ANTH250 Midterm

what was the scientific revolution and what started it

• for contemporary evolutionary theory to develop, huge shifts were needed:

  • time

  • geological process

  • diversity and complexity

  • place of humans in the natural world

• Nicolaus Copernicus’ hypothesis of heliocentrism was the main factor leading to the scientific revolution

uniformitarianism

• time aspect of the scientific revolution

• geological forces that produce gradual changes on the earth today, also did in the past

• concept developed by James Hutton

• further associated with Charles Lyell who is accredited with the spread of, and wider use of uniformitarianism as a concept through his treatise Principles of Geology

• required that earth was ancient

mutability

• accepting the possibility of biological change

microevolution

• associated with the ‘mutability’ aspect of scientific revolution

• small-scale evolutionary events occuring within a population over the span of a few generations, affecting the frequency of specific characteristics not involving species formation

• associated with Le Comte de Buffon

  • organisms are capable of being transformed as their environmental circumstances change (species not mutable though)

Species Evolution

• Associated with ‘mutability’ aspect of scientific revolution

• associated with Jean-Baptiste Lamarck

  • organisms and their environments interact dynamically to produce ever-increasing complexity of perfection

George Cuvier

• associated with ‘time’ aspect of scientific revolutionary development

• contributed to development of the comparative method

  • understanding relationships between organisms by comparing their similarities and differences

• Principles of correlation of parts

• established the fact of EXTINCTION

• systematic study of fossils

Principle of correlation of parts

• organisms are functionally integrated wholes

• barrier to accepting the possibility of evolutionary development

law of superposition

• layers (“strata” ; singular “stratum”) within a sedimentary geological deposit are laid down from oldest to most recent, permitting assignment of relative dates to items contains in the deposit

scientific method

Theory: explanatory statement or arguments to a particular set of phenomena supported by observation

hypothesis: a testable prediction about a phenomena or even, based on current knowledge

Jean Baptiste Lamarck

• gave first modern theory of species evolution

• became prof of zoology at Royal Botanical Garden in Paris

• coined term invertebrate

• published monograph Philosophie zoologique → 1809

• Lamarck’s two laws

  • Law of Use and Disuse

  • Law of Inheritance of Acquired Characteristics

Law of Inheritance of Acquired Characteristics

• adjustment of organisms to environments of culmination

  1. as environments change, the needs of animals change to maintain harmony with new circumstances

  2. new needs are stratified by changes in an organism’s behaviour and habits (called efforts by Lamarck)

  3. these behavioural changes physiologically alter-develop, enlarge, or reduce as necessary - some aspect of the organisms structure

• changes resulting from use and disuse will, if occurring in both parents, be transmitted to offspring

Law of Use and Disuse

• organisms do not proceed uniformly toward a state of perfection but must constantly adjust to changes in their circumstances

• use or disuse of parts, reflecting an organism’s needs and circumstances will cause that part to develop or reduce

darwins ideas

• evolution will occur when the following conditions are met

  1. Variation

     • naturally occurring

  2. Reproduction > Resources

     • potential to reproduce > rate that resources increase

  3. Competition for Resources

     • struggle for limited resources → mortality

  4. Differential Fitness

     • traits better suited for survival are passed on

Darwins Four Elements of Natural Selection

1. all populations vary, individualy by individual; often noticeably in terms of size and shape, but also in smaller and more subtle, yet not less important, ways. such as shades of colour or expression of behaviour

2. all populations have the potential to reproduce at a rate in excess of the rate at which necessary resources (food, space, mates, etc) increase

3. competition for limited resources occurs not jut between members of different species, but, more importantly, among, individuals within a species

4. at any given moment and in any given circumstance, heritable characteristics possessed by individ

DNA

Function: Protein Synthesis

• deoxyribonucleic acid

• double helix structure

• macromolecule

  • consisting of smaller molecules called nucleotides which are composed of a sugar, phosphate, and 1 or 4 nucleic bases

    1. Adenine (A)

    2. Guanine (G)

    3. Cytosine (C)

    4. Thymine (T)

Nucleotide

The basic structural unites of DNA or RNA molecules, consisting of a phosphate, sugar, and base

Codon

• a unit of three bases/nucleotides that code for a specific protein

transcription

• transfer of genetic information carried by DNA (cant leave the nucleus) to mRNA (can leave the nucleus)

• first stage of protein synthesis

• Process:

  • two strands of DNA molecule partially separate

  • free nucleotides arrive and join together with corresponding bases on the separated strands to form messenger RNA (mRNA)

  • mRNA leaves nucleus as single stranded molecule

translation

• Synthesis of a chain of amino acids based on a message carried in RNA

• second process in first stage in protein synthesis

• process:

  • once mRNA leaves the nucleus as a single stranded molecule, it travels into the cytoplasm

  • its message is then translated with the assistance of the ribosome, to which the messenger RNA attaches.

