Lab 9: Fossils, paleontology and the complete reconstruction

Transcription

1 Geology 103 Name: Lab 9: Fossils, paleontology and the complete reconstruction Objective: To classify fossil organisms and to demonstrate how fossil assemblages are constructed. Finally, to determine the habitat and behavior of extinct organisms from observations of fossils. Over the course of the quarter, you ve seen how sedimentary rocks (and the minerals they contain) yield information about the time and place that they were deposited. Plate tectonics gave a larger picture of how the changes over long periods of time occurred. Further, you ve briefly seen how fossils might be used to determine the type of depositional environment might be represented by a formation. In this lab, you ll do a more in-depth look at the classification and age of fossils to reconstruct a community of organisms from the distant past. Fossil preservation 1. Obtain specimens. First determine if the specimen is a trace fossil or a body fossil. If it is a body fossil, further classify it as original (pristine), a cast or a mold, a replacement (permineralized) specimen or a carbon film. If it is a replacement, determine what mineral the original fossil was replaced with. Specimen Trace or body? Type of fossilization Recrystallization mineral

2 Fossil classification On the next page is a quite incomplete tree of life, using the Linnaean classification system (named after Carolus Linnaeus, who used it in the 18 th century to classify living organisms). The science of taxonomy involves both the classification and the naming of all extant and extinct organisms. In fact, the word taxon simply means a group of organisms that share some characteristics with each other. Thus, different taxa can be grouped into a larger taxon, and so forth, which is why the classification system on the next page is hierarchical (that is, it has a definite set of finer divisions). The diagram on the next page, while incomplete, contains all the fossil taxa that you will handle in this section of the lab. The fossils themselves are numbered. 2. At one point, most of the bold-faced taxa were at the same level of division on the tree of life. Why are they now at such different levels? Hint: How might taxonomy be evolving as a science?

3 Geology 103 EXTREMELY INCOMPLETE Tree of Life Domain Bacteria Kingdom Eubacteria Phylum Cyanobacteria (stromatolites) Domain Archaea Domain Eukaryota (Eukarya) Kingdom Plantae Phylum Pteridophyta (ferns) Phylum Coniferophyta (conifer trees) Phylum Anthophyta (most flowering plants) Kingdom Animalia Phylum Porifera (sponges) Phylum Bryozoa ( moss animals ) Phylum Brachiopoda (lamp shells) Phylum Cnidaria Class Anthozoa Subclass Hexacorallia Order Rugosa (rugose or horn coral) Order Tabulata (tabulate coral) Order Scleractinia (modern coral) Phylum Annelida Phylum Arthropoda Subphylum Trilobitomorpha Class Trilobita (trilobites) Subphylum Chelicerata Class Merostomata Order Eurypterida (eurypterids) Subphylum Crustacea Phylum Mollusca Class Cephalopoda Subclass Coleoidea Order Belemnitida (belemnoids) Subclass Ammonoidea (ammonites) Subclass Nautiloidea (nautiloids) Class Bivalvia (clams, oysters) Class Gastropoda (snails, slugs) Phylum Echinodermata Class Crinoidea (crinoids) Class Blastoidea (blastoids) Class Echinoidea (sand dollars, sea urchins) Phylum Hemichordata Class Graptolithnia Phylum Chordata Class Chondrichthyes (cartilaginous fish) Class Actinopterygii (Superclass Osteichthyes bony fish) Class Reptilia (reptiles) Class Aves (birds) Class Mammalia (mammals)

4 3. Fill in the table below with the correct taxon name (you need not worry about the whole taxonomy, just the bold-faced word) and characteristics that helped you identify it. There are 27 specimens, and there are 27 bold-faced words. Use the resources available in the room to help identify and classify these organisms. Specimen number Taxon Distinguishing characteristics

