Trilobita Praktikum

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    )ection 1: Trilobites

    (ou are proided with two trilobites. " demonstration of other specimens is laid out

    on the side bench. For each of your two specimens you should prepare detailed

    and careful, scaled and annotated drawings. You should also describe the fossil

    in words, using the appropriate technical terms. You should be careful toidentify the view you are drawing, is it front, back, side, and so on. Also you

    should be careful to include values in your description for example, how many

    segments, how long is the thorax. You should use pencil and draw large outlines,

    rather than shading.

    The purpose of these is to enable you to identify the fossil and to note any unusual

    features which may be diagnostic of a particular age or life habit. &areful

    obserations are the key to palaeontology. +nformation is included in the following

    part of the booklet to help you identify and interpret such features. For each of your

    specimens you should attempt to identify the fossil to generic level and comment

    on its mode of life,if you don-t know what generic means$ leae this bit until youhae done section 3.

    Trilobite 1:

    Trilobite 2:

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    &ompound

    eye/ead

    or

    &ephalon

    Thorax

    Pygidium

    0acial suture 1 a natural break

    in the exoskeleton to facilitate

    moulting

    Glabella 1 a raised central area of the head

    under which was the stomach.

    "xial

    lobe

    Pleural lobe

    )egments 1below eachsegment was

    a limb2gill

    pair.

    "

    3.

    Trilobites can be useful for dating rocks. They are entirely Palaeo4oic$ with greatest

    abundance in the &ambrian through &arboniferous. +ndiidual species can offer greater

    precision.

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    0igure 1. The main elements of trilobite morphology. ". Calymene$ an 5rdoician predatory trilobite

    in dorsal iew$ showing the main$ well calcified$ elements of the carapace. )pecimen ! cm long. .

    Two iews of the same animal enrolled$ showing the tight fit that was made between the front of thecephalon and the back of the pygidium. &. Calymeneas it might hae looked from below$ showing

    the lightly calcified or organic skeleton including the hypostome$ legs and gills. #. The three mainadaptie strategies of trilobites away from a highly consered body plan. 6eft$ Trinucleus ,3 cm long)$

    a blind trilobite with large frontal pitted region$ which probably had a sensory function. &entre$Agnostus,2 mm long$ a tiny trilobite with much reduced thorax. 7ight$ Selenopeltis,' cm long$ a

    representatie of the extremely spiny adaptation of trilobites.

    #.

    &.

    /ypostome$

    mouth located atrear. +n

    Calymenethe

    hypostome wasfixed to the front

    of the cephalon.

    6eggill pairs. 5ne pair for each

    segment in the thorax$ probably threeunder the cephalon and seeral

    estigial ones under the pygidium.

    &entral grooe between legs. 0oodwas probably manipulated by the

    legs into this grooe and thenmoed to the mouth. The first leg

    segments are serrated to proidegripping and tearing functions.

    "ntennae

    &ephalon

    Thorax

    Pygidium

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    0igure 3. The life habits of trilobites. These examples should help you to identify the mode of

    life of most common trilobites$ based on diagnostic features of their anatomy.

    Opipeuter,below andPricyclopyge,right$

    two pelagic trilobites. This life habit was

    characterised by large eyes with good all

    round ision$ and a streamlined body form.

    Agnostus$ a tiny &ambrian trilobite with a highly

    deried morphology. This species probably swam

    8ust aboe soft sediment and fed using its body

    caity to entrain water from which the limbs

    remoed food.

    Bergamia$ an 5rdoician blind

    trilobite characteristic of deep

    water$ where it probably fed on

    suspended food particles.

    Olenus$ a &ambrian trilobite that may hae been

    adapted to farming sulphate reducing bacteria in

    low9oxygen conditions$ a lifestyle seen in modern

    organisms liing near deep sea ents and black

    smokers. Cybeloides$ an 5rdoician burrower$ with an

    eleated eye designed to emerge from the sediment

    when the rest of the animal was buried.

    Calymene$ an 5rdoician predatory

    trilobite$ eating a worm. This trilobite had

    a rigid hypostome fixed to the front of the

    cephalon$ and sharp spikes on the limbsegments for tearing prey.

    Ampyx$ an 5rdoician filter

    feeder. ater was drawn

    through the partly enrolled

    body and food remoed with

    the limbs.

    Proetus$ an 5rdoician

    deposit feeder$ at the

    end of its feeding trial.

    Cybeloides$ an

    5rdoician burrower$

    with an eleated eye

    designed to emerge from

    the sediment when the

    rest of the animal was

    buried.

    Calymene$ an 5rdoician predatory

    trilobite$ eating a worm. This trilobite had

    a rigid hypostome fixed to the front of the

    cephalon$ and sharp spikes on the limb

    segments for tearing prey.

    Ampyx$ an 5rdoician filter

    feeder. ater was drawn

    through the partly enrolledbody and food remoed with

    the limbs.

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    )ection 2: Graptolites

    (ou are proided with two graptolites. " demonstration of other specimens is laid out on the

    side bench. For each of your two specimens you should prepare detailed and careful,

    scaled and annotated drawings.

    The purpose of these is to enable you to identify the fossil and to note any unusual featureswhich may be diagnostic of a particular age or life habit. +nformation is included in the

    following part of the booklet to help you identify and interpret such features. For each of

    your specimens you should attempt to identify the fossil to generic level and comment

    on its mode of life,if you don-t know what generic means$ leae this bit until you hae done

    section 3.

    "t the end of this exercise you should be able to identify een broken fragments of graptolite

    and comment meaningfully on them.