  • Codons on the mRNA facilitate this process that specify particular amino acids.

gene

• a section of DNA made up of the specific section of bases that codes for a specific protein

  • each gene occupies a specific place on a specific chromosome = its locus

• if a gene is a word in a recipe, there can be synonyms for that word

  • eg. gene for blood type = A, B, O

• different versions of a particular gene are called alleles

  • still contain the instrcutions to make that protein, but with slight variations (eg. which antigen is going to be expressed in your red blood cells

alleles

• alternative forms of a gene

blood type

• gene’s locus is on Chromosome 9, spot will have 1 of 3 possible alleles (A, B, O)

  • blood type depends on which 2 alleles of this gene you ultimately get (1 from mum 1 from dad)

• Sometimes only one of these alleles are expressed

  • an alleles is either dominant or recessive

  • a recessive allele will not be expressed if paired with dominant allele

• A and B alleles are dominant

• O allele is recessive

• Homozygous = 2 of the same alleles

• Heterozygous = 2 different alleles

Why does varation matter?

• Natural selection acts on variation in traits

  • variation in traits that can be inherited

  • more offspring produced than resources can support

  • differential survival and reproduction

  • change in allele frequencies over time (evolution)

Gregor Mendel

• trained in physics

• spent 8 years practicing botany where he spent his time conducting hybridization experiements on plants

• chose garden pea plant (pisum sativum)

  • noted that it exhibited traits that were either present or absent - referred to today as discrete or mendelian traits (traits that are controlled by genes at a single locus)

  • self-pollinating plants gave Mendel control over which plants could become parents of the next generation (self-fertilized versus cross-fertilized)carries out breeding cycles to create pure-breeding plants (ones that produce offspring with the same physical characteristics each successive generation)

  • observed the phenotypes (Tall and yellow factors were consistenly observed while short and green factors were hidden)

  • concluded that every plant carries two factors for each trait (one from each parent)

    • reffered to as alleles

    • allele expressed is dominant while one that is hidden is recessive

Mendelian Inheritance

1. traits are transmitted by genes that occur in pairs (alleles)

2. alleles are randomly separated during the production of sex cells, so that each sex cell has only one allele from each parent

Principle of Independent Assortment

• the distribution of one pair of alleles into the sex cells does not influence the distribution of another pair of alleles

• one of two principles put forth by Mendel as a result of his pea plant experiments

Principle of Segregation

• the separation of alleles during the productions of sex cells so that each sex cell contains only one allele from each parent

• one of two principles put forth by Mendel as a result of his pea plant experiments

taxonomy

• associated with ‘diversity’ aspect of scientific revolution

• the method by which organisms are classified and assigned to a group (taxon/taxa) based on shared biological, ecological, and behavioural relationships

• associated with Carolus Linnaeus’ publication of Systema Naturae

  • binomial nomenclature → organisms labels according to genus and species (eg. H. sapien

mitosis

• division of somatic cells

• process:

  1. replication of the 46 chromosomes found in each cell - resulting in 46 double-stranded chromosomes

  2. duplicate pairs line up at the centre of the cell and then diverge so that the strands are separated

  3. the individual strands move towards opposite ends of the cell, the cell membrane constricts in the middle, and two new cells are formed, each containing 46 single-stranded chromosomes

  4. result is two identical diploid cells

meiosis

• cell division resulting in the formation of sex cells (gametes)

• involves two cell divisions and production of 4 haploid daughter cells, each containing only 23 chromosomes

• process:

  1. first stage occurs within ovarian cells (oogonia) and testicular cells (spermatogonia) → 46 single-stranded chromosomes replicate to produce 46 double-stranded chromosomes. these cells arrange themselves and line up at the centre of the cell. the pairs separate, members of each pair move to opposite ends of the cell, and the cell divides to produce two diploid daughter cells, each containing 23 double-stranded chromosomes

  2. each of the daughter cells divides and the paired chromosomes separate, resulting in 4 haploid cells

