| Geology 105 - Paleontology | ||||||
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At the end of this lab, you should be able to:
Crustaceans
Ostracods: (#93, 1682) tiny bean-shaped bivalved arthropods. They use their feathery legs for filter feeding, are found in marine and fresh water, and are immensely abundant in the modern world. As fossils, they are useful as biostratigraphic index fossils. Compare these samples to fig. 14.16 in your book.
Barnacles: (#1594, 1510, 1060-1061) These animals start life like other crustaceans, with swimming larvae. The larvae develop a bivalved shell, then settle to the bottom and replace that shell with the plates of the barnacle. Preferred habitat is rocky intertidal.
Other Crustaceans: (#1555, 118) Lobsters, crabs, shrimp, copepods and amphipods are all very abundant in the modern world, but fossilize poorly due to their chitinous skeleton (except a few crabs with calcite skeletons).
Insects: (#1874, 123) Although insects make up half the known species on earth, they have a dreadful fossil record due to their fragile bodies and largely terrestrial habits.
Eurypterids: (#149, 51, plaster model, plastic model, green dot) The "sea scorpions" are rare but important fossils in the Paleozoic, representing some of the only large predators of the time. These fossils are rarely found together with other organisms of the normal marine environment, and seem to have specialized in brackish water habitats of the coastline. They were apparently swimmers, but did not survive the Paleozoic.
Trilobites:
I. Hard part morphology - Using fig. 14.2 and the plaster reproduction (#62) , locate these morphological features: cephalon (head), thorax, pygidium (tail), appendages, the three lobes, eyes. Note lines on face where the exoskeleton split open during molting (sutures). Compare the trilobite with the horseshoe crab in the resin block.
II. Molting - (#9, 1) Like all arthropods, trilobite had to periodically shed their skeleton to grow. The #9 sample nicely shows how the skeleton split (the cheeks have broken off and been lost). This is one of several molting patterns. In the #1 sample, the cephalon has separated from the body to allow the organism to wiggle out. These trilobites are often found as a "hash" of separate cephalon, body segments, and pygidium.
III. Eyes - (#16) Trilobites had compound eyes like insects. The overlapping fields of each of the hundreds of lenses in the eye of Phacops gave it 360 degrees of stereo vision. Other trilobites, such as the tiny agnostids, had no eyes. This suggests very different modes of life for these two groups.
IV. Life Habits - Trilobites were largely epifaunal deposit feeders, with some exceptions. Early trilobites have few anti-predatory devices
1. #1213, 609,1068. Compare these samples of Elrathia kingii. Which represent molts of trilobites and which are the trilobites themselves? Suppose you were doing a population study on Elrathia. How would this observation affect your results?
2. #5 - Is this a collection of organisms that dies catastrophically, or is this an accumulation of molts or dead trilobites? What kind of preservation is this?
3. #1068, 1644, 4 - None of these trilobites have any legs. Why not?
4. Sort the pictures of trilobites into these life habit categories: swimmers, shallow burrowers, benthic surface feeders, pelagic floaters. What was the mode of life of each of these trilobites : #27, 2, no #?
5. No #- Is this a trilobite or a molt? How could you tell?
6. # 167- How is this crab preserved?
7. # 1075- how is this barnacle adapted to life in its preferred environment?
8. #1875 - From the lithology and the preservation, what can you deduce about the environment of deposition?