    Graptolite 1:

    Graptolite 2

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    )ection 3: Taxonomy

    "ll fossils hae names$ in fact a long series of names. /ere is the set for us:

    Phylum =ertebrata

    &lass >ammalia

    5rder Primates0amily /ominidae

    GenusHomo

    )peciessapiens

    This set of names reeals the fossil-s family tree and should represent a code for the

    eolutionary relationships of the group. "t one end of the scale is the phylum name.

    ?erything within a phylum shares a common ancestor and a common set of general

    characteristics$ such as symmetry elements or growth patterns. ?ach successie name

    represents a smaller subset of organisms that also share a common ancestor with a more

    precise set of related characteristics. The list also gies a sense of time. =ertebrates probably

    eoled in the &ambrian$ while the first mammals are >eso4oic in age and primates eoledin the &eno4oic. (ou hae encountered this idea already in Practical 1.

    &heck that you understand this by examining the family line in the diagram below. +t shows

    a series of branching lines representing eolutionary eents that led to the animals named at

    the top of that line. 5n this diagram draw a set of concentric lines to show what set of these

    animals constitute each of the categories listed aboe. + hae drawn in the last of these as an

    example. ;ote the times$ in millions of years$ at which each group eoled.

    "t the other end of the scale from the phylum$ the genus and species names identify one

    uni*ue member ,the species of a small group of closely related organisms ,the genus.

    These names are what you usually see on a fossil label$ for example$ Monograptus,genus

    priodon,species. )ometimes the name of the person who originally defined this species is

    added to the name$ for example$Monograptus priodon,ronn. Genera should always bewritten in italics or underlined and should begin with a capital letter. )pecies names should

    always be written in italics or underlined and should begin with a lower case letter.

    Make sure that the names of your fossils are correctly written. his seems a small

    point, but it matters.

    '!'

    2'@

    A'

    1@

    1

    >a

    Homo

    sapiens

    Homo

    erectus

    Australop

    ithecu

    s

    robu

    stus

    chimpan4ees

    lemurs

    kangaroos

    frogs

    fish

    sea

    urchins

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    )ection !: iostratigraphy

    iostratigraphy is the use of fossils to date rocks. 5biously$ this is a relatie date ,younger

    than$ or older than$ not an absolute date ,!32 million years. /oweer$ it can be a ery

    precise tool of great geological utility.

    /ere is how it works. )ets of fossils are collected from sedimentary se*uences$ and thesedata are used to construct a set of ranges for indiidual species. These are then put together

    to form a pattern of biodiersity for a period of time. Then any unknown section can be

    compared to this reference and dated accordingly. #ating is done into units of time called

    4ones. These are of unknown length but their se*uence is uni*ue. Bones can be defined on

    the first or last appearance of a useful fossil$ or by a set of fossils$ or een by the times when

    a fossil was most abundant. &learly each of these methods holds potential problems$ and it is

    a picky but useful thing to know about any particular 4one.

    Please take a few minutes to think about this problem . !elow is a block diagram showing

    how using the first appearance of a fossil can cause problems in dating. "an you

    construct similar diagrams exemplifying the problems that may arise for each of theother types of #one$

    6ocalities

    " 3

    ;ew species eoles

    in locality "

    )pecie

    smigrates

    oer

    time

    %one b&dry

    diachronous

    Time

    " 3

    " 3

    Time

    " 3

    %one based on first appearance %one based on last appearance

    %one based on a group of species %one based on species abundance

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    acuminatus

    ataus

    acinaces

    cyphus

    triangulatus

    magnus

    argenteus

    conolutus

    sedgwickii

    %ones 'anges of species

    6ower )ilurian graptolite 4ones and species ranges for the 3ritish +sles

    Glyptograptuspersculptus

    Climacograptusnormalis

    Climacograptusmedius

    iplograptusdiminutus

    iplograptusmodestus

    Climacograptus!esiculosus

    iplograptuslongissimus

    Pristiograptusincommodus

    Glyptograptusincertus

    Coronograptuscirrus

    "agarograptusacinaces

    Ata!ograptusata!us

    #haphidograptustoern$uisti

    Glyptograptussinuatus

    Coronograptusgregarius

    Pristiograptus%ragilis

    Monograptusdi%%ormis

    Orthograptuscyperoides

    Petalograptusconcinnus

    Monograptus%imbriatus

    #astriteslongispinus

    Petalograptusretro!ersus

    iplograptusmagnus

    Orthograptusinsecti%ormis

    Monograptustriangulatus

    Monoclimacislimatulus

    Monograptuslobi%erus

    Monograptussedg&ic'ii

    Cephalograptuscometa

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    /ere is a real problem in mapping complicated$ faulted and lithologically monotonous units

    in southern )cotland$ which can be resoled using graptolite biostratigraphy. + hae

    simplified the problem$ but it is a real one$ fully explained in the G) >emoir CGeology of

    the 7hins of Galloway district-$ edited by P. )tone.

    5n the facing page are the ranges of some 6ower )ilurian graptolites from the %

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    /ere you need to explore the conse*uences of what you hae deduced.

    1. Gie an example of a 4one identification that you were confident about. hat made this

    a good set of fossils for this purposeD

    2. Gie an example of a 4one identification that you were less confident about. hat made

    this set of fossils less useful for dating rocksD

    3. +n general terms$ can you list a set of criteria that make a particular fossil good or

    bad for use in biostratigraphyD

    !. +n this example$ what conclusions can you draw about the fault blocksD "re there likely

    to be any repeated units$ or is each se*uence probably uni*ueD +s there a general pattern

    relating age to position in the fault set$ for example$ east9west or north9south. +f so$ what

    is itD