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





Basic DistinctionsBrachiopods and Bivalves

What·s the difference between the two?



Indicators of Past

Environments

BIVALVES

BRACHIOPODS

CORALS



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



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



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



BRACHIOPODS



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



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



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.



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.



Solitary corals livedwith the pointedend stuck into thesea-bed. The coral

animal could reachfood in the sea withits many tentacles.

SEPTA



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



Coral reefs in the Red Sea



AMMONITES

BODYCHAMBER

WHORLS

KEEL

Ammonite shells were made of calcite.

Thisspecimenhas veryfew ribsor growth

lines onits shell.



Ammonite morphology

RIBS

WHORLS

BODYCHAMBER

KEEL



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



Detail of inside whorl



Morphological Changeswith time



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



GONIATITES

Goniatites are theancestors of theammonites and werecommon in the

Carboniferous period.

They have simplesuture lines and areusually small with

very few whorls.



Goniatites have simplesuture lines

LOBESPOINT AWAY FROMTHE BODYCHAMBER

SADDLESPOINT

TOWARDSTHE BODYCHAMBER

BODYCHAMBER



CERATITESExt inct genus of cephalopods t hat servesas an index fossil formarine rocks and t ime of t he Middle Triassic Period



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



Highly complex suturepattern in ammonites.

Lobes and saddles aredistinctly fluted.



Evolution of the Septal Suture Line over time



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



Didymograptusmurchisoni

In the Ordovicianperiod the number ofstipes per colonyreduced to two. Often

the thecae becamemore complex instructure.

THECA

TWOSTIPES



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.



What·s next for man on the

evolutionary scale?!



THE ENDTHE END

Jurassic ammonite moulds and casts, Dorset

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Understanding Fossils