What was Paranthropus robustus’ locomotor strategy? How do we know?
Trabecular bone patterns of femoral head– adapt to habitual weight loading on skeleton
Similar to living apes – frequently used highly flexed hips in climbing
Give key robust features of Paranthropus robustus
Orthognathic, concave face, with strong maxillary pillars
Flaring zygomatics Cranial cresting Large molars, molarised premolars Post‐orbital constriction Large to massive mandible
Did Paranthropus have an effect on the environment
Tools have been found at these areas and suggestions of fire use – cannot be attributed to homo or Paranthropus but either way would affect environment about them
bones found which were burnt at temperature of a campfire
- How does boisei mandibular morphology compare to that of a) other great apes and b) other species of Paranthropus?
a) Mandible is disproportionally large for body size – extreme in robustus and boisei – have a widening and deepening of mandible
b) boisei is more robust than robustus
- How does boisei post canine dentition morphology compare to that of a) other great apes and b) other species of Paranthropus?
For all teeth but M1 follow early trend set by earlier hominins, boisei departs from this (bigger larger than expected) , while robustus continues trend
What are fallback foods
Needed strength to shift diet to harder foods – low nutritional value, but important when preferred food is scarce
What is Liem’s paradox
extreme adaptations emerge to withstand the most challenging
aspect of an organism’s ecology, rather than the most common aspect
Give an example of Liem’s paradox in primates
Theropithecus gelada (has large, thick enamel):
• predominantly feeds on grasses, but shifts to tougher
underground storage organs (USOs – tubers, corms and
roots) during the dry season
How might fallback foods explain Paranthropus morphology?
Fall back foods drive anatomical adaptations for food processing while high quality foods drive behavioural adaptations for harvesting
Unique eco niche of Paranthropus – needed to eat hard (staple diet) or required lots of chewing as low quality (fall back foods)
How does a diet of leaves show up on tooth microwear
those who feed on leaves tend to exhibit fine paralleled scratches • those who feed on hard objects tend to show complex or pitted patterns
How does the diet of africanus differ from robustus
P. robustus: higher values for 11 attributes related to feature complexity, size, and depth (rougher, larger, deeper features) • Au. africanus: smoother, simple surfaces, with smaller, shallower, more aligned features
Peterson (2018)
How do diets differ between P robustus populations
P. robustus from Swartkrans and
Drimolen show similar degrees
and patterns of microwear texture
What does the microwear of boisei teeth show
relatively low complexity and anisotropy values. This suggests that none of the individuals consumed especially hard or tough foods in the days before they died.
The apparent discrepancy between microwear and functional anatomy is consistent with the idea that P. boisei presents a hominin example of Liem’s Paradox
What are C3 and C4 foods
- C3: low C13 value – all tree and bush biomass in African savannahs + herbaceous species
- C4: tropical grasses and sedges
How do we know the diet of Paranthropus robustus varied seasonally?
Laser ablation sampling – isotope ratio varies while the teeth grew, when children, c13 low (C3) – seasonally variable , flexible diet
What does isotope analysis of boisei and robustus show about their diets - what animals are their diets similar to
boisei Similar food to zebras and hippo
Robustus was closer to other hominins, boisei is specialized with high % of C4 grasses/sedges
What were the % of C4 plants in boisei and robustus diets
boisei: ≥ 75‐80% C4 plants – dominated by grasses and sedges
robustus: 30‐40% C4 plants
What do we know about aethiopicus’ diet
Early and late aethiopicus did not eat the same foods
OH5 vs KNM-ER 406: different cranial capacity and different face proportion so different masticatory mechanical advantage
• ISOTOPES: shift from mainly C3 to mainly C4 plants after 2.37 Ma
Summarise the morphology and diet of aethiopicus
Paranthropus aethiopicus
• MORPHOLOGY: less efficient masticatory adaptation (very prognathic)
than boisei or robustus
• ISOTOPES: shift from mainly C3 to mainly C4 plants after 2.37 Ma
Summarise the morphology and diet of boisei
• MORPHOLOGY: adaptations to hard object (nuts, seeds) processing
• MICROWEAR & ISOTOPES: prolonged masticatory bouts involving tough, abrasive C4 plants
• DIET: high % of C4 grasses, or sedges or their combination
• Potential role of fallback hard object foods in driving extreme
morphology unclear
Summarise the morphology and diet of robustus
• MORPHOLOGY: adaptations to hard object (nuts, seeds) processing
• MICROWEAR: diet regularly included hard objects
• ISOTOPES: similar to Au. africanus, 30‐40 % C3‐C4 plants
• DIET: fruits, nuts; diet varied seasonally and ontogentically
• Potential role of fallback hard object foods in driving extreme
morphology probable; termites dug with bone tools?