• Increases genetic variation through recombination

How does meiosis differ from mitosis

• The first two stages are the same however, there are some important differences in the female side of things

  • initial division in female ovary produces two primary oocytes but, unlike male spermatocytes, they are not created equal

  • one oocyte sequesters most of the cytoplasm

  • does not divide equally; through process of unequal cytoplasmic cleavage, one of the haploid cells (ovum) receives the majority of the cytoplasm

  • while all 4 of the resulting sperm cells are viable, only the ovum is in females

  • the other female daughter cells, (polar bodies) are reabsorbed

recombination

• crossing over

• the exchange of genes between homologous chromosomes during meiosis

• meiosis increases variation through process of recombination

• occurs when genetic material is exchanged between homologous chromosomes during cell division

• result of this nondisjunction is fewer or more chromosomes than normal

  • cell revieving extra chromosome referred to as trisomic

• Best known example of trisomy is Down Syndrome

  • results from nondisjunction of the ovarian 21st chromosome

  • at fertilization, child was three rather than 2 normal copies of chromosome 21

nondisjunction

• the failure of chromosome pairs to separate properly during meiosis

mechanisms of variation

• evolutionary forces that work on changing the frequencies of alleles in a population

  • natural selection → adaptive mechanism

  • neutral → important forces (most frequency changes seen are neutral)

  • environment during development

generation of variation

• mutations → only source of NEW alleles

redistribution of variation

• increasing or decreasing the relative frequencies of alleles in a population

types of mutations

• point mutations

  • changes in base pairs of gene sequences

• deletions

  • mutations characterized by the loss of DNA

• insertions

  • mutations characterized by the addition of DNA into a length of chromosome

• inversions

  • mutations in which a section of DNA is reversed

single nucleotide polymorphisms

• genetic variations that are produced by the substitution of a single nucleotide in a squence. SNPs are point mutations that occur in at least 1% of the population

anagenesis

• a pattern of slow, linear evolutionary change, also know as Darwinian gradualism

• species 1 goes extinct when it becomes species 2 etc.

cladogenesis

• a pattern of evolution characterized by branching, in which a single species may give rise to one (or more) “daughter” species that subsequently diverge; also known as horizontal speciation

• species 1 branches off into 2 or more separate species

adaptive radiation

• the opportunistic and relatively rapid diversification of new forms into new ecological zone through a series of speciation events

• one species diverges rapidly into multiple empty niches

cladogram

• diagram showing evolutionary relationships determined by shared traits, inherited from a common ancestor

• fewer differences between species 3 and 4 than between species 2 and 4

homologous traits

• referring to homology, which is similarity among characters as a result of inheritance from a common ancestor

homoplasies

• analogous characters in different taxa that appear as a result of independent evolution; such a character (singular form is “homoplasy”) is not present in the last common ancestor of the taxa in question

• individuals evolved similar traits completely independently of each other, because they are the best solution to a shared problem

convergent evolution

• a path towards development of homoplasy; evolution acts on different ancestral structures to converge upon a similar outcome in response to similar adaptive pressures

• form of directional selection as adaptive response

directional selection

• a form of positive of negative selection resulting in a shift toward one end of the distribution, typically occurring in dynamic and changing environments

• eg. light-coloured peppered moths are better camouflaged against a pristine environment; dark-coloured peppered moths are better camouflaged against a sooty environment → industrial revolution caused moth population to shift from a light to dark colour

stabilizing selection

• A form of selection favouring the most common phenotype at the expense of extreme expressions of a character

• eg. robins typically lay 4 eggs, and example of stabilizing selection → larger clutches may result in malnourished chicks, while smaller clutches may result in no viable offspring

diversifying selection

• a form of positive selection favouring the extremes of distribution of phenotypes and/or negative selection against the most common expression; may result in sympatric speciation

• eg. in a hypothetical population, grey and Himalayan (grey and white) rabbits are better able to blend in with a rocky environment than white rabbits, resulting in diversifying selection

natural selection

• the non-random preservation or elimination of variants through competition within and between species, promoting differential reproductive fitness

reproductive fitness

• organism best adapted to current circumstances will most likely survive and reproduce successfully, passing on successful trails

phenotype

• observable physical characteristics

genotype

• the genetic makeup of an organism

plasticity

• one genotype can produce different phenotypes depending on environmental conditions

epigenome (epigenetics)

• a particular set of chemical modifications to our DNA that affect whether a or not a gene can be expressed

