(8) Earth in space and time. The student knows that fossils provide evidence for geological and biological evolution. Students are expected to: (a) analyze and evaluate a variety of fossil types such as transitional fossils, proposed transitional fossils, fossil lineages, and significant fossil deposits with regard to their appearance, completeness, and alignment with scientific explanations in light of this fossil data; (b) explain how sedimentation, fossilization, and speciation affect the degree of completeness of the fossil record (c) evaluate the significance of the terminal Permian and Cretaceous mass extinction events, including adaptive radiations of organisms after the events. Fossilization refers to the series of changes that occurs to an organism after death, that leads to replacement of minerals in the original hard parts (shells, skeletons, teeth, horns, scales) with different minerals. • a process known as remineralization. In addition, the term "fossil" is applied in other ways, for example, to preserved soils and landscapes such as fossil dunes. Through the study of fossils, it is possible to reconstruct ancient communities of living organisms and to trace the evolution of species. Fossils are usually formed when an organism is covered by sediments (sedimentation) that then harden into sandstone, slate, mudstone or flint (lithification). Most organisms do not fossilize and those that do are usually destroyed by geological processes or they never surface for examination. Fossils that formed here, are dragged beneath the crust and destroyed in the asthenosphere. • body construction: Does the organism have hard or soft body parts? • environment: Do the surrounding conditions allow for rapid burial and preservation? Will the body be exposed to many elements of erosion? • presence of predators: Are other organisms going to destroy the body before it can be preserved? • If an individual is successfully fossilized and enters the lithosphere, ongoing tectonic activity may stretch or melt it in metamorphic processes in Earth's interior, or be weathered away at Earth's surface. • A fossil that has survived or avoided these events may even succumb to improper collection techniques at the hands of a human. All of these events and occurrences make the fossil record, at best, incomplete 1. When the original hard parts of organisms become replaced by different minerals, the process of _____ has occurred. 2. Because we study fossils we are able to do what two things? 3. What is the process whereby organisms are covered with sediment? 4. What process forms sandstone, shale, and slate, or mudstone? 5. What five things affect the completeness of the fossil record? An exception is the Burgess Shale, in British Columbia, where a number of soft-bodied creatures were fossilized under highly favorable conditions. These creatures have few relatives that have been recorded in the fossil record; this is due to the unlikelihood of the soft animals being fossilized. The Burgess Shale was discovered by paleontologist Charles Walcott in 1909, towards the end of the season's fieldwork Badlands is a term used to denote what are usually areas that are extensively eroded by wind and water, with many canyons, ravines, and gullies, and other complex geological formations. There are many “badlands” in the United States, in Utah, Montana, Colorado…North and South Dakota. All of them are fossil havens, rich in paleontological treasures. The fossils of the Badlands are important because they represent a well-preserved window into the past. They not only tell us what lived here, but also what the environment was like at the time. From fossils we can learn about food webs and food chains during ancient times and how they compare to today. Fossils are the remains or traces of an organism, or environment, from Earth’s prehistory. Biologists generally recognize two types of fossils. • the actual body or body parts Zooliths and Phyto-fossils of an organism, whether altered or not…sometimes referred to as “body fossils” any evidence of past life that is not • Ichnofossils a body fossil. Examples include footprints, trails, burrows, borings, impressions, molds, casts, and coprolites…usually referred to as “trace fossils” Geologists also recognize fossilized environments, such as sand dunes, as said earlier. 6. Where is a famous fossil site for soft-bodied organisms found? 7. Who discovered the Burgess Shale? 8. What two types of fossils do paleontologists generally recognize? 9. What is the difference between a zoolith and a phytofossil? 10. What is another name for “trace fossil”? • Unaltered remains This category includes those fossils that have Unaltered skeletal material, tar impregnation, amber entombment, refrigeration, mummification undergone little or no change in structure and composition. As a general rule an organism which lived fairly recently has a greater probability of being unaltered than a more ancient one. As the sediments that entomb fossils • Altered Remains become compressed by the weight of Permineralization overlying sediments, they slowly (petrification), become rocks. The same processes dissolution/replacement, that turn sediments into rocks can alter carbonization organic remains . Silica and Pyrite 11. Of the body fossils, describe ONE of the processes that create unaltered remains… altered remains… A fossil is any trace of past life. A fossil does not have to be an actual piece of an ancient organism. Many fossils are bones, shells, or other body parts. However footprints and other traces are fossils too. Any reproduction of the anatomical features of the internal or external surface of an organism. Animal • Mold tracks preserved in rocks may be termed external molds. Internal molds, particularly of shells, are sometimes called Steinkerns. An impression is actually and external mold. • Cast This is, in general, a duplication of the original. Casts are formed when original parts are dissolved away and the resulting space becomes