Give key differences between aethiopicus and boisei
brain size:
aethiopicus=410cc
boisei=550cc
boisei is generally the most robust of all robust hominins - this could be degrees of expression But difference in diet and fall back foods suggest different eco niches
But difference in diet and fall back foods suggest different eco niches (3)
Using primatology cf gelada eg and using morphological analysis – allows some reconstruction but doesn’t shed too much light on dietary variation and convergence can be a problem
Dental microwear texture analysis – leaf eaters display parallel scratches hile hard object eaters show complex or pitted patterns
Stable isotope – C3 vs C4 – more suggestive of area and specific about what type of vegetation was eaten, reaveals seasonality and variation
Laser ablation sampling – isotope ratio varies while the teeth grew, when children
Why is it argued that robusts should be sunk into the Australopithecine genus
Authors eg Tobias have said Paranthropus is a superspecies within the Australopithecine genus and australopiths were allometrically “ scaledvariants ” of the same morphotype
What did Kimbel find regarding Paranthropine monophyly
Strait and Grine (2004)combined 109 non-metrical traits with 89 traits based on linear measurements and, using two differently composed in-groups, also found that the three “robust ” taxa (P. robus-tus, P. boisei
and P. aethiopicus) consistently formed a monophyletic group, result also reached by the cladistic analysis by Kimbel et al. (2004).
What did Gunz find regarding the skull of robustus
Gunz et al.(2012) showed that a P. robustus
cranium, SK 48, is morelikely to be a scaled variant of P. boisei
than a scaled variant of
A. africanus - supports idea of a robust clade
Why is there a good case for robust similarities just being homoplasy
Phylogenetic studies of bovids (Gatesy et al. 1997), hippos, carnivores, Old World monkeys, elephants and equids all suggest that the evolutionary history of these groups shows evidence of substantial homoplasy during the period of time spanned by the megadont and hyper-megadont hominins.
many, but by no means all, of the characters that link
Paranthropus taxa in the same clade are related to the masticatory system. These are likely to be functionally integrated, thus potentially they are non-independent and if so, they should not be coded as individual independent characters in a cladistic analysis
the faces of
Kenyanthropus platyops and Homo rudolfensis
are, like P. boisei, both orthognathic relative to earlier hominins, but whereas the former have small or moderately sized postcanine teeth thelatter shows extreme postcanine megadontia. Since
K. platyops
and
H. rudolfensis
are generally not considered tobe closely-related to
P. boisei
, the cited similarities amongthese taxa must be due to homoplasy
What did Turner and Wood suggest about Paranthropus monophyly
Turner and Wood (1993) assessed the probability of monophyly by examining the
biogeographic patterns of African Plio-Pleistocene large mammals. They concluded that during the time range of Paranthropus ,there was evidence in at least one mammalian group of faunal dispersal between regions, with several monophyletic groups having representatives in both regions -> lends credibility to the hypothesis of
Paranthropus monophyly
What is a genus?
Generic classification in biology today, above species and below family representing:
• a group of monophyletic species
• reflect a distinct ecological niche that shapes the
evolutionary trajectory of the descendant species
How was Homo defined in late 18th Century
late 18th C: Blumenbach definition of Homo sapiens ‐ small canines, chin, short
mandible and face, large rounded skull, bipedalism
1856: discovery of the 1st Neanderthal at Feldhofer, Germany – arguments
whether it should be H sapiens or a new species H neanderthalensis. Independent of the
view, expanded the concept of Homo beyond Homo sapiens
How was the definition of Homo changed in the 20th Century
mid‐20th C: Homo as an adaptation, not morphology
Dobzhanski argued that culture allowed hominins to adapt to all ecological niches, so the human lineage had no speciation
Mayr argued that bipedalism unified all hominin species as distinct from
apes into a single ecological niche, and should therefore all be classified as
Homo
What happened in 1964
Leakey and colleagues name a new species, Homo habilis, from Olduvai
Gorge – brain size rubicon and stone‐tool manufacture [Oakley 1949 publishes
Man the Toolmaker]
Who was included in Homo in 18-19th C
What was the defining morphology
Sapiens
Eventually neanderthalensis
Pilthecanthropus erectus
small canines, chin, short
mandible and face, large rounded skull, bipedalism
What did Mayr argue about who should be included in Homo
Mayr argued that bipedalism unified all hominin species as distinct from apes into a single ecological niche, and should therefore all be classified as
Homo
Where were the first fossils of Homo habilis found? What non-Homo species did they coexist with?
Olduvai Gorge – Jonny’s child OH7
Presumed association with the stone tools found at gorge and larger brain
Co-existed with boisei
The below traits did not develop as a package
What are the diagnosing features of Homo (14)
- Bipedalism
- A fully opposable, well‐developed thumb capable of a precision grip
- a larger cranial capacity than in australopithecines, above 600 cc
- No sagittal crests
- Reduced to absent post‐orbital constriction
- Variable supraorbital torus development
- Variable degrees of facial prognathism, but no concave facial morphology (as
seen in boisei) - Variable chin development – from absent to well‐formed
- Bicuspid P3
- Molars smaller, in average, than in australopithecines
- Upper 3rd molars, in general, smaller than 2nd upper molars, which are in
general, smaller than 1st molars - Lower 3rd molars that can be significantly larger than 2nd molars
- Small incisiform canines
- No molarisation of premolars
What are the key differences between the skull of Habilis and sapiens
No flaring zygomatics and no postorbital constriction, but larger mouth than sapiens like robustus but smaller teeth and non molarised premolars
How big is the habilis brain
How does the skull appear (4)
510cc
Rounded vault, without crests Round small supraorbital torus, with a medially depressed glabella Small dentition Small third molar and bicuspid premolar
What did the virtual reconstructions of OH7
What is the age of this fossil
OH7=”Johnny’s Child”, habilis
large endocranial volume – 729‐824 cc
1.84mya
Where are fossils of Homo habilis found?