  • gene cannot be expressed if the DNA instructions are not readable (it is ‘turned off’)

• what factors can affect whether or not a gene is ‘on’ or ‘off’

  • daylight

  • infection

  • toxins

  • temperature

  • diet

  • stress

  • the behaviour and diet of your mother

gene flow

• the movement of genes with our without the movement of individuals over geographic space

• add new alleles to populations or changes the frequencies of alleles already there

• important in maintaining similarities and generating differences

  • increases genetic variation WIITHIN the new population

  • decreases genetic variation BETWEEN the two populations

genetic drift

• random changes in allele frequencies in small populations, independent of selection

  • no specific environmental cause

  • may be beneficial, neutral, or detrimental

• longterm consequence of genetic drift

  • reduced genetic variation WITHIN populations but increased variation BETWEEN populations

• a NEUTRAL mechanism

  • can lead to diversity and change without any selection having occurred

bottleneck effect

• sudden constriction in the transfer of genetic diversity from one generation to the next

• bottlenecking events:

  • natural disasters

  • disease outbreaks

  • humans!

• Cheetah bottleneck

  • ~8000 cheetahs left in the world genetically differ by only 0.1-4% (essentially identical twins?)

  • causes- last ice age (10,000ya)

  • current poaching and habitat loss

  • consequences - lack of genetic variation and inbreeding

    • low fertility

    • problems with sperm cells

    • high cub mortality

    • high sensitivity to disease

• It takes time to accumulate mutations *new alleles

founders effect

• loss of genetic variation occurring when a new population is established by a small number of individuals from a larger population

What do we (humans and other primates) have in common

• most have adaptations to arboreal lifestyle

• broad dietary plasticity

• parental investment

Primate Locomotion

• flexible locomotion - generalized skeletal structure means flexibility in movement

  • variability in how species move around

    • vertical clinging and leaping

    • brachiation

    • terrestrial and arboreal quadruped

    • biped

• all non-human primates are quadrupedal

• very flexible shoulders and collarbones

• grasping hands w/ opposable thumbs (usually grasping feet too)

• fingernails and grippy finger pads (good sense of touch)

• some monkeys have prehensile tail

Primate Sensory

• reliance on vision

  • in complex 3D world vision is imperative → particularly DEPTH PERCEPTION

  • large brains with large visual processing areas to process lots of information

• forward facing eyes → overlapping fields of view → stereoscopic vision

• eyes partly or completely enclosed by protective bony orbit → postorbital bar in prosimians and postorbital plate in monkeys, apes, humans

• decreased reliance on smell - reduction of the snout and olfactory areas of brain

  • larger neocortex

Primate Dietary Flexibility and Generalized dentition

• primates generally omnivores (fruits, leaves, insects, small mammals)

• two types of primate dentition → heterodont and diphyodont

• dental formula → number of each type of tooth in each quadrant of the jaw

  • eg. 2.1.2.3 (like humans) means that in each quadrant of the jaw there are 2 incisors, 1 canine, 2 premolars, and 3 molars (total 32)

diphyodant

• four kinds of teeth

heterodont

• two SETS of teeth

  • deciduous (baby) and adult

Primate Life History and Reproduction

• have fewer offspring than other mammals

  • longer gestation periods

  • lower reproductive rate

  • k-selection strategy

    • have fewer offspring but invest more parental care

• invest heavily in each one

  • high parental care and long period of infant dependency, increasing the likelihood of survival

  • longer period of infant dependency

• long growth period and long lifespans

  • lots of time to learn essential survival and social skills

primate classifications

• typically divided into 2 suborders

  • Stresirhini → lemurs, lorises

  • Haplorhini → tarsier, monkeys, apes, humans

• Chimps and Humans classified within subfamily Homininae

strepsirrhine

• wet nose (naked moist rhinarium)

• small

• often nocturnal

• well developed sense of smell

• tooth comb

• grooming claw

infraorder Lemuriformes (suborder Strepsirrhini)

• encompasses 5 families

• possibly as many as 100 species of lemurs as well as indris, sifakas and aye-ayes

• all species located ONLY in Madagascar

• very diverse group

  • some are nocturnal, some are diurnal

  • quadrupedal or vertical clinging and leaping

  • primarily arboreal, some are more terrestrial

  • live in social structures ranging from solitary to large groups

infraorder Lorisiformes (suborder Strepsirrhines)

