Geology 1023 Lab #6, Winter Introduction to fossils and fossilisation

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1 Name: Answers Geology 1023 Lab #6, Winter 2014 Introduction to fossils and fossilisation What is a fossil? A fossil is any evidence of ancient life preserved in sediments or rocks. Why are fossils important? Fossils are important for several different reasons: Reg. lab day: Tu W Th 1. They are used to trace the evolution of life from its beginnings to the present time. 2. They are used to determine the (relative) age of sedimentary rocks. 3. They are used to correlate sedimentary rocks. 4. They indicate environment of deposition of the rocks in which they occur. 5. They can be the main constituent of rock (limestones). Kinds of fossils There are trace and body fossils. A trace fossil is evidence of life activity such as tracks, trails, burrows, borings, coprolites, gastroliths, etc. A body fossil tells us something of the shape (morphology) of the organism itself (usually shows only a part of the organism). A body fossil may be preserved unchanged, or replaced to varying degrees, or as a mold or cast. A mold is an impression of a body part (reversed symmetry to original organism). A cast is formed when a mold is filled by new material (same symmetry as original). Organic tissue ( soft parts ) is rarely preserved because of microbial decay, predation, scavengers, and oxidation. Most body fossils are hard parts altered shells, teeth, bones, scales, etc. Fossilisation The likelihood of fossilisation is increased by: 1. Presence of hard parts. Likelihood increased if the organism moults its skeleton. 2. Abundance of individuals (influencing factors: size, geographic and temporal range). 3. Rapid burial following death (i.e., burial protects the organism). 4. Life (and death) in a depositional environment. The above criteria mean that small, shelly, marine invertebrates have a much greater likelihood of fossilisation than do terrestrial or airborne organisms. Also, life originated in the oceans and only recently (in geological terms) moved onto the land and into the air, which also biases the fossil record towards marine organisms.

2 Introduction to fossils & fossilization Winter 2014 Page 2 of 7 Types of preservation Organisms are preserved in a variety of ways. Mode of preservation Example 1 Unaltered (almost) remains a) soft parts mammoths frozen in tundra, mummification, pickled or bog people, organisms in tar pits b) hard parts shells, bones, teeth, scales 2 Carbonisation distillation from organic tissues, most commonly in plant material 3 Replacement substitution of organic material (soft tissue and hard parts) by inorganic chemicals not normally part of the organism 4 Permineralisation precipitation within pores and cavities 5 Recrystallisation crystal growth without change in composition 6 Solution inorganic dissolution of material leaving a cavity with the shape of the fossil (mold) 7 Casting mold fills with material to form a replica of the original organism (or part of organism) coal, black leaf impressions in shales, graptolites, graphitic worm in shale. silicification (now SiO 2 ) pyritisation (now FeS 2 ) solid corals petrified wood difficult to determine, particularly in hand sample, probably less common than was once thought shell molds are most common shell casts log casts trace fossil casts 8 Trace fossils tracks, trails, footprints, borings, etc. Naming and classifying fossils (taxonomy) All organisms (living and fossil) are classified using the Linnean hierarchical system shown below. Four examples are given to show evolutionary relatedness. You can see that humans are more closely related to chimps than they are to wolves than they are to dinosaurs. Example 1 Example 2 Example 3 Example 4 Kingdom Animalia Animalia Animalia Animalia Phylum Chordata Chordata Chordata Chordata Class Reptilia Mammalia Mammalia Mammalia Order Saurischia Carnivora Primates Primates Family Tyrannosauridae Canidae Pongidae Hominidae Genus Tyrannosaurus Canis Pan Homo Species Tyrannosaurus Canis lupus Pan troglodytes Homo sapiens rex troglodytes sapiens Common name T. rex Wolf Chimpanzee Human

3 Introduction to fossils & fossilization Winter 2014 Page 3 of 7 Note that when giving the specific (i.e., species) name of an organism, the generic name is often abbreviated to its initial letter, e.g., T. rex or H. sapiens sapiens. Paleoecology The paleoecology of a set of fossils is the environment in which the organisms lived as well as their relationships to each other. We can interpret some of this from the lithology (e.g., shale implies relatively quiet conditions). We can determine the ecology by understanding the morphology (shape) of the organisms, by the species associations, and by comparing fossil forms with living organisms. Fossils can help determine such features as the nature of the substrate, the clarity, turbulence, salinity, and temperature of the water as well as sedimentation rate. E.g., fossil corals (like modern ones) preferred clear, shallow, warm, water of normal salinity. Organisms that live in the water column are pelagic and are either planktic (float/drift) or nektic (actively swim). Bottom dwellers are benthic. Benthic organisms that are attached to their substrate (encrusted, cemented, rooted) or that bore into it are sessile. If they just recline on the substrate they are sedentary. If they crawl on or burrow actively into the substrate they are mobile. Epifauna live on the seafloor, infauna live beneath it. Most of the fossil record consists of benthic marine invertebrate organisms that filtered food particles from the water (filter, or suspension feeders) or ingested sediment and extracted the food from it (detritus feeders). Biostratigraphy Individual species tend to evolve and die out in geologically short time spans (a few millions of years at most). And once they ve died out they NEVER came back. So fossils tell us age (at least in relative terms) of the rocks that enclose them. An index fossil is one that has a wide geographic distribution and a short time range. Good index fossils are those that are readily identifiable (even by non-experts) and abundant. Most fossils, however, have a relatively wide age-range and time zones are usually established using the overlapping time ranges of two or more species. 1. Look at the taxonomic (naming classification) table above. a) Are both the generic and specific names of an organism capitalised? Y N b) Are both the generic and specific names underlined? Y N c) Tyrannosaurus is to genus as Tyrannosaurus rex is to species d) Tyrannosaurus is to genus as saurischia is to order.