E Africa: Olduvia gorge, Tanzania and Koobi Fora, Turkana Basin, Kenya
Sterkfontein? – contentious
Temporal range of habilis?
2.31 million years ago to 1.65 million years ago (mya).
Give the following for habilis
• Body size:
• Cranial capacity:
- Dentition:
- Cranial morphology:
- Body size: 30-42kg
- Cranial capacity: 590-730cc
- Dentition: reduced post canine dentition
- Cranial morphology: non cresting and reduced post orbital constriction
Which taxon was rudolfensis originally put into
H. habilis
because of its
large cranial capacity.
differences with habilis originally attributed to sexual dimorphism
What is the type specimen of rudolfensis
What is the cranial capacity
What is the temporal range of this species
KNM‐ER 1470
Koobi Fora, East Turkana, Kenya
775cc
2-1.8 mya
Give the dentition and cranial morphology of rudolfensis
- Cranial morphology: flared zygomatic arch, no cresting or constriction
- Dentition: large (anterior and posterior)
What was found at Ledi-Geraru? Why does it matter?
Earliest fossil of homo – demi mandible: size and symphesis similar to afarensis, but has homo traits: accessory cusps on molars, orientation of mental foramen and contour of corpus – predictable mosaic of features between Australopithecus and homo
2.8mya
What are the derived Homo traits of the demi-mandible in Chalachew Seyoum
accessory cusps on molars, orientation of mental foramen and contour of corpus
What is allometry?
How the characteristics of living creatures change with size
– i.e., how traits or processes scale with one another
What is the law of relative growth
log y = α log x + log b
where x is body size, y is organ size, log b is the intercept of the line on the y‐axis and α is the slope of the line, also known as the allometric coefficient.
What is ontogenetic allometry
when x and y are traits measured in the same individual through development, the
allometric coefficient captures the differential growth ratio between the trait (e.g. organ) and the body as a whole
What is hyperallometry
Give an example
When organgrowth rate > bodygrowth rate, α > 1, which
is called positive allometry or hyperallometry.
eg. the chela of the male fiddler crab
What is the opposite of hyperallometry
eg?
• When organgrowth rate < bodygrowth rate, α < 1, which
is called negative allometry or hypoallometry.
eg. the human head
What is isometry
• When organgrowth rate = bodygrowth rate, α = 1, which
is called isometry. Such an organ maintains a
constant proportionate size (but not absolute
size) throughout development.
What is static allometry
when x is body size and y is the size, rate or expression of a trait at the same developmental
stage within a population or species - Allometry between small and large members of the same species
These may be non‐linear allometries: the scaling relationships are not linear
on a log‐log or any scale
Applies to multiple physiological traits and ecological traits
Describe the allometry of sexually selected traits
Most sexually selected traits display positive allometries
• However, the cost‐benefit ratio of certain traits changes with increasing size, and the linear relationship is not
maintained - NB: threshold where increase in sexually selected trait size is no longer adaptive
What is evolutionary allometry? Give an example.
when x is body size and y is the size, rate or expression of a trait at the same developmental stage in different species
Scaling relationships between different species – difference in intersect or α
Evolutionary allometry between BMR and body size in marsupial and placental mammals - Marsupials have lower intersect – lower MBR for each body size equivalent
Describe the importance of slope and intercept in evolutionary allometry
Differences in the intercept of the allometric scaling relationship between species indicate differences in the
proportionate size of the trait, irrespective of body size;
• Differences in the slope of the allometric scaling relationship between species indicate differences in how the relative size of the trait changes with body size within a species;
Both the slope (α) and the intercept (b) of morphological static allometries have biological meaning –
they capture the relationship between size and form within and between species.
Why is allometry important in evolution
Evolution of form comes from changes in static allometries, leading to ontogenetic changes, result eventually in evolutionary allometry – MAYBE
True or false:
Positive evolutionary allometry does not mean positive ontogenetic allometry
true
Describe the relationship between body mass and brain size
All animals have positive relationship between body mass and brain size – but homo sapiens it is significantly larger
How does body weight relate to home range
Sum weight of a group of primates is positively correlated with home range size
Insectivores have small body size
Why does body size dictate diet
How does body size affect lifespan
Small animal – larger BMR so must have more nutritious food
Larger you are, longer you live – true for mammals and birds
How will the allometric scale look different for a precocious vs altricial species
different gradient
What is heterochrony
a change in the timing or rate of developmental
events relative to the same events in the ancestral form
What are the 3 ways heterochrony happens
Change in a) rate of growth, b) onset time, or c) offset time
What did Haeckel claim about development
How was this later adapted to be correct
“ontogeny recapitulates phylogeny” (Haeckel) [incorrect]
• Von Baer’s observation and ‘laws of embryology’ (1928): general features
appear earlier in development than specialised ones [correct]
Give different types of heterochrony (3)
Neotony = decrease in growth Predisplacement = grows sooner than in ancestor; vs postdisplacement Hypermorphosis = continues growing longer than ancestor; vs progenesis
How does the intercept and gradient differ for the following:
Change in a) rate of growth, b) onset time, or c) offset time
a) Same x intercept but different α
b) Same α but different x intercept
c) Same x intercept and α but different end point
What is Peramorphosis
Evolutionary change that results in an
increase of the rate of growth, or growth
beginning at a smaller body size or an extension of the duration of growth
Define the following
Hypermorphosis
Acceleration
Predisplacement
Hypermorphosis: more stages, longer time Acceleration: more stages, same time Predisplacement: earlier onset so that the descendant adult develops beyond the adult form of the ancestor
What is Paedomorphosis
Evolutionary change that results in a
decrease in the rate of growth, or growth
beginning at a larger body size, or a
reduction in the duration of growh.
