9/15/2014. Rock types. The fossil record. A dynamic planet. Tectonic processes

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1 Rock types The fossil record Chapter 4 Three major rock classifications: Igneous Solidified magma Most common type of rock Sedimentary Sediment that becomes compacted into rock Usually distinctly layered Metamorphic Rocks modified by heat, pressure and chemical agents In which type of rock are most fossils found? A dynamic planet A Layered Sphere Core Interior composed of solid, intensely hot metal Generates magnetic field enveloping the earth Mantle Hot, pliable layer surrounding the core Less dense than core Crust Cool, lightweight, brittle outermost layer Floats on top of mantle Tectonic processes Upper layer of mantle contains convection currents that break overlaying crust into a mosaic of tectonic plates Slide slowly across earth s surface 1

2 Tectonic processes Earthquakes are caused by grinding and jerking as plates slide past each other Mountain ranges pushed up at the margins of colliding plates Geologic time Geologic time Absolute ages are determined by radiometric dating 2

3 Dating a Fossil Radioactive decay A living mollusk takes up trace amount of 14 C and 12 C Mollusk dies; buried in sediments and is fossilized Radioactive decay of 14 C changes ratio of 14 C to 12 C Unearth fossil and measure carbon Geologic time scale Division of time Boundaries determined by geologists and are subject to revision Boundaries based on abrupt transitions in fossil record Correspond to mass extinctions Focus on eras after complex animals appeared Paleozoic Mesozoic Cenozoic Eras are divided into periods, which are divided into epochs 3

4 Fossilization Organism becomes buried in ash or sediments Rapid burial and a lack of oxygen aid in preservation The organic remains become infused with metal and mineral ions Stratification Fossils are found in sedimentary rock, which is formed in layers Deepest rock strata are assumed to be the oldest, surface layers the youngest Fossil record is incomplete Fossils have been found for about 250,000 species (less than 1% of all species) Most species weren t preserved Record is biased toward the most accessible regions and hard-bodied species 4

5 Evolutionary change is gradual within a species Fossils can confirm hypotheses Origins of higher taxa Read about the fossil evidence of origins of higher taxa in your text, including: Amphibia Birds Mammals Cetacea 5

6 Hominin evolution What is a primate? Hands and feet adapted for grasping Relatively large brains and short jaws Forward looking eyes Nails (rather than claws) Opposable thumb in anthropoids only (all but prosimians) Order Primates Suborder Prosimii Suborder Anthropoidea Suborder Prosimii Loris Lemur Prosimians Tarsiers Catarrhini Platyrrhini (new world monkeys) Tarsier Aye-Aye Prosimians Platyrrhini Mostly nocturnal insectivores Large eyes/greater brain capacity than mammals from which they were derived Evolved ~ Mya Howler Squirrel Capuchin Marmoset 6

7 New World Monkeys Split off from Old World monkeys ~ 40 Mya Arrived in New World via rafting or island hopping Diurnal, insectivorous and frugivorous Grasping tails; strictly arboreal Limited color vision (2 types of cones) Catarrhini Old world monkeys + Hominoidea Cercopithecoidea Old World Monkeys Mandrill Langur Macaque Diurnal, frugivorous, folivorous, insectivorous Tails not prehensile Ground dwelling or arboreal Excellent color vision (three types of cones) Colobine Hominoidae Gibbon Orangutan Bonobo Gorilla 7

8 Hominoids No tails Only gibbons and orangs are arboreal Variable feeding preferences (gorillas folivores, orangs vegetarian, rest fairly omnivorous) Split from Old World Monkeys ~ Mya Hominoidae Resolving the tricotomy Morphological evidence Gorilla, Pan share skeletal features, primarily associated with knucklewalking Gorilla Pan Homo Morphological evidence Most parsimonious: humans diverged first (if knuckle-walking is derived trait) Morphological evidence Shared traits between Homo and Pan: skull and tooth traits, delayed sexual maturity, genital traits 8

9 Morphological evidence Gorilla shares skull traits with extinct European ape; suggests skull traits in Homo and Pan are derived Morphological evidence Knuckle-walking either lost in human lineage, or evolved twice (Gorilla and Pan) Involves a spur on a wrist bone that allows it to be supported without bending backwards Knuckle-walking in human ancestors A. anamensis and A. afarensis wrist bone morphologically similar to gorilla, Pan; later fossils (A. africanus) more similar to modern Homo Molecular evidence Different methodologies all suggest that humans and chimps share most recent common ancestor Richmond and Strait. Nature 404:382 Molecular evidence Hominid evolution: fossil evidence Very poor fossil record No record of gorilla, chimp lineages: they lived in moist tropical forests, not conducive to fossil formation Lots of gaps: makes it difficult to know which lineages are ancestral, how many evolving lineages (species) present at once 9

10 Homeland of humanity where do we come from? closest relatives (C,B,G) all from Africa same for oldest hominid fossils specifically east Africa but ancient fossil from Chad, found 2002 contradicts theory of rift valley origins Migration of Homo sapiens Fossil hominids many species many intermediate forms documents trends show mosaic evolution oldest hominids until recently: 4.4 mya finds since 2001: 6+ mya close links with apes A timeline for some hominid species ** Paranthropus = Australopithecus Australopithecus Southern ape Robust form (robustus, boisei, aethiopicus) Big teeth, sagittal crest, may have used tools; did not contribute to ancestry of modern humans Gracile form (afaransis, africanus) 4 feet tall, walked upright, chimp-sized brain 10

11 Australopithecus Homo habilis: similar to gracile Autralopithecus, but had larger brain, tools erectus: larger body, brain, heavy brow ridge, used tools, had fire; some confusion with ergaster Homo neanderthalensis: Largest brains (larger than sapiens), diverse tools, burials sapiens: smaller brow ridge, flat face, high cranial vault Phylogeny of Homo sapiens and relatives 11

12 Hobbits of Indonesia Evolutionary trends Increased body size Retention of generalized limb, 5 digits Increased digit mobility Claws to flat nails Increased bipedalism Changes in skull, e.g. decreased snout length Change in dentition, e.g. decrease canine length Increase brain size Increase vision, binocular vision Decrease in olfaction Brain size and body size Brain size Skull endocasts in Australopithecus 12

13 Increasing Brain size Costs Large brain is energetically expensive: 2% of weight, 18% of energy Mortality risks of trial and error learning Generalization trades off with specialization (e.g. strength, speed) Increasing Brain size Benefits Outsmart predators, prey; tool use Social interaction, parental care, cooperative liaisons All select for intelligence, learning, communication Increasing Brain size Comparison of primates, other mammals Increasing Brain size Change in eating habits correlated with change in brain size in primates Frugivores have larger brains than folivores 13