˗ˏˋ hominins ´ˎ˗ Flashcards
what is a hominin?
modern-day humans and extinct bipedal ancestors.
what is a last common ancestor (LCA)?
- hypothetical final ancestor (or ancestral population) of two or more taxa before their divergence
- humans and chimpanzees
what are paleoanthropologists?
people who study human evolution.
what is morphology?
study of the form, size, or shape of things.
what is the east african rift system (EARS)?
- refers to the rift valley expanding from malawi to ethiopia
- active geological structure is responsible for much of the visibility of the paleoanthropological record in east africa
what is a site?
a place in which evidence of past societies/species/activities may be observed through archaeological or paleontological practice.
what was one of the first traits for hominins to evolve?
our bipedal locomotion.
what did early relatives have?
small brains and apelike dentition.
what is encephalization?
- expansion of the brain
- while bigger brains are a hallmark of hominins, a large brain doesn’t automatically equate intelligence
what is taxonomy?
- science of grouping and classifying organisms
- primarily based on morphology (in the past)
- now related to molecular phylogeny (e.g., based on DNA)
what are cladistics?
groups organisms based on shared derived traits.
what are clades?
a grouping based on ancestral relationships; a branch of the evolutionary tree.
what are lumpers?
researchers who prefer to lump variable specimens into a single species or taxon and who feel high levels of variation is biologically real.
what are splitters?
researchers who prefer to split a highly variable taxon into multiple groups or species.
what is a paleoenvironment?
an environment from a period in the earth’s geological past.
what are faunal assemblages?
collections of fossils of the animals found at a site.
what does reconstructing global environments look like?
using marine soil data and pollen grains.
what is the savannah hypothesis (or aridity hypothesis)?
- suggests that the expansion of the savannah (or less densely forested, drier environments) forced early hominins from an arboreal lifestyle (one living in trees) to a terrestrial one where bipedalism was a more efficient form of locomotion
- proposed by charles darwin
- popular
- idea that the LCA of humans and chimpanzees was a knuckle-walking quadruped like chimpanzees and gorillas
what is aridification?
becoming increasingly arid or dry, as related to the climate or environment.
what is arboreal?
one living in trees.
what is the evidence and interpretation for the savannah hypothesis (or aridity hypothesis)?
- evidence: cooling, drying conditions in africa about 6-8 mya
- interpretation: these things happened within our species at the same time as aridification (diversification
and bipedalism)
what is the turnover pulse hypothesis?
- climate change is associated with high faunal turnover (e.g. ungulates)
- ugulates: hoofed mammals—e.g., cows and kudu.
- faunal turnover: the rate at which species go extinct and are replaced with new species
- proposed in 1985 by palentologist elisabeth vbra
what is a generalist?
a species that can thrive in a wide variety of habitats and can have a varied diet.
what is a specialist?
a specialist species can thrive only in a narrow range of environmental conditions or has a limited diet.
what is the evidence and interpretation for the pulse turnover hypothesis?
- evidence: quaternary ice age (2.5 mya - 3 mya), faunal turnover in east africa and south africa, turkana basin indicates multiple instances of faunal turnover and extinction events, in which global climatic change resulted in changes from closed/forested to open/grassier habitats at single sites
- interpretation: debates about application to hominins and there were specialist hominin species that thrived as well as the generalist homo sapien.
what is the forest hypothesis?
- forested environments influenced bipedalism
- proposed by r.j. rayner and colleagues
- says that the LCA of chimpanzees and humans was more arboreal like orangutans, rather than knuckle-walkers like gorillas
what is the evidence and interpretation for the forest hypothesis?
- evidence: pollen evidence (south africa) and a closed habitat (referring to a woodland, or tree-filled, environment)
- interpretation: better conditions for fossilization
what is the variability selection hypothesis?
- hominin groups would experience varying degrees of natural selection due to continually changing environments and potential group isolation
- would allow certain groups to develop genetic combinations that would increase their ability to survive in shifting environments.
- these populations would then have a genetic advantage over others that were forced into habitat-specific adaptations
- proposed by richard potts
what is the evidence and interpretation for the variability selection hypothesis?
- evidence: large climatic variability and greater survival among generalists than specialists
- interpretation: flexible interpretations of evolution of bipedalism and evolution towards greater variability
what is the pulsed variability selection hypothesis?
proposes that the east african rift system (EARS) and changes in deep lakes are key drivers of diversification during early human evolution.
- EARS first developed about 10 mya and is responsible for the creation of large super lakes (e.g., lake baringo and lake turkana) within east africa
- affected by monsoons and solar precessional cycles: cyclical changes in earth’s axis rotation that have global climatic effects
what is the evidence and interpretation for the pulsed variability selection hypothesis?
- evidence: three humid phases in east africa and diversification in diet and adaptations
- interpretation: high levels of species diversity
and allopatric speciation
what is the postcranium?
skeleton from below the head.
what is obligate bipedalism?
where the primary form of locomotion for an organism is bipedal.
what are the origins of bipedalism?
- that early hominins descended from trees, and so we were a product of an arboreal last common ancestor (LCA) (most likely given skeletal morphology)
- that our LCA was a terrestrial quadrupedal knuckle-walking species, more similar to extant chimpanzees
what are the proposed selective pressures for bipedalism?