How does paedomorphosis come about
Progenesis: development stops early
Neoteny: development slowed
Postdisplacement: late onset
so that the descendant adult develops through fewer growth stages and resembles a juvenile form of the ancestor
According to Gould's clock model how does size and shape change in neoteny progenesis acceleration hypermorphosis
• Neoteny
o Size remains same but shape is that of juvenile ancestor
• Progenesis
o Size and shape are smaller than ancestor
• Ancestor
o Shape larger but size same
• Hypermorphosis
o Size and shape are both increased
How does human growth differ from chimps
What implications does this have
Slower and for longer, relatively altricial
In comparison to ape ancestor throughout
Growth stages‐ Rate and time
hypomorphosis
Major social implications in terms of infant
care
What types of heterochrony are involved in the evolution from chimp to human
Not just neoteny or hypermorphosis – different for different body parts
Compare brain growth in humans and chimps
What are the implications
Chimps: Brain size is 0.7% of maternal body mass
Reached at ~2 yrs after conception]
Humans: brains size is 0.7% of MBM at 11 months after conception Humans grows faster and for longer Adds growth stages Size and shape beyond the ancestor
RATE & TIME HYPERMORPHOSIS
Major energetic implications in terms of maternal nutrition and energy
consumption
What is the key general trend in Homo
Early humans have trend towards encephalization through heterochronic change
How can humans afford to have such big brains
But brain is 3x larger than should be – where does the extra energy come from
either: • something else is cheaper or • something else is paying for it or both
Describe the differences in adaptation between Homo and Paranthropus.
P = adapting to large teeth and muscles of mastication for different diets
Homo= little dental investment, invest in brain size per body mass
Habilis – beginning of trajectory of encephalization
How do humans fit to the line of body size vs BMR for primates
BMR of human is bang on line for body mass
Brain grows slower than in apes but at a faster RATE as a % of adult body mass than chimp
Describe the expensive tissue hypothesis
Gut- negative correlation of gut and brain size – reduce the size of another costly organ
(Aiello & Wheeler 1995)
Not necessarily true – small og sample size for example n=18
How did Homo offset the metabolic costs of an encephalised brain?
Reducing energetic costs elsewhere: Reducing gut size – evolutionary trade off
Growth:
Cost of growth put onto mother – changing life history
Early homo grew faster than modern humans but showed beginnings of slowed life history
What are Perikymata
Why are they useful
incremental growth lines that appear on the surface of tooth enamel as a series of linear grooves.
striae – can count to see how many days it took to grow (each takes ~7 days to grow?)
Can compare chronological age and biological age
What is the trend in LHS patterns in Homo
Relationship between biological (maturation) and chronological age
Early Homo shows slight delayed maturation
How did Homo reduce energy costs and allow for extra growth
Needed improved diet quality – meat
What are the advantages of meat
costs?
Meat advantages; high quality, protein - energy
Costs: compete with major carnivores, need to access the carcass and run away as fast as possible but also need to be able to separate meat from carcass
Is a larger brain needed for tool use
Habilis – believed larger brain lead to tool use
BUT tool use predates habilis but from 2mya do you see a real increase in reliance
When was there a real shift to C4 foods in Homo
2mya real shift to C4 – look at dust peaks (desertification) – significant change
When do we think tool use became essential
most cut marks on legs and head on ancient mammals – from phase 4 of decay only hyaenas and hominin scavengers could have utilized the meat
From 2mya onward – hominins were scavenging on the savannahs making tool use essential
If Homo and Paranthropu sexisted at the same time, how did Homo adapt to the periods of patchy food sources without morphological changes seen in robusts ? (4)
- being flexible forager with flexible strategies
- Microwear – different things at different times – tough veg and meat – flexibility (Ungar 2006 and 2012)
- Cooking? – Wrangham (1999) – less time eating etc – controversial – necessary but v little evidence
- More foraging – larger home range, higher travel and locomotion costs – primates have higher home ranges than carnivores so when homo invaded carnivore domain they had larger home ranges
- Hominins developed ecological relationship where they scavenge from mega-carnivore leftovers – just after 2mya that we see out of Africa dispersal – same time as when we see mega carnivores
When do we see all the traits associated with Homo
Only erectus has all the combined characteristics associated with homo – should we place grade shift before homo erectus not habilis ?