5 Developing a fossil assemblage A fossil assemblage is a group of fossil organisms that are found in the same stratum, and are thus inferred to have lived in the same place and time. Fossil assemblages are powerful tools in the reconstruction of long-ago biological communities, but can be

6 problematic: how do we know that all the fossils in that layer weren t eroded from other layers of different ages and dumped together in a more recent layer. This problem is called reworking, and one tool that can determine if a layer s fossils have been reworked is to compare the fossil age ranges, and see if it is reasonable that all the fossils in the layer could have at least been alive at the same time. Consider the following assemblage for a formation in Ohio: Specimen Binomial name Type of organism Age range (My) 4 Lingulepis tenuilineata Brachiopod Flexicalymene meeki Trilobite Lepidocyclus cooperi Brachiopod Lingula cuneata Brachiopod (?) 44 Eospirifer eastoni Brachiopod Ditoecholasma sp. Rugose coral Atrypella scheii Brachiopod Eurypterus lacustris Chelicerate Tentaculites gyracanthus Mollusk? Annelid? Brachiopod? On the graph paper provided, write the number and name of each of the fossil organisms found in the formation along the x-axis; you do not need to arrange the organisms in any particular order. You can abbreviate the genus name to one letter, so Lingulepis tenuilineata becomes L. tenuilineata. Find the smallest and largest numerical age in the entire list of organisms and use that to scale your y-axis. Remember, the units are millions of years (My). It is customary to place the youngest (smallest) age at the top. For each organism, draw a heavy black line that spans the time period that that species was extant. If there are three numbers, one of which has a question mark, the age range contains an uncertain extension either older or younger; in this case, draw a heavy black line that spans the time period that is certain, and use a dashed line to indicate the uncertain extension. 5. What might be the cause of uncertainty in an organism s age range? There are a couple reasonable reasons. 6. Does the fossil assemblage represent a community of organisms that all lived at the same time? Why or why not? (Hint: if you do not think so, show that reworking might or might not be involved.)

7 7. What age range can you infer for this member of the formation? Justify your range from your graph. Organism habitat, movement and feeding Given that all of the organisms you ve seen so far are extinct, you might think it would be difficult to figure out what their environmental niche was, or how they moved or fed. Fortunately, most extinct taxa have currently living analog relations (maybe homologous is a better word to describe the relationship). Thus, drawing from modern organisms, paleontologists can infer the habitats and behaviors of extinct organisms. So, using modern analogs, we can broadly classify marine creatures, for instance, as plankton (in the water, carried along by the current and waves), nekton (able to swim) and benthos (living in or on the ocean floor). The benthos can be further subdivided into epifaunal (living on the floor) and infaunal (living in the sediment). For feeding strategies, you ve probably heard of primary producers (generally, photosynthetic organisms), herbivores and carnivores. To this, add deposit

8 feeders, which ingest sediment and extract algae or bacteria on the sediment grain surface as food) and suspension feeders, which filter microorganisms floating past or down the water column. Finally, in terms of movement, benthos creatures may be sessile (immobile) or mobile, which includes burrowing. 8. Draw, to the best of your ability, a bryozoan, a crinoid, a brachiopod and a bivalve (clam) in a drawing similar to the drawing above. The bryozoan is a high-level suspension feeder (an individual bryozoa is small but colonies can grow tall), the crinoid is a mid-level suspension feeder, and the brachiopod is a low-level suspension feeder. The bivalve is a deposit feeder. The bivalve is infaunal; the rest of them are epifaunal. Show food particles raining down from above to indicate the suspension feeding part. Hint: Will you need to show what goes on below the ocean floor?

9 9. According to the chart above, is or was the community you drew on the previous page naturally occurring? During what time period(s) must that community have occurred? 10. What is an advantage to being a high-level suspension feeder? What is a disadvantage? 11. How do mid- and low-level suspension feeders therefore get any food at all? 12. Most authorities (e.g., Levi-Setti, R., Trilobites, 1975) suggest that at least some trilobites were nektonic predators. In a different color than you used for question 8, draw one such trilobite (again to the best of your ability) on the drawing in question Does the inclusion of the trilobite narrow down the time period in which this community could have existed? If so, to what period(s)?