• comprises 2 families

• includes 11 species of lorises and 20 species of galagos or bushbabies

• Found in Africa and SE Asia

• nocturnal and solitary

• diet of insects, fruit, eggs, snails, lizards

• quadrupedal, but bushbabies are amazing leapers

haplorrhine

• dry nose

• large

• diurnal

• large brains

• vision

• fingernails

infraorder Platyrrhine (suborder Haplorhini)

• comprise over 70 species

• divided into 5 families

  • Cebidae, Atelidae, Callitrichidae, Pitheciidae, Aotidae

• found only in Central and South America

• ‘New World’ monkeys (platyrrhines preferred)

• broad flat noses with outward-facing nostrils

• tropical and sub-tropical forests

• all diurnal (except for owl monkey)

• small body size and prehensile tail

• mainly arboreal

infraorder Tarsiformes (suborder Haplorhini)

• found only in SE Asia

• nocturnal and solitary

• grooming claw but no tooth comb

• vertical cling and leaping (4m vertical!)

• reliance on vision (no rhinarium) - large, unmoving eyes → can rotate head 180 degrees

• eats insects, frogs, lizards

infraorder Catarrhine (suborder Haplorhini)

• most widely distributed of all primates

  • narrow noses with downward-facing nostrils

  • variable sizes with a range of sexual dimorphism

• Cercopithecoids: ‘Old World’ (true monkeys preferred)

  • macaques, baboons, mandrils

  • colobus and proboscis monkeys

  • langurs

• Hominoids: apes and humans

  • gibbons and siamangs

  • orangutang, chimpanzees, gorillas

  • humans

superfamily Cercopithecoidea (infraorder Catarrhini)

• Catarrhine (true) monkeys

• found only in tropical and subtropical forests of Africa and Asia, as well as savannah and grasslands of Africa

• ischial callosities (patches of hardened skin on read end that facilitate sitting)

• more variable size and sexual dimorphisms than platyrrhines

• species include

  • sulawesi macaque

  • proboscis monkey

  • gelada baboon

  • Gee’s golden langur

superfamily Hominoidea (infraorder Catarrhini)

• Hominoids are

  • diurnal

  • no tails

  • more complex behaviour, larger brains and advanced cognitive abilities

  • longest periods of infant development and dependency

Hominoidea- Gibbons and Siamangs

• Gibbons and Siamangs

  • only found in the tropical rainforests of SE Asia

  • brachiators (4 genera, 18 sp)

Hominoidea- Great Apes

• Great Apes

  • Orangutan

    • arboreal, solitary dispersed, frugivorous

  • Gorillas

    • mainly terrestrial, highly frolivorous, social

  • Chimpanzees & Bonobos

    • arboreal and terrestrial, omnivorous, very social

Hominoidea- Humans

• unique amongst primates → obligate bipeds

  • unique skeletal adaptations to enable this efficiency

• very long gestation

• prolongued period of infant dependence

• very long lifespan

  • reprodcutive adaptations enable learning and flexibility

primate social lives

• primates are social animals

• vary substantially in group size, structure, and organization

• Primate group size, social structure and organization, and individual behaviour are shaped by the ecological conditions

benefits of primate social group life

• maximal food exploitation

• access to mating partners → increases reproductive fitness

• protection from predators

• help with offspring care

• opportunities for learning

downfalls of primate social group life

• competition over food

• competition over mates

• increased stress

• spread of disease

primate social organization

• size and type of group influenced by various factors

  • predation pressure

  • availability and distrib. of food

• arrangement of individuals in a social group can vary → # of males relative to females

• multi-male / multi-female (many : many)

  • typically found where predation pressure is high → large group #’s

  • promiscuous mating activity

  • marked sexual dimorphism

• Polygamy (one : many)

  • Polygyny

    • 1 male : many females

  • Polyandry

    • 1 female : many males

• monogamy (one : one)

dominance hierarchies

• social structures in which males or females hold positions of rank determined either through competition or inheritance

• more pronounced in single-male/multi-female and multi-male/multi-female groups

  • males must compete with each other for females

    • grounded in sexual selection

• provide social stability and reduce conflict

• top ranked individuals → alpha

how do food availability and food abundance impact primate group size

• Food abundance

  • more abundant resources can support larger groups of animals

    • eg. leaves/grass vs insects

• Food distribution

  • abundant but clustered; most efficiently exploited by small groups (or subunits of larger groups)