What do the following refer to Conditions Causes Constraints Consequences
Conditions: Timing of environmental change;
Local effect on resources
Causes: Nature of environmental change
Constraints: Adjacent empty niches;
Competitive landscape
Consequences: EVOLUTIONARY
TRANSITIONS
How do tectonics impact East African climate
Why is this important for hominin diversity
controlled by westerly monsoons over Equatorial West Africa and easterly monsoons over the Indian Ocean
uplifted areas in the east act as rain‐shadows, reducing the moisture available for rain on the eastern side of the mountains and valleys – East African aridity
Development of fault‐graben basins as catchments for lakes
emergence of lakes - lakes became attractions for hominins - increased diversity (Maslin 2014)
Give 2 moments in history that are particularly important for C4 plants
• Late Oligocene/early Miocene:
origin of C4 plants
• Late Miocene: expansion of C4 plants
What was the temperature in East Africa when C4 plants expanded
When was this
East Africa (~ 3oS – 5oN): ~8 Ma
What happened to the temperature at the end of the Pliocene
End of late Pliocene – marked decrease in temp and aridity – Paranthropus and homo;
What were the evolutionary pressures on 4 plants
C4 evolved in 2 phases – late oligocene high CO2 warm dry climate – evolution based on water availability and efficiency – C fixation
Expand under lower CO2 and temp levels with evolution pressure on CO2 and lighting availability – tropical grasslands and savannah
What is eccentricity
Earth’s orbit around the sun
What major climate changes occurred 2mya
max diversification of Paranthropus and Homo – peaks of dust, increase in C4 and increase of Walker Circulation (El Nino)
How does woodland change from the Late Miocene to Early Pleistocene
What is this period associated with in hominin evolutio
Middle Pliocene in East Afrcia is largely characterized by environments that are more wooded than those in either the Late Miocene (up to about 5.3 Mya) or the Pleistocene (,1.8 Mya onwards)
These generally more wooded conditions are coincident with the earliest clear evidence of bipedalism, and the earliest widely accepted member of the Hominini, as well as more efficient bipedalism and megadonty
How did the openness of grasslands change in the Plio-Pleistocene transition in East Africa
What is the importance of this
extent of open grasslands peaks during the Pleistocene(,1.8–0.01 Myr ago)
more wooded conditions persisted longerin the Omo Valley (into the Late Pliocene, up to about 1.8 Myr ago)than in the lower Turkana Basin.
This expansion of grasslands across the Pliocene–Pleistocene transition has been linked to global climate change and major developments in the hominin clade, such as the more obligate bipedalism of Homo, increase in encephalization, and reduction in tooth and gut proportions
How does the woodland differ for Ardipithecus and Australopithecus
soil carbonate data now make it clear that both species were surrounded by more open environments than Australopithecus, which was more efficiently bipedal and occurred in more wooded environments of both the Omo-Turkana Basin and the Awash Valley
(Cerling, 2011)
How does the terrestrial environment compare between Australopithecus and Paranthropus?
Australopithecus=Increasing wood cover – wooded – nearly ½ covered by trees
Paranthropus=Increased aridity; trend towards colder climate; shift to open, Wooded grasslands
Main tributary to lake Turkana, Shungara, was much more forested – small refuges with lots of trees
What are the causes, conditions, constraints for development of Facultative/ habitually bipedal apes limited to mosaic patches with woody cover?
7.0‐4.4 Ma, late Miocene/earliest Pliocene
Causes: increased quadrupedal locomotion
cost to apes in East Africa
Conditions: Expansion of C4
grasses, break‐up of mid‐Miocene forests
Constraints: costs of abandoning arboreal niche
What are the consequences of hominins becoming facultative bipeds in late Miocene (3)
Split of chimp/human lineage
• Invasion of terrestrial primate niche
• Selective pressure for more efficient
terrestrial locomotion
What were the key environmental changes in the mid-late Pliocene to hominin evolution
What did this lead to (2)
4.2 – 3.0 Ma, mid‐late Pliocene
• Relative increase in C3 woody cover in East Africa, woodlands/bushlands/thickets
• Diversification and expansion of Australopithecines
(including Kenyanthropus)
• development of Obligate bipedal hominins of variable efficiency, mostly limited to mosaic patches with ≥40%
woody cover
What were the causes, conditions, and constraints of development of Obligate bipedal hominins of variable
efficiency, mostly limited to mosaic patches with ≥40% woody cover in mid-late Pliocene
Causes:
• competition amongst hominin bipeds driving locomotion efficiency;
• Selective pressure for dietary diversity combining different % of arboreal resources
Conditions:
• relatively stable climate, re‐forestation of parts of East Africa
• woodland corridors between East, Central and South Africa?
Constraints:
Committed bipedalism’s cost to ecological breadth
Increasing terrestrial resources to sustain a large
ape’s diet -> Increased C3 – increased diet of harder objects
What were the consequences of development of Obligate bipedal hominins of variable
efficiency, mostly limited to mosaic patches with ≥40% woody cover in mid-late Pliocene (4)
Expansion/diversification of australopithecines
• Trend towards endemism?