filled either with sediment or mineral matter, which harden to form rock. It is very difficult to distinguish a cast from an altered body fossil, such as permineralization. • Borings and Burrows Certain worms and clams and many other invertebrates burrow into rocks, wood, shells, and all types of sediment. These burrows are frequently preserved, especially in fine-grained rocks. • Copralites Fossil excrement can sometimes give definitive knowledge about the diet and size of the animal concerned. When you know what the organism ate, you know a little more about the environment too. • These are smooth, polished stones that are often found in the abdominal cavities of the skeletons Gastroliths of dinosaurs. They are thought to have helped those huge animals grind up vegetable matter in their stomachs or gizzards just as in chickens of today. If it weren’t for their association with skeletal fossils, gastroliths would look like any polished river rocks. •Gnawings Rodents and other animals chew on plants for nourishment and on bones for the calcium content and did so in the past. Gnawed plants and bones are frequently preserved as fossils. 12. Describe and give examples of the following ichnofossils: • Mold • Cast • Coprolites • Gastroliths 13. What kinds of things can a paleontologist learn from studying coprolites? Fossils are found on every continent and even on the sea floors. By far, most of them are invertebrates with hard parts (for example, mussels). Vertebrates, the class that includes fish, amphibians, reptiles, birds and mammals, are a relatively late development, and the finding of a large, complete vertebrate fossil, with all its parts close together, is rare. Microfossils, on the other hand, are extremely common. The microfossils include very early bacteria and algae (stromatolites); the unicellular organisms called foraminiferans, which were common in the Tertiary Periods; and fossil pollen. The study of micro fossils is a specialized field called micropaleontology. • is any fossilized remains of a life form that exhibit Tiktaalik characteristics of two distinct taxonomic groups. • is the fossil of an organism near the branching point where major individual lineages diverge. • will have characteristics typical of organisms on both sides of the split. Archaeopteryx The principal use of fossils by geologists has been to date rock layers that have been deposited over millions of years, and as a guide to evolutionary processes. Evolutionary succession can easily be seen in the fossil record. Distinctive fossilized life forms that are typically associated with given intervals of geologic time are known as index fossils, or indicator species. The concepts that different fossil species correlate with different strata and that, in the absence of upheaval, older strata underlie younger ones are attributed to the English geologist William Smith, who worked in the early nineteenth century, as well as Nicholas Steno, to more fully develop the Law of Superposition. Five major mass extinctions have occurred since life began on Earth. The rest have been “background extinctions”, occurring throughout history. While extinction events may spell doom for many genera on Earth, they also spell “glory” for others. Mammals would never have gotten a strong foothold were it not for the extinction of the dinosaurs, 65,000,000 years ago. What animal group do you think will prosper and diversify when humans are extinct? 14. What is a transitional fossil, and what do they show? Give an example. 15. What is an index fossil used for? Give and example. 16. Who is responsible for the development of the Law of Superposition? It is still somewhat of a mystery as to what caused the Permian Mass extinction…if indeed it was even one event. Many speculate that it was a combination of impacts, The hardy “disaster taxa” Lystrosaurus volcanic eruptions, and other were the only abundant terrestrial geologic upheavals that vertebrates to make it through the event. caused the extinction. We do know that there was a lower There were no coal formations during this oxygen content and a higher 2 content during this time period, which leads scientists to think CO period, and that organisms that there was not enough floral biomass to able to adapt made it through the extinction. produce coal. The Permian “Great Dying” Mass extinction was responsible for the extinction of 96% of the marine life, and 70% of the terrestrial life. Without floral biomass, the herbivores like rhynchosaurs were not supported, and thus became extinct. • Generalists Resistant to extinction • Specialists Prone to extinction Adaptive radiation occurs when animal and plant groups “adapt” , evolve, and “radiate” outward… in other words, diversify. Dinosaurs wereof organisms Mass extinction events allow for adaptive radiation dominant to occur. When one group of organisms isterrestrial dominant on Earth for too long a period of time, evolutionary processes “slow down”. organisms for over 160,000,000 Mass extinctions allow for rapid bursts of speciation to occur, and years! both plants and animals flourish. The diapsids, ("reptiles“) except for turtles and a few extinct forms, rose to prominence during the latter Triassic times, later giving rise to the dinosaurs. Mass extinction is IMPORTANT to evolutionary processes. • occurred approximately 65.5 million years ago Several impact craters (Chicxulub) and massive volcanic activity, such as that in the Deccan traps, have been dated to the approximate time of the extinction event. The combination of these events may have reduced sunlight and hindered photosynthesis, also changing sea-levels, leading to a massive disruption in Earth's food webs. Many researchers believe the extinction was more gradual, perhaps taking millions of years. Either way, all the major extinctions were gateways to new evolutionary events. 17. Why are mass extinctions so important to evolutionary processes? 18. What types of factors might make organisms resistant to extinction?