Primate Evolution PDF

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Primate Evolution...

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Primate Evolution Taphonomy - The study of how bones and other materials are buried in the earth and become preserved - Further back in time you go, more scant the fossil record - The “curated fossil record” - Minute fraction of living population - Extremely small portion of animal skeletons become fossilized - Even smaller portion become discovered by researchers Primate taphonomy - Primates live in tropical forests = poor bone preservation - Best locales for preservation: - Rapid deposition (river valleys) - Minimal environmental disturbance (caves) - ATTRITIONAL ASSEMBLAGES - skeleton(s) broken and scattered overtime - Predators, scavengers - Rivers, wind, etc. - Incomplete and fragmentary fossils - Final assemblage may include many different animals - CATASTROPHIC DEATH ASSEMBLAGE - An animal or multiple animals killed in a rapid death event - River flooding, volcanic eruption, etc. - Kills and rapidly buries - Little to no disturbance by scavengers or other forces - Best preserved elements: - Teeth: hardest part of the body - Long bone shafts - Worst preserved elements: - Intact crania - Ends of long bones Process of fossilization - Death - Decay - Bury - Time - Water and minerals - Erosion PETRIFICATION - replacements/recrystallization and permineralization Geologic time

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Figure 8.6 Cenozoic - 65 mya - present Mesozoic - 248 mya - 65 mya Paleozoic = 540 mya - 248 mya For the exam: know the dates of the different epochs and the periods/dates they correspond to

CONTINENTAL DRIFT - Movement of continental land masses on top of earth’s molten mantle Types or rock - Sedimentary, igneous, metamorphic Dating methods - RELATIVE DATING - Designating an event/artifact/fossil as being older or younger than another - ABSOLUTE (CHRONOMETRIC) DATING - Dates for an event/artifact/fossil based on absolute measure of time (years, centuries, etc.) Relative dating - STRATIGRAPHY - PRINCIPLE OF HORIZONTALITY: strata are laid down horizontal to earth’s surface - PRINCIPLE OF SUPERPOSITION: lower layers are older than upper layers - BIOSTRATIGRAPHY (PRINCIPLE OF FAUNAL SUCCESSION) - Dating a find based on its association with a fossil species of a known age - INDEX FOSSILS - human made stuff in bones of other animals - LITHOSTRATIGRAPHY ABSOLUTE DATING - RADIOCARBON DATING - Compares the ratio of radioactive carbon C12 to stable carbon C14 - Accumulate the c14 during life; equal to levels in the atmosphere - After death C14 starts to decay into N14 - HALF LIFE - Time it decays one half of the original amount of a radioactive isotope to decay chemically into another isotope - Absolute dating: radiocarbon - Works on measuring anything organic - Bone - Wood - Charcoal - Shell - Hair

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- Only good for 50,000 years ago to the present ARGON ARGON DATING - Measures amount of radioactive argon 39Ar relative to stable argon 40Ar - Both measured as a gas - Looks at the amount of decay; more 40Ar = more decay (ie, older) - Can be applied to tiny samples (single crystal) - Works on volcanic rock - Half-life of 1.31 billion years - Good for samples older than 100,000 ya PALEOCIMATOLOGY - Study of ancient climate - Methods: - Isotopic analysis of glaciers, lake bottoms, etc. - Tree-rings - Others - OXYGEN ISOTOPES - How they get used to do climate reconstruction - 16O vs. 18O → these are stable isotopes (not radioactive, don’t undrego decay) - Cloud 18O changes with “raining out” of moisture - Less oxygen 18 goes up into atmosphere because its heavier - Cloud and rain become isotopically “lighter” as more 18O than 16O is lost through precipitiation across the landscape - Cenozoic Climate trends: cooling and drying

Models for Primate Origins Explaining grasping hands, generalized skeleton, and stereoscopic vision… - Arboreal adaptation - Leaping and grasping in trees - Visual predation -- model supported by textbook - Hunting insects in trees - Fruit-feeding - Reaching for fruits on the ends of tree branches - Assumes stereoscopic vision and came later Identifying primates in the fossil record - POST ORBITAL BAR -- ridge of bone over the eye orbits (cephalic index??) - Few distinct dental/skeletal traits - Generalized and primitive skeletal structure - Five digits - Clavicles - Etc. Primates’ closest living relatives - Tree shrews (scandentia)

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Flying lemurs (dermoptera) Bats (chiropetera) Common ancestor probably a generalized late mesozoic insectivore