• Selective pressure for more efficient terrestrial
locomotion
• Selective pressure for dietary shift towards
harder objects
What was happening in hominin evolution (species wise) 3-2mya (4)
What happened to the climate?
What happened to hominin locomotion
late Pliocene/early Pleistocene
• Last australopithecines in East Africa
• Evolution of first robust hominins in East Africa
• Evolution of first Homo in East Africa
• Long‐lasting survivorship of australopithecines in South Africa
Period of significant climatic deterioration ->Water becomes more rare as aridity increases
Efficient obligate bipedal hominins with multiple different dietary adaptations
When efficient obligate bipedal hominins with multiple different dietary adaptations appeared, what were the causes, conditions, and constraints?
Causes: • competition amongst australopithecines facing ecological deterioration; • Selective pressure for dietary specialisations
Conditions:
• Significant climatic deterioration; expansion of grasslands
• Savannah corridors between East and South Africa?
Constraints:
• Energetic costs of low quality diet processing and high quality diet foraging
• Water resources in increasingly arid landscapes
When efficient obligate bipedal hominins with multiple different dietary adaptations appeared, what were the consequences?
• Evolution of robust/megadont hominins
Invasion of carnivore niche
• Opposing selective pressures for specialist x
generalist strategies, endemic x pandemic
What are the costs of high vs low quality diets
Low quality diets have a cost of processing while high quality diets have a high cost for foraging
How do the evolutionary trends of South and East Africa diverge 3mya
Different trajectories from east (drier) and south Africa (remains wooded) – eastern = last australipithecines are still around but you see emergence of novel hominins (robusts and homo) which are contemporaneous with Africanus in South Africa – dichotomy
What are the 3 key landmarks in the evolution of hominin bipedality
4mya – obligate bipedalism arises
3 – efficient biped
2 – super efficient biped
Give recent arguments against Sahelanthropus being bipedal
femur found attributed to Sahelanthropus but appears to lack bipedal adaptations
Macchiarelli (2020)
however, could belong to a different primate species
the femur has been kept relatively secret since its discovery
What did Alemecija suggest about Orrorin’s femur
o Bipedal but with different adaptations to other hominins? Alemecija 2013
o Same clade but separate branch?
What is the key question regarding ramidus’ locomotion?
Why is this?
was Ardipithecus ramidus a facultative or habitual biped?
The foot has a widely abducent hallux, which was not propulsive during terrestrial bipedality. However, it lacks the highly derived tarsometatarsal laxity and inversion in extant African apes that provide maximum conformity to substrates during vertical climbing
What is the likely locomotion of ramidus
careful climber that retained adaptations to above-branch plantigrady (Lovejoy, 2009)
What is a key outstanding question regarding Austroliths?
Why is this a key question?
to what extent was Australopithecus arboreal?
- Know they had transformed postcranial anatomy to be efficient bipeds
- But retained scapulae with cranial orientation and shrugged up shoulders like apes and curved hand phalanges
- Dekika baby – arboreal features
- Cf. afarensis – laterally orientated scapula with horizontal spine and short arm comparatively
o Range of features within species or more than one taxon under name afarensis
How does Au. anamensis fit with body mass vs Time trends
much larger body mass than would be predicted for its time
What is important about the Macchiarelli et al. (2020) paper?
Study suggested S. tchadensis femur was hominin but not biped
- Where do Almecija et al. (2013) place Orrorin on a phylogeny, and why?
Same clade but separate branch because its habitual bipedality is different to that of other hominins
What did Grabowski say about trends in body size throughout hominin evolution
modern human-like large size first appeared by at least 3–3.5 Ma in some Australopithecus afarensis individuals.
argue that no reliable evidence that the body size of non-erectus early Homo differed from that of australopiths, and confirm that Homo erectus evolved larger average body size than earlier hominins.
At what rate do all early hominins grow? When does the shift to a human-like trajectory happen?
All early hominins until we get to early Homo have an ape like growth and development trajectory
Homo erectus show beginnings of slowing of growth
Cf. chimp – first shift is in early homo – relates to encephalization
- What are the outstanding questions about hominin growth and development?
Was encephalization the driver for delayed maturation – chicken =/egg q
When did childhood evolve? – humans have an additional stage of life history – very important phase
Describe the adaptive trends of hominin tooth morphology
ANCESTRAL Thick enamel and large molar -> AUSTRALOPITHECUS Trend towards enlarged molars -> HOMO Reduced posterior dentition and cranial gracilisation vs PARANTHROPUS Megadont adaptive complex
Compare the diets of Homo, robustus, and boisei
Homo:C3 > C4; + carnivory
boisei: C4»_space;> C3
robustus: C3»_space; C4
What is the evidence for tool use preceding Homo
Australopithecus africanus (~3 to 2 million years ago) and several Pleistocene hominins, traditionally considered not to have engaged in habitual tool manufacture, have a human-like trabecular bone pattern in the metacarpals consistent with forceful opposition of the thumb and fingers typically adopted during tool use
support archaeological evidence for stone tool use in australopiths and provide morphological evidence that Pliocene hominins achieved human-like hand postures much earlier and more frequently than previously considered.
