Lecture 16 Outline of Last Lecture I. Fossils Outline of Current Lecture II. Relative and absolute datingIII. Last Common AncestorIV. How do Apes and Humans differCurrent LectureTimeRelative age Anthro 1031st editionrelative dating methods - give age relative to other thingsyounger, contemporary, or older?Absolute ageHow many years? How long ago was this fossil a living organism?Chapter 8:Relative dating methods:Stratigraphic:layers of rockdeeper usually olderBiostratigraphic:"layers" of extinct speciesThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.use previous knowledge of other speciespigs, rodents, etc. - pigs are omnivorous and have similar shape to hu-mans - using what we know about other species can help us place new fossilsChemical:fluorine - amount reflects time buried; the fossil with more fluorine is olderPiltdown hoax - fossil found in Piltdown, England; there was a cranium and jaw; cranium looked like a modern homo sapien but the jaw was very ape-like (from an organgutan) and had large canine teeth; found out in the 1950's that someone intentionally buried these together as a hoax - figured this out by the amount of fluorine; the person broke off parts of the jaw so it would look like it fit better with the skullCultural:artifactsAbsolute Dating:Dendrochronologytree rings - can count rings on tree trunk to determine ageRadiometricunstable isotopes (12C and 14C) - revert to more stable form at a known ratechange predictablyother isotopes are radiocarbon, argon...Various "high tech"amino acid, fission track, paleomagnetic, electron spin - all can be usedfor dating *Need to know these exist but don't need to know the detailsDNA - Genetic Dating:How many mutations?Mutations occur at a known rateCalculate time since"Molecular clock"Image: Cladogram scaled to time - longer branches mean more mutationsMost of primate evolution between Paleocene and MiloceneIn early Milocene when it was warmer, there were more tropical rainforests - great for hominoidsTemperature cooled and got dryer so rainforests shrankLCA (last common ancestor):-is extinct species-was not a chimpanzee-not sure what it was like3 scenarios:1. lots of evolutionary change along human lineage and not along chimp lineage = lca was chimp like2. lots of evolutionary change along chimp lineage and not along hu-man lineage = lca was human-like3. evolutionary change along both lineages = lca was unlike chimps and humans - most probableHow do we differ from modern apes?1. Dentition - teeth2. Bipedalism3. Not very dimorphic - body size or canine size4. Very large brain5. Very long, slow maturation6. Dependence on complex culture (language)Only dentition and bipedalism distinguish first hominins - these are the first differences between us and apesDentition:Arcade shape - shape of maxilla (upper jaw)Shape in human is parabolicShape in ape is u-shaped - longer and thinner than human max-illaDiastema - gap between incisors and molars where large canines fitHumans do not have diastema, modern apes doBipedalism - when we walk and push off one foot, we are standing on one leg until we place that foot down and lift the other leg. For most of the time, we are standing on one leg - Human 'striding gait'Foramen magnum - centered, anterior - toward frontLong legsPelvis - short and wideFeet - arched platformBig toe (hallux) - push off of big toe to walk, in lineMore robust, larger joints to bear weight when standing on one