understanding fossils
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Understanding Fossils.
The present is the key tothe past.
To understand some basic distinctions between fossilgroups
To recognise how fossils can be used as indicators ofpast life.
To recognise how they show evolution within species
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Basic DistinctionsBrachiopods and Bivalves
What·s the difference between the two?
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Indicators of Past
Environments
BIVALVES
BRACHIOPODS
CORALS
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Bivalves UMBOTEETH
PALLIAL LINEMUSCLE SCARS
GROWTHLINES
RIBS
THICK SHELL
EVIDENCE FORMODE OF LIFE?
High energy, intertidal shorelines: Thickshell, large muscle scars, strong teeth andsocket arrangements.
SOCKET
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Pecten (scallop)
This bivalve is nearly symmetrical but the ears are notthe same and the umbo leans slightly to the left.
Strong ribsto live inhigh energywater
Thin, lightshell forfloating
Mode oflife:Pectensfloat/swimbetween
periods onthe seabed
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Burrowing bivalves
UMBO
GROWTH LINES
TEETH AND SOCKETS
MUSCLE SCARS
Bivalves which burrow are likely to be more elongatedthan those which live on the top of the sea-bed. Theymay also have a gape (the valves do not meet at oneend) so that the siphons which enable them to feed
can reach the surface of the sea-bed.
5cm
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BRACHIOPODS
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BRACHIOPODS
Brachiopods differ from bivalves in that they have a sessile modeof life they live attached to the sea-bed by a pedicle, which is a
tough ligament which emerges from the pedicle opening.
PEDICLEOPENING
GROWTHLINES
LINE OFSYMMETRYCUTSTHROUGHTHE VALVES
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Rhynchonella is a very common Jurassicbrachiopod, with heavily ribbed valves.
PEDICLEOPENING
RIBS
UMBO
Rhynchonella has two valves which close together verytightly, suggesting that they lived on intertidal shorelineswhich had high energy breaking waves.
LINE OFSYMMETRY
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Carboniferous brachiopods in black shales
These valves of the brachiopod Productus are not broken up, butthey are separated. That suggests that they have beentransported by gentle waves or currents into the area of muds
without being fragmented.
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CORALSIn this Silurian coral, Halysites, the individual corallites
have been linked together to form a coral colony, whichwould have been firmly attached to the sea-bed.
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Solitary corals livedwith the pointedend stuck into thesea-bed. The coral
animal could reachfood in the sea withits many tentacles.
SEPTA
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CORAL ENVIRONMENTSCoral reef growth is only
possible if these requirementsare met:
Marine conditions
Warm water (over 25oC)
Clear waterShallow water (photic zone)
High energy (breaking waves)
Present coral
reefs
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Coral reefs in the Red Sea
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AMMONITES
BODYCHAMBER
WHORLS
KEEL
Ammonite shells were made of calcite.
Thisspecimenhas veryfew ribsor growth
lines onits shell.
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Ammonite morphology
RIBS
WHORLS
BODYCHAMBER
KEEL
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Ammonite interiorEach chamber isseparated from
the next by acalcite septumsecreted by theanimal as itgrows larger.
These chambers have beenfilled with coarse calcite
crystals when the shell wascovered with sediments.
SEPTA
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Detail of inside whorl
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Morphological Changeswith time
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EVOLUTION in the FOSSIL
RECORD1. Describe the main
evolutionary changesseen in the horse in
the fossil recordfrom the Eocene tothe Pleistocene.
2. Suggest how these
changes may belinked to changes inthe horse·s mode oflife ?
H yracotherium to Equus
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GONIATITES
Goniatites are theancestors of theammonites and werecommon in the
Carboniferous period.
They have simplesuture lines and areusually small with
very few whorls.
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Goniatites have simplesuture lines
LOBESPOINT AWAY FROMTHE BODYCHAMBER
SADDLESPOINT
TOWARDSTHE BODYCHAMBER
BODYCHAMBER
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CERATITESExt inct genus of cephalopods t hat servesas an index fossil formarine rocks and t ime of t he Middle Triassic Period
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AMMONITE
Ammonites areexcellent indexfossils, and it is oftenpossible to link therock layer in which
they are found tospecific geologicaltime periods
This suture type is
characteristic ofJurassic andCretaceousammonoids
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Highly complex suturepattern in ammonites.
Lobes and saddles aredistinctly fluted.
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Evolution of the Septal Suture Line over time
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GRAPTOLITESThe first graptolites were colonies of animals attached to eachother on branches (stipes) and attached to the sea-bed by ahold-fast. They extracted their food from sea-water.
STIPES
HOLD-FAST
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Didymograptusmurchisoni
In the Ordovicianperiod the number ofstipes per colonyreduced to two. Often
the thecae becamemore complex instructure.
THECA
TWOSTIPES
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The evolution of graptolites shows a general
trend towards simplicity.
Throughout the Ordovician and Silurian
periods, there is a progressive reduction in
the number of stipes in successive graptolite
families.
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What·s next for man on the
evolutionary scale?!