Dating techniques: how old are the fossils?2 general types of dating techniques:Relative Datingplace finds in a sequence relative to one another, but provide no actual dates or date rangeEx: stratigraphyMakes use of the law of superposition: older layers are overlain by more recent layers (like a cake or the Grand Canyon)Bottom layers usually olderEx: “I’m taller than my daughter”Radiometric/Absolute datingProvides date estimates (in years before present, BP) for geological depositsEx: K/Ar (Potassium Argon), Ar/Ar (Argon Argon), radiocarbon, fission-track, etc.Ex: stopwatch analogyRadiocarbon datingC12: stable, does not decay, same amount whether dead or alive, same amount as C14 while aliveC14: decays through time, created constantly, plants take it through photosynthesis, we eat C14 in their bodies even though its decaying, amount is the same in all living things, still decaying after death but not being replenished.Ex: organism dying starts stopwatchGoes into C14 and N14C14 half-life: the amount of time required for a radioactive isotope to decay to half of its lifeScientists measure the amount of C12 and C14 to determine the date of deceased5,720 years x 3 half-lives = 17,190 years old don’t need to knowdecays very quickly, very hard to measure after a certain amount of yearsdepends on the material that you have available to study and testash, tuff and lava from volcanoes can be dated by K40/Ar40 radiometric dating methodshalf-life of K40 = 1.25 billion yearsusing both relative and absolute dating techniques, what can we say about the age of fossil “x”?using both radiographic and stratigraphic techniques, not necessarily testing the bonesThe Evolution of Early PrimatesOur goal: trace our lineage back in time (sometimes w/phylogeny)General Timeline for early primate evolutionMiocene (23-5 mya): hominoid radiation“planet of the apes”Proconsul (27-17 mya)First apes appear in East Africa in the late Oligocene/early MioceneThe small generalized ape exhibits a monkey-like body.But it also shares some derived traits with hominoidsNo tailSome details of the thumb and big toeHominoids originate in Africa early in the Miocene and then later spread into EurasiaMiocene hominoids in EuropeDryopithecus (Spain, 9.5 mya)The teeth are chimp-like in size and morphology including thin enamel (indicating frugivory)The cranium is ape-likeThe skeleton is ape-like but not adapted to knuckle-walkingLocomotion: brachiation (???)Miocene hominoids in AsiaSivapithecus (14-8 mya)Found in India and PakistanHad big powerful jaws with large molars and thick enamelOrangutan (Pongo) ancestorThe world became cooler and drier during the latter half of the MioceneAs a consequence of climate change (selection), the fossil record shows a shift in primate species during latter half of the Miocenefewer ape species, more monkey speciesclimate change during the Miocene sets the stage for the appearance of homininshominoids flourished early in the Miocene, but most went extinct leaving only the ancestors of the fat fewer ape species of todaywhat was it about the hominin lineage that allowed us to survive while many other hominoids went extinct in the face of the cooler, drier conditions that marked the late Miocene?Oligocene (34-23 mya): anthropoid radiationFayum Basin, EgyptThe best known early anthropoids come from early Oligocene fossil beds in the Fayum (36-33 mya)AegyptopithecusFound in sediment that dates to ~29 myaRelatively long snout and tiny brain relative to rest of headPost-orbital closure and binocular visionApe-like dental formula (2.1.2.3) in mandibleFairly pronounced stout, small brainSexual dimorphism? - bigger male skull than femaleEocene (54-34 mya): Prosimian radiationAppearance of true primates, Prosimian radiationEocene = Prosimian adaptive radiation2 larger categories (Adapids & Omomyids)sometimes considered the first true primatesgrasping hands and feet with nailsreduced prognathismEx: Ida (47 mya) is the worlds best preserved adapidPaleocene (65-54 mya): first possible primatesPlesiadapiforms (Plesiadapids)Small primate-like animals from the late PaleoceneSolitary, terrestrial and arboreal quadrupedsWell developed sense of smell, most had claws on hands and feet, and they did not have binocular visionEx: Carpolestes simposoni (56 mya)Nearly complete skeleton discovered in 2002 in WyomingC. Simpsoni had opposable big toe with nail but claws on rest of digitsWhat was it about the hominin lineage that allowed us to survive while many other hominoids went extinct in the face of the cooler, drier conditions that marked the late Miocene?Origins of BipedalismHow do we discern whether a fossil is from a hominin?Look for characteristics of humans not present in any other primates (shared derived features)The earliest and most universal derived feature of the hominid is bipedal gait, our form of which is unique among animals(walking on two legs and feet)bipedalism leaves its signature on the skeleton from head to toeIn bipeds, foramen magnum (small hole that spinal chord attaches to skull) is located under, in the middle rather than at the far rear of the skullS-shaped curvature to spine helps balance, cushion torso (also makes us prone to lower back problems)Bipeds have a broad, bowl/basin-shaped pelvis rather than a tall, narrow pelvisFemur is angled “inwards” in a biped, unlike a quadruped, which makes our legs closer to the center of gravity to balance better and keep ourselves uprightThe bipeds footArches provide extra “spring”Short, straight toesToes in line (no divergent big toe)Dating techniques: how old are the fossils?- 2 general types of dating techniques:o Relative Dating place finds in a sequence relative to one another, but provide no actual dates or date range Ex: stratigraphy  Makes use of the law of superposition: older layersare overlain by more recent layers (like a cake or the Grand Canyon) Bottom layers usually older Ex: “I’m taller than my daughter”o Radiometric/Absolute dating Provides date estimates (in years before present, BP) forgeological deposits Ex: K/Ar (Potassium Argon), Ar/Ar (Argon Argon), radiocarbon, fission-track, etc.  Ex: stopwatch analogy Radiocarbon dating C12: stable, does not decay, same amount whether dead or alive, same amount as C14 whilealive  C14: decays through time, created constantly, plants take it through photosynthesis, we eat C14 in their bodies even though its decaying, amount is