• Food seasonality

  • if groups need to move around a territory throughout the year, it is easier for smaller groups to do so

predation pressure

• larger group sizes are an advantage if predation pressure is high

  • eg. you live on the African savannah

  • optimum group size for Kenyan yellow baboons: 50-70

agonistic behaviours in primates

disrupt group cohesion

• occur between members of the same sex or opposite sex, related or unrelated, between different ranks

• examples:

  • aggression

  • threats (facial expressions + gesture like teeth baring)

  • displays

• common in many primate communities

  • males competing for access to females (eg. polygyny)

• frequency of agonistic acts depends on # of factors:

  • availability of food resources

  • mating partners

  • space

• male conflicts → tend to be brief

• female conflicts → tend to be prolonged

affiliative behaviours in primates

promote group cohesion

• grooming

  • one of the most common affiliative behaviour (altruistic behvaiour)

  • reduces stress, builds social bonds, removes ectoparasites, etc…

  • larger groups tend to spend more time grooming

• social alliances / cooporation

  • evolved through kin selection

  • tendency of primates to direct beneficial behaviours to relatives

  • often formed to get access to food resources and mating partners

• reconciliation

  • approaching victim of aggression

    • touching, kissing, embracing, grooming one’s opponent → vocalizations

primate sexual dimorphism

• differences in physical characteristics between males and females of the same species

primate sexual behaviour (how do females signal that they’re ready to mate?)

• most primates only sexually receptive around ovulation

• behvaiours that signal receptivity → proceptive behvaiours

  • presenting hindquarters to males

  • sexual swelling (swelling and pink colouration of genitals)

  • olfactory cues → secretion of aliphatic acids (essentially pheromones)

  • changes in facial skin colour

  • specific vocal cues

reproductive cycle variability in primates

• considerable variation

  • in length and constituent phases

• ex.

  • ~15 days in common marmoset

  • ~ 30 days in humans

  • 50+ days in mouse lemurs

Primate sexual strategies - Female

• incite males to compete through agonistic encounter

• may choose male that demonstrates affiliative behaviours (rearing assistance?)

• may mate with multiple males → more help from males that think offspring in theirs

• compete w/ other females for food resources

• synchronize ovulation w/ other females

• females of some primate species do not advertise ovulation

  • conceal fertility from males

    • confuse paternity to reduce risk of infanticide

    • prevent dominant male monopolization of mating

Primate Sexual Strategies - Male

• limiting factor of success → access to receptive females

• aggressive competition

• sperm competition

• infanticide

Inter-birth interval and male primate behaviour

• virtually no male assitance with child-rearing

  • 8 years → orangutans

• lots of male assitance with child rearing:

  • 4.5 years → gorilla

• Cooporative breeders

  • 3.7 years → humans (and marmosets!)

primate tool use

• earliest documentation of tool use among primates in Western scientific discourse:

  • 1960s, Jane Goodall - termite dipping in chimps

• tool use has been documented in wild orangutans, bonobos, and to come degree gorillas as well

• other examples:

  • chimps using composite tools (hammer stones and anvils) to open nuts

  • sticks to dig for tubers, roots, and bulbs

  • spear use (made of twigs) t capture prosimians (bushbabies)

  • sponges (made of leaves) used to soak up water

primate culture

• transmission of tool use and other novel behaviours among chimps → from one community to another

  • spread of ant-fishing

• transmission of cultural behaviours appears to occur primarily through females, who leave their group after reaching se

what are fossils?

• any remains of life preserved in rock

  • bones, teeth, impressions, footprints, natural molds, termite nests, worm burrows, etc

• very rare

  • of all life that has ever existed, only an extremely small % of it is in the fossil record

  • due to their rarity, there are many gaps in our record of life in the past

how are fossils formed

• when animals, plants, and other organisms die, they typically decay completely

• process of fossilization

  • groundwater carrying minerals such as iron and calcium carbonate from the surrounding sediments infiltrates the microscopic cavities in bones and deposits the minerals into them, turning the bones into stone

what has to happen in order to find fossils?

• right conditions for preservation

  • slow decomposition: limit access of bacteria/fungi

• right conditions to be found

  • exposed at surface somehow

• organism might get buried very quickly

  • eg. seabed, or stuck in sap

• a body can get buried in an environment inhospitable to bateria/fungi

  • eg. tar pit

good fossil sites

• places where geological activity has exposed buried fossils

• cave sites can accumulate high fossil concentrations

bad fossil sites

• moist, high rate of decomp., many bateria/fungi/insects, very difficult to excavate

  • eg. tropical forest