- energy conservation: modern bipedal humans conserve more energy than extant chimpanzees, which are predominantly knuckle-walking quadrupeds when walking over land
- thermoregulation: maintaining body temperature through physiologically cooling or warming the body
- bipedalism freed up our ancestors’ hands such that they could more easily gather food and carry tools or infants
what is mosaic evolution?
the concept that evolutionary change does not occur homogeneously throughout the body in organisms.
what is sahelanthropus tchadensis?
- 7 mya (earliest dated hominin find)
- discovered in chad in 2001 by ahounta djimdoumalbaye
- announced in nature in 2002 by a team led by french paleontologist michel brunet
- small cranial
- larger canines than homo
- possibly bipedal
what is orrorin tugenesis?
- 6-5.7 mya
- kenya
- small cheek teeth (hind dentition, molars and premolars)
- thick enamel
- apelike canines
- bipedal adaptations (post-cranium)
what is ardipithecus ramidus?
- 4.4 mya
- found in ethiopia
- small brain
- bipedal
- had ancestral traits (pposable hallux, or big toe)
- had derived traits (pelvis)
- large sample size of over 110 specimens
what is ardipithecus kadabba?
- 5.2-5.7 mya
- found in the middle awash region (ethiopia)
- post-crania: push-off ability of big toe
- name means “oldest ancestor” in the afar language
what is the importance of teeth?
- preserves very well
- can show diet
- can reveal environment
- can show relations to other species
- can demonstrate sexual dimorphism
- tells about social structure
- a reduction in teeth and a more generalist dental morphology could also indicate an increase in softer and more variable foods, such as the inclusion of more meat
what are general dental trends?
- dental formula of 2:1:2:3
- large, flat incisors that occlude (teeth from the maxilla come into contact with the teeth in the mandible)
- incisiform: referring to a canine that app ears more incisor-like in morphology
- reduced canine size
- reduced/eliminated canine diastema
- hind dentition indicates generalist diet
- u-shaped dental arch
- enamel and cusps
what is the genus australopithecus?
- varyrying degrees of arborealism and bipedality
- includes gracile australopithecus and robust australopithecus
- gracile: slender, less rugged, or pronounced features
- robust: rugged or exaggerated features
- large posterior dentition
- large chewing muscles
what does the gracile australopithecus include?
- east afrirican australopithecines: anamensis, afarensis, and garhi
- south african australopithecines: africanus and sediba
what is australopithecus anamensis?
- gracile
- 4.2-3.8 mya
- found in kenya, ethiopia
- small/medium sized brains
- large canines
- projecting cheekbones
- primitive ear-holes
- bipedal: tibia, femur
- primitive traits (upper limbs, arboreal)
what is australopithecus afarensis?
- gracile
- 2.9-3.9 mya
- found in tanzania, kenya, ethiopia
- “lucy” (3.2 mya)
- reduced canines, molars (vs. apes), prognathic face, strong chewing muscles
- sexual dimorphism
- bipedal: pelvis, lower limbs, footprints (laetoli)
what is australopithecus garhi?
- gracile
- one of the highly contested/debated species
- 2.5 mya
- found in ethiopia
- 450 cc (larger brain)
- primitive stone tools
- often compared to gracile australopithecines: larger hind dentition, longer limbs
what is australopithecus africanus?
- gracile
- taung Child (discovered 1924)
- 3.3-2.1 mya
- 400-500 cc brain
- small canines, no diastema
- postcranial: bipedalism
what is australopithecus sediba?
- gracile
- 1.97 mya
- had mosaic features: 420-450 cc (larger brain), gracile mandible, small teeth and postcrania (arboreal and bipedal traits)
what is the cradle of human kind?
limestone caves with well-preserved fossils.
what is paranthropus “robust” australopithecines?
- includes aethipicus, boisei, and robustus
- large, broad, dish-shaped face
- cheekbone arches that are forward facing, including a large mandible with extremely large posterior dentition
what is paranthropus aethiopicus?
- robust
- 2.7-2.3 mya
- found in tanzania, kenya, and ethiopia in the EARS system
- sagittal crest
- aproximal tibia indicates bipedality and similar body size to au. afarensis.
what is paranthropus boisei?
- robust
- 2.4-1.4 mya
- found in countries in east africa at sites such as kenya, malawi, tanzania, and ethiopia
- tools dated to 2.5 mya in ethiopia have been argued to possibly belong to this species
what is paranthropus robustus?
- robust
- 2.3-1.0 mya
- the only taxon from the genus to be discovered in south africa
- less derived, more general features that are shared with both east african species (e.g., the sagittal crest and zygomatic flaring)
what are fallback foods?
foods that may not be preferred by an animal (e.g., foods that are not nutritionally dense) but that are essential for survival in times of stress or scarcity.
what is knapping?
- the fracturing of rocks for the manufacture of tools
- earlier stone age technology (ESA): 3 mya - 300,000
what is a techno-complex?
- encompassing multiple assemblages that share similar traits in terms of artifact production and morphology
- lomekwian (kenya) techno-complex, 3.3 mya
- oldowan (tanzania) techno-complex, 2.6 mya, earliest stone-tool industry consisting of simple flakes and choppers