Skinner, 2015
What is the argument against morphological hand adaptations to tool making 3mya
Harmand et al. argue, the decisive adaptation enabling “Lomekwian” stone knapping (to yet-unidentified hominins) was likely neurological
How does Almécija argue against Skinner’s evidence for afarensis being adapted to using tools (2) (2015)
Skinner et al. base their con-clusions on their previous comparative analysis of trabecular structure in the hominoid third metacarpal. However, this analysis was un-able to separate humans from gibbons or orang-utans, and it failed to provide any direct evidence that observed differences be-tween taxa were actually due to variation in life-time mechanical loading. Inherently, extrapolating from this potentially phylogenetically dependent correlation in the third metacarpal to all meta-carpals renders the conclusions of Skinner even more speculative
external morphology that australopith hands were, in some ways, more similar to those of humans than to apes, and thus were likely capable of human-like manipulation (4–8). However, this does not mean that human hands evolved for the sole purpose of making and using stone tools, for which cognitive capabilities should be also considered, as Napier and others indicated before
What are the 5 key transitions hominins have experienced since the chimp-human LCA according to Foley and Gamble (give timings of each)
(i) African ape to terrestrial bipedal ape(approx.4Ma)
(ii) Terrestrial bipedal ape (australopithecine) to ‘early Homo’(approx. 2.0 Ma).
(iii) Early Homo to Homo heidelbergensis (1.0–0.8 Ma)
(iv) Homo heidelbergensis to larger brained Homo (from 500 ka).
(v) Larger-brained Homo to H. sapiens (200–0 ka)
Why do Foley and Gamble say the first key transition (African ape to bipedal ape) happened 4mya
broadly coincides with the emergence and radiation of the australopithecines
What are the significant consequences of transition 2 (Terrestrial bipedal ape (australopithecine) to ‘early Homo’(approx. 2.0 Ma).) according to Foley and Gamble (2009)
posture shifts from australopithecus to human-like
brain size increases substantially, and patterns of dental development indicate a delayed process of maturation (i.e. a shift in the life-history strategy)
dispersal across Africa
Why do Foley and Gamble highlight the importance of the emergence of heidelbergensis
it is when the true ‘Acheulean’ stone technology develops (mode 2B), and spreads across much of Eurasia, providing the first significant colonization of more northerly environments
What is important about the 4th transition in hominin evolution described by Foley and Gamble (2009) - 4 key developments
increase in the rate of evolution of the brain. This can be seen in two lineages (Homo sapiens and neanderthalensis), and may be a single evolutionary event, followed by later divergence or convergence
in this period you also see shifts in life history, the development of mode 3 technology and changes in subsistence behaviour
What is the general consensus for why hominins descended from the trees
Were hominins special
at the end of the Miocene and into the Early Pliocene there was pronounced global cooling, with creasing aridity, a decline in closed forest habitats and a spread of more wooded, bushed and grassy environments, often with pronounced seasonality. Longer day ranges were key
this was a general trend towards terrestriality among the catarrhines where hominins were the hominoid extreme
What were the key changes in behavioural ecology in the 2nd hominin transition (Foley and Gamble, 2009)
what are the implications of this change
extensive meat-eating
tool use
more reliable access to high-quality resources, especially during dry seasons, and a smoothing out of seasonal variation
This change led to a greater availability of energy for mothers, and a relaxation of the constraints on the energetic costs of larger brains, especially when tied to a delayed life-history strategy
What do Foley and Gamble (2009) argue is the key adaptive change in the 3rd hominin transition (Early Homo to heidelbergensis (1.0–0.8 Ma).)
why
cooking
means of making meat in larger quantities energetically viable within a time budget + increases the digestibility of plant foods
impact on social interactions - hearths created/ strengthened family units
What do Foley and Gamble claim is the most important implication of the emergence of Acheulean tools
demonstrate ability of focused attention - could focus not only on tools but other individuals for long time
termed ‘Acheulean gaze’
Using the correlation between brain and community size, Dunbar (2003)has proposed that hominins in this period possessed a theory of mind and Gamble argued there became a selection pressure for behaviours such as dance and music to promote social cohesion
What is the archaeological evidence for culture emerging between 500 and 200kya
What is the importance
What biological changes may underlie this
greater regionality of artifacts
this period sees a greater emphasis of groups as units-
precondition for evolution of cultural capacity?
during this period almost 30% of hominin encephalization occurred - could relate to increased community size or may also have been selected for by the greater cognitive demand of maintaining social relationships over distance and time
When did the fission-fusion of human populations drastically increase
What happened
evidence?
500-200kya
individuals, families, bands, etc. can split up for very long periods of time, and disperse over large distances, while still maintaining a common social network - Human society is essentially a chimpanzee community with exploded fission–fusion
lithic raw materials were extracted and transported over greater distances than before
What are the 3 key features of the 5th hominin transition (Gamble and Foley, 2009)
1) appearance of our current anatomical and gen-etic characteristics in Africa
2) global dispersal of these characteristics allied, often with a novel technology, to the previously uninhabited 75 per cent of the globe
3) rapid increase in population numbers following the retreat of the last glaciation that began 16 kya
How did the global dispersal of modern human characteristics allied, often with a novel technology, to the previously uninhabited 75 per cent of the globe begin and end?
began with the sea crossing to Australia 60 ka ago.
concludes with the settlement of remote Polynesia within the last millennium
Give evidence or complexity in intergroup relationships in the last 200ky
A rise in the quantity and diversity of cultural forms, including composite tools, art and architecture, is matched by widespread distributions of distinctive cultural markers that signal group affiliation at a large geographical scale.