10 14. Some graptolites were plaktonic suspension feeders (Sam Noble Museum, Common Fossils of Oklahoma, In a different color than you used so far, draw one such graptolite (again to the best of your ability) on the drawing in question 8 (it s getting mighty crowded). 15. Does the inclusion of the graptolite further narrow down the time period in which this community could have existed? If so, to what period(s)? 16. Your drawing in question 8 how deep marine are you imagining this environment? Use the depositional environment terms. Give a reason for your choice. 17. Suppose the floor of your drawing in question 8 is not clastic but is carbonate specifically, a patch reef made of stromatoporoids (a sponge-like creature, phylum Porifera) and tabulate corals. Does your answer to question 16 change? If so, what depth are you now imagining your drawing to be? Habitat factors that are harder to preserve in the rock record Your drawing in question 8 may look reasonable all the organisms did live in the same time period and probably at the same depths as you ve shown. However, there are a large number of other factors that do not preserve in the rock record that affect where an

11 organism will live. In this part of the lab, you ll use a modern situation to study the effects of water temperature, ocean acidity (ph) and ocean salinity. Temperatures in the Atlantic Ocean Geographic range Mean annual temperature ( C) North of the Tropic of Capricorn S (Montevideo) to the Tropic of Capricorn S to 35 S S to 40 S 10 South of 50 S 5 Temperatures in the Pacific Ocean Geographic range Mean annual temperature ( C) North of 2 N 30 Border of Peru/Chile to 2 N S to border of Peru/Chile S to 40 S 10 South of 45 S 5 Acidity in the Atlantic Ocean Geographic range ph North of the Tropic of Capricorn S to the Tropic of Capricorn S to 37 S 8.20 Cape Horn to 50 S 8.12 South of Cape Horn 8.07 Acidity in the Pacific Ocean Geographic range ph North of 2 N 7.90 The Equator to 2 N S to the Equator S to 15 S 7.95 South of 20 S 8.07 Salinity in the Atlantic Ocean Geographic range Salinity (ppt) North of the Equator 35 The Equator to 10 S S to 20 S S to 35 S (Montevideo) S (Montevideo) to 37 S 35 South of 37 S 34

12 Salinity in the Pacific Ocean Geographic range Salinity (ppt) North of the Equator 33 The Equator to 10 S S to 30 S S to 40 S S to 50 S 33 South of 50 S 34 Note: ppt means part per thousand. 18. On the map of South America provided, mark the temperature ranges outward from each coast (in other words, draw a horizontal line in the Pacific Ocean at 2 N, and that will separate 30 C water from 20 C water yes, the change is temperature is not that sudden but this is an exercise). In a different color, mark the ph ranges in the same way, outward horizontally from each coast. Finally, in yet a different color, mark the salinity ranges, outward horizontally from each coast. Organism Temperature range ( C) ph Salinity range (ppt) Scleractinian coral Kelp Environment Great white shark For simplicity, consider that there are only two marine environments: continental shelf and abyssal (deep ocean). In the environment column of the table above, write which environment(s) each organism would live in. Remember, some organisms may be capable of living in both environments! 20. On your map of South America, the Pacific coast has a narrow continental shelf (3 mm on the scale of the map) and the Atlantic coast has a wide continental shelf (15 mm). Using three different colors than you ve already used, mark the habitat of all three organisms. Remember, for an area to be an organism s habitat, it must fulfill all four of the conditions given on the table above. 21. Will any Lagerstatte in the future preserve all three organisms (coral, kelp and shark)? Mark these areas with a highlighter or Sharpie.

13 22. What misleading conclusion might future paleontologists draw about the habitat of these three animals?

14