Trilobita Praktikum
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Transcript of 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