Mobility ceases to be the key foraging tactic as more long-lived settlements occur in response to greater demographic packing.
Territorial markers appear in the form of cemeteries and defended settlements, while extensive networks of exchange are now found through which items such as shell, obsidian, amber and other localized resources are channelled.
How do Foley and Gamble argue modern humans emerged following the 5th hominin transition
prolonged and cumulative transition, stretching from the biological changes over 150ka to the emergence of a fully sedentary, agricultural and ethnically complex world in the last 15 ka
What do Foley and Gamble (2009) argue coincide with shifts in human behaviour
climatic changes but also endogenous elements of the hominins themselves—including technology, fire and cultural mechanisms for maintaining larger groups
How were the remains of Sahelanthropus and Bahrelghazli dated
Hard to tell age from stratigraphy so must be dated through fauna found in deposits
Which hominins have been found in Malawi
boisei
rudolfensis
(very fragmentary)
Which hominins are found in South Africa
Prometheus Africanus Sediba Robustus erectus
According to Strait and Wood what taxon has the same position in all phylogenies?
All have afarensis as the root of the tree (sometimes africanus is side branch, sometimes direct ancestor of P and/or Homo)
In how many phylogenies is Paranthropus monophyletic?
Monophyletic in 5, doubtful in 1, and split in the other 4 – splits are not stable (sometimes aethiopicus and boisei are linked, sometimes boisei and robustus are linked)
Why do we think there were dispersals from East Africa 3-4mya
bahrelghazali and prometheus found in chad and south africa respectively
Phylogeny missing an early dispersal of australopithecines between 4‐3 Ma That gave rise to A prometheus in South Africa, and A bahrelghazli in Central Africa
While there may have been wooded corridors for the dispersal into Africa from east Africa 3.8-3mya, it is unlikely that central Africa was wooded for bahrelgahzali
Give one hypothesis for how africanus came to be in S Africa, where Homo does not come from africanus
What is a key issue with this
> 3mya: dispersal to SA of LCA of africanus and Homo
EA branch becomes Homo
SA branch becomes africanus and sediba
But how does the link with habilis between sediba and homo – is it closer to homo or other australopiths – cannot be both
What is the implication of rudolfensis’ position on Lieberman’s (2001) phylogeny?
Positions K. platyops as rudolfensis’ ancestor, making rudolfensis NOT homo – implies encephalization occurred in parallel in 2 separate lineages
Give a possible explanation for how boisei and robustus arose
How does this explain different niches
2.7 Ma: aethiopicus in EA • <2.3 Ma: dispersal to SA of LCA boisei/robustus • Subsequent differentiation of boisei and robustus, with adaptation to C3‐ based diet in robustus
Dispersed through grassland corridors and robustus would have invaded S. Africa C3 niche – would explain how they can be monophlyetic
What do the Paranthropus maxillary pillars say about their phylogeny
Au. africanus and P. robustus share a very pronounced distinctive anterior pillar
P. robustus and P. boisei share many traits that form the robust complex (tooth
size, sagittal crests, deep mandibles, flaring zygomatics, pronounced post‐orbital constriction, etc.)
The internal structure of the circumnasal region of Au. africanus and P. robustus is extremely different (hollow cortical bone in africanus vs dense trabecular bone in robustus)
- P. boisei does not often have a maxillary pillar; however, its internal morphology made of dense trabecular bone is very similar to that of robustus.
- [P./Au.] aethiopicus (who also does not show an external maxillary pillar) does not have the internal dense trabecular bone of boisei and robustus, and is similar to afarensis
What does comparative evolutionary biology suggest about Paranthropus monophyly
Convergence – lemurs
In absence of anthropoids some lemurs evolved into niche of apes and came to have locomotion v similar to gorillas
Hadropithecus – lemur that became megadont
Flaring zygomatics, molarised premolars
What is anagenesis
What is cladogenesis
What is the difference
species formation without branching of the evolutionary line of descent.
the formation of a new group of organisms or higher taxon by evolutionary divergence from an ancestral form.
Can be the same - may be a matter of scope - how much to zoom in
Can a species be contemporaneous with its ancestral species
Yes
You can have:
Cladogenesis with survival of ancestral species
OR
Cladogenesis with extinction of ancestral species and two daughter species
What are the 4 conditions of an adaptive radiation
- Monophyly
- Strong phenotype‐environment correlation across species
- Trait‐utility
- Rapid speciation
What is the expectation of an adaptive radiation
- Expected high levels of homoplasy
- Expected low within‐species variance in adaptive traits
- Expected high between‐species variance in adaptive traits related to local conditions
What are the trait-utilities hypothesised for the different adaptive radiations
- incipient bipedalism
- obligate bipedalism
- megadontia
- Homo package (carnivory, technology, fire?
Loss of ape body size/shape & life‐history)
