GL4, E3 The Fossil Record, Key Idea 1 (a), (b), (c),(d)
Interpreting Fossils
Classification
Fossils represent the remains of organisms which lived millions of years ago, but we classify them in the same way as we classify modern animals and plants.
For example:
A human being is classified like this.
Kingdom:Animals
Phylum:Chordates (this means vertebrates basically)
Class:Mammals
Order:Primates
Genus:Homo
Species:Homo sapiens
Fossil organisms are classified using the same structure.
Morphology and modes of life
The form and structure of a fossil organism is called the morphology. At AS you learned about the morphologies of some of the most important groups of fossils.
Exercise 1
For each of the following fossil groups, make a typical sketch showing the main morphological features. Textbook references are only to help you if you get stuck.
Brachiopods (showing pedicle and brachial valves ,the symmetry, pedicle foramen, hinge line, adductor & diductor muscle scars) See page 191 McLeish.
Bivalves (showing valves, symmetry, muscle scars, hinge line, teeth and sockets, umbo, pallial line, sinus, gape). See page197 McLeish.
Ammonites (showing suture lines, shell, chambers, keel) See page 201 McLeish.
Corals (showing septa, colonial and solitary corals) See page 211 McLeish.
Trilobites (showing cephalon, glabella, genal spines, eyes, thorax, segments, pygidium.) See page 213 McLeish.
Plants (showing leaf, stem, root, pollen, seeds) See page 222 McLeish.
Graptolites (showing theca, stipe). See page 194 McLeish.
The morphology of an organism is related to its mode of life and its environment. For example, a giraffe has a long neck so it can browse the tall trees present on the African plains and long legs to escape predators. In the same way we can make informed guesses about the modes of life of extinct organisms based on their morphologies and on similar organisms living today.
Modes of life of brachiopods and bivalves
There are a number of similarities between the morphologies of brachiopods and bivalves.
Exercise 2
Make a list in each box of as many similarities and differences between brachiopods and bivalves. Think about their morphologies.
Similarities / DifferencesExercise 3 - Modes of life of bivalves.
Book references: Webster (yellow book) page 124, McLeish page198. You may also wish to examine specimens of the different fossils.
Show how a gape and a pallial sinus are related to the mode of life of the bivalve Mya.
How is the irregular shape of an oyster (Ostrea) is related to its mode of life?
Mytilus (mussel) lives attached to the seabed. Sketch a diagram showing the means of attachment.
How is the mode of life related to the broad, flat shape of the scallop (Pecten)?
Exercise 4
Book references: Webster page 122, McLeish page 191. Examine available specimens.
One type of brachiopod called Lingula burrows in the sediment. Sketch a diagram to show this. Does it have siphons like the bivalves?
Many brachiopods like Terebratula live attached to the sea bed. Show this in a diagram. How does the size of the pedicle foramen relate to the movement of the sea?
Productus is a brachiopod which remains in one place but is not attached. How does the shape and size of the shell allow it to remain in place?
Modes of life of trilobites
Trilobites are an extinct group of arthropods (like insects, crabs and centipedes). Their closest living relative is the horseshoe crab. We can interpret their modes of life by examining the morphology of trilobite fossils.
Exercise 5
Page references Webster page 120, McLeish page 214. Use any available specimens.
We think that Paradoxides is an example of trilobite which crawled across the seabed and Agnostus is believed to have been a swimmer. Use diagrams to compare their morphologies and explain how they relate to these modes of life.
Sketch a diagram of Trinucleus. How does the morphology relate to the mode of life.
The fossil record
Relatively few organisms that existed in the past have been preserved as fossils, we say that the fossil record is biased and incomplete. A number of factors can either increase or decrease the chance of the organism being preserved in the fossil record.
Exercise 6
For each factor explain whether it makes preservation as a fossil, more or less likely:
Organism has hard parts.
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Predators.
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Scavenging
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Diagenesis.
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Living in an environment of deposition (e.g. sea)
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Living in an environment of erosion. (e.g. mountain top)
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ESTA GEOTREX The Geology Teachers Resource Exchange Contributor: Owain Thomas Establishment: AmmanValleySchool Date: 22:04:05
A2 Geology, Module GL4, Interpreting fossilsPage 1