Paleocene: 65-55 mya - Adaptive radiation of the mammals - Mammals begin filling various ecological niches around the world - Roots of the primate order (c. 63 mya) - Suborder PLESIADAPIFORMES - Proto-primates that give rise to primates but their line goes extinct - “primate -like” mammals - Has similar era structure, some grasping ability - Lacks post-orbital bar - Small insectivores Eocene Epoch: 55-34 mya - Paleoecology: - Primarily tropical environment - Early prosimian-like primates - Post-orbital bar - Adaptive radiation: over 200 species - By late eocene, early anthropoids had diverged - Eocene primates - ADAPIDS - ancestral to lemurs - Europe and N. America (continents still connected) - OMOMYIDS - eurasia , N. america, maybe africa Late eocene - anthropoid emergence - POST-ORBITAL BAR/WALL - unfused /fused frontal, mandible - Latter is haplorhine trait Oligocene: 34-23 mya - Radiation of anthropoids - Reduced snouts = greater vision, less sight - Quadrepeds, no specialized locomotion (limb ratio is 1 to 1) - Africa, asia, south america - Paleoecology: - drying , spread of grasslands Oligocene - Origins of New World Monkeys - Platyrrhine (new world monkeys, flat faces) - Catarrhine (old work monkeys, apes, humans) split = 40 mya (genetics) - Originally from Africa

- First appear in South America around 26 mya - How did they get to South America? - Fayum, Egypt - AEGYPTOPITHECUS - Early anthropoid, 33-35 mya - 2,1,2,3 dental formula - Ealy catarrhine Miocene Epoch: 23-5 mya - Appearance and radiation of hominoids - 30 genera; only 5 today (including us) - Monkey - ape split = 25 mya - Early miocene: - Africa separated from Eurasia - Mid to late miocene: - Africa docks during mid-miocene - Hominoids spread to all parts of europe and asia - Paleoecology - Spread of tropical forest, especially in Africa - Miocene hominoid characteristics - Mostly large bodied - Like gorillas, orangutans, and chimps - Many of the miocene hominoids do not have living descendants - Y-5 molars, refers to the first mandibular molar, has five cusps - Apes and humans have these - More primitive form - Bilophodont molars - Old world monkeys - DENTAL APES - APE TEETH, MONKEYLIKE BODIES - Miocene - PROCONSUL - Early hominoid - Africa - Quadruped - Tail? No bones found, possible tendon attachments - SIVAPITHECUS - Cranium very similar to modern day orangutans - Asia - GIGANTOPITHECUS - Probable vegetarian, gorilla-like - PIEROLAPITHECUS - european forms - DRYOPITHECUS - OREOPITHECUS - Mid-miocene: monkey vs. ape - Arboreal quadreped - monkey

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- Tend to leaf eating - monkey - Brachiator - ape - Tend to fruit; diversified diet - ape - Most environment, forests widespread - Apes outnumber monkeys late -miocene (11-5 mya) - Decline in ape species; proliferation in monkey species - Why? - Decline in fruit bearing trees? - Drying, reduction of forest - Knuckle-walkers = brachiators adapted ground - R-vs. k-selection in reproduction; adapting to changing environments? - Monkeys have more offspring over shorter period of time, behaviorally less complex than apes - Better at adapting to environmental shifts

***(be able to explain this)Traditional hominoid classification - Based on morphology, adpation, socio-intellectual complexity - Captures similarities and groups them together (evolutionary systematics approach) Revised hominoid classification - aligned with the cladistics approach - Based on genetics, better reflects evolutionary history Where do we start? Hominins - Humans are more like chimpanzees and bonobos than any other living animal - Anatomy - Behavior - DNA - 98% genetically the same - So we need to look for our LAST COMMON ANCESTOR with chimpanzees and bonobos - When? - DNA suggests the split between humans and chimps was 6 - 8 mya - Probable time period for first hominids - What are the two (three) fundamental ANATOMICAL differences between humans and chimpanzees? - Bipedalism - brain/skull size - Canine tooth size (chimps - large honing canine) - Humans also have thick enamel, less body hair, and other stuff… - What came first? - Big brains? - Bipedalism? - comes first - There was a bit of confusion till the mid 20th century - Fossils found in reverse order

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- Neandertals, homo erectus, australopithecus Piltdown hoax

ANATOMY OF BIPEDALISM - S-shaped vertebral column - Big toe in-line with other toes, metatarsal and phalange enlarged but in line with other toes - More robust pedal phalanges (especially first digit) - Shorter, broader innominate - Chimps have longer illium/shift in ox coxa is a key identifier of hominins in the fossil record - Overall differences in musculature on back - Elongation of legs and configuration of the knee joint - Foramen magnum at base of skull (where spine enters the base of the skull) - More forward set, closer to maxilla than it is on chimpanzees - Shifts center of gravity of head on top of body - Change in teeth (also because of other factors) —> humans have much reduced canines - We are the odd ones out, changed/lost in evolutionary line - Also lost the diastema (have diastemas so canines slide past each other) - Also changes in enamel thickness —> clue to type of diet - Bigger layer of enamel, we ate harder/tougher foods than chimps - Puzzling because enamel thickness has changed multiple times throughout line - Humans have a flat face (orthognathism), creates a better center of gravity WHY BIPEDALITY? - Energy efficiency —> moving longer distances is easier/efficiently - Frees up arms —> tool use, carrying things - Being able to see over tall grasses; ranging over distances of environments with less tree cover - Also relates to reducing surface area exposed to sun (reduction of forest/trees in Africa) - Also loss of body hair because hair = hotter - grasping/reaching up higher in trees - Probably not just one factor WHAT ENVIRONMENT? WHY BIG BRAINS? - Key is brain to body size - Tool use? - Ecological knowledge? - Social intelligence? BRAIN SIZE