4 Introduction to fossils & fossilization Winter 2014 Page 4 of 7 2. Circle all the correct choice(s). a) Each order contains one or more: classes families genera kingdoms orders phyla species b) Each phylum contains one or more: classes families genera kingdoms orders phyla species c) A particular genus will belong to a particular: class family genus kingdom order phylum species d) A particular phylum will belong to a particular: class family genus kingdom order phylum species 3. Rank the following organisms by numbering them 1 to 4 in order of increasing likelihood of preservation in the fossil record (# 1 is least, #4 is most likely). a) jellyfish 1/2 fish 3 clam 4* human 2/1 b) fox 3/2 moth 1/2 spider 2/3 coral 4* c) plankton 4* mammoth 3/2 T. Rex 2/3 eagle 1 4. Rank the following environments (locations) in order of increasing likelihood of preserving fossils. a) alluvial fan 1* reef 3/2 beach 2/3 lagoon 4 A wide range of fossils is on display at the back of the lab (collection #1). Examine them before and during the following exercises to help you answer the questions. 5. Determine the type of preservation in collection #2 (specimens ) by comparing with the samples in collection #1. Note that two sets of collection #2 are provided. #227 unaltered #228 #229 carbonized #230 #231 replacement #232 #233 molds #234 #235 trace unaltered replacement permineralized unaltered cast

5 Introduction to fossils & fossilization Winter 2014 Page 5 of 7 6. Collection #3 (specimens ) is a set of fossils from the Horton Bluff Formation (HBF), collection #4 (specimens ) is from the Windsor Group (WG). a) What is the likely environment of deposition of each (marine/non-marine)? HBF non-marine WG marine b) Why? HBF Land plant fossils WG Marine fossils (shells) The following exercise uses a modern analogy to help you think about fossil assemblages. Fossil assemblages in a rock can be thought of as photographs. If you know enough about the things in the photo you can tell when it was taken. Similarly if you know enough about the various fossil species in a rock you can tell how old the rock is. 7. The diagram below show a photograph taken of a particular location. Here are some facts. 1. Tree A (of unknown age) was cut down in Person B is a member of a family that lived in the area between 1987 and Building C was built in 1991 (and is still standing). Fill in the following chart by putting x in each year possible for each item. Pre Post 99 A B C X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X

6 Introduction to fossils & fossilization Winter 2014 Page 6 of 7 a) In what time period was the photo taken? b) What item or items bracket the possible time best? A and C (tree, house) Note there is a period of several years when the photo could have been taken. That does not mean that the photo took that length of time to take. This is an important point of comparison with rocks. A Devonian (for example) fossil age for a rock does not mean that the rock took the entire Devonian to be deposited. The photo represents an instant within its potential range and the rock represents a geological instant sometime within its potential depositional time. Now let s try some fossils. 8. Examine the fossils (from the fossil set in the drawers) listed in the table below. a) Using the identification sheets, identify each genus and enter it in the following table. Genus Camb. Ord Sil. Dev. Miss. Penn. Perm. Trias. Juras. Cret. Tert. Quat. F2 F10 F19 Mucrospirifer Favosites Bellerophon X X X X X X X X X X X b) Using the identification sheets enter the age range of each genus in the above table by marking an X in the appropriate boxes. c) Is there an excellent index fossil in this assemblage? d) Which genus cannot be used as an index fossil? yes Bellerophon or Favosites e) Why? Too long time range f) Assuming that these specimens came from a single rock unit (Layer A), what genus or genera constrain the age of that rock unit best? F2, Mucrospirifer g) What would be the age of that rock layer A? h) Is this a marine or non-marine assemblage? Devonian marine

7 Introduction to fossils & fossilization Winter 2014 Page 7 of 7 9. Examine the fossils (from the fossil set in the drawers) listed in the table below. a) Use the identification sheets to identify each genus and enter the genus name and age range in the table. Genus Camb. Ord Sil. Dev. Miss. Penn. Perm. Trias. Juras. Cret. Tert. Quat. F1 F3 F7 F14 F21 Athyris Chonetes Archimedes Pentremites Girtyocoelia X X X X X X X X X X X X X X X X X b) Assuming that these specimens came from a single rock unit (Layer C ), what genus or genera constrain the age of layer C best? F21, Girtyocoelia and F14, Pentremites c) What is the age of this assemblage? d) Is this a marine or non-marine assemblage? Pennsylvanian marine 10. Given the fossil age of Layer A (from Q. 8, above) and the fossil age of layer C (from Q. 9, above). What is the possible age of a layer B that is sandwiched between layers A and C? It will help to enter all the ages (age ranges) in the spaces below. Layer C (Q. 9) Layer B Layer A (Q. 8) Pennsylvanian Devonian Pennsylvanian Devonian