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Other apes hover around 400/500 cubic centimeters Genus homo — things start increasing - Early homo = 600/700 and continues to increase Allometry = brain size to body size/shape - Encephelization quotient —>function of brain size and body weight - Humans have largest quotient

SUMMARY OF WHAT WE KNOW 1) Bipedal hominins emerge about 6 mya in Africa 2) About 2 mya, brain size increase and hominins make stone tools used to butcher animals and eventually hunt a) Early homo and homo erectus b) Expansion out of Africa 3) Abotu .5 mya, brain size increases even more, increased behavioral complexity a) At least some of these hominins give rise to us CP3 Honing Complex - P3 = 1st premolar - P4 = second premolar - Canines slide past premolar, first premolar is wider than the second - Humans lost this Contenders for earliest hominins - SAHELANTHROPUS TCHADENSIS - Skull and mandible fragments (“toumai”) - toros -menalla, Chad - 7.0 - 5.2 mya - Biostratigraphy, not found in volcanic layers - Why a hominin? - Small canines, reduced Cp3 complex - Minimal prognathism - Orientation of neck muscle attachments - Why non a hominin? - Small brain size (320-380 cc) - No post-cranial bones - Debate over foramen magnum position - ORRORIN TUGENESIS - 6 mya - Named after found in Tugen Hills, Kenya - Teeth, arm, leg fragments - 5 individuals - Why a hominin? - Small molars with thick enamel - Bipedal-like femur

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Why not a hominin? - Post-cranial elements do not indicate clear-cut biped

Brings us to genus ardipithecus Ardipithecus kadabba 5.8 - 5.2 mya - More apelike dentition than A. ramidus Another contender for early human: ARDIPITHECUS RAMIDUS - Aramis and middle awash, ethiopia - 4.4 mya - Reduction in cp3 honing complex - Why a hominin? - Reduced prognathism - Reduced canine - Foramen magnum position - Reduced height of ilium - S-shaped vertebral column - Loss of curvature in foot bones - Why not a hominin? - Divergent big toes - Ape like lower innominate - Long arms - Thinner enamel (but thicker than chimps) - *out of the early three, it is the best contender What do the early contenders share? - Absence of the cp3 honing complex - Mosaic anatomy that facilitated bipedalsim and arboreality AUSTRALOPITHECUS ANAMENSIS - 4.2 - 3.9 mya - Definite biped - Lake turkana, kenya - Teeth, skull fragments, arm and leg bones - Why a hominin? - Morphology of the tibia at knee - Thick enamel - Broader molars - Apelike characteristics - Large canine teeth - Parallel dental rows - U-shaped dental arcae

AUSTRALOPITHECUS AFARENSIS - 4.0-2.9 mya - Hadar, Ethiopia and others - Best understood australopithecine - Fragments of 300 individuals - “Lucy” - Hominin characteristics - Shorter, broader pelvis - Weight-bearing knee - Teeth - Apelike characteristics - Small brain size - Prognathism - Teeth - anterior teeth intermediate between apes and modern humans - “Lucy” - 3’’3” - Female - 3.2 mya - Males of the species are larger - Lucy’s “baby” - Dikika, ethiopia, 3.3 mya - Laetoli footprints - 3.25 - 3 mya - Pair with sexual dimorphism? - Tanzania KENYANTHROPUS PLATYOPS - 3.5 mya - Lake Turkana, Kenya - Like A. afarensis - Small brain - Not like afarensis - Flat faced - Small molars - These are homo traits - Flat face = fossil damage? AUSTRALOPITHECUS GARHI - Middle Awash, ethiopia - 2.5 mya - Incomplete cranium - Long bones - Cranial characteristics - 450 cc

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- Projecting face - Large teeth Post crania - Long forelimbs, like other australopithecines - But longer legs, more like homo Stone tools Found with faunal remains - Cutmarks - Intentional breakage - Probably scavenging Better candidate for ancestor of Homo

Hominins from South Africa - Sterfontein - Primarily found in limestone caves - Difficult to date - Foudn with bones, teeth, horn remains of other animals (osteodontokeratic) ROBUST AUSTRALOPITHECINES - 3 species - A ROBUSTUS - A AETHIOPICUS - A BOSEI - Robust crania, not body - East and southa frica - Some researchers call PARANTHROPUS...